800A 480V Breaker Panel - Bond to structure or not?

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zach.bes

zach.bes

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Location
Porterville
Hey everyone,

Just passed my CA Journeyman test and have a lot more responsibility. And I like to do things correctly so I figured I would consult with the experts.

I'm installing (2) 800A 480V MLO Breaker Panels that are fed from a 2000A Main service switchgear (Protected via 800A breakers of course) and the boss and I have been going back and forth in regards to properly grounding/bonding these panels.

Each panel is fed via parallel 600MCM with 1/O EGC's. The panels are roughly 12ft from the structure I-beams (grounding electrode).

What do we need to do to properly and safely ground/bond these panels?

Boss says 1/O bond to I-Beam

I say 3/O bond to I-Beam. Using formula from 2014 NEC 250.102

I also don't think we need to bond these AT ALL to the I-Beam since they are sub panels. We don't want objectionable current, right?

What are your thoughts?

I'm new to this so forgive my lack of knowledge.
I always keep my 2014 NEC with me but it can be confusing at times.

Thanks.

Zach


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infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
All that you need is the EGC within the feeder. You can bond it to the steel if you want but it's IMO a waste of time and money.
 
jumper

jumper

Senior Member
Location
3 Hr 2 Min from Winged Horses
To add to what Infinity posted.

The I beam should have already been bonded from the MDP or switchgear.

If used as part of the GES, it would be a 3/0 using T250.66.

If just be being bonded it would be a 3/0 using T250.102(C)(1), which you posted above, using the formula from note 1. This a supply side jumper from the MDP.

However, if you ran a jumper from the sub panel to steel this just be an extraneous/unneeded load side jumper and 250.102(D) says use T250.122 which gives you a 1/0.
 
augie47

augie47

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Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
As a point of conversation, note that 250.136(A) states the the metal frame of the building can not be used as an equipment grounding conductor so IF you elect to install a bond to the steel, you would still need to provide an equipment ground meeting the requirements of 250.118,
 
zach.bes

zach.bes

Member
Location
Porterville
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Here is what I'm dealing with. Thanks everyone.

Zach


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zach.bes

zach.bes

Member
Location
Porterville
We wasted time and money. But not much. Already had a scrap piece of 3/O with my crew. If it were completely up to me I wouldn't bond at all, but boss wanted it bonded so I said if we are bonding at all we should 3/O.


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J

JFletcher

Senior Member
Location
Williamsburg, VA
Welcome to the forum. Gratzon passing your test. I see your question has been resolved, tho I wanted to address one point:
zach.bes said:
I also don't think we need to bond these AT ALL to the I-Beam since they are sub panels. We don't want objectionable current, right?
Click to expand...

You do not want more than one path for the neutral from panel to subpanel. You have no neutral feed here anyway, which begs the question (again): what are the small white wires in the bottom of the cabinet? You cannot remark white wires to be ungrounded conductors unless they are part of a cable assembly.
 
kwired

kwired

Electron manager
Location
NE Nebraska
If your "subpanel" is in a separate building or structure then you need to establish a grounding electrode system in that other building/structure. If your subpanel is in same building/structure as where it receives it's supply from then you should already have a grounding electrode system at the building service/main disconnecting means.
 
zach.bes

zach.bes

Member
Location
Porterville
kwired said:
If your "subpanel" is in a separate building or structure then you need to establish a grounding electrode system in that other building/structure. If your subpanel is in same building/structure as where it receives it's supply from then you should already have a grounding electrode system at the building service/main disconnecting means.
Click to expand...

That's what I thought.


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jumper

jumper

Senior Member
Location
3 Hr 2 Min from Winged Horses
zach.bes said:
1/O EGC per pipe was code for parallel 600mcm's. I would state which one if I had it on me right now.


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Click to expand...

EGCs are sized according to the OCPD protecting the phase conductors.

For parallel conductors a full sized EGC must pulled in each conduit per 250.122(F), a 1/0 CU in your case for a 800A OCPD per T250.122
 
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