back to back service

[newinspector1]

Where in the NEC does it talk about back to back services and seperating the nuetrals and grounds on a 4-wire service. Also if it is a back to back service but the electrician runs 4-wire do they still have to seperate the grounds and nuetrals? What is the purpose in seperating them. I get these questions alot. Thanks for the help.

 

[ultramegabob]

your "grounded conductor" often refered to as "neutral or common" is part of the circuit and carries current under load, the "grounding conductor" is what bonds all the metal parts together so that everything has the same potential, if they are connected anywhere else other than the main disconnect, metal casings on electrical equipment can become part of circuit and someone could get a shock.

 

[augie47]

As far as Code references, the NEC does not directly address "back to back" The two sections involved moist are 230,70(A)(1) and 250.24(A)(5).
230.70 determines the service disconnect location and 250 requires neutral-grounding separation anywhere after the service disconnect.
The "Back to back" arrangement normally allows you to install your service disconnect in the interior panel thus no separation. If the E/c chooses for any reason to install the service disconnect outside, even on a back-to back, then separation on the interior panel is required.

 

[LarryFine]

Mr. 1, as Augie said, it depends on where the main disconnect is. If it's outside, then 4 wires are needed (even if the panel has a redundant main.) If it's inside, only 3 wires are needed.

 

[augie47]

I have seen AHJ have the opinion that the old meter socket can not be used as a "j box" etc., so you might want to clear that part of the plan.
Secondly, if your grounding electrode, intersystem bonding, etc. is presently at the old meter, how to you propose to comply with the grounding electrode conductor being connected to the grounded conductor ?