Conductor size suggestions

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nizak

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I have to get power from an established 320A service on a garage that’s 275’ away from a new construction residence.

House load center will be 200 A 120/240V single phase.

Calculated load ( with current info from owner) is 130 amps.

It will be underground. I’m planning on using a single set of 250 MCM AL for the feeders.

300 MCM would give me a bit more leeway as far a VD if they choose to add say a EV charger down the road.

At this point they see no load addition in the near future.( Heard that before)

Would you just go with the 250 that’s readily available or opt for the 300 that’s a special order at this point.

Also, 250 will fit all the lugs that I will be terminating on ( disco, load center) 300 will need reducers to fit.

It’s direct burial that takes a very wayward path from A to B because of the terrain, conduit isn’t a practical option.

Any suggestions welcome.
 
I would go for the 300kmcil or suggest conduit so that you can repull it later if things change.

I think you will probably be okay either way though.
 
According to the Southwire VD calculator for 130 amp load you'll be under 3% with 300's. 250's would be a hair over 3%.
 
Elect117 said:
I would go for the 300kmcil or suggest conduit so that you can repull it later if things change.

I think you will probably be okay either way though.
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infinity said:
According to the Southwire VD calculator for 130 amp load you'll be under 3% with 300's. 250's would be a hair over 3%.
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I opened up the utility 320A meter base and I see that they are feeding their underground from the transformer with one set of 3/0 AL
Their run is about 175’ from the pole mounted transformer to the meter.

Does the fact that their underground lateral being that size compound my issue even more?


The 320A service was all new just last year when the new garage was built. Apparently the then electrician set it up telling the owner that’s the best way to do it for the future build of the house.

Now what’s actually happening is that the secondary power 120/240 is traveling 450’ to get to the house.

When The actual pole with the transformer sits 80’ from where my feeder will enter the basement.

Kinda screwed up by my way of thinking.
 
nizak said:
I opened up the utility 320A meter base and I see that they are feeding their underground from the transformer with one set of 3/0 AL
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The POCO is always undersized, especially compared to us.

nizak said:
Does the fact that their underground lateral being that size compound my issue even more?
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It certainly doesn't help. It was probably based on a load calc.
 
nizak said:
I opened up the utility 320A meter base and I see that they are feeding their underground from the transformer with one set of 3/0 AL
Their run is about 175’ from the pole mounted transformer to the meter.

Does the fact that their underground lateral being that size compound my issue even more?


The 320A service was all new just last year when the new garage was built. Apparently the then electrician set it up telling the owner that’s the best way to do it for the future build of the house.

Now what’s actually happening is that the secondary power 120/240 is traveling 450’ to get to the house.

When The actual pole with the transformer sits 80’ from where my feeder will enter the basement.

Kinda screwed up by my way of thinking.
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Can you run a seperate service from the transformer to the house? I know it would be 2 meters but I've wired several house/detached garages that way.
 
No. The Utility service is established and this is the way power to the house has to be routed.

I would like to talk to the Electrical Contractor that set things up this way just last year.

It makes such little sense, there must have been other factors that caused it to be done this way.


qcroanoke said:
Can you run a seperate service from the transformer to the house? I know it would be 2 meters but I've wired several house/detached garages that way.
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I'd go with the 250s. The NEC calculated is almost never reached. I'd say never reached, but never is pretty absolute. Typically, the true load will be well under half the calculated load. So even if they add stuff and the calculated load gets near 200A, the actual load won't be over 100A very often.
 
suemarkp said:
I'd go with the 250s. The NEC calculated is almost never reached. I'd say never reached, but never is pretty absolute. Typically, the true load will be well under half the calculated load. So even if they add stuff and the calculated load gets near 200A, the actual load won't be over 100A very often.
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Sounds very reasonable.

Thank you.
 
electrofelon said:
I would probably also choose 250 AL for that. I would use 230.40 exception #3 so I could run 3 wire.
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The grounding electrode has already been established at the garage service point with driven rods.

The new house has a foundation u-fer . I will still need to connect to it and take it back to the garage .. Correct?
 
nizak said:
The grounding electrode has already been established at the garage service point with driven rods.

The new house has a foundation u-fer . I will still need to connect to it and take it back to the garage .. Correct?
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It doesn't matter if a building is served by a feeder or service conductors, each structure gets its own GES anyway. You never bring a grounding electrode/conductor over to a different building.
 
nizak said:
Now what’s actually happening is that the secondary power 120/240 is traveling 450’ to get to the house.

When The actual pole with the transformer sits 80’ from where my feeder will enter the basement.

Kinda screwed up by my way of thinking.
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If it were my house I'd definitely say its worth a phone call to the utility engineer to find out why.
qcroanoke said:
Can you run a seperate service from the transformer to the house? I know it would be 2 meters but I've wired several house/detached garages that way.
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Yeah that is what I would do and abandon that other service all together.
Sounds like someone screwed up that does not mean you need to build off it.
 
Thank you.

electrofelon said:
I would probably also choose 250 AL for that. I would use 230.40 exception #3 so I could run 3 wire.
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It can still be just a 3 wire feeder even if it comes from a dusconnect that’s already established and not from the utility meter base?

Thought it needs to be 4 wire after the first disconnect means.
 
nizak said:
Thank you.


It can still be just a 3 wire feeder even if it comes from a dusconnect that’s already established and not from the utility meter base?

Thought it needs to be 4 wire after the first disconnect means.
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Right you would need to keep them service conductors (no disconnect) to run 3 wire. Are there two disconnects after the meter base? Can you get rid of one? Running a fourth wire probably isn't much of a big deal in this case, probably about a dollar a foot, unless maybe it bumped you up to a larger pipe size or something (but I think you said you were direct burying anyway).
 
electrofelon said:
Right you would need to keep them service conductors (no disconnect) to run 3 wire. Are there two disconnects after the meter base? Can you get rid of one? Running a fourth wire probably isn't much of a big deal in this case, probably about a dollar a foot, unless maybe it bumped you up to a larger pipe size or something (but I think you said you were direct burying anyway).
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2 disconnects. One in service supplying the garage that the gear is mounted to and the other is empty intended for the new home which is now being built.

Another thought on my part.
Would the disconnect at the garage serve as the required Emergency Disconnect?

Regardless, I am going to put one on the house because the wiring needs to travel through the crawl space 30’ to get to the panel inside the house.
 
nizak said:
2 disconnects. One in service supplying the garage that the gear is mounted to and the other is empty intended for the new home which is now being built.

Another thought on my part.
Would the disconnect at the garage serve as the required Emergency Disconnect?

Regardless, I am going to put one on the house because the wiring needs to travel through the crawl space 30’ to get to the panel inside the house.
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It is too bad the person who set that up apparently did not know about exception number 3, resulting in more costs, more connections and more unsightly equipment.

I believe the 2020 code did not specify a distance, just that it be in a "readily accessible location". 2023 added "within sight"
 
electrofelon said:
It is too bad the person who set that up apparently did not know about exception number 3, resulting in more costs, more connections and more unsightly equipment.

I believe the 2020 code did not specify a distance, just that it be in a "readily accessible location". 2023 added "within sight"
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You’re suggestions are helpful.

I am going to remove the one disconnect, add a junction box in its place and make a 3 wire connection.

Wires will then be service conductors from the meter directly to the house.

Saves $300+ on wire and screwing around getting into that disconnect that’s in an odd place on the exterior.
 
nizak said:
You’re suggestions are helpful.

I am going to remove the one disconnect, add a junction box in its place and make a 3 wire connection.

Wires will then be service conductors from the meter directly to the house.

Saves $300+ on wire and screwing around getting into that disconnect that’s in an odd place on the exterior.
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👍. Can you come right out of the meter base and skip the j box?

By the way, might want to just confirm that's okay with the utility, I have heard of a few utilities that don't allow the use of that exception.
 
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