Supply bonding jumper at transformer or at first point of disconnect main panel?

[Jpflex]

To my understanding the neutral is to be bonded to grounds only at one location to mitigate objectionable currents. For this reason you cannot ground the neutral within both the transformer and at the main bonding jumper in main panel/ first point of disconnect.


Therefore, if you are installing or inspecting a main panel and there is no main bonding jumper bonding ground, neutral and metal of main panel then how would you know it has been done at the transformer?

If you assume it was not done at transformer and place one in the main panel / first point of disconnect but the transformer had one then you’ll have code violating objectionable current.

 

[SSDriver]

One or the other. You would have access to the transformer and the panel. POCO transformers don't matter, you bond at main panel(or meter) if a service. POCO will have requirements of where they want YOU to bond at.

 

[infinity]

If the transformer is a utility transformer as SS mentioned then it doesn't matter. If the transformer is an SDS then the either location rule for the SBJ would apply.

 

[augie47]

........then how would you know it has been done at the transformer?......

If the SBJ is not in place you likely won't show any continuity between neutral and grounding conductors and/or if the system is active, you will show erratic voltages to ground.
Just a couple of points of order, there are exceptions that allow a SBJ at both the source and 1st disconnect and your GEC should be connected at the same point as your SBJ.

 

[Jpflex]

The transformers are utility owned and pole mounted so I don’t have access to them. However, there was no bonding jumper in main panel first point of disconnect between neutral/ground buss and metal panel case. This is what got me wondering

 

[xformer]

The transformers are utility owned and pole mounted so I don’t have access to them. However, there was no bonding jumper in main panel first point of disconnect between neutral/ground buss and metal panel case. This is what got me wondering

........then how would you know it has been done at the transformer?......

If the SBJ is not in place you likely won't show any continuity between neutral and grounding conductors and/or if the system is active, you will show erratic voltages to ground.
Just a couple of points of order, there are exceptions that allow a SBJ at both the source and 1st disconnect and your GEC should be connected at the same point as your SBJ.

Most residential service drops are either aerial, which cannot have objectional current on the aerial drop or pvc from underground which can't carry current due to its high impedance composition. So, for residential, bonding neutral to ground at the utility Transformer, and bonding again at the first means of disconnect is permissible. The bonding of the Neutral at the first means of disconnect is required by the NEC. The Poco has their own codes to follow.

 

[augie47]

If they are POCO transformers then you dealing with services and not SDS and as xformer states 250.24/250.28 require a main bonding jumper at all service disconnects on grounded systems (250.20) . There is rarely a path for "objectionable current" and, in the rare event there is one, it is acceptable.