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By Mike Holt for EC&M Magazine
Q1. A meter and main breaker panel is connected by a PVC and the neutral is bonded to the meter enclosure and the panel enclosure. The service conductors enter the meter enclosure through a hub with rigid metal conduit. Is there any more bonding required for the service?
A1. Additional bonding is not required for this service. The metal riser is bonded to the meter enclosure by the threaded hub, provided the connection is made up wrench tight as required in 250.92(B)(2). The meter enclosure is bonded to the grounded (neutral) conductor because the neutral terminal is bonded to the meter enclosure in this case [250.92(B)(3)]. The service disconnect is bonded by the main bonding jumper that is located in the panel enclosure [250.28 and 250.92(B)(3)].
While the Code required bonding has been provided [250.92], the service must be grounded to a suitable electrode in accordance with 250.24(A) and 250.50.
Q2. On a 1,600A 277/480V service, is the neutral conductor from the utility transformer to the service disconnect considered a current carrying conductor if the only line-to-neutral loads is a 200A lighting panel?
A2. The neutral (grounded) service conductor
for this installation is not considered a current carrying conductor (for conductor ampacity
adjustment purposes) [310.15(B)(2)(a)]. The grounded (neutral) conductor of a three-phase,
4-wire wye system is only required to be counted as a current carrying conductor when
a major portion of the load is nonlinear [310.15(B)(4)(c)]. In this case, the maximum
neutral load is only 12.5% of the service rating.
A3. No, 517.30(C)(3) requires emergency system branch circuit conductors be protected by a nonflexible metal raceway or by MI cable.
Q4. Is it permissible to install line and load wiring in the same raceway?
A4. The NEC does not restrict the installation of line and load conductors within a common raceway, but it does prohibit the installation of service conductors within raceway with non-service conductors [230.7].
Q5. Is GFCI protection required for a hard-wired spa?
A5. GFCI protection is required for
both cord-and-plug and hard-wired spas containing single-phase equipment.
A6. The installation is fine as long
as the calculated load does not exceed 510A. Lets go through the steps:
Note: When performing conductor ampacity, use the conductor ampacity based on the insulation rating of the conductor NOT the ampacity based on the terminal rating of the equipment!
Step 2 Determine the adjusted ampacity
based on four current-carrying conductors [310.15(B)(2)(a)] located in an ambient temperature
of 100°F [Table 310.16].
Conductor Adjusted Ampacity = 350A x
0.80 x 0.91
A8. No. A transfer switch is not permitted
ahead of the service disconnecting means [230.82], however a transfer switch that is listed
as "suitable for use as service equipment" (means it have a main with overcurrent
protection, and a main bonding jumper) is permitted.
Q10. Is an antishort bushing required for Type MC cable of the interlocked type?
A10. No, the NEC does not require the use of antishort bushings for the terminations of MC cable, but 320.40 requires the termination fittings to be listed and identified for the terminations of this type of cable. However, many manufacturers of MC cable provide antishort bushings with the cable, and they do provide protection of the conductors.
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