Unbonded XFMR

[BLoyd]

Is it legal to leave the XO unbonded (no bond/ground conductor of any kind attached to the XO) on a XFMR if it is only used as an isolation XFMR?

 

[GoldDigger]

There is a detailed list of the types of supply for which one conductor must be grounded, along with some exceptions based on the intended usage.
A question is why you need an isolation transformer in the first place.

 

[ActionDave]

Is it legal to leave the XO unbonded (no bond/ground conductor of any kind attached to the XO) on a XFMR if it is only used as an isolation XFMR?

Check out 250.20 and 250.21.

 

[don_resqcapt19]

In general, if there is a circuit conductor connected to XO, the system is required to be a grounded system.

 

[BLoyd]

There is a detailed list of the types of supply for which one conductor must be grounded, along with some exceptions based on the intended usage.
A question is why you need an isolation transformer in the first place.

There are 12 of these XFMR's installed at a casino. I'm told they are used as filter XFMR's for clean power.

 

[don_resqcapt19]

There are 12 of these XFMR's installed at a casino. I'm told they are used as filter XFMR's for clean power.

What they are used for, doesn't have anything to do with the code rules that require the use of grounded systems.

There is a list of systems that are required to be grounded in 250.20. I expect that the secondary voltage system is one of the systems that 250.20 requires to be a grounded system.

 

[Pharon]

I don't understand why you would ever not want to ground an isolation transformer. It sort of defeats the whole purpose of having one.