Charlie Trout, author of Code FAQs and Code Question of the Day, has retired. For the rest of 2013, enjoy these snippets from his daily responses.
Follow specs or nameplate?
With regard to the correct size of conductors on any unit (e.g., RTUs, VAVs, AHUs), the nameplate rating or the specs shall be followed (whichever conductor is bigger). In other words, this nameplate overruled any addition to size of conductor. So, if the unit calls for 58.5 amperes (A), then you need to use the next standard size overcurrent protection device (which is 60A). Therefore, No. 6 copper is acceptable. If, for some reason, the engineer wrote down No. 4 on the specs, then it shall be followed. Electricians at job sites don’t usually compute for any discrepancies. Most of the time, they follow whatever is written on specifications or the nameplate.
Let’s go through this completely. The motor nameplate shows 58.5A. However 430.6(A)(1) requires that Table 430.250 be used for determining the motor full-load current (FLC) rating for three-phase alternating current (AC) motors instead of the actual motor nameplate FLC rating. Table 430.250 shows an FLC rating for a 50-horsepower (hp), 460-volt (V) motor to be 65A. The reason for using the FLC ratings shown in Table 430.250 is that the actual full-load current rating for motors of the same horsepower may vary, and requiring the use of the table ensures that, if a motor must be replaced, this can be accomplished without making changes to other component parts of the circuit. NEC 430.22 requires the conductors supplying a single motor to have an ampacity not less than 125 percent of the motor FLC as determined by Table 430.250. Multiply 65 × 1.25 = 81.2, and, as shown in Table 310.15(B)(16), this requires a 4 AWG conductor.
Section: Table 430.250, 310.15(B)(16), 430.22, 430.6(A)
Service panel makeup
I’m an inspector with a question on service panel makeup. I have an electrician that ties all the neutrals into pairs with a wire twist nut and pigtails out to the neutral bar. My understanding is that, unless he balances the disconnect placement with one disconnect on L1 and the other on L2 on two 20A disconnects, he can produce 40A on the number 12 neutral wire. Where can I read about this in the NEC?
Your reference is to three-wire circuits where the neutral conductor is shared. Check out the definition in Article 100 of Branch Circuit, Multiwire, where it shows two or more ungrounded conductors with a voltage between them and a grounded conductor that has an equal voltage between it and each ungrounded conductor of the circuit. If the two circuit conductors are placed on the same phase, the neutral conductor—which they are sharing—will carry the full load of both conductors rather than just the unbalanced load. So your second statement is correct. The other part of your question—where the installer is splicing neutrals together and pigtailing onto the neutral—is not in conformance with 408.41, which requires each grounded conductor to terminate in an individual terminal that is not also used by another conductor.
IC-rated fixtures and insulation
My inspector red-tagged my residential project, saying that the insulation in the attic cannot be in contact with the recessed fixtures I’ve installed. He said there must be at least 3 feet of clearance all around and no insulation installed above the fixture. The fixtures are listed and marked “IC” rated. Am I missing something, or is this inspector requiring something above Code minimum?
Section 410.116(B) covers installations of recessed fixtures and clearly indicates that, if the fixture is marked “Type IC,” then thermal insulation can be in contact with the fixture. You may have to show the marking on the fixture and the section of the Code that specifically permits thermal insulation to be in contact where so identified. The inspector has the responsibility for interpretations and approvals of installations as provided in 90.4. Sometimes electrical contractors and electricians have to help them get it right.
Supplying a heat-fan-light
Can a 1,500-watt (W) heat-fan-light unit be supplied from the required 20A receptacle branch circuit in the bathroom of a dwelling unit?
The full-load current of this unit exceeds 50 percent of the bathroom branch-circuit rating and is not permitted on the required receptacle circuit. The exception to 210.11(3)(C) permits other loads to be supplied from this 20A circuit if it supplies a single bathroom, but 210.23(A)(2) limits the load of utilization equipment that is fastened in place to 50 percent of the ampere rating of the branch circuit.
Section: 210.11(3)(C), 210.23(A)
What to use for an MBJ
A 200A service upgrade has taken place at a residence. The grounding electrode conductors are too short to reach the neutral bar but will make it to a listed and labeled auxiliary ground bar. The ground bar has been installed per the panel manufacturer’s installation instructions using the supplied hardware. The electrical contractor has connected a properly sized bonding jumper, in this case No. 4 copper, from the neutral bar to the properly installed auxiliary ground bar. The green main bonding jumper (MBJ) screw is still in place. This creates a redundant MBJ. Given this situation, is it permissible to connect grounding electrode conductors to the auxiliary ground bar? Should the green screw remain in place, or should it be removed?
I believe you mean equipment grounding conductors (EGC), and, based on your information, it would be better to use the green screw as the MBJ because that is how the equipment is listed. The wire-type MBJ is not necessary if the screw-type MBJ is installed and connects the neutral bus of the equipment to the metal panel enclosure.
Doing the minimum
I’ve noticed with Code Question of the Day, no one asks whether exceeding the Code is permissible. Sometimes exceeding the Code is better than doing the minimum, which is what the Code requires. When I worked the shops, it helped the business [to provide] a better product, which the customers appreciated. Each and every one of us owes a responsibility to furnish the best job possible, and I believe if you explain to your customers, they won’t mind the additional cost. Workmanship does count, and neatness is obvious.
CQD has often discussed NEC 90.1(B) Adequacy, which states in part that “Compliance therewith and proper maintenance results in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use.” Also CQD has always pointed out to subscribers that the NEC states in 90.1(C) that it is not intended as a design specification—but thanks for the reminder. It costs just as much to do a job wrong as to do it properly, so I don’t think there would be additional cost. The National Electrical Contractors Association (NECA) has an industry-accepted standard NECA 1 2010, “Good Workmanship in Electrical Construction,” that describes and illustrates neat and workmanlike electrical installations.
Section: 90.1(B) and (C)
Neutral at switch locations
There is a requirement to install a neutral at switch locations. The rule does not say one has to connect the neutral or use it. The issue is that I can still purchase an occupancy sensor switch with a neutral pigtail and a switch that has only an equipment grounding (green) conductor pigtail. Both are listed and available by more than one manufacturer. Is it a violation to install the switch without the neutral pigtail if both are listed and available when the NEC just requires the neutral to be installed in the switch location?
The NEC requires that, where switches controlling lighting loads are supplied by a grounded general-purpose branch circuit, the grounded circuit conductor (neutral) for the controlled lighting circuit shall be provided at the switch location. The intent of this new requirement is that the neutral is required to be installed in that location, so if a listed switch requires the neutral, it can be connected to the device. This keeps load current off the equipment grounding conductor.
The NEC does not currently require the connection of the installed neutral to that device, but perhaps it should. The listing of the product does. If there are two listed switches available on the market for installation that have a neutral and that do not, then it appears as though the product standard needs to be revised. There is a restriction of load-side grounding connections located in 250.24(A)(5) and 250.30(A) that could also be used to require the correct switch to be used.
Section: 404.2(C), 110.3(B), 250.24(A)(5) and 250.30(A)