2008 NEC Questions and Answers April Part 2

NEC Questions Based on the 2008 NEC Code

April Part 2

Here is the follow up to yesterday’s newsletter. This includes all of the answers to the questions sent yesterday so you can see how you did.

By Mike Holt, for EC&M Magazine

Q1. How far away can a meter be from the service disconnect?

A1. The NEC doesn’t have a minimum or maximum length for service conductors between meter equipment and service disconnect, so there are no distance requirements for the proximity of the meter to the service equipment. If the meter is located outside and the service equipment is located inside, the service disconnecting means must be placed at a readily accessible location nearest the point of service conductor entry [230.70(A)(1)].

Warning: Because service-entrance conductors don’t have short-circuit or ground-fault protection, their length must be limited when installed inside a building. Some local jurisdictions have a specific requirement as to the maximum length permitted within a building.

Q2. How many receptacles can be installed on a general-purpose branch circuit?

A2. The NEC doesn’t limit the number of GFCI-protected receptacle outlets on a general-purpose branch circuit in a dwelling unit [220.14(J)], but for other than dwelling units, the NEC limit is 13 receptacle outlets each at 180VA per mounting strap [220.14(I).

Circuit VA = Volts x Amperes

Circuit VA = 120V x 20A

Circuit VA = 2,400 VA

Number of Receptacles = 2,400 VA/180 VA

Number of Receptacles = 13

Q3. How many 12 AWG conductors can I install in a 1” EMT conduit?

A3. EMT must be large enough to permit the installation and removal of conductors without damaging the conductor insulation [358.22], and this is accomplished by complying with conductor fill limitations of Table 1 of Chapter 9. Since all of the conductors are the same size, Annex C, Table C.1 can be used to determine the number of conductors; twenty-six conductors.

Although the NEC permits twenty-six 12 THHN conductors in trade size 1 EMT, 310.15(B)(2)(a) requires the ampacity of the conductors to be adjusted when installing more than three current-carrying conductors in the raceway.

Q4. Can the lights in a dwelling unit bathroom be on the same circuit as the bathroom receptacles?

A4. According to 210.11(C)(3) one 20A, 120V branch circuit must be provided for the receptacle outlets required by 210.52(D) for a dwelling unit bathroom. This 20A bathroom receptacle circuit must not serve any other outlet, such as bathroom lighting outlets or receptacles in other rooms. However, the exception to this rule allows a single 20A, 120V branch circuit to supply all outlets in a single bathroom, as long as no single load fastened in place is rated more than 10A [210.23(A)].

Q5. After driving two ground rods, we still can’t get the ground resistance to be 25 ohms or less. What do we do?

A5. The NEC does not require that you achieve a 25 ohm ground resistance if you have two ground rods, so just go home and call it a day. The rule is that when the grounding electrode system consists of a single ground rod having a contact resistance to the earth of over 25 ohms, it must be augmented with an additional electrode located not less than 6 ft away [250.56].

Q6. What are the NEC requirements when using Type MC or NM cable as the feed and switch-leg for a single-pole switch?

A6. The white conductor within the cable must be used to supply the power to the switch and it must be permanently reidentified at each location where the conductor is visible to indicate its use as an ungrounded conductor [200.7(C)(2)]. The black conductor is to be used as the switch leg to the luminaire.

Q7. What are the rules for terminating more than one conductor on a terminal??

A7. The general requirement is that all terminals are rated for the termination of only one conductor. Terminals suitable for more than one conductor must be identified for this purpose, either within the equipment instructions or on the terminal itself [110.14(A)]. Some circuit breakers which are rated 30A or less are listed for the termination of two conductors and this information is contained in the product instructions.

Q8. What are the GFCI protection requirements for 15A and 20A, 125V receptacles?

A8. GFCI protection is required for all 15A and 20A, 125V receptacles located in the following dwelling unit locations [210.8(A)]:

(1) Bathroom Area. GFCI protection is required for all 15A and 20A, 125V receptacles in the bathroom area of a dwelling unit.

(2) Garages and Accessory Buildings. GFCI protection is required for all 15A and 20A, 125V receptacles in garages, and in grade-level portions of accessory buildings used for storage or work areas of a dwelling unit.

(3) Outdoors. All 15A and 20A, 125V receptacles located outdoors of dwelling units, including receptacles installed under the eaves of roofs, must be GFCI protected.

Exception to (3): GFCI protection isn’t required for a fixed electric snow-melting or deicing equipment receptacle supplied by a dedicated branch circuit, if the receptacle isn’t readily accessible and the equipment or receptacle has ground-fault protection of equipment (GFPE) [426.28].

(4) Crawl Spaces. All 15A and 20A, 125V receptacles installed in crawl spaces at or below grade of a dwelling unit must be GFCI protected.

(5) Unfinished Basements. GFCI protection is required for all 15A and 20A, 125V receptacles located in the unfinished portion of a basement not intended as a habitable room and limited to storage and work areas.

Exception: A receptacle supplying only a permanently installed fire alarm or burglar alarm system is not required to be GFCI protected [760.41(B) and 760.121(B)].

(6) Kitchen Countertop Surfaces. GFCI protection is required for all 15A and 20A, 125V receptacles that serve countertop surfaces in a dwelling unit.

(7) Laundry, Utility, and Wet Bar Sinks. GFCI protection is required for all 15A and 20A, 125V receptacles located within an arc measurement of 6 ft from the sink.

(8) Boathouses. GFCI protection is required for all 15A and 20A, 125V receptacles located in a dwelling unit boathouse.

GFCI protection is required for all 15A and 20A, 125V receptacles installed in the following nondwelling locations:

(1) Bathrooms. All 15A and 20A, 125V receptacles installed in commercial or industrial bathrooms must be GFCI protected.

(2) Kitchens. All 15A and 20A, 125V receptacles installed in an area with a sink and permanent facilities for food preparation and cooking [Article 100], even those that don’t supply the countertop surface , must be GFCI protected.

(3) Rooftops. All 15A and 20A, 125V receptacles installed on rooftops must be GFCI protected.

(4) Outdoors. All 15A and 20A, 125V receptacles installed outdoors must be GFCI protected.

Exception No. 1 to (3) and (4): Exception: GFCI protection isn’t required for a fixed electric snow-melting or deicing equipment receptacle supplied by a dedicated branch circuit, if the receptacle isn’t readily accessible and the equipment or receptacle has ground-fault protection of equipment (GFPE) [426.28].

(5) Sinks. All 15A and 20A, 125V receptacles installed within 6 ft of the outside edge of a sink must be GFCI protected.

Additional GFCI protection requirements are contained in Article 590 for temporary wiring as well as Article 680 for pools, spas and hot tubs, fountains, and hydromassage bathtubs.

Q9. What are the separation requirements when installing signaling and communications cables in cable trays with Type MC and TC cables?

A9. None. However, if the power conductors are installed as individual conductors, then a separation of 2 in. or a barrier required, in accordance with:

Coaxial Cables, 820.133(A)(1)(b) Ex 1

Class 2 and 3 Cables, 725.136(B) and 725.136(I)

Communications Cables, 800.133(A)(2) Ex 1

Fire Alarm Cables, 760.136(G)

Optical Fiber Cables, 770.133(B)

Intrinsically Safe Systems Cables, 504.30(A)(2) Ex 1

Radio and Television Cables, 810.18(B) Ex 1

Q10. What are working space requirements for telecommunications equipment?

A10. The working space requirement for power equipment contained in 110.26(A) do not apply to communications equipment [90.3], however the telecommunications equipment cannot be located in the required workspace for power equipment

Q11. Can a receptacle for a LCD projector that is cord-and-plug-connected be located above a suspended ceiling?

A11. No, cords are not permitted to be run through holes in structural or suspended/dropped ceilings [400.8(2)] and they are also not allowed to be concealed by walls, floors, or ceilings, or located above suspended or dropped ceilings [400.8(5)].

Q12. What are the cable fill limitations when installing telecom cable in a raceway?

A12. Where communications cables are installed in a Chapter 3 raceway, the raceway must be installed in accordance with Chapter 3, except for the raceway fill requirements, which do not apply [800.110].

Comments

We certainly do like your tests. I copy them and give them to the inspectors to complete and we go over them when we get time. They really make us think and search. Keep up the good work.

Donna
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The answer for Question 11 referring to cords above a drop ceiling is not complete. A corded condensate pump for HVAC equipment IS PERMITTED when terminated in a receptacle dedicated for that purpose In a drop ceiling. Since the pump is UL listed with the molded plug you can not cut it off. I have never seen a pump that permits hardwiring.

Marc Polan
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Q2. If branch circuit breakers at 15amp/1pole and 20amp/1pole are only rated to carry 80% capacity, would this not reduce the quantity of devices per circuit to 8 and 10 respectively. My understanding from overcurrent protection device manufacturer's, they don't make breakers this small that are 100% rated. Most inpsectors in San Francisco apply this rule.

Brian
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NEC Questions Based on the 2008 NEC Code

April Part 2

Question #9, separation if individual power conductors are used in conduit they must be separated... or have a barrier. Does this apply to dielectric (nonmetallic) fiber cables?

FHC
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Re: Q12 and raceway fill for communications. I am speaking from a Canadian code perspective here so no dispute as to the accuracy of your answer but a comment on intent. I am surprised there is no fill rules for communications conductors as I think the principals would still apply as they apply to mechanical strain place on the cables to install them. High speed networks require very specific and careful installation to get the rated performance from the structured wiring. Conduit fill is partly specified to prevent undue stress on the conductors when they are installed or removed. Pulling a cat 5 cable too hard can adversely affect performance and a raceway that can accomodate just 1 more teensy little cable is prime for damaging the cable as well as some of the ones already installed. I therefore find it surprising that the NEC does not include communications cable. FYI it is for that reason that CEC tables apply for all cables and wires.

Mike
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I would like to add some locations to question #8. Section 511.12 Repair Garages Section 513.12 Aircraft Hangers Section 555.22 Boatyards (which pulls in Art 511 if applicable) References are 2005, apologiies if 2008 is different. Thanks for periodic Code workout.

Larry
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I still don't get it! In your commercial calculations unit 11, figure 11.7 you are showing a single phase AC unit, 230 volts with an RLA of 18 amps. This AC unit is fed with #12 THHN, rated at 25 amps and is fused at the disconnect with 40 amp fuses? Maybe because I am not a student of fuses and their characteristics so I don't understand how the 40 amp fuses will ever come into play, so this is my question. This disconnect is fed with #12 THHN, so somewhere on the line side these #12's are surely going back to a panel or sub panel and these #12's are surely landing on a 20 amp breaker. So I do not see how these 40 amp fuses will ever protect anything in the circuit as long as the 20 amp breaker is doing it's job? Maybe a nano second spike?

Doyle Mills
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Mike,

Regarding your 2008 NEC Questions and Answers April Part 2. I think you need to review the answer to question #2. I sent the following to my crack team this morning:

Yesterday I forwarded Mike Holt’s answers to some code questions. Look at Mike’s answer to question #2.

Bill Berger, being ever alert and good looking, correctly observed that Mike’s answer is probably wrong! A 20 amp CB is rated at 80% (the industry default rating), so a load of 16 amps is all a 20 amp circuit breaker can be loaded. At 120 volts this is 1920 VA. Dividing 1920 by the code allowed 180 VA per receptacle, results in only 10 receptacles per 20 amp circuit. So the correct answer is 10!

By the way, our standard is only six receptacles per circuit, not ten. We do this to be conservative. Many of our clients have similar limits. If you have computers, we only want three or four receptacles per circuit.

Note, if you want to pay a lot more, you can buy a 20 amp circuit breaker rated at 100%. In that case, Mike’s answer would be correct. In all my years, I have only specified a 100% rated branch circuit breaker twice.

Mike, I base this on the fact that unless the breaker is rated at 100%, common breakers and fuses are rated at 80% of their name plate. Hence the 16 amp maximum rather than the 20 amp name plate.

You have probably received a lot of comments on this. Keep up the good work.

Thank you,

Max Billington, P.E. Chief Electrical Engineer LEED® Accredited Professional mbillington@rmhgroup.com

The RMH Group, Inc. 12600 West Colfax Ave., Suite A-400 Lakewood, Colorado 80215

P 303-239-2734 F 303-235-0218

Max Billington, P.E.
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I left my NEC book home. Do the new 2008 GFCI outlet requirements of question #8 now apply to dedicated outlets for appliances?

matt
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If you are using a circuit breaker the breaker is only rated at 80% of the nameplate. So a 20A breaker can only handle 16A, therefore only 10 receptacles can be put on a 20A branch circuit. 20Ax80%=16A 16Ax120V=1920VA 1920VA/180VA=10

Matt Bergheger
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Mike, The NEC allows the service disconnect to be located in an accessible location either outside the building or inside the building according to 230.70(A)(1).. If located inside the building the disconnect must be located nearest the point of entry and the AHJ determines how near near is. However, according to NEC 230.6 Conductors are considered outside the building if they are under 2" of concrete, or surrounded by 2" of concrete, or in a vault, or under a building in conduit and 18" below earth. This means that when we meet the conditions of NEC 230.6, then we can place the disconnect anywhere in a building and still meet the requirements of 230.70(A)(1). If the disconnect is located "at" the point of entry into the building, the AHJ must allow it unless their jurisdiction has documention of exceptions to this part of the NEC.

Bill
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i thought you can run a 20amp circuit to a gfci outlet in one bathroom and load side out to other plugs in another bathroom?

jim
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Mike, I\'ve been an electrician for fourty years. I started at Dallas Power & Light in 1968 as a Power Plant Maintaince Electrician. Your web site is the best access to information I have ever seen. I think your doing a really great job. Please keep it up.

Jack

JACK
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Thank you for your continue input on NEC Code, answer and question you provide to the industry.

Victor Fernandez
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Reply from: Victor Fernandez
I believe the light on the bathroom should not be on the GFCI
Reply to Victor Fernandez

What are the requirements for an existing building being used as a doctors office, in regards to the patient treatment rooms.

Ken
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The two ground rod rule might sound strange but it has to do with the way electrical energy enters the earth. Two electrodes gives increased surface area therefore the 25 ohm requirement is no longer needed as it would for a single rod. This grounding would not be sufficient for a light ends unit of an oil refinery but it suffices for lightning grounding for a residence. However, should someone cut your neutral between the transformer and house your connected neutral-which could be a bare as it is in older installation-could be at a dangerous potential to ground. That is why I hate bare neutrals. Of course if someone does cut that neutral your 29 inch brand new flat screen could be fried-In a word, you'll know something ain't right.

Bob
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Q4. Can the lights in a dwelling unit bathroom be on the same circuit as the bathroom receptacles?

Is it not true that the NEC specifies all bathroom outlets have GFCI Protection? Reading further, you address this issue in question 8 (1). I believe that safety would insist, and I have always followed this rule that these two sources be separate and not branched.

Jerry
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