This article was posted 08/11/2006 and is most likely outdated.

Grounding vs Bonding: 250.134 Grounding (Bonding)—Fixed Equipment
 

 
Subject - Grounding vs Bonding: 250.134 Grounding (Bonding)—Fixed Equipment

August 11, 2006  

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250.134 Grounding (Bonding)—Fixed Equipment.

Metal parts of fixed electrical equipment, raceways, and enclosures must be grounded (bonded) to an effective ground-fault current path in accordance with (A) or (B), except where they are grounded (bonded) to the grounded neutral conductor as permitted by 250.142.

(A) Equipment Grounding (Bonding) Types. Metal parts of fixed electrical equipment, raceways, and enclosures can be grounded (bonded) by any of the equipment grounding (bonding) types specified in 250.118.

(B) With Circuit Conductors. Where an equipment grounding (bonding) conductor of the wire type provides the effective ground-fault current path, it must be installed with the circuit conductors in the same raceway, cable tray, trench, cable, or cord. Figures 250–179 and 250–180

Exception 1: The equipment grounding (bonding) conductor can be run separately from the circuit conductors when necessary to comply with 250.130(C).

FPN No. 1: Where the equipment bonding jumper is installed outside a raceway, its length must not exceed 6 ft and it must be routed with the raceway [250.102(E)].


Figure 250–179
(Click on image to enlarge)


Figure 250–180
(Click on image to enlarge)

     

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Comments
  • I forgot about 300.3(B)(1) exception as well.

    Direct current circuits are theoretically allowed to be isolated phase, neutral, and equipment ground in aboveground applications. This used to be an explicit exception but would now fall under 90.4 alternative methods.

    Advantages of isolated phase, neutral, and equipment ground for underground installations is that it is easier to make paralled conductors the same length and conductors do not have to cross each other at terminations. If say 500 KCM copper wires are crossing each other at terminations a they are allowed to press against each other, insulation can cold flow and create a short circuit. Some people do not pay attention to that when running say 3/0 through LB fittings leading to premature failure. Usually takes 5 to 40 years to happen.

    Michael R.Cole

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