create sub-feed panel from existing

[Inspector 102]

I have had a couple of situation where a project involved the installation of a disconnect switch to provide clearance to gas meter, etc. This involves relocating the meter, installing a disconnect switch, then to the existing panel location. I am always asked if 3 wire can be used and I inform them that load side panels need the 4 wire with isolated grounding to comply. My question is, if the existing panel has a main breaker in the assembly, and the disconnect ground/neutral is bonded also, what is the hazard? Does this affect the way a main will recognize a fault? Will it create faults through the premise wiring if the grounds / neutrals are not isolated. Is there ever a case where 3 wire from the disconnect to the panel is acceptable. Thank you.

 

[steveray]

I believe you can have service disco and service OCPD be seperate....but I think the wording is immmediately adjacent....Someone way smarter than me will answer soon....

 

[Dennis]

If you have a service disconnect then everything on the load side of the disconnect must have the grounded conductor(neutral) and equipment grounding conductor separated. At the service you normally have a meter and then a panel either outside next to it or inside as near as possible where the service conductors enter the building. Those wires would be 3 wire-- no equipment grounding conductor required.

Some areas require a disconnect outside next to the meter while others will allow you go a certain distance without adding overcurrent protective device.

In either case once you get past the main you isolate the neutrals and grounds. Would it be the end of the world. Probably not but you would have to bond the sub panel so that all neutrals and equipment grounding conductor where attached. Now the neutral conductor is bonded to the box and in the case of a faulty neutral you would be sending current through the box which could be potentially dangerous.

 

[chris kennedy]

I am always asked if 3 wire can be used and I inform them that load side panels need the 4 wire with isolated grounding to comply.

A qualified person would never have to ask that question. Scary.

To clarify your use of "with isolated grounding" should be replaced with 'with an equipment grounding conductor'. I believe we all have a good idea what you meant, just saying.