NEC Questions and Answers - by Mike Holt (2)

[Following is reprinted from Mike Holt's Newsletter]
Subscribe

Written for Code Quandary EC&M Magazine

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, “There shall not be more than the equivalent of four quarter bends (360 degrees total) between pull points.” 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

Author’s 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 is correct?

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 mechanical means.

Author’s 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 assembly.

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. I’m confused, why does the NEC require a No. 4/0 and the utility only needs to bring a No. 1/0.

A. I don’t know anything about National Electric Safety Code (utility code) so I can’t respond as to how the utility performs their calculations. But, they have a long history of supplying power to building and I’m sure they have a good understanding as to how to properly size service conductor’s outdoors.

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.

Author’s 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 fixed equipment.

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 building?

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.

Author’s 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 ¾ through 1¼ inch, or if the combined length of liquidtight flexible metal conduit in the same ground return path does exceeds 6 ft [250-118(7)].

(2) The appliance is cord- and plug-connected and it exceeds 80 percent of the branch-circuit ampere rating [210-23(a)], or

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 can’t be done, then a permanent installed barrier must be installed between the adjacent switches. Figure 4.

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).

Author’s 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)].

Author’s 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 once).

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)].

Author’s 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.

Author’s 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 725-61(a)].

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 exist?

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.