Three phase panel question

zschary · Jun 14, 2016

Just moved to a new shop. Power is a sub panel. Three phase with neutral wires. The metered main panel is not near the unit. Hooking up a panel that will have three phase only. Can I run it off the sub in the unit.? I assume the ground wire grounds to the metal box not the neutral connection at my units panel ? Thanks

Larry Dickman · Jun 15, 2016

I would say, if you're not sure, get an electrician. What you're trying to do won't be that expensive to have it done right.

Vancbiker · Jun 15, 2016

zschary said:
.....I assume the ground wire grounds to the metal box not the neutral connection at my units panel

Bad idea to assume anything when dealing with mains power.

EJD3 · Jun 15, 2016

Pictures would help..
If you're running a sub-panel there should be a grounding bar in the new panel.. This should be bonded to the system ground, ie, the main panel, with a ground wire at least as large as the feeders to the sub-panel. The ground wires for each connection in the sub-panel can then be connected to the grounding bar, using the same size ground wire as the supply conductors for each breaker.
You'll need to pull a permit to do anything like this; and that takes an electrician.

zschary · Jun 15, 2016

Thank you..
I assume the ground only connects to neutral at the main panel service entrance like home electrical systems.. I was also wondering if its common to have a sub feeding off of what is technically a sub in the shop.. just trying to get pieces together and figure it out..

SeymourDumore · Jun 15, 2016

Local codes might override national codes, so it's best if you do check with someone in the know.

With that said, typically the mains panel ( the very first one after the transformer ) has the Neutral and Ground bonded together.
This is THE ONLY PLACE!!! where the two is bonded and can be considered equipotential.
Any and all other subpanels must be wired with separate Ground and Neutral conductors, and they never again be bonded together or interchanged.

Now you did say you have 3ph and Neutral, which would suggest you have a 3ph-Wye supply.
I do not know what the code says about this specific case, but I would check with someone to make sure if you're allowed to install a subpanel
onto a 5 wire ( L1-L2-L3-N-G) system with only a 4 wire ( L1-L2-L3-G) hookup.
I could quite possibly be wrong, but for some reason I think a Wye supply must carry throughout the installation, regardless of the need.

zschary · Jun 15, 2016

thanks for the notes..
I will have this checked out regarding wye and neutral.. the sub I have from another install I wanted to use has a setup for neutral, or a bus..
I was planning to just ground with a lug to the box itself instead of the bus so the box itself is grounded as well.. is that ok to use the box or should I find one that has no provision for neutral..

ewlsey · Jun 15, 2016

EJD3 said:
Pictures would help..
If you're running a sub-panel there should be a grounding bar in the new panel.. This should be bonded to the system ground, ie, the main panel, with a ground wire at least as large as the feeders to the sub-panel. The ground wires for each connection in the sub-panel can then be connected to the grounding bar, using the same size ground wire as the supply conductors for each breaker.
You'll need to pull a permit to do anything like this; and that takes an electrician.

I've never pulled a permit for a sub panel but I guess you probably should.

Also, ground conductor size is based on the breaker size per the table in "the book". Often it is smaller than the conductor size.

EJD3 · Jun 16, 2016

according to the state inspector here, you are required to pull permits for almost any electrical work..
except replacing failed stuff like outlets and switches

Nami · Jun 16, 2016

Every assumption you've made so far has been wrong. It sounds like you really have no business attempting this. Quit being so cheap and get a qualified and vetted electrician; unless of course your life, equipment, family, etc. are worth less than what it'll cost you.

Dan from Oakland · Jun 16, 2016

What Seymour stated about the neutral and ground only being bonded in the main service entry panel is 100% correct! The neutral is a current carrying conductor and should never be connected to ground in a sub panel. Good luck.
Dan

zschary · Jun 16, 2016

Nami said:
Every assumption you've made so far has been wrong. It sounds like you really have no business attempting this. Quit being so cheap and get a qualified and vetted electrician; unless of course your life, equipment, family, etc. are worth less than what it'll cost you.

wow.. all of them wrong .. hmmmm which ones?

Nami · Jun 16, 2016

"I assume the ground wire grounds to the metal box not the neutral connection at my units panel"

"I assume the ground only connects to neutral at the main panel service entrance like home electrical systems."

zschary · Jun 16, 2016

Both are true statements I am sorry to say.. I really am
read some of the other posts above.. key here is the ground and neutral are connected at the main panel only.. Not a huge issue.. just relax.. I am not endangering my family or myself.. I am almost 50 and have been doing this kind of stuff for a long time.. reason I have lived this long is that I ask a bunch of questions,and picked up a bunch over the years, and secondarily, I really like electrical, its cool.. In reality a licensed electrician came and looked over my work today and thought it was a very solid install, of course I am mostly giving credit to the guys on here to keep me from making mistakes..
even though I don't know you I appreciate your interest in my safety.. and I thank everyone else here for the notes in this continuing journey..

Nami said:
"I assume the ground wire grounds to the metal box not the neutral connection at my units panel"

"I assume the ground only connects to neutral at the main panel service entrance like home electrical systems."

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