bonds and grounds again

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I've inspected a 3 phase 430 volt sec. pad mount transformer thats feeding 5 building and the sec. side of the transformers neutral is not grounded to the frame of the transformer. The neutral goes to the MDP neutral bar but is not bonded to the ground bar. The frame of the transformer has a ground going to the ground bar in the MDP. The ground bar is grounded at a grounded electrode. The MDP has a main that feeds five breakers in it which feeds 5 sub-panels at each bldgs. they only ran 3 hots and a neutral to each sub-panel located 500 ft. away. The sub-panel at the panel has a green ground going to a ground rod, but the neutral and ground are not bonded there either. I believe that this is a floating neutral. What should be done in this situation if they cant run an additional ground from the MDP to the sub-panel. Would it be safe to say that they can bond the neutral and ground at each point meaning the sub-panel, MDP and the transformer. Oh, these are also new bldgs.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
I've inspected a 3 phase 430 volt sec. pad mount transformer thats feeding 5 building and the sec. side of the transformers neutral is not grounded to the frame of the transformer. The neutral goes to the MDP neutral bar but is not bonded to the ground bar. The frame of the transformer has a ground going to the ground bar in the MDP. The ground bar is grounded at a grounded electrode. The MDP has a main that feeds five breakers in it which feeds 5 sub-panels at each bldgs. they only ran 3 hots and a neutral to each sub-panel located 500 ft. away. The sub-panel at the panel has a green ground going to a ground rod, but the neutral and ground are not bonded there either. I believe that this is a floating neutral. What should be done in this situation if they cant run an additional ground from the MDP to the sub-panel. Would it be safe to say that they can bond the neutral and ground at each point meaning the sub-panel, MDP and the transformer. Oh, these are also new bldgs.

This is a little hard to follow. Where is the system bonding jumper for the SDS as per 250.30(A) located?
 

cadpoint

Senior Member
Location
Durham, NC
I've inspected a 3 phase 430 volt sec. pad mount transformer thats feeding 5 building and the sec. side of the transformers neutral is not grounded to the frame of the transformer. The neutral goes to the MDP neutral bar but is not bonded to the ground bar. The frame of the transformer has a ground going to the ground bar in the MDP. The ground bar is grounded at a grounded electrode. The MDP has a main that feeds five breakers in it which feeds 5 sub-panels at each bldgs. they only ran 3 hots and a neutral to each sub-panel located 500 ft. away. The sub-panel at the panel has a green ground going to a ground rod, but the neutral and ground are not bonded there either. I believe that this is a floating neutral. What should be done in this situation if they cant run an additional ground from the MDP to the sub-panel. Would it be safe to say that they can bond the neutral and ground at each point meaning the sub-panel, MDP and the transformer. Oh, these are also new bldgs.

Is that secondary, the POCO's or the owners?
 

RUWired

Senior Member
Location
Pa.
Prior to 2008 nec, if there are not any metallic paths from other systems, seperate buildings were allow to be grounded under article 250.32 (A)2. What are the wiring methods used to these out buildings? and are you inspecting these buildings as remedial work or as new construction.
 
the wiring methods are as followed a 3 phase 11kv transformer (owner supplied pad mount) 430v sec. all wire being used is a xlpe type cable. Basiclly it is a armored so type cable with no conduit. I'm not sure if i should bond at all 3 locations or what. the grounding in the code book is quite confusing at times. I'm not sure what a SDS is.
 

Smart $

Esteemed Member
Location
Ohio
the wiring methods are as followed a 3 phase 11kv transformer (owner supplied pad mount) 430v sec. all wire being used is a xlpe type cable. Basiclly it is a armored so type cable with no conduit. I'm not sure if i should bond at all 3 locations or what. the grounding in the code book is quite confusing at times. I'm not sure what a SDS is.

SDS is a separately derived system. If there is no direct connection between primary and secondary terminals of this transformer, it is a SDS. However, if powered by the utility co. with no NEC service disconnect on the primary side, the secondary is treated as a service, not an SDS.

Getting to the bottom of your main issue depends heavily on what code edition you are under...
 

RUWired

Senior Member
Location
Pa.
Since the transformer is owner supplied and there is a grounding electrode conductor connected between the transformer and the building MDP, one option would be to bond the neutral and ground in the MDP.

With the out buildings, you should investigate if the armored cable qualifies as an equipment ground. If it does not, and there are not any metallic utilities between the buildings, one option would be to bond the neutral and ground in the sub buildings panel. If there are, then there are other options available at a greater expense. With the 2008 code, a seperate equipment grounding conductor is required now between all sub panels and new out buildings that are fed from a common building.
 
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