5 NEC Questions Based on the 2014 NEC by Mike Holt

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By
Mike Holt for EC&M Magazine
 
Note:
These questions are based on the 2014 NEC®. Any underlined text indicates a
change to the Code rule for the 2014 NEC.
 
Q1.
What are the working space requirements for electrical equipment?
A1.
For the purpose of safe operation and maintenance of equipment, access and
working space must be provided about all electrical equipment.
Equipment
that may need examination, adjustment, servicing, or maintenance while
energized must have working space provided in accordance with 110.26(A)(1),
(2), and (3):
Author’s
Comment:
The
phrase “while energized” is the root of many debates. As always, check with the
AHJ to see what equipment he or she believes needs a clear working space.
The
working space, which is measured from the enclosure front, must not be less
than the distances contained in Table 110.26(A)(1)
.Image
§ Condition 1—Exposed live parts on one side of
the working space and no live or grounded parts, including concrete, brick, or
tile walls are on the other side of the working space.
§ Condition 2—Exposed live parts on one side of
the working space and grounded parts, including concrete, brick, or tile walls
are on the other side of the working space.
§ Condition 3—Exposed live parts on both sides
of the working space.
Working
space isn’t required for the back or sides of assemblies where all connections
and all renewable or adjustable parts are accessible from the front
[110.26(A)(1)(a)].
If
special permission is granted in accordance with 90.4, working space for
equipment that operates at not more than 30V ac or 60V dc can be less than the
distance in Table 110.26(A)(1) [110.26(A)(1)(b)].
Author’s
Comment:
See
the definition of “Special Permission” in Article 100.
If
electrical equipment is being replaced, Condition 2 of Table 110.26(A)(1) is
permitted between dead-front switchboards, switchgear, panelboards, or motor control centers located across the aisle
from each other where conditions of maintenance and supervision ensure that
written procedures have been adopted to prohibit equipment on both sides of the
aisle from being open at the same time, and only authorized, qualified persons
will service the installation [110.26(A)(1)(c)].
Author’s
Comment:
The
working space requirements of 110.26 don’t apply to equipment included in
Chapter 8—Communications Circuits [90.3].
(2)
Width of Working Space. The width of the working space must be a minimum of 30
in., but in no case less than the width of the equipment [110.26(A)(2)].
Author’s
Comment:
The
width of the working space can be measured from left-to-right, from right-to-left,
or simply centered on the equipment, and the working space can overlap the
working space for other electrical equipment.
In
all cases, the working space must be of sufficient width, depth, and height to
permit all equipment doors to open 90 degrees.
The
height of the working space in front of equipment must not be less than 6½ ft,
measured from the grade, floor, platform, or the equipment height, whichever is
greater [110.26(A)(3)].
Equipment
such as raceways, cables, wireways, cabinets, panels, and so on, can be located
above or below electrical equipment, but must not extend more than 6 in. into
the equipment’s working space.
Ex
1: The minimum headroom requirement doesn’t apply to service equipment or
panelboards rated 200A or less located in an existing dwelling unit.
Author’s
Comment:
See
the definition of “Dwelling Unit” in Article 100.
Ex
2: Meters are permitted to extend beyond the other equipment.
The
working space required by this section must be clear at all times. Therefore,
this space isn’t permitted for storage [110.26(B)].
When
normally enclosed live parts are exposed for inspection or servicing, the
working space, if in a passageway or general open space, must be suitably
guarded.
Author’s
Comment:
When
working in a passageway, the working space should be guarded from occupants
using it. When working on electrical equipment in a passageway one must be
mindful of a fire alarm evacuation with numerous occupants congregated and
moving through the area.
CAUTION:
It’s very dangerous to service energized parts in the first place, and it’s
unacceptable to be subjected to additional dangers by working around bicycles,
boxes, crates, appliances, and other impediments.
Author’s
Comment:
Signaling
and communications equipment must not be installed in a manner that encroaches
on the working space of the electrical equipment.
 
Q2.
What are the rules related to the installation of conductors from different
voltage systems, such as 120V, 208V, 240V, 277V, and 480V in the same raceway
or enclosure?
A2.
If the premises wiring system contains branch circuits supplied from more than
one voltage system, each ungrounded conductor must be identified by phase and
system at all termination, connection, and splice points in accordance with 210.5(C)(1)(a) and (b) [210.5(C)(1)].
Identification
can be by color coding, marking tape, tagging, or other means approved by the
authority having jurisdiction [210.5(C)(1)(a)].
The
method of identification must be documented in a manner that’s readily
available or permanently posted at each branch-circuit panelboard
[210.5(C)(1)(b)].
 
Author’s
Comment:
When
a premises has more than one voltage system supplying branch circuits, the
ungrounded conductors must be identified by phase and system. This can be done
by permanently posting an identification legend that describes the method used,
such as color-coded marking tape or color-coded insulation.
Conductors
with insulation that’s green or green with one or more yellow stripes can’t be
used for an ungrounded or neutral conductor [250.119].
Although
the NEC doesn’t require a specific color code for ungrounded conductors,
electricians often use the following color system for power and lighting
conductor identification:
§ 120/240V, single-phase—black, red, and white
§ 120/208V, three-phase—black, red, blue, and
white
§ 120/240V, three-phase—black, orange, blue, and
white
§ 277/480V, three-phase—brown, orange, yellow,
and gray; or, brown, purple, yellow, and gray
Power
conductors of alternating-current and direct-current systems rated 1,000V or
less can occupy the same raceway, cable, or enclosure if all conductors have an
insulation voltage rating not less than the maximum circuit voltage
[300.3(C)(1)].
 
Q3.
What are the rules related to the installation of conductors under 50V with
conductors from 120V, 208V, 240V, 277V, and 480V systems in the same raceway or
enclosure?
A3.
Class 1 circuit conductors can be installed with associated power conductors
[725.48(B)(1)] if all conductors have an insulation voltage rating not less
than the maximum circuit voltage [300.3(C)(1)].
A
Class 2 circuit that’s been reclassified as a Class 1 circuit [725.130(A) Ex 2]
can be installed with associated power conductors [725.48(B)(1)] if all
conductors have an insulation voltage rating not less than the maximum circuit
voltage [300.3(C)(1)].
Note
2: PV system conductors, both direct current and alternating current, are
permitted to be installed in the same raceways, outlet and junction boxes, or
similar fittings with each other, but they must be kept entirely independent of
all other non-PV system wiring [690.31(B)].
 
Author’s
Comment:
Control,
signal, and communications wiring must be separated from power and lighting
circuits so the higher-voltage conductors don’t accidentally energize the control,
signal, or communications wiring:
§  CATV Coaxial Cable, 820.133(A)
§  Class 1 control circuits, 725.48
§  Class 2 and Class 3 Control Circuits,
725.136(A)
§  Communications Circuits, 800.133(A)(1)(c)
§  Fire Alarm Circuits, 760.136(A)
§  Instrumentation Tray Cable, 727.5
§  Sound Circuits, 640.9(C)
Q4.
What are the uses permitted and not permitted for flexible cords?
A4.
Flexible cords and flexible cables within the scope of Article 400 can be used
for the following applications [400.7(A)]:
(1)
Pendants [210.50(A) and 314.23(H)].
Author’s
Comment:
Only
cords identified for use as pendants in Table 400.4 may be used for pendants
[400.4].
(2)
Wiring of luminaires [410.24(A) and 410.62(B)].
(3)
Connection of portable luminaires, portable and mobile signs, or appliances.
(4)
Elevator cables.
(5)
Wiring of cranes and hoists.
(6)
Connection of utilization equipment to facilitate frequent interchange
[422.16].
(7)
Prevention of the transmission of noise or vibration [422.16].
(8)
Appliances where the fastening means and mechanical connections are
specifically designed to permit ready removal for maintenance and repair, and
the appliance is intended or identified for flexible cord connections.
(9)
Connection of moving parts.
 
Author’s
Comment:
Flexible
cords and flexible cables are permitted for fixed permanent wiring by 501.10,
501.140, 502.10 502.140, 503.10, 503.140, 550.10(B), 553.7(B), and
555.13(A)(2).
Attachment
plugs are required for flexible cords used in any of the following applications
[400.7(B)]:
§ Portable luminaires, portable and mobile
signs, or appliances [400.7(A)(3)].
§ Stationary equipment to facilitate its
frequent interchange [400.7(A)(6)].
§ Appliances specifically designed to permit
ready removal for maintenance and repair, and identified for flexible cord
connection [400.7(A)(8)].
Author’s
Comment:
An
attachment plug can serve as the disconnecting means for stationary appliances
[422.33] and room air conditioners [440.63].
Unless
specifically permitted in 400.7, the following uses are not permitted [400.8]:
(1)
Flexible cords must not be used as a substitute for the fixed wiring of a
structure.
(2)
Flexible cords must not be run through holes in walls, structural ceilings,
suspended or dropped ceilings, or floors.
Author’s
Comment:
Article
400 requirements only apply to flexible cords [UL 62]; power supply cords [UL
817] don’t fall within the scope of Article 400, therefore a power supply cord
is permitted to run through a cabinet wall for an appliance.
(3)
Flexible cords must not be run through doorways, windows, or similar openings.
(4)
Flexible cords must not be attached to building surfaces.
(5)
Flexible cords must not be concealed by walls, floors, or ceilings, or located
above suspended or dropped ceilings.
 
Author’s
Comment:
Flexible
cords are permitted under a raised floor (with removable panels) not used for
environmental air, because this area isn’t considered a concealed space. See
the definition of “Exposed” in Article 100.
Article
400 requirements only apply to flexible cords [UL 62]; power supply cords [UL
817] do not fall within the scope of Article 400, therefore a power supply cord
is permitted to run through or be located above a suspended ceiling.
(6)
Flexible cords must not be installed in raceways, except as permitted by 400.14
for industrial establishments where the conditions of maintenance and
supervision ensure that only qualified persons will service the installation.
(7)
Flexible cords must not be subject to physical damage.
Author’s
Comment:
Even
cords listed as “extra-hard usage” must not be used where subject to physical
damage.
 
Q5.
What are the tap conductor requirements to supply household ranges,
wall-mounted ovens, and counter-mounted cooking units?
A5.
Branch-circuit conductors that supply household ranges, wall-mounted ovens or
counter-mounted cooking units must have an ampacity not less than the rating of
the branch circuit, and not less than the maximum load to be served. For ranges
of 8¾ kW or more rating, the minimum branch-circuit ampere rating is 40A
[210.19(A)(3)].
Ex
1: Conductors tapped from a 50A branch circuit for electric ranges,
wall-mounted electric ovens and counter-mounted electric cooking units must
have an ampacity not less than 20A, and must have sufficient ampacity for the
load to be served. The taps must not be longer than necessary for servicing the
appliances.

 

 
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