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Joe Willie 04-11-2011 10:54 AM

voltage drop
 
I just used a web calculator to discover my voltage drop for 240v @ 215' would be half that of 120v at ther same distance. This may be a stupid question... can I wire it so it is 240v from the house subpanel to the shop subpanel using 6-3 or 10-3 (less voltage drop) then distribute it as 120v?

Grampa Bud 04-11-2011 11:24 AM

Yes you could, but you say shop. This makes me think you may be planning to use power tools in your shop, so I say STOP. What is your house panel fed with from your meter? Probably 0000. A compressor, some lathes or milling machines, large table saws and planers do come with applicable 240VAC options, so try to figure out what your load will be and if nothing else feed the shop with no less than what the house is fed with especially at 215'.

Furd 04-11-2011 01:19 PM

Yes, but. The first thing you need to do is to do a demand load calculation for the shop. Essentially determine ALL the electrical loads and then determine what items may be used at at one time. Generally you would add all the lighting plus any auto-start equipment such as air compressor, electric heaters and air conditioners. (Obviously you wouldn't be running the heat and the A/C at the same time so use the larger load.)

If you are going to be working alone then this is easy, if you will sometimes have a friend or partner working too then it becomes a little harder. Once you have the maximum demand you can then go about sizing the feeder from the house Service panel to the shop sub-panel.

Yes, you CAN reduce voltage drop by going to 240/120 volts but ONLY if the 120 volt loads are fairly well balanced between the two "hot" leads and thereby minimizing the unbalanced current on the "neutral" lead.

Dahammer 04-11-2011 02:45 PM

It's not going to work exactly like you may have been thinking. If you run a 240 volt circuit over the same distance as a 120 volt circuit, then yes the voltage drop is half as much on the 240 volt circuit as the 120 volt circuit, because the voltage is twice as much. However, each of those 120 volt legs (e.g. 2 120 volt legs combine to make your 240 volt circuit) are still going to have the same amount of voltage drop as they would if you ran a 120 volt circuit. So, you haven't gained a thing by doing that if you plan on using 120 volt circuits instead of equipment that uses 240 volts. The only way to overcome that is to either run larger wire or install a transformer.

In other words, running 2 120 volt legs (for 240 volts) does not magically eliminate a voltage drop problem with a single 120 volt leg. You need to consider the load and run what you need for that load.

Joe Willie 04-11-2011 02:57 PM

Hammer,
Thank you. That answers my question.

wareagle 04-11-2011 04:53 PM

Quote DaHammer"In other words, running 2 120 volt legs (for 240 volts) does not magically eliminate a voltage drop problem with a single 120 volt leg. You need to consider the load and run what you need for that load."

Thats not exactly true. Example:say you have 10 amps at 120 volts going to you garage and VD= 6 volts. If you run 240 volts to the garage you connect 5 amps on one leg and 5 amps on the other leg and the VD = 3 volts. You have to balance the load between the two hot legs

Dahammer 04-11-2011 05:16 PM

Quote:

Originally Posted by wareagle (Post 627436)
Quote DaHammer"In other words, running 2 120 volt legs (for 240 volts) does not magically eliminate a voltage drop problem with a single 120 volt leg. You need to consider the load and run what you need for that load."

Thats not exactly true. Example:say you have 10 amps at 120 volts going to you garage and VD= 6 volts. If you run 240 volts to the garage you connect 5 amps on one leg and 5 amps on the other leg and the VD = 3 volts. You have to balance the loadbetween the two hot legs

Well that's true, but that assumes he can split the load between 2 circuits in order to cut the load on a single circuit in half. I assumed he could not.

It really just depends on what your intended load is. But you have to be careful if you're talking circuits where drawing 10 or 15 amps on a single leg would cause excessive voltage drops, since someone not knowing the circuits limitations could very easily do just that. I suppose you could stick a 10 amp breaker in the subpanel, but you'd probably have to special order it.

Missouri Bound 04-11-2011 09:49 PM

Actually it's not true. The voltage drop won't change whether you run 120 or 240 volts, it only changes when you use 120 or 240 volt loads. The only way to lessen the voltage drop is to increase wire size.

wareagle 04-12-2011 11:57 AM

Quote:

Originally Posted by Missouri Bound (Post 627695)
Actually it's not true. The voltage drop won't change whether you run 120 or 240 volts, it only changes when you use 120 or 240 volt loads. The only way to lessen the voltage drop is to increase wire size.

Actually it is true. With 240 volts you only have 1/2 the amperage on the conductor for the same wattage at 120 volts.

Missouri Bound 04-12-2011 09:46 PM

Wareagle... Semantics being what they are, you are correct. But referencing the original post is the key to understanding the issue. Bringing two 120 volt legs to the shop won't diminish the voltage drop. The voltage drop will be the same on each leg unless a larger conductor is used. Dahammer explained this exactly as it would be in the 4th post. And yes, the higher the voltage, the lower the amperage. But unless you are USING a 240 volt LOAD, everthing equates to a 120 volt circuit......and that is what the OP question was based on, an incorrect assumption.

Joe Willie 04-13-2011 06:24 AM

Thanks guys. So if I used a single conductor...like a 4 or 6 gauge with ground and neutral in a PVC conduit from a 50A breaker at the house... I would have the lower voltage drop and I could split the amps in a sub panel at the shed to a 30A and a 20A for 120V circuits:huh:...right?

NJMarine 04-13-2011 06:33 AM

voltage drop
 
I did not see what wire you used for the orginal calculations.
Enter a larger wire size until you get under 5% voltage drop. This will be correct wire size to use on the 50 amp breaker.

Joe Willie 04-13-2011 06:47 AM

OK, I was just throwing those numbers out. I know that using conduit is cheaper than using UF. Like I said, $ is the limiting factor, not sweat. I want the most, safe power I can get for under $1000. I sold a Master Grader implement the other day...so I'm getting closer to starting this project. Give me any suggestions to what I can do with this. I don't weld. The enclosed building is 12x24 under roof with 3- 16x24 bays under a shed roof where I keep a 2815 Mahindra, a trailer, and a boat. I have a 8'x3' work bench under the shed. I have a large vegetable garden and I'm getting into chickens. I want my fridgerator and lights and outlets for basics with possibly a 5000 BTU window unit.

AllanJ 04-13-2011 10:04 AM

I would suggest at least #6 gauge wires (the 4'th wire for ground can ge #10).

This will allow you about 70 amps at 120 volts at 3% voltage drop over the 215' distance provided that the load, if that large, is roughly balanced on both sides of the 120/240 volt line. (80 amps if equally balanced)

(During times that only one side of the line was drawn from, there would be a 3% voltage drop for 20 amps and 6% for 40 amps.)

If you will have large power tools out there and more than one person will be working at the same time, using #4 gauge wires (#8 gauge ground) would be better.

Joe Willie 04-13-2011 10:37 AM

Allan, Thanks. Are you referring to 2x6 gauge hots at 35v each?


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