[mdemosiuk]

200 amp panel in house, what size wire for 100 amp sub panel in pole barn 150 feet away?

[shivajirao]

sr.pl. send to icwa answer paper to my e-mail id

[donf]

Please, this post was added just as the network went toes up! It is incomplete at best. It was based on a guess of 240 VAC Single Phase using a VD calculation of 3%.

100 amp at 150' copper I would suggest #4 AWG or #3 AWG Aluminum.

Are you going to use conduit or direct bury cabling?

[jcaron2]

There's a good voltage drop calculator here:

American Wire Gauge table and AWG Electrical Current Load Limits

I just ran 100A service to my pole barn 450' from the house. I used 4/0-4/0-2/0 wire plus a separate ground wire, but mostly because I happened to find a really good deal on a 500' spool of it. In my case a lot of the things drawing significant current (e.g. a hot water heater and a clothes dryer) are 240V, so the current on the neutral conductor should be well less than 100A. Maybe it's the same for you?

You might be able to use 2-2-2-4 aluminum service entrance cable if you can tolerate the voltage drop. It would be about 4% at 240V which is certainly tolerable for most things you'd have in a barn. Closer to 8% though if you draw the full 100 amps on a single 110V circuit. That number goes back to 4% if you have multiple 110V circuits and you balance them properly between the two 110V poles.

[jcaron2]

Donf, I'm pretty sure those wires are slightly undersized to meet code for 100A, regardless of the length of the run.

I think most direct burial cable is rated for 90C, but even then you'd still have to upsize to #3 copper or #2 aluminum.

Ampacity Charts

[donf]

Jarcon,

If you used 4/0 - 4/0 - 2/0 - and ground, then you have an undersized neutral, assuming that you are using the 2/0 as neutral.

[jcaron2]

My apologies, Don. I shouldn't have doubted you. :-)


As for my barn, I'm pretty sure the 2/0 neutral wire is still rated to handle more than 100A. I'm not particularly worried about the fact that there'd be 9.5% voltage drop at that current level, because I'm never going to be drawing anywhere close to that much current at 120V. In fact I'll probably only end up with two single-pole breakers, 20 amps each, and they'll be on opposite poles, so the neutral will never have more than 20 amps running through it.

All that being said, since I've already paid for doubting you once, am I missing something here?

[tkrussell]

I am considering closing this thread for several reasons.

Need to know to attempt to answer:

If the line will be underground or overhead

What the load in amps or watts.

Types of loads? Lighting? Motors? Size of motors?

What voltages of loads?

What type of wire is desired? Copper? Aluminum?

Knowing that there will be a 100 amp panel is not enough.

Trying to answer this question without knowing more detail only results in guessing.

No guessing allowed when dealing with electricity and the National Electric Code.

FYI, a few points I would like to clear up:

Minimum size wire for a 100 amp residential feeder is #4 copper or #2 aluminum of certain types of typical insulation.

The amperages found in the chart in first answer
American Wire Gauge table and AWG Electrical Current Load Limits

Should NOT BE USED.

Per the note found at the beginning of that wire chart:
NOTE: For installations that need to conform to the National Electrical Code, you must use their guidelines.

Only amperages found in National Electric Code Table 310.16 should be used.

The wire chart is also much different regarding resistance values.The NEC Table 8 found in Chapter Nine is to be used.

I also find the voltage drop calculator at that website to be in error, when compared to the NEC Table 8, since it uses the resistance values found in that chart.

I see a reference to using the 90 Deg D column. That is wrong.

The amperages found listed in the 90 Deg C column are reserved when the electrical equipment and terminations are rated 90 Deg C.

This is not the case with this installation. 90 Deg C equipment and terminations are found only in large industrial equipment, never residential.

Unless the original poster gets back with the detail I listed, please refrain from answering this question.

Without knowing ALL the details related to a long feeder, voltage drop calculations will be nothing more that guessing, never mind not understanding all the issues involving voltage drop.

[mdemosiuk]

I see I need to supply moe info, underground from house to pole barn, with mostly 120 volt circuits. Possible 240 volt for air compressor. That why 100 amp panel will do the job. As what to use conduit or direct burial cable not sure yet, depends on price.

[tkrussell]

This is what detail is needed:

Need to know to attempt to answer:

If the line will be underground or overhead

What the load in amps or watts.

Types of loads? Lighting? Motors? Size of motors?

What voltages of loads?

What type of wire is desired? Copper? Aluminum?

[tkrussell]

Stan knows that.

We are all waiting in anticipation of an answer from mdemosiuk.

[donf]

TK,

In your previous <sloppy typing removed> response, you mentioned motors. What motors were you referring to?

Also, given that the OP said 100 amp, aren't we limited to that number. Are you stating that we should never trust a given number or are you going on past experience and knowledge and stating that 100 Amps would not be a sufficient load for a pole bar?

[tkrussell]

TK,

In your deleted response, you mentioned motors. What motors were you refering to?

Do you mean my detailed response?

I am asking if there will be any motors and what volts and size.

Motors react negatively to voltage drop, and compounds the issue with large starting currents, and need to be considered, not just running amps.

Also, given that the OP said 100 amp, aren't we limited to that number. Are you stating that we should never trust a given number or are you going on past experiance and knowledge and stating that 100 Amps would not be a sufficient load for a pole bar?

My point is not to just use 100 amps as info, and using a full 100 amps may not be practical to sue in calculations.

[donf]

TK,

"Deleted" was a very incorrect word. Thanks for pointing that out.

Given your experience ( I am trying to pick your brain) would you say that it is necessary to approach the electrical service sizing much the same as you would size a residence or a commercial building?

"Know as much as possible about the demand then size the required load." Is there a minimum load you would expect to need for a Pole Barn as Opposed to a normal Barn for cattle or horses? I might add that while we were living in Lexington, KY, some of the horse barns we saw would put most mansions to shame.

[tkrussell]

I have no idea what load would be in a pole barn. Only the owner can fill in the details.

Any structure with a new feeder needs to have a load calculation done, and done in accordance with Article 220, as there are different demand factors for residential, commercial, etc. Not sure what category a pole barn would fall under, but a reasonable judgment could be made.

[donf]

TK,

Thanks for the follow-up.