Define Sub and Main?

[Rustynuts]

I've been in a discussion with an electrician friend of mine about what constitutes a "sub panel" and whether these neutrals should be isolated or not. I have my opinions and he his. I'll see if I can explain this correctly.
It?s not uncommon to derive power from a Traffic controller for additional equipment added to traffic systems installed internally or externally.
These systems don?t always have a metered service, power is brought in and connected to an internal lug/main breaker that will supply power to a breaker pack. Because of the sensitivity and possible conflicts? to some of these systems, it was suggested power to be taken before the main breaker for adding on to system.
Lets say you take power source directly from incoming power lug before main disconnect in first cabinet and use it to supply breakers in a second cabinet. Does this define new cabinet as "sub" or "Main??
I say sub and therefore neutrals and grounds should be isolated but he says no. Because the power source is taken before the main disconnect in the first cabinet, it is now considered its own main service. I do own the 2008 NEC but have not found reference yet.

 

[augie47]

Main would be the first (normally service) disconnecting means... downstream of that is a sub.
There should be no connection between the grounded conductor and grounding conductor except at the service or source of an SDS {250.24(A)(5)}. If the breaker in your first cabinet is the service disconnect (it should be rated as such if it is) and it is being suppled directly by the utility with phase and grounded conductors, then if you tap ahead of that breaker to a second cabinet that second cabinet must also have a service rated disconnect and the grounded conductor will be bonded. There would be no equipment grounding conductor required.

 

[cadpoint]

...Lets say you take power source directly from incoming power lug before main disconnect in first cabinet and use it to supply breakers in a second cabinet. Does this define new cabinet as "sub" or "Main??

I have to ask why are you tapping infront of main disconnect? And are you setting up a very dangerous situation, it frankly scarey reading this. One only establishes one main, OK 98% of the time, that 2% is only 3 wild so don't worry about that, your not there.

You'll need to breaker both for rated services as stated...

Order of flow is required, breaker a service comes to mind.. just like light traffic control...

Welcome to where we note the trees from the forrest!

 

[John120/240]

Main would be the first (normally service) disconnecting means... downstream of that is a sub.
There should be no connection between the grounded conductor and grounding conductor except at the service or source of an SDS {250.24(A)(5)}. If the breaker in your first cabinet is the service disconnect (it should be rated as such if it is) and it is being suppled directly by the utility with phase and grounded conductors, then if you tap ahead of that breaker to a second cabinet that second cabinet must also have a service rated disconnect and the grounded conductor will be bonded. There would be no equipment grounding conductor required.

Augie "...if you tap ahead of that breaker to a second cabinet..." so you would

have two main breakers? Is my logic right ?

 

[augie47]

Yes.
But, that said, let me emphasize cadpoint's concern.
I was attempting to answer a question that possibly should have remained unanswered. Though factually correct (I think) the plan is full of possible Code and safety pitfalls depending on the methods used including 230.72

 

[sameguy]

Tap ahead would make it an other service latteral, i.e. main.

 

[LarryFine]

Lets say you take power source directly from incoming power lug before main disconnect in first cabinet and use it to supply breakers in a second cabinet. Does this define new cabinet as "sub" or "Main??

Sounds like two mains to me. The second main would not benefit from a separate EGC under fault conditions; the neutral suffices.

 

[hurk27]

I agree this would be another main, but there will be a problem if they re-bond the grounded conductor in the same cabinet, as they will now have parallel paths for the neutral current, and some of this neutral current could be on the grounding, now if this second service tap left the first cabinet and was run LLN to the a second installation then the MBJ would not be a problem.

This is no different then having a 320 meter with double lugs feeding a main in the house and a main in a garage.

 

[tryinghard]

Sounds like utility not premises to me (ahead of main). If so NESC & GO95 rather then NEC.