PM Q: Services in Mid East

[George Stolz]

From a PM:

George, I am on a large instalation in the mid east and have several issues here, one there are several gen sets that step up voltage to 11KV run through out the base then at 4 locations step down to 200/400v the main bonding jumpers are cables run to a common grounding grid that follows the MV cable around the base and has several ground plates next to each transformer. In short the nuetrals have a cable to this plate and also the grounds from the switch boards acting as the service equipment. Is this suitable? it does work.
Problem 2, the main service disconnecting has several swithes that the feed free standing outdoor switch boards with a 4 wire cable and a ground wire following it. The nuetrals and grounds are isolated even into each building panel. the building sometimes have the water system bonded but most of the time only wire present is the loose isolated ground wire reun to the outdoor free standing switchboard. Shouldnt each building be bonded with the service disconnect ground nuetral/ water main bonding jumper to comply with NEC 408.3C ?
Hope this not to much for you.?
Thanks

 

[George Stolz]

Okay, I've taken a little more time to read this.

George, I am on a large instalation in the mid east and have several issues here, one there are several gen sets that step up voltage to 11KV run through out the base then at 4 locations step down to 200/400v the main bonding jumpers are cables run to a common grounding grid that follows the MV cable around the base and has several ground plates next to each transformer. In short the nuetrals have a cable to this plate and also the grounds from the switch boards acting as the service equipment. Is this suitable? it does work.

I don't work voltages higher than 480V, hopefully somebody can chime in on that part.

Problem 2, the main service disconnecting has several swithes that the feed free standing outdoor switch boards with a 4 wire cable and a ground wire following it. The nuetrals and grounds are isolated even into each building panel. the building sometimes have the water system bonded but most of the time only wire present is the loose isolated ground wire reun to the outdoor free standing switchboard. Shouldnt each building be bonded with the service disconnect ground nuetral/ water main bonding jumper to comply with NEC 408.3C ?

The NEC is difficult to apply to this installation. A typical NEC-compliant installation does not have an Equipment Grounding Conductor (EGC) run with the service conductors. Therefore, the EGCs on the load side of the disconnect are connected to the utility's neutral conductor at the service disconnect, and the EGS (EG System) begins there.

I suppose, if all equipment is owned by the same entity (and it's governed by the NEC), then the installation is compliant as described. The neutrals and EGCs would be kept seperate in the feeder disconnects, but bonded at the first disconnecting means after the transformers (or at the transformers) before those disconnects.

 

[benaround]

I agree with you George, the neutral and the EGC are joined at the transformers' grounding

grid ( ground ring ). That loose EGC is pretty much the MBJ.

 

[ahartma]

4 wire needs to be bonded neutral and the gtound together. Only on a 5 wire system does the neutral and ground be isolated.