Class C Grounding for a Temporary Construction Service
A Class C electrician is asked to energize a temporary construction service for a new house. The service is a 200 A single-phase 120/240 V panel mounted on a temporary pole. The grounding electrode is a single 16 mm ground rod driven 2.4 m into dry gravelly soil. The neutral is bonded to the panel enclosure, and the equipment grounding conductor for the temporary receptacles is connected to the same neutral bar. A 15 A receptacle at the pole has no GFCI protection. The general contractor wants power for tools the next morning. The nearest utility transformer is 40 m away.
1. Identify the grounding and bonding deficiencies in this temporary service.
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The service neutral is bonded at the service, which is correct for a service, but the equipment grounding conductor must land on the grounding bar, not the neutral bar, unless this is the service disconnect where neutral and ground are bonded. At a temporary service panel that is the service equipment, the main bonding jumper is permitted, but downstream receptacles must use a separate equipment grounding conductor.
A single ground rod in dry gravel may not achieve the required low resistance. Temporary services typically require at least one additional electrode or verification of resistance, and the electrode must be effectively bonded to the service neutral.
The missing GFCI protection on the 15 A receptacle is a serious deficiency. Temporary construction receptacles require ground-fault protection for personnel. I would require GFCI protection on all temporary receptacles, a second grounding electrode or resistance verification, and confirmation that the equipment grounding conductor is separate from the neutral at the receptacles.
2. What must be corrected and verified before you authorize energization?
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Before energization I would require the electrician to install GFCI protection on the temporary receptacles, add a supplemental grounding electrode or demonstrate the ground rod meets the resistance limit, and verify the neutral-to-ground bond is at the service only. I would visually inspect the panel interior to confirm the equipment grounding conductor terminates on the grounding bar and the neutral bar is isolated from the enclosure except at the bonding point.
I would require a continuity test of the equipment grounding path and a polarity check at each receptacle. I would also confirm the temporary pole is mechanically secure and the conductors are protected from damage.
My authorization would be conditional on these corrections and a reinspection. The schedule pressure from the general contractor does not justify energizing a temporary service without GFCI protection and a verified grounding electrode system.