Sub-panel

[Xknob&tube]

On a service upgrade on an old house, can the old existing ser cable that is 4/3 non-grounded be used to turn the existing panel in the house into a sub-panel? There is no access to replace the ser cable without tearing things up.

 

[kwired]

Your first issue is you have no equipment grounding conductor. There is no exceptions, if this is changed to a sub panel you will need to supply it with an equipment grounding conductor.


Another problem is if this was previously using 310.15(B)(7) for ampacity selection, it must still be supplying the entire dwelling load to still be able to use 310.15(B)(7). Now you could reduce the overcurrent protection on it if the load allows, but IMO the lack of an equipment grounding conductor kind of trumps this issue.

A couple other ways around this are to supply 240 volts to a transformer with 120/240 out - but you still need to bond the secondary to the grounding electrode at the service somehow, plus the transformer is likely to cost more than other options, or if there is no 240 volt loads and the 120 volt load is low enough - you could supply it with 120 volts only.

 

[jxofaltrds]

On a service upgrade on an old house, can the old existing ser cable that is 4/3 non-grounded be used to turn the existing panel in the house into a sub-panel? There is no access to replace the ser cable without tearing things up.

YES.

90.4
"By special permission, the authority having jurisdiction
may waive specific requirements in this Code or permit
alternative methods where it is assured that equivalent objectives
can be achieved by establishing and maintaining
effective safety."

I do not know if I would do that but it is possible.

 

[kwired]

YES.

90.4
"By special permission, the authority having jurisdiction
may waive specific requirements in this Code or permit
alternative methods where it is assured that equivalent objectives
can be achieved by establishing and maintaining
effective safety."

I do not know if I would do that but it is possible.

Well, 90.4 is the exception to anything else in the code:blink:

 

[jxofaltrds]

Well, 90.4 is the exception to anything else in the code:blink:

True but it may be possible to have a 'sub' fed with only a 3-wire that is perfectly safe.

 

[augie47]

It has been allowed in specific situations in this area, but only by special permission ie: 90.4

 

[ptonsparky]

I never had the bravado to even ask for an exemption like that. First, I make money selling materials, secondly I make money doing the work.

 

[kwired]

I never had the bravado to even ask for an exemption like that. First, I make money selling materials, secondly I make money doing the work.

You and I both know NE state inspectors are not very likely to make any exception either, and in general they are not that hard to get along with either, but requests to go against the rules need good reason, and I really see no good reason to do this anywhere. NEC even eliminated the permission to do this with outside feeders supplying separate buildings more recently meaning there must be a reason not to use grounded conductor for equipment grounding.

jxofaltrds

Originally Posted by kwired
Well, 90.4 is the exception to anything else in the code:blink:



True but it may be possible to have a 'sub' fed with only a 3-wire that is perfectly safe.​

Any voltage drop on the grounded conductor is going to appear as EGC to earth voltage if you do use it for equipment grounding.

If there is current flow there is voltage drop.

 

[GoldDigger]

You and I both know NE state inspectors are not very likely to make any exception either, and in general they are not that hard to get along with either, but requests to go against the rules need good reason, and I really see no good reason to do this anywhere. NEC even eliminated the permission to do this with outside feeders supplying separate buildings more recently meaning there must be a reason not to use grounded conductor for equipment grounding.

Any voltage drop on the grounded conductor is going to appear as EGC to earth voltage if you do use it for equipment grounding.

If there is current flow there is voltage drop.

+1

I think that the very best that the OP could realistically hope for would be permission to run a new properly sized EGC separate from the existing cable. (If there is a path to do it that does not involve as much destruction as replacing the entire 4/3 cable, that is.)