three wire four wire

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enireh

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Canyon Lake,TX
I'm doing a 320 amp service at a primary pole for a farm with two structures both with meters. We are doing away with the meters so we have one meter at the new 320 amp service. The old services have three wire to them. When the new service gets connected, the old ones will be disconnected. I want to leave the wire going to them so it would be easy hooking them in at new service. Is it ok to drive a ground rod at the old services and separate the grounds and neutral there?

thank you
 
If you have a service disconnect switch (with OCPD) at the new meter location the old service wires become feeders and I do think there are any applicable exceptions to allow you to use only three wires.
If the wires downstream of the meter remain service conductors (regardless of where the POCO service point is located), then three wire with NEC compliant building GES at each structure would be OK.
Probably more than just "a ground rod".
 
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enireh said:
so is it safe to install a ground wire at both of the old services and separate the neutral bar from the ground bar?
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I don't think you understood what I said.
If it is a feeder, you *must* pull 4 wires (2 hot, 1 neutral and 1 EGC). And you must separate ground from neutral in panel. And you must supply *all* NEC required ground electrodes connected to the ground bar.
If it is service wires, you use 3. And you *must* bond ground to neutral. And you must supply *all* NEC required electrodes connected to the combined ground and neutral bar(s).
You cannot pull 3wires, separate ground from neutral and install local ground as the only connection to the ground bar. That would leave no adequate path for ground fault current. The electrodes will not supply that path.
 
enireh said:
so is it safe to install a ground wire at both of the old services and separate the neutral bar from the ground bar?
Click to expand...
No matter what code allows do not create a situation where earth is a part of the path of the EGC, I'd much rather see an improper 3 VS 4 wire situation then to utilize the earth as part of the equipment grounding path.

If there are no other conductive paths between buildings/structures you are likely able to comply with exceptions that would allow you to leave an existing 3 wire feeder in place, if these actually are feeders, if they are still service conductors there is no issue to consider.
 
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