grounding of remote panel

[donhawley]

We find 3 wire feeds to a remote (sub panel) from a service panel quite often in our area. The question is if a remote panel is fed by a 3 wire conductor (H H N) but no ground wire or metallic conduit connection to the grounded neutral in the service box, how do you configure the 12-w/g wiring for the load circuits. I understand the neutral must be isolated but I also believe the grounds and neutrals are not allowed to be connected together past the service box. Not connecting the grounds to the neutral would mean these circuits were not grounded. This would be old construction in the same building (ie basement, attached garage etc), how do you bring this up to current code. Could the sub panel be treated as a service panel with a new ground rod or must the ground come the service panel?

 

[iwire]

We find 3 wire feeds to a remote (sub panel) from a service panel quite often in our area. The question is if a remote panel is fed by a 3 wire conductor (H H N) but no ground wire or metallic conduit connection to the grounded neutral in the service box, how do you configure the 12-w/g wiring for the load circuits. I understand the neutral must be isolated but I also believe the grounds and neutrals are not allowed to be connected together past the service box. Not connecting the grounds to the neutral would mean these circuits were not grounded. This would be old construction in the same building (ie basement, attached garage etc), how do you bring this up to current code. Could the sub panel be treated as a service panel with a new ground rod or must the ground come the service panel?

That installation method was allowed until recently and is still allowed to be added too.

As you mentioned it ends up being set up just like a service

You use the grounded (white) conductor as the grounding conductor. You also have to set up a grounding electrode system at the remote panel.

See NEC 250.32

 

[GoldDigger]

Could the sub panel be treated as a service panel with a new ground rod or must the ground come the service panel?

Under current NEC rules for new installations there must be an EGC run from the service panel to the subpanel under all conditions.
Note that the important part is that the EGC will provide a low impedance path for fault current back to the POCO service, allowing OCPD to trip quickly, while a local ground rod at the subpanel will rarely be able to serve that purpose.

In answer to your specific question, an earth ground must be supplied locally if the subpanel is at a separate building, what comes from the service panel as a separate wire from the neutral is the EGC.
In the subpanel the EGC connects to the ground bus, as does the local ground electrode(s), and there is no connection between the ground/EGC bus and the neutral bus in that panel.

 

[iwire]

Under current NEC rules for new installations there must be an EGC run from the service panel to the subpanel under all conditions.

The important word above is 'new' the OP is asking about existing I believe.

Existing can remain in use and have circuits added to it.

 

[GoldDigger]

The important word above is 'new' the OP is asking about existing I believe.

Existing can remain in use and have circuits added to it.

True.
And in existing installations the need for a metallic return path for fault current requires that local EGCs and local neutrals both be bonded to the incoming feeder neutral. As the OP suggested, it must be treated like a service with respect to grounding and bonding.
If it is already configured that way, keep it. If it is not currently configured that way, make it so.
JMO

 

[iwire]

OP,

I apologize I read the title of your thread 'remote panel' and thought you meant in a detached garage.

I read your post a second time and see you mean in the same building.

In that case it is not allowed and is a violation.

 

[donhawley]

OP,

I apologize I read the title of your thread 'remote panel' and thought you meant in a detached garage.

I read your post a second time and see you mean in the same building.

In that case it is not allowed and is a violation.

Please explain why a grounding source can not be added to the remote (sub panel). My reasoning is if the neutral must be isolated then the panel itself is neither bonded or grounded and presents a shock hazard if a ground fault occurs, because the only path to ground is now some poor home owner standing barefoot on a damp concrete floor opening the panel box to reset a breaker. Is it not better to improve a bad situation than to allow it to exist because it is grandfathered in. Would a correct fix then be to run a ground wire back to the GEC at the service panel, if so can this be a bare wire or must is have insulation.

 

[GoldDigger]

Please explain why a grounding source can not be added to the remote (sub panel). My reasoning is if the neutral must be isolated then the panel itself is neither bonded or grounded and presents a shock hazard if a ground fault occurs, because the only path to ground is now some poor home owner standing barefoot on a damp concrete floor opening the panel box to reset a breaker. Is it not better to improve a bad situation than to allow it to exist because it is grandfathered in. Would a correct fix then be to run a ground wire back to the GEC at the service panel, if so can this be a bare wire or must is have insulation.

If it is a subpanel in the same building, the problem is not that you cannot add a grounding source, it is that you are not allowed to leave out the EGC in the feeder circuit.
It can be either a raceway EGC (with appropriate bonding if needed) or a wire EGC, or both. But it must be there.

If you supply a local ground rod and bond the panel EGC bus to the neutral bus then you are allowing normal current to flow through the EGC and/or ground instead of confining it to the neutral where it belongs.
If you do not bond the ground to neutral, then the local ground rod will not carry enough current to trip the breaker if a short occurs, leaving the neutral and the grounds at a dangerous voltage even if it is not full line voltage.

Would you rather have 120V on your exposed metal for a few cycles or have 80 volts on your exposed metal indefinitely?

Leaving the details of the "why" aside for the moment, just accept that it is what the NEC requires.

If an existing subpanel feeder goes back so far that the NEC did not yet require EGCs (not likely if there is a breaker panel rather than a fuse panel!) then I would still not do any additions to the system without bringing that aspect up to code.