Can I bond 480VAC equipment to 120VAC equipment?

[IamJonscranium]

250.30A (1) sounds like it's saying I need to bond my ground conductors from my SDS back to my 480V GEC at ONE point only. Is that an accurate understanding of this section?

What I am considering is bonding the ground or chassis from a piece of 480V equipment to the ground of the 120V equipment. Would this create a parallel path?

 

[Gregg Harris]

250.30A (1) sounds like it's saying I need to bond my ground conductors from my SDS back to my 480V GEC at ONE point only. Is that an accurate understanding of this section?

What I am considering is bonding the ground or chassis from a piece of 480V equipment to the ground of the 120V equipment. Would this create a parallel path?

Are you asking about bonding a 480 volt transformer?

 

[IamJonscranium]

Are you asking about bonding a 480 volt transformer?

No. I have a piece of machinery fed with 480. I have another piece of machinery fed with 120. Can I bond the ground conductor, or chassis of each machine to each other? Basically connecting 480V GEC with 120V ground?

This is not the main 120V disconnect or overcurrent device or source as specified in 250.30. Just between two random machines.

Edit: For instance, can you bond a 480V motor control panel to a 120V control panel which is on a separately derived system?

 

[kwired]

Each system already has its required system bonding done. You must bring the equipment grounding conductor from each system to practically everything associated with conductors of each system. You must also tie equipment grounding conductors to non current carrying components of connected equipment. This will connect the two EGC conductors together in multiple places most of the time. This will result in parallel paths for fault current, but even in the case of a single voltage system, you end up with multiple paths over equipment grounding conductors where there are conductive paths between equipment. Throw in a steel structure and fault current has virtually unlimited possibilities of ways to go. But equipment grounding is intended to create low as possible impedance to allow for quick operation of overcurrent devices, and by nature of this intention there often will be many potential paths.

 

[IamJonscranium]

Each system already has its required system bonding done. You must bring the equipment grounding conductor from each system to practically everything associated with conductors of each system. You must also tie equipment grounding conductors to non current carrying components of connected equipment. This will connect the two EGC conductors together in multiple places most of the time. This will result in parallel paths for fault current, but even in the case of a single voltage system, you end up with multiple paths over equipment grounding conductors where there are conductive paths between equipment. Throw in a steel structure and fault current has virtually unlimited possibilities of ways to go. But equipment grounding is intended to create low as possible impedance to allow for quick operation of overcurrent devices, and by nature of this intention there often will be many potential paths.

That helps, thank you.

 

[IamJonscranium]

Fixed it. It was in fact a grounding issue. Grounded the load end of the charger back to the disconnect and the arcing stopped.

I was worried there was a problem with the plant grounding in general so I didn't want to bond back to the 480V, but I ran a couple tests and everything looked fine.