3phase 3 wire solidly grounded neutral

[dvcraven0522!]

I have and MCC 3 phase 3 wire with S/G/N. It is my understanding I do not need to run a neutral conductor the MCC. I only need to ground the MCC ground bus to its metal parts and to ground rod, steel, etc., I do have transformer fed from this MCC where I will provide N-G connections. Do I understand this correctly.

Thank you
Dan Craven

 

[Elect117]

What does S/G/N stand for?

If the service is grounded then you should be running an EGC with the feeder to the ground bus at the MCC.

If the MCC has a neutral bus then I would suggest running a neutral and a equipment grounding conductor for the ground bus. With no bonding jumper between the neutral and the equipment grounding conductor (like a subpanel would be wired).

Separately derived systems (transformers) have a neutral to ground bond on their secondary side and a rederived grounding system so that any fault goes back to it's source which is the secondary side of the transformer.

 

[dvcraven0522!]

I have no N-G loads.

 

[dvcraven0522!]

Phase to neutral loads is what I intended to say.

 

[don_resqcapt19]

I have and MCC 3 phase 3 wire with S/G/N. It is my understanding I do not need to run a neutral conductor the MCC. I only need to ground the MCC ground bus to its metal parts and to ground rod, steel, etc., I do have transformer fed from this MCC where I will provide N-G connections. Do I understand this correctly.

Thank you
Dan Craven

Why are you doing that. An EGC needs to be run to the MCC with the feeder circuit.

 

[Jraef]

If your MCC is not feeding anything that needs the Neutral, you do not need a Neutral bus nor to run a Neutral cable to it.

UNLESS, the MCC Main is the Service Entrance point. If it is, most MCC mfrs have an option for a "Neutral Landing Pad", basically a short little N bus only in the Main section with the SUSE label on it, that gives you a termination point for the service Neutral.

 

[LarryFine]

What does S/G/N stand for?

See the title of the thread.

 

[Elect117]

See the title of the thread.

Thanks lol. I have never seen it abbreviated with slashes.

 

[jaggedben]

If you truly have a 3 phase 3-wire system then you don't have a neutral. Is it only the feeder that is 3-wire? There is a solidly grounded neutral that is just not present at the MCC?

 

[dvcraven0522!]

Yes the MCC does have a neutral pad.

 

[augie47]

Yes the MCC does have a neutral pad.

The fact that it has a neutral pad does not mean you are required to pull a neutral to it unless it's being used as service equipment on a grounded system.

 

[dvcraven0522!]

Yes - I am starting get that now.

 

[__dan]

You are missing two key pieces of information.

Look at the MCC source transformer nameplate for the secondary winding configuration. You want to know if your MCC source, transformer winding secondary, is Delta or Y.

Then you would have to confirm the presence of the main bonding jumper, usually by physically seeing it, in its expected location.

Two bits of information gives you four different possible configs, floating delta, floating Y, grounded delta, grounded Y.

There is no problem with the load side of any of those, being 3 phase 3 wire, except that if you have a floating supply you would want to know that, and if you have drives downstream loaded on the MCC, they are looking for a solidly grounded Y supply.

You can easily have a grounded Y supply and carry only 3 phase 3 wire to the loads, plus the contiguous EGC. But if you have one of the other possible supply configs, that's what you want to know.