100 subpanel bonding??

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Hello everybody I have a simple question that I keep going back and forth on in my head and just need an answer if someone can help me... I have a cargo container I am putting 100 amp sub panel and at an asphalt plant, I am coming off of a 480 volt panel through a disconnect and a transformer then to the sub panel I am going to drive ground rods for the new ground of the sub panel, do I still need to pull the ground screw because it is a sub panel and bond the transformer neutral? Or do I leave the bonding screw in because it's now considered a new service? Thanks for any and all responses
 

kwired

Electron manager
Location
NE Nebraska
It is not a service, service is what is supplied from the utility. You do not bond the grounded conductor beyond service equipment.

What you do have is a separately derived system. You do have to bond the grounded conductor, but it must be done at either the source or first disconnecting means, beyond there you still keep grounded conductor separated from equipment grounding. Exceptions used to be allowed for separate buildings or structures but those have been gone since 2008 NEC other then permission to leave them if they were previously allowed and are existing.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Ok thank you, so just to clarify, do not bond the neutral in the sub panel but do bond the neutral in the transformer correct?
It is your choice....the required bond can be at either location, but you can't bond it at both. In either case you will need a supply side bonding jumper between the transformer and the panel.
 

kwired

Electron manager
Location
NE Nebraska
It is your choice....the required bond can be at either location, but you can't bond it at both. In either case you will need a supply side bonding jumper between the transformer and the panel.
I have to clarify for OP, the panel in question to be bonded has to contain the first disconnecting means of the separately derived system, and the following of tap rules generally means that it will be close to the transformer as well.
 
So same job here,... I've got the transformer hooked up x0 is bonded on the secondary side. I put my meter from x0 to x1 I only get 60 volts I put my Leads from x0 to x2 I get 120 volts... I put my Leads between x1 and x2 and I have about one hundred and ninety volts.... ( these are all on the secondary side of course) I'm not sure what the problem is here and why I can't get 208 volts between x1 and x2 is this may be an indication that this transformer isn't working right? It looks like it's at least 25 years old.... I tested the ground and everything was good in the whole system from ground rod through the sub panel to the transformer frame I'm spinning my wheels here and my boss is making me feel like a jackass for not being able to figure it out...... I'm hoping it's the transformer and not me just my own ignorance
 

kwired

Electron manager
Location
NE Nebraska
So same job here,... I've got the transformer hooked up x0 is bonded on the secondary side. I put my meter from x0 to x1 I only get 60 volts I put my Leads from x0 to x2 I get 120 volts... I put my Leads between x1 and x2 and I have about one hundred and ninety volts.... ( these are all on the secondary side of course) I'm not sure what the problem is here and why I can't get 208 volts between x1 and x2 is this may be an indication that this transformer isn't working right? It looks like it's at least 25 years old.... I tested the ground and everything was good in the whole system from ground rod through the sub panel to the transformer frame I'm spinning my wheels here and my boss is making me feel like a jackass for not being able to figure it out...... I'm hoping it's the transformer and not me just my own ignorance

Did you check to see if you have proper primary voltage on all three lines? Sounds like you could be missing one input.
 

kwired

Electron manager
Location
NE Nebraska
Is it possible that I'm missing a jumper connection between x1 and X3? Since there are 60 volts on each leg?
If properly working, a jumper between any of the X terminals will result in short circuit current flowing between those terminals.

I still think you likely lost a primary line.
 
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