[Following is reprinted from Mike Holt's Newsletter]
Written for Code Quandary EC&M Magazine
By Mike Holt
All answers based on the 1999 NEC.
Q1. What is the maximum distance between pull points specified in the NEC?
A. None. The Code only contains requirements on the number and size of
conductors in a raceway, not the maximum conductor length. Effectively the
maximum length between pull boxes will be determined to the length of the wire
you purchase. However, all of the raceway articles have a requirement that
specifies, ďThere shall not be more than the equivalent of four quarter
bends (360 degrees total) between pull points.Ē Be sure to consider
conductor voltage drop when you have long conductor runs. For more information
about how to perform voltage drop calculations, visit http://www.mikeholt.com/studies/vd.htm
Authorís Comment: I have a 600-foot run to a 100 ampere panel supplying a
workshop at my home without any junction boxes!
Q2. My inspector states that the NEC requires each corner of the ceiling grid
where a recessed fixture is installed be secured to the building structure. I
(contractor) contend that if the fixture is independently attached to the
building structure with a ceiling wire on opposite corners of the fixture the
intent of the Code is meet. My electrician states there is no need to add any
special support systems to the ceiling grid for recessed fixtures, and that
the fixture is only required to be secured to the ceiling framing members. Who
A. The electrician. Section 410-16(c) states the framing members of suspended
ceiling systems used to support fixtures shall be securely fastened to each
other and shall be securely attached to the building structure at appropriate
intervals. Fixtures shall be securely fastened to the ceiling framing member
by mechanical means such as bolts, screws, rivets or listed clips. Figure 1.
(Graphics not contained in this newsletter).
If the suspended ceiling is installed in accordance with the building code,
there is no need for additional support of the ceiling-framing members. Just
install the fixture and securely fasten it to the ceiling-framing members by
Authorís Comment: There might be a building code requirement to
independently secure fixtures to the building structure if the building is in
a seismic zone (earthquake) or if the ceiling is part of a fire rated
Q3. I am installing a 200A 120/240V underground, residential service. The
utility company used 2 - No. 1/0 and 1 - No. 2 (USE XLP/HPXLP) aluminum. NEC
Table 310-15(b)(6) requires No. 4/0 aluminum for a 200 ampere residential
service. When I asked the utility about this, they claimed that their No. 1/0
was okay if the run was 100 feet or less. Iím confused, why does the NEC
require a No. 4/0 and the utility only needs to bring a No. 1/0.
A. I donít know anything about National Electric Safety Code (utility code)
so I canít respond as to how the utility performs their calculations. But,
they have a long history of supplying power to building and Iím sure they
have a good understanding as to how to properly size service conductorís
Q4. In a recent medical office installation, the electrical inspector rejected
the use of short lengths of flexible metal conduit in patient care areas. He
said Section 517-13(b) disallowed flexible metal conduit as a ground fault
return path. I contend that if the flexible raceway meets the grounding
requirements of Section 250-118(6), it should be permitted. Am I right?
A. Yes. Section 517-13(b) states that all branch circuits serving patient care
areas shall be provided with a ground path for fault current by installation
in a metal raceway system or cable assembly. The metal raceway system, or
cable armor or sheath assembly, shall itself qualify as an equipment grounding
path in accordance with Section 250-118.
Listed flexible metal conduit is suitable as an equipment grounding conductor
if the circuit conductors contained in the conduit are protected by
overcurrent devices rated at 20 amperes or less and the combined length of
flexible metal conduit in the same ground return path does not exceed 6 ft
[250-118(6)]. Figure 2.
Authorís Comment: Section 517-17(a) requires the grounding terminals of all
receptacles and all noncurrent-carrying conductive surfaces of fixed electric
equipment to be grounded by an insulated copper conductor installed in metal
raceways with the branch-circuit conductors supplying these receptacles or
Q5. I've always made certain that service conductors did not extend/penetrate
more than 5ft thru the building envelope without a disconnect. Does the NEC
specify a maximum distance that service entrance conductors can enter a
A. No. Section 230-70(a) requires the service disconnecting means to be
installed at a readily accessible location either outside of a building or
structure or inside nearest the point of entrance of the service conductors.
Service entrance conductors within a building should be limited because these
conductors present a serious fire hazard in the event of a line-to-ground
fault. This is a judgment call by the electrical inspector; some inspectors do
not allow service entrance conductors to enter the building at all, some allow
5 ft, others 10 ft, etc.
Authorís Comment: Conductors are considered outside of a building if they
are installed beneath a building or if the raceway is encased in concrete or
brick not less than 2 in. thick [230-6].
Q6. I am the general foreman at Lawrence Livermore National Laboratory, our
inspector states that the NEC requires a bonding jumper to be installed around
all liquidtight flexible conduit larger than 1-1/4" whether or not a
ground wire is run within the raceway." Is this true?
A. No. Where an equipment bonding jumper is needed for flexible metal raceways
[250-118], it can be installed on the outside or the inside of the raceway
[250-102(e)]. If the equipment bonding jumper is installed on the outside of
the raceway, the length of the bonding jumper shall not exceed 6 ft and it
must be routed with the raceway, Figure 3.
An equipment bonding jumper is required for flexible metal conduit if the
circuit conductors contained in the conduit are protected by overcurrent
devices rated more than 20 amperes or if the combined length of flexible metal
conduit in the same ground return path exceeds 6 ft [250-118(6)].
An equipment bonding jumper is required for liquidtight flexible metal conduit
if the circuit conductors contained in the conduit are protected by
overcurrent devices rated more than 20 amperes for 3/8 and 1/2 inch, more than
60 ampere for sizes ĺ through 1ľ inch, or if the combined length of
liquidtight flexible metal conduit in the same ground return path does exceeds
6 ft [250-118(7)].
Q7. I was told that a microwave oven is required to be on a separate circuit
by itself. Is this true?
A. Maybe. A separate circuit is required for the microwave oven (or any
The installation instructors specify a separate circuit [110-3(b)],
The appliance is cord- and plug-connected and it exceeds 80 percent of the
branch-circuit ampere rating [210-23(a)], or
The appliance is fastened in place and it exceeds 50 percent of the
branch-circuit ampere rating [210-23(a)].
Q8. Is a barrier required between 277 and 120 snap switches?
A. Yes a barrier is required because the voltage between the adjacent switches
could be as much as 380 volts, depending on the phase arrangements the
individual conductors. Section 380-8(b) requires snap switches be arranged so
that the voltage between adjacent switches does not exceed 300 volts. If this
canít be done, then a permanent installed barrier must be installed between
the adjacent switches. Figure 4.
Q9. Can EMT be used outdoors if compression fittings are used?
A. Yes. EMT is permitted outdoors [UL Guide Information] as long as the
raceway on exterior surfaces of building is raintight and arranged to drain
[225-22 and 230-53]. This is only accomplished by the use of fitting
specifically listed for this purpose (compression fitting).
Authorís Comment: The NEC restricts armored cable, nonmetallic sheath cable,
surface metal raceways, and multioutlet assembly to dry locations.
Q10. I've been looking in the National Electric Code for hours. Does the NEC
have any specific reference to wire color-coding for the phase conductors for
a 3-phase wye system where the voltage between phases is 480 volts and the
voltage to ground from each ungrounded conductor is 277 volts?
A. Yes and No. The NEC requires grounded (neutral) conductors to be white or
gray [200-6], grounding conductors to be green or bare [250-119], and the
high-leg conductor from a 120/240 volt, 3-phase delta system must be durably
and permanently marked by an outer finish that is orange in color [384-3(e)].
Authorís Comment: The reason the high-leg conductor must be identified is
because the voltage from this conductor to ground is 208 volts (120 volts x
1.732). Even with the identification of the high-leg, it is not uncommon for
the installer to inadvertently connect 120 volt loads to this 208 volt to
ground terminal within the panelboard, with unfortunate results (I did it
Where more than one nominal voltage system exists in a building such as
480/277 and 208/120, each ungrounded conductor of a multiwire branch circuit,
where accessible, shall be identified by phase and system by separate color
coding, marking tape, tagging, or other approved means [210-4(d)].
Authorís Comment: The NEC does not specify a color code to use, but the
generally accepted practice is brown, orange, yellow and gray (BOY) for the
480 volt circuit and black, red, blue and white for the 120/208 volt system.
Q11. Can the wires feeding the line side of a 3 phase disconnect be in the
same straight pull box or raceway as the load wires from the same disconnect?
A. Yes, Line and load conductors can be installed in the same raceway or
enclosure. However, service conductors cannot be mixed with other conductors
in the same service raceway or service cable. Figure 5
Q12. In hospitals, the wiring of the emergency system shall be mechanically
protected by installation in nonflexible metal raceways. Must these raceways
be painted red?
A. No, the emergency circuit raceway does not need to be identified in any
manner (painted red). Section 517-30(c)(3) contains the requirements for
mechanical protection for emergency circuit conductors, but there is no
requirement that the raceway be painted red. However, 700-9(a) requires all
boxes and enclosures (including transfer switches, generators, and power
panels) for emergency circuits to be permanently marked so they will be
readily identified as a component of an emergency circuit or system.
Authorís Comment: NFPA 99 - Health Care Facilities and NFPA 110 -
Emergency and Standby Power Systems does not contain any requirements that the
raceways for emergency circuits be identified.
Q13. I am an Audio/Video/Lighting contractor in Arizona. In a suspended
ceiling space, when am I required to have my Class 2 speaker cable installed
within electrical metallic tubing and when must the cables be plenum rated?
A. If the suspended ceiling space is use to move environmental air
[300-22(c)], then the Class 2 cables must be plenum rated (CL2P) [725-61(a)]
or the cable can be nonplenum rated (CL2) if installed within electrical
metallic tubing or other raceway listed in Section 300-22(c) [Exception to
If the suspended ceiling is not used for environmental air movement, then the
cable is not required to be plenum rated (CL2), nor is it required to be
installed in a metal raceway, [725-61(e)]. Graphic 6.
Q14. I have a panelboard with a plug-in main breaker. I have been told that
plug-in breakers must be either of the "bolt on" type or it must be
strapped in place. I cannot find this in the code. Does such a requirement
A. Yes. Section 384-16(g) requires plug-in-type overcurrent protection devices
or plug-in type main lug assemblies used to terminate field-installed
ungrounded supply conductors to be secured in place by a fastener that
requires other than a pull to release the overcurrent device from the mounting
means on the panel.