NEC Questions Based on the 2008 NEC
December

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 are being told that we must bond our raceways containing phone cables to the cable tray when the raceway leaves the cable tray. How do we size the bonding conductor?

A1. Systems operating below 50V (such as communications systems) are not required to be grounded [250.20(A)], so there is no requirement to bond the raceways to anything.

 

Q2. What are the standard heights for mounting receptacles and switches in a commercial building?

A2. If the building or space is required to be accessible to disabled persons, the standard unobstructed reach ranges are from 15 to 48 in. [Section 308 of ICC/ANSI A117.1-2003].

 

Q3. How do I size the equipment grounding conductor for parallel conductors in a cable tray?

A3. When circuit conductors are run in parallel [310.4], an equipment grounding conductor must be sized in accordance with Table 250.122, based on the rating of the circuit overcurrent device [250.122(F)]. Remember that single conductors used as equipment grounding conductors in cable trays must be sized 4 AWG or larger [392.3(B)(1)(c)].

 

Q4. Where does the code address which way the grounding terminal of a receptacle goes (up or down)?

A4. Position of the ground terminal of a receptacle isn’t specified in the NEC. The ground terminal can be up, down, or to the side. Proposals to specify the mounting position of the ground terminal have been rejected through many Code cycles.

 

Q5. In a two family dwelling, is it legal to have the panel in one unit, so the other unit does not have access to it?

A5. No, each occupant must have ready access to the overcurrent devices for their occupancy [240.24(B)].

 

Q6. What is the difference between Class 1, Class 2, and Class 3 circuits?

A6. 725.2 defines these circuits as:

 

Class 1 Circuit. That wiring system between the load side of the Class 1 circuit overcurrent device and the connected equipment such as relays, controllers, lights, audible devices, etc.

Author’s Comment: Class 1 nonpower-limited circuits can operate at up to 600V and the power output isn’t limited [725.41(B)].

 

Class 2 Circuit. The wiring system between the load side of a Class 2 power supply and the connected Class 2 equipment. Class 2 circuits are rendered safe by limiting the power supply to 100 VA for circuits that operate at 30V or less and the current to 5 mA for circuits over 30V [Chapter 9, Table 11].

Author’s Comment: Class 2 circuits typically include wiring for low-energy, low-voltage loads such as thermostats, programmable controllers, burglar alarms, and security systems. This type of circuit also includes twisted-pair or coaxial cable that interconnects computers for Local Area Networks (LANs) and programmable controller I/O circuits [725.121(A)(3)].

 

Class 3 Circuit. The wiring system between the load side of a Class 3 power supply and the connected Class 3 equipment. Figure 725−4

Author’s Comment: Class 3 circuits are used when the power demand exceeds 0.50 VA, but not more than 100 VA, for circuits over 30V [Chapter 9, Table 11].

 

Q7. We are being told that the 2008 NEC now has requirements for wearing personal protection equipment. Can you show us where in the Code we can find this?

A7. The NEC is an installation standard, so it does not address personal protection equipment (PPE).

 

Q8. Are there any rules regarding electrical outlets that are close to sinks in a school?

A8. All 15A and 20A, 125V receptacles installed within 6 ft of the outside edge of a sink must be GFCI protected [210.8(B)(5)].

 

Q9. Can we use Type NM Cable (Romex) in a four story apartment building?

A9. If your apartment building is constructed of (or permitted to be constructed of) Type III, IV or V construction, it may be used [334.10(2)].

 

Q10. Is there an exception to the 30-inch burial requirement for a ground ring?

A10. No, a ground ring encircling the building or structure, consisting of at least 20 ft of bare copper conductor not smaller than 2 AWG, must be buried not less than 30 in. [250.53(F)].

 

Q11. Is it legal to tape a white wire black and use it a phase conductor in a raceway?

A11. No, a conductor with white insulation can only be used for the ungrounded conductor in a raceway [200.7(C)].

 

Q12. Can a junction box contain both 277V and 120V conductors?

A12. Yes since all conductors have an insulation voltage rating not less than the maximum circuit voltage (277V) [300.3(C)].

 

Q13. Is it acceptable to install a ground rod at the base of light poles for a commercial parking lot?

A13. Acceptable? Yes. Required? No. Does it serve any safety purpose? No.

 

Q14. Can a GFCI receptacle be installed on an AFCI-protected circuit?

A14. Yes.