|By Mike Holt for EC&M Magazine
Q1. I have heard that unused wires must be removed unless they are tagged for future use.
My plant has lots of unused conduit runs with the old feed wires taped up in the
panel. Is there some where in the code where it says these runs should be
removed? It is starting to look like a spider web in some spots.
NEC does not require unused power and lighting conductors be removed, except for
cellular and underfloor raceways [372.13, 374.7, and 390.7].
the accessible portions of abandoned low-voltage and limited-energy cables shall
be removed. According to Chapters 7 and 8, abandoned cables are those that do
not terminate at equipment and are not identified for future use.
it illegal to affix a permanent lock on an electrical panel? I want to be able
to quickly shut off breakers or the whole panel in case of an
A2. The NEC does not prohibit a permanent lock on a panelboard
or disconnect switch. This means that a switch could be locked open or locked
closed. I realize that in some cases either of these two conditions could be a
hazard, but this issue is not within the scope of the NEC.
Q3. Is there a
code requirement as to the height of a receptacle outlet?
A3. No, unless
the receptacle is specifically required by the NEC. For example, the required
wall receptacle outlets for a dwelling unit shall not be located above 5.5 ft
[210.52]. Required dwelling unit kitchen counter top receptacles shall not be
located more than 20 in. above the countertop [210.52(C)(5)], and required
outdoor receptacles for one and two family dwellings shall not be located more
than 6.5 ft above grade [210.52(E)].
Q4. How close to a shower stall or
hydromassage bathtub can I install a switch?
A4. Switches are not
permitted to be located within the wet location of a tub, shower space, or
hydromassage tub [404.4 and 680.72]. Which means it can be located "next" to the
tub or shower space. However, switches must be located at least 5 ft from pools,
spa's and hot tubs [680.22(C)].
Q5. Two times in the last couple of
months I have been instructed by the inspector to install a second ground rod. I
took ohm readings both times and explained that the ohm readings were less than
25 ohms. To top it off, one inspector wanted it less than six feet, the second
inspector wanted it over six feet.
A5. If a rod electrode does not have a
resistance to ground of 25 ohms or less, it must be supplemented by a second
electrode located not less than 6' away.[250.56]
Q6. In your book
"Understanding the NEC," you show service conductors feeding through the first
disconnect to the second disconnect. You make it sound like this is okay even
though you refer us back to 230.7.
A6. Section 230.7 states that
"Conductors other than service conductors shall not be installed in the same
service raceway or service cable." Service conductors are permitted in the same
Q7. I hear that the NEC no longer allows receptacles to be
located above a suspended ceiling. Frequently there is the desire to have a
receptacle above the ceiling to plug in a ceiling-mounted LCD video projector,
or small transformer for security installations. I can't find the NEC rule that
prohibits locating receptacles above a suspended ceiling.
are permitted above a suspended ceiling, however cords are not permitted to be
concealed by walls, floors, or ceilings nor are they permitted to be located
above suspended or dropped ceilings [400.8(5)]. For the example in your
question, a receptacle would have to be mounted in the ceiling, accessible from
below. However, a receptacle above the suspended ceiling might be required or
desirable for use for portable equipment and/or tools.
210.63 requires a 125V, single-phase, 15- or 20-ampere-rated receptacle outlet
at an accessible location for the servicing of heating, air-conditioning, and
Q8. I designed a chiller plant based on a shop
drawing that listed:
· Rated-load current (RLC) as 147A
· Minimum circuit
ampere as 184A
· Maximum overcurrent protection at 250A
I specified a
250A circuit breaker with 4/0 AWG conductors (184A x 1.25 = 230A). However, a
couple of engineers in our office say that 3/0 AWG, rated 200A at 75C, could be
used, because you don't multiply the minimum circuit ampere by 1.25. They also
say if I use 3/0 AWG, then the circuit protection device must be sized not
greater than 200A
A8. Your buddies are almost correct.
Size. It is true that the minimum circuit conductors size is based on the
"minimum circuit ampacity" as identified on the equipment nameplate, which is
184A. This is because the rated minimum circuit ampacity for motor-compressor
already includes 125 percent of the motor-compressor rated-load current
[440.32]. 147A x 1.25 = 184A
Table 310.16 identifies 3/0 AWG conductor at
75C as having an ampacity of 200A, which is acceptable for this minimum circuit
Circuit/Equipment Protection. The branch-circuit conductors,
control apparatus, and motors in circuits supplying hermetic refrigerant
motor-compressors must be protected against overcurrent due to short circuits
and grounds by a protective device having a rating or setting not exceeding 175
percent of the motor-compressor rated-load current [440.22]. 147A x 1.75 =
So a 250A circuit breaker is fine to protect the 3/0 AWG conductor
for hermetic refrigerant motor-compressors.
Q9. I would like your
thoughts on a situation where my inspector is requiring the rebar within a
building's footing to be bonded to the service grounding electrode. Section
250.50 indicates that if this item is available on the premises then it is to be
bonded so that it's part of the building's grounding electrode system. What if
the concrete has already been poured? I remember reading somewhere that the NEC
does not require the concrete to be chipped out to gain access to the footing
steel. It seems to me that chipping out the footing creates other problems, and
that there are other reasonable methods to establish an earth ground.
According to the NFPA Formal Interpretation 78-4, it is not the intent that
reinforcing steel be made available for grounding. See the NEC Handbook, page
272 for specifics.
Q10. What is the maximum conduit run length for rigid
nonmetallic conduit, before a junction or pull box is required?
only NEC limitations on conduit run length include splices not permitted in a
raceway [300.13(A)] and no more than 360 degrees of conduit bending radius
Copyright © 2004 Mike Holt Enterprises,Inc.