NEC Questions Based on the 2008 NEC Code

April Part 1

 

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. Am I required to secure Type MC cable that is located under a raised floor?

A1. Yes. All wiring methods under raised floors must be secured in accordance with the wiring method requirements [645.5(D)(2)]. For example, Type MC cable with four or less conductors sized no larger than 10 AWG must be secured within 12 in. of every outlet box, junction box, cabinet, or fitting and at intervals not exceeding 6 ft [330.30].

 

Q2. Can I connect the neutral conductor to the equipment grounding terminal at both the transformer and the first disconnect?

A2. No. The NEC requires the neutral conductor of a transformer that meets the definition of a separately derived system to be connected to the equipment grounding conductor at the transformer or the disconnecting means or overcurrent device on the secondary, but not at both locations [250.30(A)(3)]. The connection of the neutral conductor to the equipment grounding conductor is called a system bonding jumper, and it provides a low-impedance fault current path to the power supply to facilitate the clearing of a ground fault by opening the circuit overcurrent device. For more information, see 250.2, 250.4(A)(5), 250.28, and 250.30(A)(1).

 

CAUTION: Dangerous objectionable neutral current will flow on conductive metal parts of electrical equipment as well as metal piping and structural steel, in violation of 250.6(A), if more than one system bonding jumper is installed.

Objectionable neutral current on metal parts can cause electric shock, fires, and improper operation of electronic equipment and overcurrent devices such as GFPs, GFCIs, and AFCIs.

 

Q3. Does the Code allow equipment rooms containing overcurrent devices to be locked? What about locking panel covers and disconnecting means?

A3. Yes, electrical equipment rooms and enclosures housing electrical equipment or apparatus can be locked [110.26(G)].

 

Q4. Can a single transfer switch be used to supply two separate panels?

A4. It depends on the type of loads the panels serve. Emergency lighting or another load that the AHJ deems emergency (Article 700) must be supplied by it’s own separate transfer switch [700.6(D)]. Legally required standby and/or optional standby system loads are permitted to be supplied by a single transfer switch.

 

Q5. Does the NEC require GFCI protection for a 15A/125V receptacle in a basement for a sump pump?

A5. Yes. 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 [210.8(A)(5)].

 

Q6. What are the disconnect requirements for appliances, such as dishwashers in a dwelling unit or a hand dryer in a restaurant?

A6. Each appliance requires a means of disconnect [422.30]. A unit switch with a marked “off” position that is a part of the appliance can serve as the appliance disconnect, if it disconnects all ungrounded conductors [422.34]. If a unit switch is not provided on the appliance, then a switch or circuit breaker located within sight from the appliance can serve as the appliance disconnecting means, unless the switch or circuit breaker is capable of being locked in the open position [422.31(A)].

 

Q7. Is a disconnect required to be within sight of electric space heating equipment if the unit has a factory installed circuit breaker?

A7. No. A unit switch with a marked “off” position that is an integral part of the equipment can serve as the heater disconnecting means, if it disconnects all ungrounded conductors of the circuit [424.19(C)].

 

Q8. What are the requirements for installing isolated ground receptacles?

A8.The grounding terminal of an isolated ground receptacle must be connected to an insulated equipment grounding conductor run with the circuit conductors [250.146(D)].

The circuit equipment grounding conductor is permitted to terminate to the panelboard supplying the power or it is permitted to pass through the panelboard [408.40 Ex], boxes, wireways, or other enclosures [250.148 Ex] without a connection to the enclosure as long as it terminates at an equipment grounding conductor terminal of the derived system or service.

 

Q9. I’m confused, when must I use a 4-wire cord for dryers and ranges?

A9.The frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet boxes that are part of the circuit for these appliances must be connected to the equipment grounding conductor (4-wire cord/receptacle) [250.134(A) and 250.140].

CAUTION: Ranges, dryers, and ovens have their metal cases connected to the neutral conductor at the factory. This neutral-to-case connection must be removed when these appliances are installed in new construction, and a 4-wire cord and receptacle must be used [250.142(B)].

For existing installations where an equipment grounding conductor isn’t present in the outlet box, the frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet boxes that are part of the circuit for these appliances may be connected to the neutral conductor (3-wire cord/receptacle) [250.140 Ex].

 

Q10. What are the grounding and bonding requirements for hydromassage bathtub?

A10. If the building contains a metal piping system, it must be bonded, with a solid copper equipotential bonding jumper, sized not smaller than 8 AWG, to the circulating pump (if it’s not double insulated), and to any other grounded metal parts that contact the circulating water. This equipotential hydromassage bonding jumper is not required to be connected to any remote panelboard, service equipment, or electrode [680.74].