Temporary Power for a Construction Site: GFCI and Grounding
A construction site uses a temporary 120/240V single-phase power supply from a generator. The generator is rated 15 kW and is located 50 meters from the work area. The contractor runs 12 AWG extension cords to power tools, including a 15A circular saw and a 10A grinder. The generator has a 30A, 240V receptacle and two 20A, 120V receptacles. The contractor uses a 30A to 20A adapter to connect a 12 AWG cord to the 30A receptacle. The generator frame is grounded to a ground rod, but the neutral is not bonded to the frame. The contractor has not installed GFCI protection on the temporary receptacles. An electrician is asked to inspect the setup. The site is muddy, and workers are using the tools outdoors. The electrical safety officer is concerned about shock hazards.
1. What are the grounding and bonding requirements for this temporary generator installation, and is the current setup compliant?
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The generator is a separately derived system and must be grounded and bonded in accordance with the Canadian Electrical Code. The generator neutral must be bonded to the generator frame, and the frame must be connected to a grounding electrode. The contractor has grounded the frame but failed to bond the neutral to the frame. This is a violation. Without the neutral-ground bond, fault current may not have a low-impedance path, and the overcurrent device may not trip. Additionally, the equipment grounding conductor (EGC) in the extension cords must be connected to the generator frame. The use of a 30A to 20A adapter may not provide proper overcurrent protection for the 12 AWG cord, which is rated for 20A. The 30A receptacle does not protect the 12 AWG cord from overload. The contractor must install a properly sized overcurrent device or use a cord with a 30A rating. The setup is not compliant due to missing neutral-ground bond and inadequate overcurrent protection.
2. What GFCI protection is required for temporary power on a construction site, and how should the contractor address the shock hazard?
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The Canadian Electrical Code requires GFCI protection for all temporary receptacles on construction sites, including those supplied by generators. The contractor must provide GFCI protection for the 120V receptacles. This can be achieved by using GFCI receptacles, GFCI circuit breakers, or portable GFCI units. The 30A receptacle also requires GFCI protection if it supplies 120V loads, but since it is 240V, it may not require GFCI unless required by the authority having jurisdiction. However, the extension cords and tools used outdoors in muddy conditions present a high shock risk. The contractor should use GFCI protection for all 120V circuits, test GFCIs before use, and ensure all equipment is properly grounded. Additionally, the contractor should use cords with strain relief and keep connections out of water. The electrical safety officer should enforce the GFCI requirement and ensure the generator is properly bonded and grounded before work continues.