Grounding Transformer

[rocketmenno]

I am looking at a new service installation with 480 utility service to an MDP. The MDP is serving Multiple Step Down Transformers which are feeding a panel with a main breaker. The code commentary says the GEC connection can be at any point between the source terminals and the first disconnecting means.

If the GEC is at the transformer then the neutral bar in the panel should be isolated. If the GEC is at the transformer then the Neutral bar in the panel would need to be bonded.

The electrician put a ground rod at the transformer AND at the panel.

Is this ok? and if it is should the Neutral bar in the panel be bonded??

 

[raider1]

Welcome to the forum.

The GEC should be connected to the separately derived system at the same location as the system bonding jumper.

Where is the system bonding jumpers located for the transformers?

250.30 gives you the requirements for grounding and bonding of separately derived systems.

Chris

 

[augie47]

Your mention of grounds rods causes me to ask that you make particular note of 250.30(A)(7). Although ground rods are permissible, they are low on the priority list of SDS electrodes and you made no mention of other possibly available (and required) methods
such as building steel and metallic water lines.

 

[rocketmenno]

I forgot to mention the system bonding jumper is at the transformer. The building steel and water pipe are also connected at the panel ground.

 

[raider1]

The building steel and water pipe connections should be made at the transformer as well.

Take a look at 250.30(A)(3).

Chris

 

[raider1]

Here is an illustration from Mike Holt that might help.




Chris

 

[rocketmenno]

thanks for your replies i am still a little uncertain about this.

I took the image from the NEC handbook and modified it to illustrate what has been installed.

I am wondering if this installation is ok and I am wondering if the neutral bar in the panel should be bonded to the ground bar??

Thanks for your feedback

 

[raider1]

thanks for your replies i am still a little uncertain about this.

I took the image from the NEC handbook and modified it to illustrate what has been installed.

I am wondering if this installation is ok and I am wondering if the neutral bar in the panel should be bonded to the ground bar??

Thanks for your feedback

NO!!! the neutral bar at the panel must be isolated from the equipment grounding conductor bar and the panel can.

The building steel and water pipe should be connected at the transformer because that is where the system bonding jumper is located. (Again see 250.30(A)(3))

Once you have made you system bonding jumper connection you must keep the grounded conductor isolated from the equipment grounding conductor. If you don't then the EGC will be in parallel with the grounded conductor and neutral current will flow on all the grounded equipment.

Chris