2008 NEC Questions and Answers - March

NEC Questions Based on the 2008 NEC

March - 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. We drove a ½ inch ground rod with a tested resistance of less than 10 ohms. We are now being told that this rod needs to be 5/8 inch because it isn’t listed. If the rod is less than 25 ohms, do I really have to make it bigger?

A1. Well, unlisted ground rods of stainless steel, copper coated steel, or zinc coated steel must have a diameter of at least ⁵/8 in. and listed ground rods must have a diameter of at least ½ in., so your inspector is correct [250.52(A)(5)(b)].

Q2. We have been written up for installing 15A receptacles on the 20A circuits for a residential kitchen. Have we been doing this wrong for all of these years, or is this a new rule?

A2. Where connected to a branch circuit that supplies two or more receptacles, receptacles must have an ampere rating in accordance with the values listed in Table 210.21(B)(3). Remember that a duplex receptacle has two contact devices on the same yoke [Article 100], which means even one duplex receptacle on a circuit makes that circuit a multioutlet branch circuit. With that said, a 15A duplex receptacle is allowed on a 20A branch circuit.

Q3. Is there somewhere in the Code that tells us the largest size of conductor that can be spliced under a wire nut?

A3. Not really. The closest thing you are going to find is 110.14, which tells us that conductor splicing devices must be identified for the conductor material and they must be properly installed and used. The answer to how many conductors and what size can be installed in a wire connector is simply “whatever the connector is listed for.”

Q4. We installed a two wire circuit plus a four twisted pair conductor cable for communications inside of a raceway to some gasoline dispensers. Now we are being told that we have ten current carrying conductors inside of the raceway and need to adjust the conductor ampacity down. Do we really have to do this?

A4. Well I have good news and bad news for you. The good news is the ampacity doesn’t have to be adjusted because twisted pair cables are not considered current carrying conductors. The bad news is communications conductors must not be placed in any raceway, compartment, outlet box, junction box, or similar fitting with conductors of electric power or Class 1 circuits [800.133(A)(1)(c)]. These means you have to pull those cables out of the raceway altogether.

Q5. I am having a hard time understanding the rule on how to size the circuit breaker/fuse for a motor that has separate overload protection. Can you please help me understand this rule?

A5. Sure. The motor branch-circuit short-circuit and ground-fault protective device must comply with 430.52(B) and 430.52(C).

(B) All Motors. A motor branch-circuit short-circuit and ground-fault protective device must be capable of carrying the motor’s starting current.

(1) Each motor branch circuit must be protected against short circuit and ground faults by a protective device sized no greater than the following percentages listed in Table 430.52.

Example: What size conductor and inverse time circuit breaker are required for a 2 hp, 230V, single-phase motor?

Step 1: Determine the branch-circuit conductor [Table 310.16, 430.22(A), and Table 430.248]:

12A x 1.25 = 15A, 14 AWG, rated 20A at 75°C [Table 310.16]

Step 2: Determine the branch-circuit protection [240.6(A), 430.52(C)(1), and Table 430.248]: 12A x 2.50 = 30A

Q6. I have two 225A roof top units with integral circuit breakers. We have an 800A breaker that we are going to use to feed both units, and are wondering if we can use a tap rule to save some money. The 800A breaker is installed outside, and there are two raceways to the units which will also be outside. Can you help us size the feeder circuits?

A6. Using the outside feeder tap of unlimited length [240.21(B)(5)], you could use 4/0 AWG (rated 230A at 75°) to each unit. The rules for this type of tap are as follows:

(1) The tap conductors must be suitably protected from physical damage in a raceway or manner approved by the authority having jurisdiction.

(2) The tap conductors must terminate at a single circuit breaker or a single set of fuses that limits the load to the ampacity of the conductors.

(3) The overcurrent device for the tap conductors must be an integral part of the disconnecting means, or it must be located immediately adjacent to it.

Q7. Can we use EMT in a masonry wall, or must we use RMC?

A7. Electrical metallic tubing, elbows, couplings, and fittings can be installed in concrete, in direct contact with the earth, or in areas subject to severe corrosive influences where protected by corrosion protection and judged suitable for the condition [358.10(B)]. According to the UL White Book (Category FJMX), “galvanized EMT installed in concrete on grade or above generally requires no supplementary corrosion protection.”

Q8. Does a fire alarm control panel need to have the working space discussed in 110.26?

A8. Yes, it does. For the purpose of safe operation and maintenance of equipment, sufficient access and working space in accordance with 110.26 must be provided. Remember that Article 110 contains the general requirements of the Code, and is applicable to all installations covered in Chapters one through seven (such as fire alarms in Article 760). Nothing in Article 760 supplements or modifies [90.3] the general rule of 110.26, so compliance is mandatory.

Note: Where special permission is granted in accordance with 90.4, working space for equipment that operates at not more than 30V ac or 60V dc can be less than the distance in Table 110.26(A)(1) [110.26(A)(a)].

Q9. We are being told that we must GFCI protect our receptacle for the washing machine if it is within six feet of the laundry sink. We chose to use a single receptacle for the washer and the inspector still won’t pass it.

A9. Your inspector is correct that GFCI protection is required for all 15A and 20A, 125V receptacles located within an arc measurement of 6 ft from the sink [210.8(A)(7)], even if a single receptacle is employed.

Q10. We have a load of 2000A, and we are using a busway to provide power. Because of voltage drop, we are finding that we need to use a 2500A busway. The inspector is now saying that we must use a 2500A breaker instead of a 2000A breaker, which is going to cost us a lot of money. Is the inspector correct?

A10. No. 368.17(A) requires that busway be provided with overcurrent protection in accordance with the rating of the busway, but this doesn’t mean you can’t have a smaller breaker than the rating of the busway. This would be similar to saying that you can’t put 10 AWG conductors on a 20A breaker, a practice that occurs every day for parking lot lighting.

Q11. We cut our wire too short in a few outlet boxes so I spliced on a couple inches of conductor so that I had six inches of free conductor at each location. The inspector says the free conductor must be “unspliced.” Is he right?

A11. Nope. He is correct that the NEC requires at least 6 in. of free conductor, measured from the point in the box where the conductors enter the enclosure, must be left at each outlet, junction, and switch point for splices or terminations of luminaires or devices [300.14]. Nowhere in this rule does it require that free length of conductor be unspliced.

Q12. I have a hot tub disconnect located fifteen feet from a hot tub and it’s plainly visible from the tub. Someone told me that the disconnect is required to be visible from the motor as well. Is this true?

A12. No. The maintenance disconnecting means for hot tubs must be readily accessible and located within sight and at least 5 ft from the hot tub unless separated from the open water by a permanently installed barrier that provides a 5 ft reach path or greater. This horizontal distance is measured from the water’s edge along the shortest path required to reach the disconnecting means [680.12].