120/208v voltage troubleshooting

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Since the EGC will be bonded at the transformer to the grounded conductor, the bonding screw in the panel should be removed, correct?
There is no equipment grounding conductor between the transformer and the first OCPD. It is a supply side bonding jumper and is sized from Table 250.102(C)(1).
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
If you bond in the transformer, you run separate neutral and EGC, and don't bond like in a sub-panel.

If you don't bond in the transformer, you run only the neutral, and you do bond like in a main panel.
No matter where the system bonding jumper is installed, you need a supply side bonding jumper between the transformer and the first OCPD.
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
Since the EGC will be bonded at the transformer to the grounded conductor, the bonding screw in the panel should be removed, correct?
This is the big difference between separately derived systems and services. More specifically systems where the transformer is installed indoors. The neutral must be bonded in the transformer and there must be a system bonding jumper from the transformer to the ground bar and enclosure of the main disconnect. There is an exception that applies to outdoor transformers, which brings them more in line with the way we do services.
 
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