Redundant sub feed panel circuit breaker

[James M. Clarke]

I have a question involving sub panels. I have seen many cases recently where a subfed 100A panel is added to an industrial plant and is fed from a existing 225A main panel. In many of these cases the contractor reused an existing 100A panel that they had which already had a 100A c.b. in the panel. In some cases the 100A c.b. in the subfed panel was the main c.b. and in other cases it was installed just like a branch circuit c.b. I go looking at the panel and the subfeed and find that the contractor has a 100A c.b. in the 225A main panel feeding the main or added 100A c.b. in the subpanel.

In my opinion this should have been done using only a 100A c.b. in the 225A panel for a subfeed c.b. and the subfeed conductors should have been terminated at the 100A subpanel on the main lugs (not on a subfed panel c.b.).

This obviously is functional since the systems are working but I wanted to know if it is justfied in correcting this situation by getting the plant to order main lugs for the 100A panel and removing the 100A main c.b. in the subfed panel. It looks like the contractor took the easy way out and used the spare electrical components that were available rather than ordering the correct main lugs for the panel. Is there a section of the NEC that addresses this issue? Thanks

 

[480sparky]

I'm thoroughly confused. Are you saying there's a breaker in the main panel as well as in the sub?

If so, as long as the breaker in the main is sized to protect the feeders and the subpanel, and both are sized to carry the load, there's no problem.

 

[augie47]

agree. no problem. it's done fairly often. some folks like it because it gives them a main AT the subpanel. For the record, the size of the breaker at the sub can be larger as it's serving as a disconnect only.
If they are backfeeding thru a branch breaker, 408.36(D) would need to be addressed (retaining means)

 

[James M. Clarke]

Redundant subfed circuit breaker

Redundant subfed circuit breaker

Yes, there is a c.b. in the main panel and a c.b. in the sub panel. It looks like that this type of installation was not done on purpose (so that there would be a subfeed disconnect) but instead was done because the contractor had a used 100A panel laying around that could be reused and didn't have any main lugs which had been removed in the past. As long as it is fine to use the subfeed panel main c.b. (either seperately mounted in the panel or along with the branch circuit c.b.'s) as a disconnect rather than a protective device than I will not suggest to spend the labor hours to correct this. I have seen this occurence over seven times in one plant between the main and subfed panel.

 

[roger]

There would also be nothing wrong with this installation if the sub-panel had a main breaker that would be larger than 100 amps, the OCPD in the 225 amp panel would still protect the feeder conductors and sub-panel at 100 amps.

Roger

 

[mcclary's electrical]

also, he would need a hold down screw to make this legal. sounds fine to me

 

[masterinbama]

As for the contractor being the one with the used panel on hand. Around here a lot of the companies I do work for will save demoed equipment for reuse especially old MCC buckets. With one of our local school systems I have installed the same 200 amp fused disconnect 4 times in 5 years at different schools. These schools were slated for upgrades so a temporary solution made good $$ sense.