IAEI Southern Nevada Chapter

Transformers that are located too close to a residential service may let through too much current in the event of a fault. Residential service equipment is usually limited to 22k, but even that is superseded by the limitation of a 10k main. In order to verify that the available fault current is low enough to be safely interrupted by the overcurrent protective device, calculations must be performed. To calculate the available fault current at the service equipment, the following information is necessary: available fault current at the transformer and the size and length of the conductors. Placing the transformer farther away from the service equipment will decrease the available fault current due to the impedance of the wire connecting the equipment.

Updated 11/25/09

Manufactured wiring systems and pre-wired systems are not the same thing. Manufactured wiring systems are covered under Article 604, but pre-wired systems are covered under the entire NEC, not a specific article. Some pre-wired systems are listed by NRTLs. Pre-wired systems must comply with the requirements in the NEC including conductors sizing, grounding, etc. A pre-wired system is also know as a prefabricated wiring system, and UL lists them under category QQYZ "Wiring Assemblies."

Updated 11/25/09