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By Mike Holt for EC&M Magazine
June 2005 Part 1 Questions and Answers
1. I was told that there is a 30-day limit for extension cord use in a commercial building. What's the story?
A. Extension cords cannot be used as a substitute for fixed wiring [400.8(1)], and in addition cords can only be used for temporary wiring if approved by the authority having jurisdiction (AHJ) [590.2(B)].
But temporary wiring is only permitted for construction, remodeling, maintenance, repair, or demolition of buildings, structures, equipment, or similar activities or for emergencies and for tests, experiments, and developmental work. When temporary wiring is permitted by the AHJ, the wiring (cords) must be removed immediately upon completion of construction or purpose for which the wiring was installed [590.3].
A. Where a lightning protection system is installed, it must be bonded to the building or structure grounding electrode system as per 250.106. In addition, the grounding electrode for the lightning protection system cannot be used for the building or structure grounding electrode [250.60].
See NFPA 780, Standard for the Installation of Lightning Protection Systems for additional details on grounding and bonding requirements for lightning protection.
3. If a 480:120/208V three-phase transformer has primary protection set at no more than 125% of the primary current rating in accordance with 450.3(B), what is the maximum secondary conductor length from the transformer?
A. The primary protection of a transformer does not provide secondary conductor protection for a four-wire secondary. Therefore secondary conductors must not be run more than 25 ft without overcurrent protection if [240.21(C)(6)]:
4. When does the Code require low-voltage or power-limited control or signaling cables to be plenum rated?
A. Plenum rating is required for all low-voltage and power-limited cables that are installed either exposed or within a plenum-rated raceway above a suspended ceiling or below a raised floor used for environmental air movement [725.3(C) and 725.61(A)].
Nonplenum-rated cables are permitted above a suspended ceiling or below a raised floor that is used for environmental air if installed within a metal wiring method in accordance with 300.22(C)(1).
Author's Comment: Low-voltage and power-limited cables installed beneath a raised floor in an information technology equipment room (computer room) aren't required to be plenum rated [300.22(D) and 645.5(D)(5)(c)]. Figure 725-14
5. What is the correct method for conduit sealing of low-voltage and power-energy cables installed in a Class 1 hazardous (classified) location? My inspector wants the cable jacket removed within the sealing fitting and the conductors spread apart before the compound is poured. This is an almost impossible task.
A. Where a cable seal is required [501.15(A) and (B)] it must be installed in accordance with 501.15(C). However the removal of shielding material or the separation of the twisted pairs isn't required within the cable seal fitting [501.15(D)(2) Ex and 501.15(E)(1) Ex 2].
6. A separate 20A, 120V circuit is required for dwelling unit bathroom receptacles. Are we required to include 1,500 VA for this circuit when calculating the service load?
A. When performing dwelling unit load calculations, a 1,500 VA load is required for each small-appliance and laundry branch circuit [220.52(A) and (B)], but this does not apply to the bathroom receptacle outlet branch circuit.
A. Changes to 250.50 were made to clarify that where any of the following "are present" they must be bonded together to create the grounding electrode system.
The intent of the change to 250.50 and the addition of the exception is intended to require the use of concrete-encased foundation or footer steel as part of the building or structure grounding electrode system in new construction, since it is considered "present" before they pour concrete.
For example, if a new building contains rebar in the footing or foundation, it must be used as a grounding electrode. This electrode can also be used as the supplement to the water pipe electrode, required by 250.53(D)(2).
The reason this was added into the code is because the concrete encase electrode is considered by many to be the best electrode, and therefore should be used whenever present.
Note: One effect of this change is that ground rods will no longer be required for new construction.
8. When is a 2-pole breaker required for a multiwire branch circuit?
A. Multiwire and multiple branch circuits that supply devices or equipment on the same yoke (also called a strap) must be provided with a means to disconnect simultaneously all ungrounded conductors that supply those devices or equipment [210.4(B) and 210.7(B)]. Individual single-pole circuit breakers with handle ties identified for the purpose, or a breaker with common internal trip, can be used for this application [240.20(B)(1)].
Note: The intent of this rule is to prevent people from working on energized circuits that they thought were disconnected.
9. How close can I run underground service conductors in a raceway to an outdoor pool?
A. According to 680.10, underground wiring isn't permitted under or within 5 ft horizontally from the inside wall of a permanently installed pools, storable pools, outdoor spas, outdoor hot tubs, or fountains.
However, where space limitations prevent wiring from being at least 5 ft away, underground wiring would be permitted if within rigid metal conduit, intermediate metal conduit, or rigid nonmetallic conduit having a minimum burial depth of 6 in. for metal raceways and 18 in. for nonmetallic raceways.
10. Is there any Code requirement as to how close a switch can be to a shower or bathtub?
A. Switches and circuit breakers used as switches can be located next to, but not within, a bathtub, hydromassage bathtub or shower space [404.4, 680.70 and 680.72]. However, switches must be located not less than 5 ft from pools [680.22(C)], outdoor spas and hot tubs [680.40], and indoor spas or hot tubs [680.43(C)].
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