|By Mike Holt, for EC&M Magazine
Q1. I can't recall anything in the NEC about the orientation of a panel. Is there a
specific way that it has to be mounted? I have come across some customers who
prefer that the panel be mounted horizontally instead of vertically?
240.33 Vertical Position
Enclosures containing overcurrent protection
devices shall be mounted in a vertical position unless this is impracticable.
Circuit breaker enclosures can be installed horizontally, if the circuit
breakers are installed in accordance with 240.81. Figure 240-28
240.81 specifies that where circuit breaker handles are operated vertically, the
"up" position of the handle shall be in the "on" position. So in effect, an
enclosure that contains one circuit breaker can be mounted horizontally, but an
enclosure containing a panelboard with multiple circuit breakers would have to
be mounted vertically.
Q2. Is GFCI protection required for a 20A,
single-phase 208V pool pump motor that is hard wired?
A2. No, but
the1999 NEC text in 680.22(A)(1) gave the impression that GFCI protection was
required for hard-wired pool pump motors.
Q3. How is the working space
width requirement of 110.26(A)(2) measured?
A4. The working space shall
be a minimum of 30 in. wide, but in no case less than the width of the
equipment. The width of the working space is measured from left to right, from
right to left, or simply from the centerline of the equipment. In all cases, the
working space shall be of sufficient width, depth, and height to permit at least
a 90° opening of all equipment doors.
Q3. What is the maximum grounding
electrode resistance required by the NEC? I have heard values ranging from 25
ohms to as little as 1 ohm.
A3. There is no maximum grounding electrode
resistance; however, when the resistance of a single ground rod is over 25 ohms,
one additional electrode shall be installed at least 6 ft away to augment the
single ground rod electrode [250.56]. The NEC does not require more than two
ground rods to be installed, even if the total resistance of the two parallel
ground rods exceeds 25 ohms. The grounding electrode conductor to the first
ground rod, and between the two ground rods is not required to be larger than 6
Q4. Can a 24V Class 2 cable containing conductors for
control or signaling be run in the same raceway with 120V power
A4. The general requirement is that Class 2 circuit
conductors shall not be placed in the same raceway with conductors of power or
Class 1 conductors [725.55(A)(1)].
However, a Class 2 circuit can be
installed with power or Class 1 circuits, if the Class 2 circuit is reclassified
as Class 1 and installed in accordance with the requirements for Class 1 Circuit
(Article 725, Part II). In addition, the Class 2 marking on the equipment must
be removed, and overcurrent protection is provided in accordance with 725.23
[725.52(A)(1) Ex No. 2]. One final comment, Class 1 circuits are only permitted
to be in the same cable, enclosure or raceway with power-supply circuits where
the equipment powered is functionally associated with the Class 1 circuit
Q5. I have wired many pools over the years and I always
used Type UF cable underground for the pool pump motor. A new inspector is
telling me that the NEC does not permit this. What the deal?
A5. Type UF
is not permitted outdoors for pool, spa or hot tub wiring [680.21(A)], except as
a supply for a double insulated motor [680.21(B)].
Q6. Can communications
cable be installed within supply and return air ducts?
Communications cables can be installed in ducts, plenums, and other spaces used
for environmental air, but the cable must be Type CMP [800.53(A)].
What is the reason we are required to ground separately derived systems to an
acceptable electrode (earth)?
A7. I don't think there is any technical
reason to ground a separately derived system to an electrode. Because a
separately derived system is required to be bonded to the metal parts of the
electrical installation [250.30(A)(1)] this establishes a zero system reference,
stabilizes the system, and provides the low impedance path necessary to clear a
ground fault. Oh yeah, system bonding [250.30(A)(1)] automatically grounds the
system to the building grounding electrode system, via the effective
ground-fault path. Mike C, we need a graphic for this point.
learned today that the state electrical inspector does not require electrical
equipment to be listed or labeled. As a result unlisted equipment is typically
installed in our industrial facility. Does the inspector have the right to wave
this significant NEC requirement?
A9. The NEC does not require all
electrical equipment to be listed, it specifies that the authority having
jurisdiction (AHJ) has the responsibility for deciding on the approval of
equipment and materials [90.4 and 110.2]. The key to understanding this concept
is that electrical equipment is required to be "approved" by the AHJ, not
"listed or labeled." Approved, means "acceptable to the authority having
jurisdiction" [Article 100].
However, listing and labeling is often the
basis for approval [90.7], and Section 110.3 provides guidance for the
evaluation of equipment by the AHJ.
Q10. I am going to run three rigid
nonmetallic conduits, each containing 500 kcmil conductors, to supply a 1200A
panel. According to Table 250.122, I am required to supply a 3/0 AWG ground
wire. Do I have to pull a ground wire in each of the conduits?
let's first get the feeder conductor properly sized. A 1200A feeder requires 600
kcmil conductors, not 500 kcmil. This is because the ampacity of 500 kcmil is
only rated 1140A (380A x 3) at 75C [110.14(C) and 240.4(C)]. Now to your
question. The equipment grounding (bonding) conductor is required to be a
minimum of 3/0 AWG, and it is required to be installed in each of the
Q11. What is the minimum wire size permitted for an extension
cord that is plugged in a 20A circuit?
A11. Section 240.5(B)(3) permits
listed extension cord sets of 16 AWG or larger to be protected by 20A or less
branch-circuit overcurrent devices.
Q12. In our industrial facility, we
use cords for motor connections in a Class I hazardous location. I have been
told that the cord is required to be explosionproof. Is there such a thing as an
A12. There is no such thing as an explosionproof
cord. This is because the NEC only requires that the cord be of a type listed
for extra-hard usage in accordance with Table 400.4.
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Copyright © 2003 Mike Holt Enterprises,Inc.