What wire size would you use here?

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olly

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Berthoud, Colorado
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Master Electrician
125-amp breaker, from pole / main to barn 120'. I know minimum size would be 1/0 AL for the phases. Its in conduit by the way. I was thinking 2/0 for the phases. I don't know where in the code to properly size the neutral but its always 2 sizes down in triplex. So am I good to pull 2/0 AL for the hots a #1 AL for the neutral and #6 CU for the equipment ground?
As far as load... mainly lighting and LED to boot, there is a RV and weld outlet but those will rarely be used. Thanks in advance for your advice and input on this matter!
 
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olly said:
125-amp breaker, from pole / main to barn 120'. I know minimum size would be 1/0 AL for the phases. Its in conduit by the way. I was thinking 2/0 for the phases. I don't know where in the code to properly size the neutral but its always 2 sizes down in triplex. So am I good to pull 2/0 AL for the hots a #1 AL for the neutral and #6 CU for the equipment ground?
As far as load... mainly lighting and LED to boot, there is a RV and weld outlet but those will rarely be used. Thanks in advance for your advice and input on this matter!
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2/0 AL easily does it, prob what I would use. I def wouldnt go bigger - 2/0 is often the max size for 100 and 125A equipment.

edit: and yes I concur with your other sizes. Could check if the supply house has "4 wire URD" or "mobile home feeder" in 2/0
 
You have a 125 amp breaker at the pole or at the barn, both?

Sounds like 60 amp supply is possibly sufficient, many will go with 100 anyway.

If 125 amp breaker is at pole keep in mind you could still run a 60 amp feeder to this building if that is all that is needed, upsize conductors if you think is necessary for voltage drop, and as long as you have a 60 amp main at the building the conductors to the pole are "outdoor feeder taps" and are still ok on the 125 amp breaker per feeder tap rules.
 
Remember the 'increased in size' rule for the EGC. If the minimum required for the circuit is 1/0 and you upsize to 2/0, then you have to upsize the EGC the same way.

-Jon
 
kwired said:
You have a 125 amp breaker at the pole or at the barn, both?

Sounds like 60 amp supply is possibly sufficient, many will go with 100 anyway.

If 125 amp breaker is at pole keep in mind you could still run a 60 amp feeder to this building if that is all that is needed, upsize conductors if you think is necessary for voltage drop, and as long as you have a 60 amp main at the building the conductors to the pole are "outdoor feeder taps" and are still ok on the 125 amp breaker per feeder tap rules.
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Im intrigued, I did not know this... So If I have a 125a main at the pole I can run smaller wire say 60amp wire to the barn?
 
olly said:
Im intrigued, I did not know this... So If I have a 125a main at the pole I can run smaller wire say 60amp wire to the barn?
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That is the whole point of 'tap rules'. You have a conductor protected from short circuit by a upstream breaker of higher trip rating than it's ampacity, and protected from overload by the downstream breaker. But there are specific limits that you have to follow, including length and ratio of upstream breaker to conductor ampacity.

In some cases outside taps of unlimited length are permitted.

-Jon
 
If you're concerned with voltage drop or future increase, go with commonly-available 4/0 direct-bury.
 
winnie said:
That is the whole point of 'tap rules'. You have a conductor protected from short circuit by a upstream breaker of higher trip rating than it's ampacity, and protected from overload by the downstream breaker. But there are specific limits that you have to follow, including length and ratio of upstream breaker to conductor ampacity.

In some cases outside taps of unlimited length are permitted.

-Jon
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All outdoor feeder taps can be unlimited length. There are conditions that go with it just like the other tap rules though.

In OP's case if he wanted to run 60 amp conductors, the other thing to remember is the feeder OCPD is 125 amps and that he will have a larger EGC than if he had a 60 amp feeder OCPD.
 
Something else to consider if that 125 amp breaker at the pole is POCO provided site isolation device - some places don't recognize that as the service disconnecting means if it is POCO installed/maintained. They can easily change it to something that has no OCPD down the road and then it no longer complies as a service disconnect. Here they do see it that way and all conductors leaving such a disconnect are still treated as though they are service conductors. Main impact here since they would be feeders(/taps) otherwise is the need to run a separate EGC.
 
kwired said:
All outdoor feeder taps can be unlimited length. There are conditions that go with it just like the other tap rules though.

In OP's case if he wanted to run 60 amp conductors, the other thing to remember is the feeder OCPD is 125 amps and that he will have a larger EGC than if he had a 60 amp feeder OCPD.
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I have decided to go with 2/0 AL hots a #1 AL neutral and a # 6 CU EGC can you please tell me if the neutral and EGC are sized appropriately? Thanks
 
In most cases the neutral can be sized 2 sizes down for a feeder or service on a residence. Sizes the equipment grounding conductor is down based on Table 250.122

If you have a lot of 240v circuits without a neutral then obviously the neutral can be downsized but technically a calculation is needed
 
olly said:
I have decided to go with 2/0 AL hots a #1 AL neutral and a # 6 CU EGC can you please tell me if the neutral and EGC are sized appropriately? Thanks
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For 125 amp feeder 1/0 aluminum is fine if load calculation is 120 or less.

6 copper EGC is fine, if you had larger circuit conductors because of VD then you must increase EGC by same proportion.

The grounded (neutral) conductor only needs sized to maximum unbalance load you can encounter, but in no case can be smaller than the required EGC.

That two conductor sizes smaller for services and feeders that seems to be common for neutrals is sort of an unwritten rule that many inspectors will allow such without you having to prove any calculations for neutral loading.

I do a lot of grain storage bin work and often run the minimum size allowed for neutrals in recent years. All my loads are typically line to line (single or three phase) and there is usually only a couple 120 volt circuits in the entire installation - doesn't justify full size neutral, especially on a 400 amp service or feeder when that neutral likely never sees more than maybe 40 amps ever.
 
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