CT Cabinet Case to Ground Fault

[ddcawley]

First, if a line to case fault were to occur in a CT cabinet and the CT enclosure did become energized how do you know when the fuses in the transformer will open? It seems that the potential for a 3?x 3? energized metal enclosure could be a real danger. I once heard that the galvanized mast of a service began to glow due to unopened fuses in the transformer (story less than confirmed though).

Second, this CT cabinet is mounted to a stanchion 10? away from the utility pole 100? away from the main disconnect mounted on the residence. Is there any need to ground this cabinet to ground rods for lightning path and if so, should they be connected to the utility ground rod which is driven a couple feet from the stanchion.

Thanks for any help.

 

[shortcircuit2]

Re: CT Cabinet Case to Ground Fault

ddcawley...the CT cabinet is required to be bonded to the grounded conductor within the enclosure. Done properly, a line to enclosure fault may cause the utility fuse to open...if it does not, something should burn clear.

It is very important to have tight connections between the grounded conductor and all service equipment to insure a low impedance path for fault current to the source. The glowing pipe would be an example of what would happen when there is not an effective ground-fault current path.

The code doesn't require a grounding electrode at the CT cabinet...

shortcircuit2

 

[iwire]

Re: CT Cabinet Case to Ground Fault

Originally posted by ddcawley:
First, if a line to case fault were to occur in a CT cabinet and the CT enclosure did become energized how do you know when the fuses in the transformer will open?

You don't, the power company fuses may never open.

Originally posted by ddcawley:
It seems that the potential for a 3?x 3? energized metal enclosure could be a real danger.

Yes it could be.

Originally posted by ddcawley:
I once heard that the galvanized mast of a service began to glow due to unopened fuses in the transformer (story less than confirmed though).

I would say that is entirely possible, have a look at a piece of 4" RMC that had a service conductor fault in it.



Bob