NEC Questions Based on the 2008 NEC

February

 

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. What are the NEC requirements when installing a panel directly underneath another panel?

A1. Equipment such as raceways, cables, wireways, cabinets, panels, etc., can be located above or below electrical equipment, but it must not extend more than 6 in. into the equipment’s working space [110.26(A)(3)].

Q2. In an industrial environment, do we have to pull an equipment grounding conductor through our EMT raceways?

A2. No. An equipment grounding conductor can be any one or a combination of the items listed in 250.118, and this includes EMT, so no equipment grounding conductor of the wire type would be required inside of the raceway.

Q3. What are the lighting and switching requirements for stairways?

A3. In dwelling units, not less than one wall switch-controlled lighting outlet must be installed [210.70(A)(2)(a)]. Where the stairway between floor levels has six risers or more, a wall switch must be located at each floor level and at each landing level that includes an entryway to control the illumination for the stairway [210.70(A)(2)(c)]. There are no NEC requirements for other than dwelling units.

Q4. How do we size primary overcurrent device and conductors for a 45 kVA transformer 480 to 120/208V?

A4. The primary winding of a transformer must be protected against overcurrent in accordance with the percentages listed in Table 450.3(B) and all applicable notes.

Step 1: Determine the primary current:

I = VA/(E x 1.732)

I = 45,000 VA/(480V x 1.732)

I = 54A

Step 2: Determine the primary overcurrent device rating [240.6(A)]:

54A x 1.25 = 68A, next size up 70A, Table 450.3(B), Note 1

Step 3: The primary conductor must be sized to carry 54A continuously (54A x 1.25 = 68A) [215.2(A)(1)] and be protected by a 70A overcurrent device [240.4(B)]. A 4 AWG conductor rated 85A at 75°C meets all of these requirements [110.14(C)(1) and 310.16].

Q5. What are the requirements for supporting communications raceways and cables above a suspended ceiling?

A5. Communications raceways and communications cable assemblies must be securely fastened in place, and ceiling-support wires or the ceiling grid must not be used to support communications raceways or communications cables [800.24]. Raceways and cables are permitted to be supported by independent support wires attached to the suspended ceiling [300.11].

Q6. We are being told that you can only have one bedroom on an AFCI-protected circuit. Is this true?

A6. No. The NEC doesn’t limit the number of receptacle outlets on a general-purpose branch circuit in a dwelling unit. Although there’s no limit on the number of receptacle outlets on dwelling general-purpose branch circuits, the NEC does require a minimum number of circuits to be installed for general-purpose receptacles and lighting outlets [210.11(A)] for the dwelling. In addition, the receptacle and lighting loads must be evenly distributed among the required circuits [210.11(B)].

Q7. We installed florescent lighting in a warehouse and the inspector says that the fixtures must have a ‘heavy duty’ rating because they are on a 30A circuit. Can we use 20A inline fuses to get around this issue?

A7. No. The NEC specifically states that “lampholders connected to a branch circuit rated over 20A must be of the heavy-duty type. According to 210.3, the rating of a branch circuit is determined by the rating of the branch-circuit overcurrent device. An inline fuse is is a supplementary overcurrent device [Article 100] and are not permitted to serve as the required branch-circuit overcurrent device [240.10].

Q8. We have interconnected office furniture, and the inspector says we need to have simultaneous disconnect for ALL circuits that feed it, is this true?

A8. No, only multiwire branch circuits must have a means to simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates [210.4(B) and605.6].

A multiwire branch circuit consists of two or more ungrounded circuit conductors with a common neutral conductor. There must be a difference of potential (voltage) between the ungrounded conductors and an equal difference of potential (voltage) from each ungrounded conductor to the neutral conductor [Article 100 Branch Circuit, Multiwire].

Q9. Can the ground wire from a ground rod terminate in the meter socket enclosure, or must it terminate in the service disconnect?

A9. Either location is fine with the NEC. The rule states that the grounding electrode conductor must connect the service neutral conductor to the grounding electrode at any accessible location, from the load end of the service drop or service lateral, up to and including the service disconnecting means [205.24(A)(1)].

Q10. What are the requirements about installing receptacles face up on counter tops in a commercial occupancy?

A10. None, but 406.4(E) states that receptacles must not be installed in a face-up position in countertops or similar work surface areas in a dwelling unit.

Q11. What are the bonding requirements for pool water?

A11. A minimum conductive surface area of 9 sq in. must be installed in contact with the pool water. This water bond is permitted to consist of metal parts that are required to be bonded in 680.26(B).