# Transformer Primary Conductors Calculation



## The_Electrician (Apr 30, 2019)

Hey Guys,

We have a Solar system installed with the following specs:
- Voltage: 480 V
- Current: 1080 A

This is fed into the secondary of the 1000 kVA transformer with 4kV on the primary whose spec. is:
kVA= (1.732 x 480 x 1080)/1000 = 897.895 kVA (1000 kVA is used)

From this the primary current will be:
I = 897.995*1000/1.732*4000 = 129.6 A

The primary is interconnected to the grid

The POCO asked us to use a 2/0 wire for the primary, but I wanted to verify this so, Can someone please provide a step by step process to calculate the conductor size for the primary according to NEC?

Thanks in Advance


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## Tonedeaf (Nov 26, 2012)

you gota use what the POCO wants, they have their own guidelines for services and they do not necessarily use the NEC.

around here u can use #2 awg Cooper MV cable for that load.


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## The_Electrician (Apr 30, 2019)

Tonedeaf said:


> you gota use what the POCO wants, they have their own guidelines for services and they do not necessarily use the NEC.
> 
> around here u can use #2 awg Cooper MV cable for that load.


Hey, Thank you, did you come up with #2 using 310.15(B)(16) 90 degree Temp.? Also, do I have to install a primary side protection for even if I am connecting directly to the utility line?


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## Tonedeaf (Nov 26, 2012)

The_Electrician said:


> Hey, Thank you, did you come up with #2 using 310.15(B)(16) 90 degree Temp.? Also, do I have to install a primary side protection for even if I am connecting directly to the utility line?




we have to use 15KV cable and terminations for 4160V....utililites around here don't want to stock 5kv stuff and they are trying to phase out 4160.

15KV XPLE #2 awg cooper xple or epr is good for 150-165 amps in duct. I think its 90 table


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## The_Electrician (Apr 30, 2019)

Tonedeaf said:


> we have to use 15KV cable and terminations for 4160V....utililites around here don't want to stock 5kv stuff and they are trying to phase out 4160.
> 
> 15KV XPLE #2 awg cooper xple or epr is good for 150-165 amps in duct. I think its 90 table


Now I got it!, I couldn't find table 90 is it in article 310?


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## Tonedeaf (Nov 26, 2012)

https://www.mysouthwire.com/medias/...duct-specifications/hca/hb8/8854088417310.pdf

here's tables from southwire

90 degree induct #2 good for 150 amps


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## The_Electrician (Apr 30, 2019)

Tonedeaf said:


> here's tables from southwire
> 
> 90 degree induct #2 good for 150 amps


Thanks man, appreciate it. I have one more doubt, Do I have to have a primary protection for the transformer like a service disconnect even if I connect the primary of the transformer directly to 4kV line of the utility?


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