Underground Secondary Going Overhead

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eeee

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I am installing a pad mounted transformer so my aerial distributed ground mounted transformers can be taken away so there are no more live parts and are classified as a NEC violation.

I am not taking any utility poles away right now on a long run of utility poles to save money. Therefore my pad mounted transformer will have a secondary that goes underground for a short distance then connects with the existing overhead secondary.

Can I splice my underground secondary from the pad mounted 12KV primary, 208/120 volt secondary delta-wye, 3 phase, 300KVA transformer with the existing overhead secondary?? The existing overhead secondary consists of four 500MCM cables, that later are tapped in to two separate set of four 300MCM cables just before the service entrance. My underground cable emanating from the pad mounted transformer will be XLP and #2. I fear that I can not do this???

I fear that can not take a secondary underground then go overhead from my 3 phase pad mounted transformer simply because the cable types are different. One is for overhead distribution and the other is for underground. How could you splilce them together???
 
Re: Underground Secondary Going Overhead

eeee

If you are splicing 600 volt cable to 600 volt cable there will be no problem. Utilities splice overhead and ug secondary cables every day without any difficulties.

I am not sure why your secondary leads from the padmount are #2. A 300 KVA transformer has 833 amps of capacity. I've been folowing your previous posts about these installatios, and don't remember #2 AWG conductors.

Can you explain before we go much farther.

Jim T
 
Re: Underground Secondary Going Overhead

Yes,

I am splicing 600 volt underground secondary cable to 600 volt overhead secondary cable.

The amperage capacity of the building is 100amps and this considers growth.

Referring to the Ugly's book and NEC, #2 should be used for the range of 104 degrees farenheit to 176 degrees farenheit for underground in conduit and overhead in air.

The facility used to have much more equipment in it. It used to have a very large compressor, etc. for machine work I believe. That is why I suspect the secondary is presently 500MCM. The thing is, I don't believe I want to splice in to 500MCM overhead secondary cable with a #2 XLP 100% concentric neutral underground secondary cable???
 
Re: Underground Secondary Going Overhead

I don't use a lot of concentric neutral ug secondary, as the neutral usually needs to be insulated. It is fine for primary cable, but may create problems with NEC governed installations. Perhaps your neutal is insulated.

When you overcome any NEC concerns, you can peel back the neutral, attach it to the overhead neutral with a kearney or some other suitable connector. The other wires would connect similarly. It will be hard to find a splice that goes from 500 to #2, so you will probably have to use a mechanical connector, either a split bolt, or a compression connector. Tape them up, and you are good to go.

Insulation compatibility is no concern.

Jim T
 
Re: Underground Secondary Going Overhead

Jim T.

Your right. I need to get away from the concentric nuetral cable for the secondary. I will just go with a 4 wire, #2/0, 1 #6 ground in a two hole (one for spare) 5" duct system, concrete encased on three sides.
 
Re: Underground Secondary Going Overhead

I made a mistake I believe. I need 3 wire and a ground for the MDP. I would need 4 wire and a ground if I were running my secondary to a lighting panel I believe.
 
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