100 amp sub-panel, 600 ft from source

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Wes Smith

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I'm looking for a few ideas for a friend who wants to set a 100 amp sub-panel, 600 ft from his
200 amp main panel at his house. He wants to do it underground. I did a quick voltage drop Calcand came up (4) conductor, 400 kcmil alum. URD.

I'm thinking their must be a better way, plus you wouldn't be able to terminate the 400 kcmil al on a 100 amp breaker. So I'm thinking his best bet is to get the utility company to do a drop at
the out-building.

Any ideas?
 
have you considered a transformer at each end?

i would call whoever the local POCO uses for putting in poles and see what they would charge to run the poles and wire. I have heard they can sometimes do the poles for $500 or less each. if he insists on UG, this is not an option, but a 600 ft trench is going to be pricey.

is there a utility line near the outbuilding already? if not, you may be out of luck there.

in any case, it will not be cheap.
 
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What's the load?

What's the load?

Do you know what the load is going to be for the sub-panel? You can calculate the voltage drop for the load, not for the OCPD.

Also if it is 120/240 and you can "balance" the loads on both hots, that will help on the voltage drop as well.
 
Wes Smith said:
I'm looking for a few ideas for a friend who wants to set a 100 amp sub-panel, 600 ft from his
200 amp main panel at his house. He wants to do it underground. I did a quick voltage drop Calcand came up (4) conductor, 400 kcmil alum. URD.

I'm thinking their must be a better way, plus you wouldn't be able to terminate the 400 kcmil al on a 100 amp breaker. So I'm thinking his best bet is to get the utility company to do a drop at
the out-building.

Any ideas?
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Your friend needs to determine how important it is to have power at this building and what kind of voltage tolerances can be taken. You want to feed with 100 amp breaker, chances are there is not actually 100 amps of load. Do a voltage drop calculation @ actual expected load plus any extra you want for just in case.

Stepping up voltage and stepping down again will work, but transformers and needed accessories are not cheap either, and can result in similar cost either way you do it sometimes. The transformer idea means you can run 2 hots and equipment ground vs. 2 hots, neutral and EGC, so factor that in also.

Instead of using 400 kcmil see what kind of voltage drop you get with paralleled smaller conductors, 2-2/0 is same ampacity, but is not same circular mils and probably cost less per foot than the 400's. You will need splice boxes to reduce conductor size at each end so you can land a conductor small enough to fit in a 100 amp device - this needs consideration in total cost of a particular method also.
 
Ok Guys, thanks for your help on this. He's in the research phase at this time to see what the options are and what kind of cost he's looking at. Thanks again.
 
An electrical contractor that I know & respect did a cost comparison on wiring a golf course that required electrical at each station. He used step up & step down transformers and was able to do it entire job in # 10UF. Saving a bunch. So as mentioned above, it would be worth a comparison.:slaphead:
 
JDB3 said:
An electrical contractor that I know & respect did a cost comparison on wiring a golf course that required electrical at each station. He used step up & step down transformers and was able to do it entire job in # 10UF. Saving a bunch. So as mentioned above, it would be worth a comparison.:slaphead:
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Now I wonder how much that golf course is spending on transformers idling 24-7?
 
JDB3 said:
An electrical contractor that I know & respect did a cost comparison on wiring a golf course that required electrical at each station. He used step up & step down transformers and was able to do it entire job in # 10UF. Saving a bunch. So as mentioned above, it would be worth a comparison.:slaphead:
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I quoted something similar for a golf course, two fans at about every other hole, around 1200' on average. They didn't like my price. Someone else ended up doing it and I would say with a much smaller wire from the price I heard it went for. I didn't see any transformers at the holes either, so they must have used the existing 208 volts for the 240 volt fans. Glad we didn't get it anyway, they had no idea where all of the irrigation lines, controls, and private utilities were located.
 
Wes Smith said:
I'm looking for a few ideas for a friend who wants to set a 100 amp sub-panel, 600 ft from his
200 amp main panel at his house. He wants to do it underground. I did a quick voltage drop Calcand came up (4) conductor, 400 kcmil alum. URD.

I'm thinking their must be a better way, plus you wouldn't be able to terminate the 400 kcmil al on a 100 amp breaker. So I'm thinking his best bet is to get the utility company to do a drop at
the out-building.

Any ideas?
Click to expand...
Actual load or load calcs are needed, otherwise voltage drop calculations are useless.
 
JDB3 said:
An electrical contractor that I know & respect did a cost comparison on wiring a golf course that required electrical at each station. He used step up & step down transformers and was able to do it entire job in # 10UF. Saving a bunch. So as mentioned above, it would be worth a comparison.:slaphead:
Click to expand...
Had a call a few years ago at a local golf course about voltage problems in their maintenance shed. Shed was supplied from where the irrigation well is located. Of course when they installed it they did not want to go straight line across the course (which still would have been significant length) instead they followed the cart trail around the course as much as possible. IIRC total length of run was in 1900 foot range and I believe it was 2 AWG aluminum. They could not run much of anything in the maintenance shed without noticing a significant voltage change. I informed them that the conductors were too small for the distance is what the problem was - to the best of my knowledge they are still putting up with this problem and it may have been getting close to 10 years since I looked at it.
 
Wes Smith said:
I'm looking for a few ideas for a friend who wants to set a 100 amp sub-panel, 600 ft from his 200 amp main panel at his house. He wants to do it underground. I did a quick voltage drop Calcand came up (4) conductor, 400 kcmil alum. URD. I'm thinking their must be a better way, plus you wouldn't be able to terminate the 400 kcmil al on a 100 amp breaker. So I'm thinking his best bet is to get the utility company to do a drop atthe out-building. Any ideas?
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Another alternative to the two step-up/stepdown transformers is a single buck/boost transformer, just have to realize that you're paying for the power loss due to the voltage drop.
 
weressl said:
Another alternative to the two step-up/stepdown transformers is a single buck/boost transformer, just have to realize that you're paying for the power loss due to the voltage drop.
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That may be fine for a fixed load, but for general purpose use where loads will vary you will have high voltage when the amount of load is low and it will get closer to desired voltage the closer the load comes to what you designed for.
 
kwired said:
That may be fine for a fixed load, but for general purpose use where loads will vary you will have high voltage when the amount of load is low and it will get closer to desired voltage the closer the load comes to what you designed for.
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You are correct, it will not work well if your load varies greatly, but if it is always around +/- 15% of a number you can adjust your tap to that. Of course if you have great variation on the supply voltage either from the utility or from the 200A panel's loading it will further aggravate the problem. I suggested this as an alternative to the step-up/step down solution, but it is more restrictive on suitability.
 
Cow said:
Now I wonder how much that golf course is spending on transformers idling 24-7?
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Transformers are generally highly efficent converters and depends on the use the feeder can be turned off to them if it is only for use during operating hours. Don't forget that voltage drop itself is not only results in the inefficient operation of the driven equipment but it actually produces losses that costs money.
 
Wes Smith said:
I'm looking for a few ideas for a friend who wants to set a 100 amp sub-panel, 600 ft from his 200 amp main panel at his house. He wants to do it underground. ... Any ideas?
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Well, as mentioned, fat wire, or a pair of 240/600V, 25kva xfm are the best options. There are some if he doesn't have to have 24kw. What is the planned load?

ice
 
iceworm said:
Just curious. What is the going rate on 24KW Solar installs? $10/W?

ice
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First of all, the size of the system depends on overall usage, and you can't assume what that is based on the 100A figure mentioned. Most likely he won't need anywhere near a 24kW system.

As for the going rate, for off-grid at 24kW, probably about 7$/W, but it's fairly useless to quote an industry average figure without knowing the specifics of the job.
 
jaggedben said:
First of all, the size of the system depends on overall usage, and you can't assume what that is based on the 100A figure mentioned. Most likely he won't need anywhere near a 24kW system..
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The he would not need to consdier the voltage-drop/wire sizing for 100A either! Correct?!
jaggedben said:
As for the going rate, for off-grid at 24kW, probably about 7$/W, but it's fairly useless to quote an industry average figure without knowing the specifics of the job.
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Complete with battery bank?
 
jaggedben said:
.... Most likely he won't need anywhere near a 24kW system.

... probably about 7$/W ....
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weressl said:
...Complete with battery bank?
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I just wanted to make sure i had the numbers in perspective. For similar costs as a 24KW install, 600 feet of fat wire (or skinny wire and xfms), ditch, replacing the grass, feeders, disconnects, and panels, the customer can get about 2.4KW on Solar.

ice
 
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