I have worked many (most) jobs that require steel fittings, these are much stronger than Pot metal.

I agree that most components work well when properly selected and installed. Unfortunately, throughout my many years as a consultant, 99% of the times I have checked inside a set-screw type coupling, I have found the conduit to be deformed and usually a sharp edge.

Most all government projects as well any projects designed to use UNION electrical contractors spec. compression because they take longer to install. Thus running up the labor cost and putting more money in the contractors pocket on T&M jobs. These tactics are well used and I have first hand knowlege since I've been associated with UNION and NONUNION contractors as an employee. Yes I do believe that compression does better in a slab and I know it's required by the NEC in a slab, but beyond that setscrew is the best.

I've been led to believe compression fittings are better in high humidity environments as they keep condensation out of the raceway. I would appreciate comments by others on this.

I have been in the business of electrical engineering over 50 years. Recently I was employed as an expert witness in an electrocution case. Although not contributing to the fatality, many of the emt couplings had loose screws. Surveying most of the adjacent conduit found almost half of the screws were not tightened enough to provide a successful installation. The installation was in a warehouse constructed over ten years ago, and modified to a degree, perhaps leading to the loose conduit connection. Perhaps this is a good reason to avoid the set screw approach.

Compression fittings are generally listed raintight, no set screw fittings are to my knowledge. That said I've observed more compression fittings separated due to settling and vibration than I have similar failure in set screw fittings.

We agree that steel set screw couplings and connectors are a better install when indoors. The compression couplings, especially the larger sizes, tend to strip out.

Also, I remember reading an EC&M article afer the '94 earthquake here in Los Angeles and the engineers found that the steel set screw couplings held better than the compression

Based on the descriptions here I can imagine the set screw couplings either worrying their way into the metal or distorting the tube ID in response to linear or axial movement of the conduit. This could be expected to occur on long runs suspended from a factory ceiling that rises and falls upon wind load or environmental pressure changes. It could also occur due to motion from thermal expansion while undergoing temperature cycling.

Compression couplings are not likely to distort the tubing under these types of loads do to the hoop strength of the circular cross section. Set screw couplings distort the tubing out of the hoop shape and so might be observed to be loose not long after being correctly installed.

Either design is likely good enough in most all applications, but we should not expect set screws to be tight long after installation unless the physical environment is extraordinarilly uniform.

Finally some one said it! Thank you Mike. I have been doing a project at an air force base which specs out compression fittings and solid wire. What a pain in the butt.

I will say either type is a good product. I have never see during my 73 yo an incomplete compression connector but countless pieces without one screw instead. Regards from Quito.

Mike --

Some of us are old enough to have used crimp couplers and connectors on small (1/2") EMT. These hold super tight and fit easily thru 7/8" drilled holes and the connectors thru 1" holes.

Deformation of the conduit inside is minimal. These used to be in common use in the Chicago suburban area.

Regards . . .

Jim

P.S.: One downside is that you can not undo these fittings, once crimped.

Most engineers do not rely on the Conduit for the circuit ground and require a ground conductor to be installed within the raceway, however it is important to remember is that the metal conduit must maintain a ground for itself and neither type accomplishes this until the fittings are tightened properly. The installer must understand this and do his job properly. It comes back to quality control for which ever type you use.

Compresion fittings are used for weather proof purposes also.

Although "cast fittings" are legal I've never felt comfortable installing them. Many jobs spec steel, and many of those spec compression type. In my opinion it's going to be the installation that determines the integrity of the conduit. Cast fittings on properly secured conduit should work fine. Other considerations such as weather, wind movement, ect should be addressed at the planning stage, not installation. And yes, it will cost more both for material and labor, as always, you get what you pay for! ( at least you should!)

Sir: I do prefer compression couplings for EMT conduit. My principal reason is that they do a good job of maintaining the structural integrity of the system. I, like you, never depend on conduit alone as a ground return path. I always use an equipment grounding conductor. I will accept set screw fittings if necessary, but have one major requirement for their use. If you use them always have the set screws on the top of the conduit. Most times they are overtightened and this will deform the conduit slightly. If this happens on the sides or especially the bottom, it creates a sharp ridge in the conduit. When the wire is pulled in, especially large wire, the insulation can get skinned off on that edge. As long as the contractor understands this concern, there is usually no problem. Hope this is helpful. Phillip in Kentucky, doing consulting engineering for 35 years.

I failed to mention this in my last post, but of course the die-cast fittings cannot be used on my projects. They are weak metal and often break when the screws are run up. Only stamped steel is allowed on my jobs, if I allow set screw fittings.

My own opinion I like compression couplings because they are more estable when it come to motion matters. also for wheather conditions,better looking and most of the time it is better conections in between conduits. hope my opinion help anyone. Thank . Santo Nina. unlimited licensed electrician in north carolina.

I have been installing zero-fault-tolerant line & LV wiring systems since ... a few decades before the term was coined. Whenever possible, I prefer to use (steel) SS connectors with EMT. There are conditions precluding their use, such as slab, wet & high moisture environments.

As others have noted, fully tightened set screws will slightly "indent" the tubing wall. However, if the tubing has been properly reamed and fully inserted into the connector, this should not usually present a problem as the indents are sufficiently distanced from the lip of the tubing.

It's been my observation that compression couplings are MORE likely to be improperly installed, mainly by either not being tightened, or by working loose as additional pipes are installed. I know, this observation is the opposite of what "engineer thinking" would suggest.

In any event, the issue is moot: both types have to pass the exact same standards.

The only situation where I find compression fittings to have an advantage is where the fitting is installed in a threaded hub (such as an LB). In that situation, you have no control over where the the screw will point,

If the all the set screw are in line and located in the top portion of the pipe - the indentation is not an issure. If good set screw steel fittings are use and properly installed - they are better than compression - I have stripped out coupling on compression. All of our job we work on require a ground to be pulled

Conduit is a very good ground when installed correctly and when continuity is maintained (better than the ground wire). This does not mean, as an engineer, I allow the equipment grounding conductor to be omitted (I prefer belt & suspenders, or to put it another way: "there is not compromise when it comes to safety" and your systems will be less prone to noise and interference). I prefer compression couplings for conduit and typically do not allow screw type, but it would certainly depend on the application and if you are wiring a motor or say some sensitive electronic equipment. For a very specific industry reference, you can quote: "EPRI's Power Quality for Electrical Contractors, Applications Guide, Volume 2: Recommended Practices, 1994", it states, "The quality of joints is critical for all conduit and raceway, especially for EMT where compression fittings are recommended over set-screw type."

In over 40 years as an Electrical Engineer I have seen numerious cases where the set screw have come loose and left the conduit end resting on exposed conductors. I've seen a few cases where over tighten screws have left a dimple in the conduit end. Thus becoming a very good wire stripper resulting in shots in rthe conduit.

In my experience I have found that compression & set screw products are comparable as long as they are properly installed, i.e. tightened. I have investigated two incidents, one a fatality, that were caused by a loose EMT coupling and the resulting ineffective bond. Both installations dated to an era before a separate bond wire was required.

One problem we run into with set screw fittings, is that it's hard to use a vacuum to get strings through on long pipe runs. My company favors compression over set screw.

I use compression fittings because in my opinion, they will maintain ground continuity better over the real long run (time), rather than a single point screw, which has a very small contact area and may work its way loose over time due to microseismic activity, temperature changes, etc. The moisture proofing and "professional look" of the compression fittings, are worth the extra money to me--and appreciated by my customers.

After 17 years in the field I have never come acroos a project that required compression fittings and felt like they were not needed. I think their both are great, however I would rather have more in stock because I could use compression fittings in more places than set screws fittings.

I seem to remember a study done after one of the majoe earthquakes in California that clearly showed the SS fittings held much better than the compression type. I also never rely on the conduit (or EMT) for adequate grounding.

A big point seems to have received little comment in the replies to this subject: Compression fittings are NOT automatically raintight. I believe the standard changed some ±20 years ago and only the ones listed as raintight are suitable for that use. Concrete tight is another standard; and some (mostly set-screw type) require a wrap of tape to remain concrete tight.

If you want to exclude rain, use raintight. And arrange the conduit to drain. If you want to exclude "moisture", seal the conduit on each end and dry it with something other than 80% humidity air we have in Florida! It is VERY easy to fail getting the conduit fully seated in both sides of a short compression coupling. Different manufacturers use longer steel sleeves on SS fittings, which seem to make a stronger installation.

As always, the pressures to work faster, use lesser trained and experienced mechanics, and "just get by" can give a bad job using any material.

Lynn Adams

Just a side note. Most think of compressson fittings as watertight or for wet locations, in fact many are only for dry locations.

I would like to ask what all should be done when installing a portable generator per article 702 and 445 ?

I agree, compression fittings in interior locations are subject to way to many human errors when tightening. The engineer says he does not consider the conduit a ground so he must be requiring the electrician to install an equipment ground wire in all conduits. With that being said rewrite the spec!!! I tire of "blanket specs" that engineers enforce when it is to their advantage. He also states he respects the experience and integrity of of some contractors (not all) - same here I respect the experience and integrity of some engineers (not all).

We rarley see compression fittings specified anymore. In the cases that they are specified the client and the A&E will generally accept a cost savings alternate to go to set screw type fittings.

SS couplings are value engineering for your clients. First, the cost of the actual coupling is less. Secondly, they are easier to install thus contractor can bid less for installation. Third, a properly fastened set screw coupling will stay tight as good or better than compression type.

I have never liked compression fittings compared to set screw fittings, except the added level of water protection it provides.

I remember reading about a study in one of the electrical trade magazines,which found that the set screw fittings were actually better. Probably due to ease of proper installation. Now unless specified or required by location we use only set screw fittings.

I HAVE BEEN AN ELECTRITION AND ENGINEER FOR OVER 40 YEARS. I DONT UNDERSTAND WHY COMPRESSION FITTINGS ARE SPECFIED THEY COST MORE AND ARE LABOR INTENSIVE. AND WITH THE CODES NOW REQURING GROUND WIRES IN ALL CONDUITS WE SHOULD BE LOOKING TO WAYS TO SAVE THE CLIANTS MONEY.ALSO I REMBER A STUDY I DONT HAVE THE NAME OF THE PERSOP WHO PUBLISHED IT. BUT IT SHOWED THAT IN STRESS TESTS THE SET SCREW CONNECTORS HELD THE CONDUITS TOGETHER MUCH BETTER MECHANICALLY THAN COMPRESSION FITTINGS. IN MY YEARS IN THE FIELD I HAVE NOTICED THE SAME ANICADOTLY.

Interesting comments above. I've had this discussion before, and most people feel strongly one way or the other. In most facilities, I've been allowing the electrician decide based on their preference for many years.

The Air Force required compression fittings because they considered them superior in longevity & EMI protection.

The only standards based reason for one fitting over the other that I'm aware of can be found in IEEE Standard 1100 "IEEE Recommended Practice for Powering and Grounding Electronic Equipment". This standard is concerned with the performance of electronic equipment and how the power system plays a part in that. Paragraph 8.4.8.2 (on EMT) "Sections of this conduit are typically joined by means of setscrew or compression-type connectors, which do not provide the same magnitude of grounding integrity as threaded conections. Accordingly, the shielding and grounding effectiveness is reduced. Recommended practice is to join sections of electrical metallic tubing with compression-type couplings. Set-screw-type couplings should be avoided. Connections to enclosures should be made up tight using compression-type connectors." In this instance, I believe the text is referring to high-frequency grounding paths and EMI concerns. In paragraph 8.4.8.5, "Conduit Fittings", there are several methods concerning bonding-type bushings, locknuts, etc. that are above and beyond the code minimum and above standard practice for most electricians. It all refers to high frequency EMI.

We must use compression connectors where the actual space the conduit runs through is protected with a chemical fire suppression system. Additionally, the conduit opening in any box within that space is sealed using duct seal. These spaces are periodically "fan tested" to insure air tight integrity.

The problem with compression couplings is no one ever really tightens them,and you would never know by looking at them that they are tightened. Set screw couplings are always tightened, its a habit with electricians to tighten them.

I agree with Larry and Bob if the person that is installing the compresson couplings is a good mechanic and uses steel compression fitting I think it is a much better connection than set screw connectors.

One modification, the set screw fitting needs to be steel and not cast. The reputable electrical contractors we visited with made it clear that cast EMT set screw fittings tend to crack or break. So our specifications now state Galvanize EMT fittings shall be steel compression type or steel set screw type.

The foreman for the electrical contractors like the set screw type. The find it is a lot easier for them to check apprentices work with set screw fittings than compression fittings.

We've found that steel compression fittings make a better seal on larger conduit and ease sucking in a string. You can see the difference on anything larger than 2". I have been on several jobs recently that spec'd "steel compression fittings".

In my opinion after 30 plus years in the trade, I feel steel set screw fittings are great for the proper application. I'm not real keene on die cast fittings. They are a labor saver and cost less than compression fittings. With today's economy I feel good value is very important.

I too agree that a set screw coupling has cost and installation advantages over the compression conduit fittings, when properly used. Some of the specification pages are "Boiler Plate" and just printed out and added to any RFQ with out being checked or read thoroughly. One can bid "As Specified" and then add as an addendum package/pages to their bid that would show cost advantages by implementing some or all the suggested recommendations in the addendum. This way the company requesting the bid will get an actual bid as they requested, but also receive information on cost saving methods and/or materials. This would demonstrate that they are dealing with a contractor that understands the bottom line and is willing to help keep costs in line.

I have been on both sides of the fence, as a contractor responding to RFQ's and also preparing, issuing, and evaluating the received bid package from contractors. A contractor who gives suggestions how to reduce costs was always appreciated and carefully considered, generally more than a contractor that submitted a straight bid.

Just my two cents..

25 years ago, I investigated a "near miss" situation where an employee received an electrical shock when a set screw coupling came apart. This was old wiring, when the raceway was used as an equipment ground. Since that incident, I have specified compression couplings and also require that a green wire be added to provide a solid equipment ground. However, I agree with the comments about properly-installed set screw connectors, especially where the equipment grounding conductor is installed. The incident I investigated could have just been a case of poor workmanship.

I beleive that regardless of what type of fitting you use, whether it be compression or set screw, you must maintain good tight connections and continuity between all joints. you can not soley rely on an EGC. EGC's are not bonded to the conduits in between the bonded boxes. if a screw happens to run through a hot conductor in the middle pipe that has a poor or no conductivity to ground, he or she who comes in contact with it may be the ground.

Our facility also specs compression fittings. I also agree that setscrew are just as good. Some contractors like the compression for a tighter seal for their vaccuum when installing a pull string

well theorhetically our compression fittings are waterproofing fittings...but in reality...due to the nature of EMT isnt really waterproof . . .weatherproof..certainly . .so that would be the minor difference.

They will get used over set screw because of an plan or specification . . . .with a little medicated goo...one can make either fitting waterproof , , . . .so the answer is very little difference . . .and NO I would never use conduit as ground path

As for the compression fitting being a better bond and stronger, the only conduits I have ever seen that pulled apart in an industrial environment have been compression.

Kevin,

I think the most important part of this question is if the specifications require an equipment grounding conductor in all conduits. (I have never found a spec that does not require this) Some specs also state compression fitings unless an equipment grounding conductor is installed, then set-screw fittings are allowed. I have always felt that for general electrical installations, set-screw connectors are the best choice. I also prefer steel over the die cast since some brands of die cast tend to crack easily. If you did not install an equipment grounding conductor, compression would probably be a better choice as it ofers more surface contact area for bonding the conduit together. Hope this helps.

I remember seeing some photos some years ago in EC&M magazine showing damage to electrical systems from an earthquake. Many conduits coupled with compression-type couplings had become separated. Most conduits coupled with set-screw couplings remained coupled. I think that the deformation of the conduit by the set-screw is the key to the better connection integrity. Also, in my opinion, compression-style coupling installation quality is much more sensitive to workmanship. Particularly in the larger sizes, electricians sometimes try to tighten couplings with slip-joint pliers that are too small (or worse: one set of pliers and a hand). Even with properly installed tight couplings, a slight twist or rotation of the conduit while tightening a downstream coupling can loosen an already tight upstream coupling. Related issue: mechanical strength of die-cast zinc fittings vs. steel fittings.

Hi Kevin and Mike: Set Screw Connectors have a torque whether cast or Stainlees Steel.

Compression also has a torque; however, Most don't take the time to put to practice 110.3(B) or the UL White Book to find the listing and find out what the intended use is.

I have been in the contracting and engineering side for over 30 years and have had the same experience both installing and specifying fittings. Set -screws are absolutely and equal in my opinion. Further, with a set-screw connector you can readily identify if a fitting has been tightened by looking at the screws. With a compression connector this is not always the case. Also, in my experience doing inspections, a compression connector requires two wrenches to properly tighten. I have found many compression connectors that have been hand tightened only and are easily opened. A set-screw fitting requires only a screw-driver which all electricians carry as oppossed to two wrenches ( Channel locks). The additional cost for compression connectors is also not warranted in most cases unless required for a specific situation.

ok

Years ago and possibly still today engineering firms were paid % of cost of project. Compression cost more. Check out specs in other areas and you will probably find items there also that could be replaced with a less expensive item and do the same job.

I have found that if you intend to use a vaccuum to pull strings through your conduit, that compression couplings provide a good tight raceway. I also have seen SS cast couplings which were broken over time.

Agreed. SS is not only a more effective link in the bond path, but it is way, way easier to inspect and identify when the path is broken with only a visual inspection. I only wonder why it took an Engineer 48 years to ask! (Just kidding - it is always hard to have fresh eyes and examine why we do things the way we do.)

I use both, set screw sometimes are a problem when connecting to LB's etc as the set screw is sometimes in the wrong direction (like against a wall) when the fitting is tight. Also I once ran a run thru a grid ceiling of about 200 feet and then couldn't suck a line thru it as the set screw fittings were leaking too much air. The extra time it took to get the pull line in was not worth the difference in costs! There is a place for both and a good electrician will soon know when either is better!

Why anyone would use compression fittings on EMT is beyond me... the contact pressure of a setscrew fitting is much greater than compression and the slight indentation made by the screw makes pulling apart almost impossible. Setscrew fitting in a slab all but guarantee no lost raceways, compression is a crapshoot especially if the slabs are pumped.

I have found over the years that the majority of engineers` specs wanted compression fittings which I always questioned. They took longer to install ensuring they were tightened and fastened properly. My perfered fitting is and always will be SS set screw. Now I am in the position of being a customer working w/ engineers and I require them when ever possible.

If installed properly they are fine. Most are not and come apart after a few years, the screws will also vibrate loose if not tight. The same thing happens with compression fittings, but not as much.

We require grounds in all conduits for state buildings in North Carolina so this is not issue with us. We also require compression fittings.

I have long been an advocate of set screw fittings, however compression fittings have their purpose in outdoor application. I do not support conduit, rigid or emt, as a ground conductor regardless of installation. I have seen many compression fittings, whether in high vibration areas or not, loose and/or separated; enough to say that the service has questionable ground return path. Gimmee' the good 'ol green wire.

To all my fellow electrical types, I have also been on both sides of the fence, (Mechanic, Installer, Contractor, Engineer, Owner and State Inspector). I have been on jobs that the AHJ required or liked one connector/coupling over the other. I was also on one job that two journeymen got into a fist fight over this same issue. Both serve a purpose. So far no one has brought up: NEC 2008, Article 110.3 Examination, Identification, Installation, and Use of Equipment, (A) Examination. (B) Installation and Use. If the EMT connector/coupling is properly installed as listed you should not have any problems? I have been doing electrical work for 27 years, for me the use of these parts is based on: Environment, Time, Cost, Code Rules and also if I can make my local inspector feel good about the job. Compression fitting do cover more surface area. A ½” EMT connector/coupling, set screw has a No.10 set screw, this has a contact area of 0.02761” at one contact point. A ½” EMT compression fitting with an inside diameter of 0.7150” has two contact points on the bushing this contact area is 2.24624” x 2 = 4.49248”surface area. So if I was to use the EMT as a ground path as listed in Article 358.60, I think I would use a compression fitting. Just my opinion. Remember no fist fights.

Ozzie Woodcock

As far as poor quality workmanship goes. “neat and workmanlike manner” requirement in 110.12 Coves that. Who is responsible for that on any job, the management, not the worker. Management is mandated by code, employees are mandated by code and management enforces the code. The meaning of “neat and workmanlike manner” requirement in 110.12 is brought to your attention the moment you walk on the job. Keywords....tight, level, plumb, instructions, pay. You do substandard work, you get substandard pay. Have I made myself perfectly clear....good.

Set Screw verses Compression.

Set Screw because each and every one can be checked visually, compression can not. From an engineers pespective.... Steel Set Screw.....2 selling points, strong and can be checked visually.

As far as what I use, if it is mandated to be used then... that's what is installed. If it's not mandated then the least expensive (listed) is used. KISS

I still remember (1970's) when set screw fittings, die cast or steel, were understood for indoor use and compression fittings were for outdoor use. We used to say "set screw or raintight fittings". Egineers require compression fittings in almost all specifications, so the term raintight is no longer used. Nevertheless, the installer is the one who makes sure the fitting is tight, whether set screw or compression. I agree that steel fittings are stronger, but they can rust. I've noticed that our electricians complain a lot about how the compression fittings are easy to strip out and the constant loss of the interior compression rings take up time to find and/or replace. You can almost always find a screw to replace a missing set screw. My biggest complaint with using compression fittings is when the helper leaves out our can't find the interior compression ring, but still installs the fittings. No visual inspection will spot this.

Mike regarding the question from Kevin Cassidy on Set-Screw fittings; as you know I have been a member of CMP-8 and have represented the Conduit & Tubing industry for many years. CMP-8 added language in 358.6 to require all fittings to be listed. Underwriter Laboratories added test parameters a number of years ago for these fittings. Therefore, both the set-screw type and the compression type does provide equal performance. In addition the Testing done a number of years ago by The Georgia Institute of Technology (GA-TECH) use both types in their field testing to validate the GEMI software program. Both performed equal. 358.30 covers EMT support requirements and 314.23 covers box support requirements if these requirements are followed the fittings should not be stressed under normal field conditions. For additional information go to; www.steelconduit.org

Richard E. Loyd

One positive area for set screws may be with bonding, it does allow for good contact when you bury a screw into the pipe. Set screw fittings may also create uneven pipe joining when installed inverted (screws pointing down) and create an edge, possibly damaging, for the wire being pulled into the conduit.

Several times I have gone into existing electrical installations and seen EMT joints seperated, hanging, wire exposed, and the like.

95% of the time (or higher), set screw couplings were used.

When the EMT is installed properly, i.e., number and location of supports, pipe inserted ALL THE WAY into the connectors, etc., set crew connectors are fine, but -

Face it! Connectors do not always get tightened properly, conduit fittings ARE sometimes "cheated".

Even when a compression fitting is not adequately tightened, I feel it provides a better grounding integrity that an untightened set screw connector.

I am a union electrical contractor and electrician. I always prefer compression, even though it costs more in material and labor. In addition to reasons above - I do not like the "dimple" made in the pipe by set screws. And if the connector is later disassembled/reassembled (for whatever reasons ...), you have more dimples, or a dimple half way over another - definitely not a good connection ...)

The exception: On larger conduits (say 2" and larger), with the double sets of set screws - I have NOT seen these conduits hanging and/or separated. Price WOULD dictate set-screw over compression ...

However, other union electricians disagree with me and want set screw - I think mostly because they are quicker and easier to use.

Who knows HOW to tighten a set screw connector?

Should the set screw be turned until it is COMPLETELY seated, in as far as it will go (which often ends up in pipe distortion)?

SNUG? Tight enough for a good connection, but not to tight, possibly stripping the set screw threads or damaging the pipe?

JUST TOUCHING and then 1/4 turn (or 1/2 turn)?

Ask 10 electricians and see how many answers you get.

Perhaps compression provides better and more consistent surface to surface contact than set screw?

Mike what are your thoughts are knowledge on changing out panels with combo arch fault breakers to help reduce the risk of fires with alum. branch circuit wiring? Are there any statistics or information that I should be made aware of before practicing this method?

There are reasons compression fittings are desired by engineers. It comes down to risk.

1. Most compression fittings are rated for ground bonding. Not many screw type fittings are. Without the ground wire in each conduit system, this may become a hazzard.

2. Many contractors do not overtighten the compression fittings. Many screw type I have inspected were over tightened.

3. Compression fittings are better around damp locations that use to be dry location.

4. Compression fittings avoid the set screw being stripped.

Back in 1991 I had to open up a wall and reconnect a EMT that had been installed using a compression fitting. Since then, I have seen a lot of both types of conduit fittings that haver come loose.

The reduction in EMT cross section when using a setscrew box connector is immaterial - very rarely have I seen a conduit accept the absolute maximum that NEC allows and even then we needed a lot of wire pulling lubricant. I have also seen instances where THWN was a lot thicker than NEC said it should be or that the wire strands were somehow anticompact stranded. Wire pulls are easier anyways if the conduit is noversized particularly if I cannot connect a forklift truck or a station wagon to the pulling rope.

I have never passed an EMT job if a separate ground was not pulled. The common sense here is that no inspector is going to go up into a ceiling cavity & check each fitting for continuity. I would much rather have a CU ground return than a steel one.

The second part is that in NY state with the exception of a several cities there is no licensing requirements for electricians so you never know what you are going to get in the suburban townships as far as workmanship.

I am retired from the Federal Aviation Administration and they also have a standard that requires compression fittings only. For the better part of 30 years I have also tried to figure as to why. The same standard also requires a seperate ground wire which negates the use of the raceway as a ground as noted by Mr. Cassidy. I personally prefer the SS fittings, especially for larger pipe, since it will more likely be made up as a continuous system as required due to the fact that the screws are more accessable than getting a large pair of pliers onto the fitting to insure tightness.

The main reason I thought engineers would spec compression was because of sprinkler systems. This keeps the majority of your system water tight.

Using the 110.3(B) is a "cop out". You can use the stab-in connections on the back of switches and receptacles "according to (specs)", but that dioes not make it better, not even equal to, the quality obtained when wrapping a conductor around and tightening it with a screw.

Using set screw connectors does not make it better, or even equal to, getting a pair of channel locks and locking a coupling or connector onto a piece of pipe.

But if you really do want to look up the torque on a set screw connector, check the NEC - it will refer you to the White Book - that will refer you to the manufacturer, that will not even ask the tensile strength of the pipe you are using.

Have you noticed that different manufacturer's steel have different hardnesses, even though they are with toleerance of the UL (but maybe not with in tolerance of an electric/hyrdaullic bender?

Using set screw connectors on some piepe is like using aluminum instead of copper connectors - it will be tight when you finish, but will not stay that way ...

Set screw versus compression - consider this:

What type of connection would you prefer when joining the service drop to your service entrance conductors - compression or set screw?

Which is more likely to become a loose connection over time?

Now, extend your reasoning to conduits.

Compression fitting cost more so they are spec because firms get a percentage of toal cost.

In light of Kevin Cassidy statement, "as I do not and never have regarded conduits as grounds". I can only ask a rhetorical question, if a fault occurs to the conduit system how will it operate the OCP?

I darn sure better be an effective ground fault path! It may not be the only fault path but it is required to be bonded (250.96(A)).

I've seen a few people refer to EC&M in reference to a "study" done in California after an earthquake. I have done exhaustive searches and come up empty. However, it may be noteworthy that At&T (and others ...) INSIST on compression fittings in seismic locations, as in Section 2.5.15 of their installations requirements.

https://ebiznet.sbc.com/sbcnebs/Documents/TP76300/ATT-TP-76300-I.pdf

Hi Kevin you are right, it just depends on the contract, I work for the Government and their specifications state all compression connectors, compession connectors if tightened correctly will not open where set screws can. Also compession conectors can seal out water, it just depends on your use and their specs, I guess your company like the State Department has standards, and that way they keep every thing on same page...I Personally I would love to use a 4Inch set screw than a 4 Inch Compression, but that is not the specs.....

As i recently heard from Heider Electric the compression fittings offer more surface contact than the set screw.Especially if you scuff the pipe a little.

We feel that even through we use a grounding conductor we still want a compression coupling to ensure the conduit ground path is maintained as well as the fitting helps to contain explosive gases in the event of a fault in the pipe. I have had several large electrical contractors in the NY tri-state area also indicate that the fittings provide additional rigidity in the installation. Our designs are utilized in critical facilities such as data centers.

For what it's worth, after working over ten years as an industrial electrician, I prefer screw connections for ease of installation. When standing on a scissors lift, twenty feet off the deck and leaning over to make a connectiion, it would take three hands to tighten a compression fitting, two for the wrenches and one to hold the pipe tight. With a set screw, one hand could hold the pipe together and one to tighten the setscrew. Much easier and no need for a helper (or a third arm). My connections never failed. My method for any setscrew: tighten, loosen a bit, retighten. Never fails.

OK guys how about this take: ever seen a set screw coupling on an oil or water line? Compression coulplings are used on those and are very close to the same design. That should give some indication of the advantage going to compression in some cases, again it all boils down to proper training and proper installation, and last but not least attention to detail

I have to agree with Mike that set screw fittings provide as good a ground as compression. Although in the early years of my career (1970) we relied on the steel conduit as a ground path, I now have exclusively installed an equipment ground conductor(s) in all conduits, especially those with compression fittings.

This whole discussion boils down to the installation quality. If the work is installed properly, with UL listed components, there should be no real issue.

In my 30+ years as an licensed electrician and contractor, I have developed my own preferences. Overall, I am in the compression camp, but also know that in a disaster, set-screw connectors/couplings will hang on longer than compression. But I don't like the dimple the SS causes in the conduit. Deforming of the conduit can and does causes problems when pulling cable and can damage conductors.

I agree with the comments that steel is preferred over cast. Generally the cast will break because of too much pressure being applied. The steel seems to work much better.

And where is the discussion about the indentor-type "compression" fittings? They seem to have been long forgotten, but presented the same problems as SS fittings do today. But they certainly would hang on forever.

Quality has a price, both in materials and labor. A ECG provides that extra layer of assurance that the operation of the OCP will function should the end device have a failure to ground.

Just my 2-cents.

I would specify steel set screw connectors and couplings

I have used both . I agree that Raintight being the compression type fitting make the best continuous bond if installed correctly . Many times , seems especially when using set - screw type on larger conduit sizes , that the screw tap is coated with excess paint or not tapped correctly that contact or pressure point is not enough to bond securely . If the bond does make and you are attempting to go out on a limb to make your next attach- to point the screw indent has wobbled enough to stay loose . 30 plus years .

I certainly have seen more conduits open at compression fittings than set screw ones. I think electricians also install set screw fittings more reliably than compression fittings. It is easier to be satisfied the raceway is fully inserted into the fitting on set screw fittings. In compression fittings the ring often interferes with an easy and reliable fit. Sure electricians should be ensuring proper insertion but removing as many possible errors in the choice of fittings can help. Yes i know more than a few sparkys that are remiss in tightening set screws too. This spec has been on the books for so long that I thought that compression fittings must have come to market at the time when EMT fittings were installed with a dimpler. Even in concrete I prefer set screw Steel fittings. As for fault return path and lower impedance? I expect the compression fittings might be better the first fault but any second faults would be about equal after all the spot welds are made.

The difference and that being the only one, is that some eletricians have tightened the set screws tight enoug that it wil leave a small indent in the pipe and sometimes making a warp to the pipe itself. Thi is the only difference I have ever sen that can resultfrom the set screw vs the compression and the compression I have seen tofail over time.

My experience has been that after a good sized earthquake (here in So Calif.) we will find a large quantity of compression couplings have come apart from the conduit. Whether is was from poor workmanship or the violent movements of things moving in ceiling areas, I'm not sure. But where we came across set screw couplings, they were still intact (more so than the compression). The other thing I like about set screw coupling or connectors is that I can visually tell if the workman have tightened them down on the conduit or not.

I guess from the responses, what we are seeing is that the main problem is that a good many electricians do not use the fittings properly. They also seem to do a better job using the set screw (because it is easier) and often avoid tightening compression fittings as they should be.

So, do we spec a job in anticipation of poor workmanship? Do we not insist on better materials becaus we know that electricians will not do the required work?

Anyway, if the fittings are installed properly, I still cannot imagine set screw over compression.

Push down on a pipe with your finger tip as hard as you can and have someone pull the other end.

Wrap your finger around a pipe without nearly so much tension and have someone pull the other end.

Who holds the pipe easier?

Codes for most power plants require rigid steel conduit. This type of conduit is usually only screwed using a non tapered thread couplings. I know of no compression coupling that would give better conductivity to ridgid than properly made up screwed connectors- unless someone is foolishly teflon taping the threads.

I entirely agree ss coupling do a better job.

According to UL Standard 486 A-B, a terminal/lug/connector must be listed and marked for use with conductors stranded in other than Class B. With no marking or factory literature/instructions to the contrary, the terminal may only be used with conductors with the most common Class B stranded conductors. They are not suitable and should not be used with fine-stranded cables. UL engineers have said that few (if any) of the normal screw-type mechanical terminals that the PV industry commonly uses have been listed for use with fine stranded wires. The terminal must be marked or labeled specifically for use with fine-stranded conductors.

I have been the trade for 25+ years. It is my experience That compression fittings should only be used for weatherproofing such as water or snow. In snow areas ss fittings tend to break if set too tight.

I agree that set screw couplings are perfectly acceptable with EMT, especially the double set screws in larger sizes. Although I will accept the use of threaded conduit for grounding, I would never allow EMT to be used for grounding as I have seen many set screw and compression couplings pulled apart in the field.

I have been in the trade for 22 years and one instance that comes to mind which should require compression fittings, that is not part of a watertight assembly, is plenum ceilings. I have notice that electricians in my area of the country do not use plenum boxes or compression fittings in plenum return systems.

Having worked many GSA jobs, I have found older installations must have required these provisions. It seems ,as of late, that this practice is no longer recognized and/or enforced.

25 years in the trade, I have seen standards/specifications go from steel compression to whatever. In my experience die cast is a lesser connector in either compression or set screw. I prefer if the specifications allow to use compression steel up to two inch and steel two set screw on either side on anything above two inch. My greatest heartburn is finding fittings made in the USA for goverment jobs as all the major manufacturers have moved manufacturing offshore leaving only one niche market manufacturer I am aware who provide a product made in the USA but it is woefully less product as I am certain had I been handed a 3/4" coupling with only a 5/8" throat to install conduit with I would have requested/demanded (Nice words for it) a standard length coupling.