EGC for existing parallel feeder

[jjhahn]

An existing single building with two services (3000A and 1600A, both 480V 3 Phase) is fed by a utility transformer located across the street. The secondaries run under the road approx 100 feet (8 and 4 sets of parallel 500 kcmil conductors with neutrals in 4 inch PVC conduits for each service). The service entrances, switchboards and grounding are currently in the basement of the building.

We plan to provide a new generator, switchgear and ATSs in the parking lot next to the utility transformer (across the street from the building). This involves interrupting the secondaries and providing new disconnects and grounding near the transformer, generator, generator switchgear and ATSs. (moving the service entrance from the basement across the street to near the transformer). We need to disconnect the neutral and ground in the basement (old service entrance location) and tie the two grounds together.

Question: The conduit/conductors under the road now become a feeder instead of service entrance conductors. Do all twelve sets of existing conductors have to be pulled out and repulled with a grounded conductor in each conduit per 250.122(F), or is it acceptable to provide a full size grounded conductor (one for each service) in spare duct bank conduits that run parallel to the existing conductors?

Is there an alternative configuration to avoid repulling existing conductors?

 

[charlie]

Re: EGC for existing parallel feeder

90.1(B) Adequacy. This Code contains provisions that are considered necessary for safety. Compliance therewith and proper maintenance will result in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use.
90.8(A) Future Expansion and Convenience. Plans and specifications that provide ample space in raceways, spare raceways, and additional spaces allow for future increases in the use of electricity.

The above quotes just serve to rub a bit of salt into the wound. This is the price paid for not looking to the future and squeezing the buck. Can you make use of 300.5(I) Exc. 2? For what it is worth, I think you are going to have pull them out and pull in a grounding conductor with each run.

 

[don_resqcapt19]

Re: EGC for existing parallel feeder

jjhahn,
You cannot place the EGCs in spare conduit. A full sized EGC is required in each raceway. You need a 4/0 in each of the raceways for the 1600 amp circuit and a 400 kcmil in each raceway for the 3000 amp circuit. You may be able to avoid this if your installation can comply with 250.32(B)(2).
Don

 

[bennie]

Re: EGC for existing parallel feeder

Does the type of conduit have any effect?

It seems strange to install a smaller wire, than is already available, for clearing a fault. Adding equipment ground conductors will increase the total loop impedance.

[ April 29, 2003, 07:27 PM: Message edited by: bennie ]