Grounding on legacy system.

S

SKhaja

Member
Location
Illinois
Occupation
designer
Gentlemen,

Have a question here about converting a TN-C ground system to TN-S.

we want to run 4/C cables plus ground cable to an existing main junction box that only has cables for 3-phase and neutral. This junction box sends cables to two existing service mains.

can any one give some advice on how to proceed on this as per the NEC?
My initial thinking has been to install a earth terminal board and connect to the ground at main jb, run the separate ground wires from JB to existing two service mains.

Thanks in advance for the input.
 
Our systems are TN-C from the utility to the service equipment. A main bonding jumper is installed in the service equipment and the system is TN-S from that point on.

TN-C has never been permitted downstream of the service equipment by the NEC.
 
to clarify things more here...
the present transformer is being relocated and we will be installing a service entrance breaker near the transformer.
this breaker will then feed the main junction box to the two existing service mains.
hope that this helps.
 
SKhaja said:
...
we want to run 4/C cables plus ground cable to an existing main junction box that only has cables for 3-phase and neutral. This junction box sends cables to two existing service mains.
..
Click to expand...
Your description could include more detail, but this sounds like there is no need for the 'plus ground' because you are on the supply side of the service disconnects. The junction box and other metal parts can be bonded the neutral until you are on the load side.
 
don_resqcapt19 said:
Our systems are TN-C from the utility to the service equipment. A main bonding jumper is installed in the service equipment and the system is TN-S from that point on.

TN-C has never been permitted downstream of the service equipment by the NEC.
Click to expand...
i tried to reply on your post but my post is being reviewed by the moderator.
 
SKhaja said:
to clarify things more here...
the present transformer is being relocated and we will be installing a service entrance breaker near the transformer.
this breaker will then feed the main junction box to the two existing service mains.
hope that this helps.
Click to expand...
Who owns the transformer that will be relocated? Where is the service point as defined in the NEC? It sounds like these may be feeder circuits and not service conductors.
 
don_resqcapt19 said:
Who owns the transformer that will be relocated? Where is the service point as defined in the NEC? It sounds like these may be feeder circuits and not service conductors.
Click to expand...
Its owned by the utility company. The service point will be more than 250 ft away from the jb which is located next to the existing location of the transformer.
 
SKhaja said:
Its owned by the utility company. The service point will be more than 250 ft away from the jb which is located next to the existing location of the transformer.
Click to expand...
Are there multiple sets of service conductors from the service point to multiple service disconnects?
If there are, those service conductors would be TN-C, and everything on the load side of the service disconnects must be TN-S.
 
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