Transformer X0 question

[engineer84]

I am installing a 50 kva delta to wye transformer on the secondary side for grounding I have the following:

X0 tap--- 1) neutral to machine
2) ground wire to lug on frame

Frame ground bar--- 1) system ground from bus duct
2) ground to machine
3) ground to building steel
4) ground wire to X0


Is this acceptable? Any advice?

 

[Mico Opus]

Looks good to me.

Optimally I prefer to use a type of lug on the transformer case that will allow me to have the bonding conductor from the conduit go through the lug on the case and terminate on one of two lugs on X0. The other lug on X0 has the neutral. A separate lug on the case will have the heavy (#6) bare copper going to building steel.
Note that using building steel is not going to be fully effective unless the switchgear is bonded to the building steel. If you're not familiar with the site then it's worth checking.

 

[engineer84]

Sounds good thanks! Anyone else have any thoughts. There is some question as to whether or not the GEC to building steel has to be terminated directly on the XO Lug or it is okay the way I have it listed above. Any help greatly appreciated.

 

[don_resqcapt19]

250.30(A)(5) requires the GEC to directly connect to the grounded conductor, but there are exceptions.

 

[engineer84]

250.30(A)(5) requires the GEC to directly connect to the grounded conductor, but there are exceptions.

Thanks Don for the quick response. When I review 250.30(A)(5) and take a look at Exception 1 it says that if the system bonding jumper is a wire then the GEC is permitted to be connected to the equipment grounding terminal.


So is my interpretation correct to say that since I have a wire connected from X0 to the equipment grounding terminal which I believe to be defined as my system bonding jumper that it is acceptable to terminate my Grounding Electrode Conductor directly to the equipment grounding terminal which I believe to be my frame ground? If so then I what I have listed above would be acceptable?

 

[don_resqcapt19]

Thanks Don for the quick response. When I review 250.30(A)(5) and take a look at Exception 1 it says that if the system bonding jumper is a wire then the GEC is permitted to be connected to the equipment grounding terminal.


So is my interpretation correct to say that since I have a wire connected from X0 to the equipment grounding terminal which I believe to be defined as my system bonding jumper that it is acceptable to terminate my Grounding Electrode Conductor directly to the equipment grounding terminal which I believe to be my frame ground? If so then I what I have listed above would be acceptable?

I don't I have ever run across a transformer with an equipment grounding bar. If yours has one, I think the exception applies.

 

[engineer84]

I don't I have ever run across a transformer with an equipment grounding bar. If yours has one, I think the exception applies.

Don, it's not actually a grounding bar it's a multiple barrel lug on the transformer frame ground.

 

[don_resqcapt19]

Don, it's not actually a grounding bar it's a multiple barrel lug on the transformer frame ground.

That should meet the requirements of the exception.

 

[joebell]

Don, it's not actually a grounding bar it's a multiple barrel lug on the transformer frame ground.

The exception still applies to your installation.