Utility voltage of 12.4KV, do I multiply that by square root of 3?

[ElectricNewEngland]

I am trying to size some conductors. The voltage is 12.4KV. The conductors are feeding a 2,500KVA transformer.
If I size the conductors to the transformer, is my amp calculation 2,500KVA / 12.4KV = 201 amps? (use 250KCMIL conductors)
Or is it 2,500KVA / (12.4KV X square root of 3) = 117 amps? (use 1/0 conductors)

Which is it?
Thanks in advance. I appreciate any help.

 

[zog]

Wye or Delta?

 

[ElectricNewEngland]

Delta, I think.

 

[Jraef]

I am trying to size some conductors. The voltage is 12.4KV. The conductors are feeding a 2,500KVA transformer.
If I size the conductors to the transformer, is my amp calculation 2,500KVA / 12.4KV = 201 amps? (use 250KCMIL conductors)
Or is it 2,500KVA / (12.4KV X square root of 3) = 117 amps? (use 1/0 conductors)

Which is it?
Thanks in advance. I appreciate any help.

Delta, I think.

No offense intended, but something in the back of my mind is nagging me that this has to be said.

If you have to ask this question, a better one might be "Do you think you are qualified to be making this kind of decision on 12kV power?" The consequences of making a small mistake here can be big.

 

[Smart $]

I am trying to size some conductors. The voltage is 12.4KV. The conductors are feeding a 2,500KVA transformer.
If I size the conductors to the transformer, is my amp calculation 2,500KVA / 12.4KV = 201 amps? (use 250KCMIL conductors)
Or is it 2,500KVA / (12.4KV X square root of 3) = 117 amps? (use 1/0 conductors)

Which is it?
Thanks in advance. I appreciate any help.

Wye or Delta?

Of no consequence aside from downsizing neutral.

2500kVA ? 12.47kV ? sqrt(3) = 116A

If service, primary conductor ampacity is minimum non-continuous plus 125% continuous loads. If feeder supplying only one or more transformers, 116A plus nameplate rating of other supplied transformers, if any.

 

[ElectricNewEngland]

No offense intended, but something in the back of my mind is nagging me that this has to be said.

If you have to ask this question, a better one might be "Do you think you are qualified to be making this kind of decision on 12kV power?" The consequences of making a small mistake here can be big.

You have a good point. I don't have a lot of experience with high voltage.

 

[david luchini]

If I size the conductors to the transformer, is my amp calculation 2,500KVA / 12.4KV = 201 amps? (use 250KCMIL conductors)
Or is it 2,500KVA / (12.4KV X square root of 3) = 117 amps? (use 1/0 conductors)

1/0 conductors would likely be much larger than you need. Probably #4 or #2 would be adequate depending on your installation method. See the ampacity tables starting at 310.60(C)(67) for over 2000Volts.

 

[Smart $]

1/0 conductors would likely be much larger than you need. Probably #4 or #2 would be adequate depending on your installation method. See the ampacity tables starting at 310.60(C)(67) for over 2000Volts.

Still have to use Table 310.15(B)(16) for termination temperature limitations [110.14(C)].

 

[Besoeker]

I am trying to size some conductors. The voltage is 12.4KV. The conductors are feeding a 2,500KVA transformer.
If I size the conductors to the transformer, is my amp calculation 2,500KVA / 12.4KV = 201 amps? (use 250KCMIL conductors)
Or is it 2,500KVA / (12.4KV X square root of 3) = 117 amps? (use 1/0 conductors)

Which is it?
Thanks in advance. I appreciate any help.

The second calculation.
kVA=sqrt(3)*V_L*I_L/1000

 

[david luchini]

Still have to use Table 310.15(B)(16) for termination temperature limitations [110.14(C)].

That is not correct. Table 310.15(B)(16) applies only to conductors "up to and including 2000V." These conductors are decidedly over 2000V.

See 310.60(B), 310.60(C) and 110.40.

 

[Jraef]

You have a good point. I don't have a lot of experience with high voltage.

Don't know about NH, but in a lot of states you are required to have a specific certification or endorsement to your electrical license for handling anything over 600V, which comes from taking training classes. You might want to check into that before you get yourself in hot water.

 

[jim dungar]

You have a good point. I don't have a lot of experience with high voltage.

Just to be nit picky.
The proper term for 12,470V is Medium Voltage. In the power/utility world, High Voltage begins around 48kV.

Now go have a Merry Christmas.

 

[TimK]

Just to be nit picky.
The proper term for 12,470V is Medium Voltage. In the power/utility world, High Voltage begins around 48kV.

Now go have a Merry Christmas.

I don't know about that, first read Art. 328.2, then Art. 490.2.:roll:

 

[zog]

I don't know about that, first read Art. 328.2, then Art. 490.2.:roll:

and then the IEEE definitions

 

[iceworm]

... If you have to ask this question, a better one might be "Do you think you are qualified to be making this kind of decision on 12kV power?" The consequences of making a small mistake here can be big.

Why would that matter? This forum promotes DIY engineering.

ENE -
Ask away - and learn. Your questions are not out of line with most of the DIY engineering discussed here.

Don't know about NH, but in a lot of states you are required to have a specific certification or endorsement to your electrical license for handling anything over 600V, which comes from taking training classes. You might want to check into that before you get yourself in hot water.

The OP works for a "Lighting, Power and Fire Alarm design firm" - which means they are doing "engineering for hire". They will have to have a PE to sign for ENG's work.

I've never heard of an "over 600V certification" a PE ticket. AFAIK I can stamp anything I want. The state thinks I'm smart enough to know if I should.

Just curious, what are some of the states differing?

ice

 

[iceworm]

I appologize for the hit and run. I'm working for the next few weeks and only had a bit of time. I'll be happy to take any lumps when I get back.

ice

 

[jim dungar]

I don't know about that, first read Art. 328.2, then Art. 490.2.:roll:

328.2 confirms my position about nominal 15kV being called Medium Voltage.
490.2 specifically says its definition only applies to Article 490.

The note to the Article 100 definition of Voltage, Nominal refers you to ANSI C84.1 which is a 'sister' document to the one from IEEE

 

[Smart $]

That is not correct. Table 310.15(B)(16) applies only to conductors "up to and including 2000V." These conductors are decidedly over 2000V.

See 310.60(B), 310.60(C) and 110.40.

Thank you for the correction. I was unaware there was a 110.40.

 

[TimK]

328.2 confirms my position about nominal 15kV being called Medium Voltage.
490.2 specifically says its definition only applies to Article 490.

The note to the Article 100 definition of Voltage, Nominal refers you to ANSI C84.1 which is a 'sister' document to the one from IEEE

Sorry Jim, by no means was I trying to correct you, I just thought it funny with two different definitions that I happen to look up back to back like that.

 

[jim dungar]

Sorry Jim, by no means was I trying to correct you...

No foul.

I am just in the Holiday spirit, where I am looking to dump on anyone I can.