Sub-panel to sub-panel wire guage

[WagMan]

Here is some background:
I have a cabin in northern Wisconsin. I have 200 amp service to the cabin, and a 100 amp main breaker sub-panel in the garage. The sub-panel in the garage is fed with 2-2-2-4 MHF and protected in the main panel with a 70 amp breaker. The distance from the house to the garage is 48'. The garage has no big loads at all, a few light, some outlets, and 2 garage door openers. I have a 28' x 40' pole barn approx 125' from the garage, which has no power or anything else ran to it.


The plan:
What I would like to do is run some 4 x 1 AWG XHHW-2 Aluminum Building Wire, in conduit, from the garage to the pole barn. I would put a 50 amp breaker in the garage and put another 100 amp main breaker sub-panel in the pole barn. I will pond 2 ground rods at the pole barn. The load in the pole barn will just be some lights, outlets, and a garage door opener. No big tools, compressors, heaters, or anything.

My questions are:

1. Is it ok that the wire to the pole barn is bigger than the wire to the garage?

2. Does this plan sound ok?

Thanks

 

[rockwithjason]

The plan:
What I would like to do is run some 4 x 1 AWG XHHW-2 Aluminum Building Wire, in conduit, from the garage to the pole barn. I would put a 50 amp breaker in the garage and put another 100 amp main breaker sub-panel in the pole barn. I will pond 2 ground rods at the pole barn. The load in the pole barn will just be some lights, outlets, and a garage door opener. No big tools, compressors, heaters, or anything.

My questions are:

1. Is it ok that the wire to the pole barn is bigger than the wire to the garage?

no issue with this. it may have needed to be upsized for distance anyway but not quite that big.

2. Does this plan sound ok?

i think it will work. i would have to look but there may be a requirement for a disconnect on the outside of the pole barn

Thanks

all in all it should work for what you want

 

[wyliesdiesels]

Why is the breaker feeding the MHF ONLY 70a? U could go upto 90...

 

[WagMan]

Thanks for the replies.

Why is the breaker feeding the MHF ONLY 70a? U could go upto 90...

Those are just the breakers I had on hand. All the panels in my house and cabin are QO panels, so I have extra breakers. I would eventually like to put a 90 amp breaker at the house, for the garage. then I would probably take the 70 amp breaker and put it in the garage to feed the pole barn.

Thanks

 

[pattenp]

The problem you need to work around is your 70A breaker won't handle #1 wire. #2 is max wire size for a 70A QO breaker. You need at least a 80A to fit #1 wire. Which raises a question of why do you need #1? Is it distance?

 

[WagMan]

The problem you need to work around is your 70A breaker won't handle #1 wire. #2 is max wire size for a 70A QO breaker. You need at least a 80A to fit #1 wire. Which raises a question of why do you need #1? Is it distance?

Thanks for the reply!

I don't really need #1. It just seems like it will give me a little room to spare.

Are you saying that at 125' or so, that i could use more 2-2-2-4 MHF and breaker it at 70 amps and that would be ok?

What would you do?

My other question is:
Is a pvc LB considered a 90 deg bend for the 360 rule?

I would like to go out the back of my panel through the siding with an LB, a 90 deg sweep at the bottom of the trench. Then another 90 deg sweep coming out of the trench, and another LB into the back of the new panel. That's 360, but gives no option for any other bends.

Thanks

 

[Charles (in GA)]

Thanks for the reply!

I don't really need #1. It just seems like it will give me a little room to spare.

Are you saying that at 125' or so, that i could use more 2-2-2-4 MHF and breaker it at 70 amps and that would be ok?

What would you do?

My other question is:
Is a pvc LB considered a 90 deg bend for the 360 rule?

I would like to go out the back of my panel through the siding with an LB, a 90 deg sweep at the bottom of the trench. Then another 90 deg sweep coming out of the trench, and another LB into the back of the new panel. That's 360, but gives no option for any other bends.

Thanks

The LB's don't count when you are counting toward the 360° between pull points. The LB's are pull points themselves.

 

[pattenp]

You need to take into account that you have 48' for the first run of #2 and then the second run of 125'. So using 175' of #2 you'd be a little over 3% voltage drop with a full load of 70 amps at the end. 3% is the recommended max VD, but no more than 5% is the absolute limit you should have. Also you need to think about any constant loads back at the garage. Bottom line is I'd use a 90A breaker at the house and a 70A breaker at the garage and not have a worry with #2. You can use the #1 to mitigate some of the possible VD at the pole barn and feed it with an 80A breaker. Using #1 will get you 80A max load at the end with a little ove 3% VD. Only you know what your potential load will be to make the choice to go with #1 or not. The cost will be the difference in wire and having to buy one more breaker. You can get reducers to use the #1 in a 70A breaker.

 

[justsam]

Based on your description for current and future loads for both buildings, it seems that you are going a bit oversized. Certainly no harm, but your anticipated loads sound more like about 40 AMPS at best for both buildings combined.