breaker gauge size

[Karl Fields]

Shopping for a 100 amp 2 pole breaker for my Homeline box. The few that list wire size usually have max (if any listed) of 2/0. My run requires 3/0.

So do I go with a bigger breaker (125a?) that hopefully will take a 3/0? Go with 2/0 and hope it doesn't overheat? or ...?

 

[ddawg16]

Why do you think you need 3/0 wire?

2/0 Is good for 145A....use 90C wire and you're good for 195A

http://www.usawire-cable.com/pdfs/nec ampacities.pdf

 

[Karl Fields]

240 volt, 100 amp, 400', 3% comes up 4/0 AU, but I can live with 5% which comes up 3/0 AU.
Am I missing something?

 

[dw1]

240 volt, 100 amp, 400', 3% comes up 4/0 AU, but I can live with 5% which comes up 3/0 AU.
Am I missing something?

400' of 3/0 (AU is Gold) (CU is copper) is there anyway to get the power company closer to your building? it might save you a lot in the long run if you were to call the power company and see what they could/would do (for free)
I just bought 3/0 copper, if you have 3 pieces at 400' you are looking at over $3300 and since its a sub panel, you would need # 6 ground with it. (That's THHN so it would need to be in PVC.)

 

[Speedy Petey]

Why do you think you need 3/0 wire?

2/0 Is good for 145A....use 90C wire and you're good for 195A

http://www.usawire-cable.com/pdfs/nec ampacities.pdf

You can never use the 90C column when figuring ampacity. Basically this column is only used for derating 90C wire.

 

[Speedy Petey]

240 volt, 100 amp, 400', 3% comes up 4/0 AU, but I can live with 5% which comes up 3/0 AU.
Am I missing something?

What are you basing this VD calculation on? The full 100A? And if so, WHY?

 

[Karl Fields]

Just finishing the 3" PVC run, and yes, the pricing the wire is starting to FEEL like it's gold. AU, CU close enough!
So here is my current thinking. I run the 2/0, from a 150amp breaker at the main to the 100 amp sub panel. Since the sub is breaker at 100 amp there shouldn't be an issue?
This is not an inspected instal

 

[rockwithjason]

Shopping for a 100 amp 2 pole breaker for my Homeline box. The few that list wire size usually have max (if any listed) of 2/0. My run requires 3/0.

So do I go with a bigger breaker (125a?) that hopefully will take a 3/0? Go with 2/0 and hope it doesn't overheat? or ...?

Without getting into any redesign questions, the answer to your question is to use pin adapters to reduce the cable to the correct size for the breaker.

 

[alfredeneuman]

As an alternative to the pin adapters, which take a specialized crimper to install, you could use Polaris connectors and splice the wire to the smaller size

http://www.polarisconnectors.com/pdfs/NSi/ISR_series.pdf

 

[Karl Fields]

Wouldn't either of these reducers defeat the effectiveness of the /0 cable?

 

[offroadsteve]

In this case no, because the 2/0 is more than enough to carry the 100 amps. You had to upsize to 3/0 because of the length of wire run and the resistance inherent to the wire. A short pigtail of 2/0 won't significantly increase the overall resistance of the circuit.

 

[Norcal]

No. It would not.

 

[dw1]

As an alternative to the pin adapters, which take a specialized crimper to install, you could use Polaris connectors and splice the wire to the smaller size

http://www.polarisconnectors.com/pdfs/NSi/ISR_series.pdf

I second this recommendation, they are quick and easy and do not require any special tools for installation. They work great.

 

[wyliesdiesels]

Shopping for a 100 amp 2 pole breaker for my Homeline box. The few that list wire size usually have max (if any listed) of 2/0. My run requires 3/0.

So do I go with a bigger breaker (125a?) that hopefully will take a 3/0? Go with 2/0 and hope it doesn't overheat? or ...?

what are your loads? One man shop?

And how would 2/0 overheat with a 125a breaker? Its good for 135a....

240 volt, 100 amp, 400', 3% comes up 4/0 AU, but I can live with 5% which comes up 3/0 AU.
Am I missing something?

Not sure how youre doing calcs but i got 4.2% VD with 3/0 AL...and this is at full load. I highly doubt u will ever be running at full load.

Just finishing the 3" PVC run, and yes, the pricing the wire is starting to FEEL like it's gold. AU, CU close enough!
So here is my current thinking. I run the 2/0, from a 150amp breaker at the main to the 100 amp sub panel. Since the sub is breaker at 100 amp there shouldn't be an issue?
This is not an inspected instal

Why would u waste money on a 150a breaker if all your doing is a 100a feed? If u dont have crazy loads, stick with the 2/0 and use a 100a breaker!

 

[Karl Fields]

what are your loads? One man shop?

Power to two 5th wheels. Both at 50amp.

And how would 2/0 overheat with a 125a breaker? Its good for 135a....

No clue. Just sounded right. I guess the real issue would be perhaps dereased voltage at the destination?

Not sure how youre doing calcs but i got 4.2% VD with 3/0 AL...and this is at full load. I highly doubt u will ever be running at full load.

Some on line calculator.

Why would u waste money on a 150a breaker if all your doing is a 100a feed? If u dont have crazy loads, stick with the 2/0 and use a 100a breaker!

You are probably correct. I will go with the 2/0 which will actually fit in the 100amp breaker. But that Polaris connector sounds interesting. So many things I never knew

Thanks!