Any electricians available? Wire size question...

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bighammer

bighammer

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I'm wanting to run power to my shop, which is about 250 feet from my house. I don't need to pull a lot of amps, but I want a 240 circuit as well as lights and outlets throughout, the shop is 30x60. I'm thinking a 100 amp sub panel will be fine, and I won't have to worry about overloading my main panel.

I'd like to use "direct burial" aluminum service cable. There are many many different types of cable, some with a total of 3 conductors, some with four.. Sometimes the neutral is smaller than the main conductors. The one I'm considering is:
300' 4-4-4 Aluminum URD Vassar Triplex cable underground wire

Does this seem appropriate? Overkill? Too small?

Thanks!

Mark
 
There are several on line calculators to help.
 
bighammer said:
I'm wanting to run power to my shop, which is about 250 feet from my house. I don't need to pull a lot of amps, but I want a 240 circuit as well as lights and outlets throughout, the shop is 30x60. I'm thinking a 100 amp sub panel will be fine, and I won't have to worry about overloading my main panel.

I'd like to use "direct burial" aluminum service cable. There are many many different types of cable, some with a total of 3 conductors, some with four.. Sometimes the neutral is smaller than the main conductors. The one I'm considering is:
300' 4-4-4 Aluminum URD Vassar Triplex cable underground wire

Does this seem appropriate? Overkill? Too small?

Thanks!

Mark
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Your #4 will work fine. You should probably pull four wires though. We have to float the neutral seperate from the ground on a subfed panel in WA state.
 
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If you want to have both 110 and 220 volt service (or only 110 service), you need to run 4 wires from the panel to your shop (the 2 110 legs, a neutral and a ground), but if you want only 220 service you can get by with only 3 wires (you can omit the neutral).

I am going to guess that you will probably get something like 2 gauge. Buy it by the spool at Home Depot or Lowe's. That is much cheaper, on a per-foot basis, than buying smaller amounts. The problem is that you'd have to run 2-gauge in an underground plastic conduit. That's what I had to wind up doing.
 
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Nothing wrong going with a larger wire. It's when. You go to small when you have issues
 
DDodger said:
Why anyone would do this over the price of one more wire does not make sense. It aways seems like a lot when the trench is dug, 2-10 years from now you forgot all aboout it
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You're right, of course, DDodger, but bighammer asked how many wires he had to run, so I told him.
 
DesertRat said:
Your #4 will work fine. You should probably pull four wires though. We have to float the neutral seperate from the ground on a subfed panel in WA state.
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I'm sorry, DesertRat, but I don't think 4 gauge wire is nearly large enough for a 100-amp current draw over the distance involved.
 
Bill Crowell said:
You're right, of course, DDodger, but bighammer asked how many wires he had to run, so I told him.
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Here's an example of why you might want to run only 3 wires: in constructing a long extension cord from flexible stranded copper wire, you find that 10-3 wire is readily available but 10-4 is not nearly as common. So I constructed my long cord to operate only at 220 with 3 wires. If I need 110 at the far end, I use a cheap voltage converter transformer, where the secondary of the transformer is center-tapped. The center tap re-creates the neutral circuit for 110 use. And by running only 220 on the extension cord, you get only half the voltage drop (for a given load) that you would get by using a 110 cord.
 
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4AWG is rated for 105 amps on a se cable so you should be just fine with that in the distance you are running. To meed National electric code it needs to be buried a minimum of 24" below grade. I have alway thrown a 2x4 over the top of direct burial cable so it atleast gives someone a clue there may be something going on if they are digging and hit it.
 
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Here is what I got starting with 240 volts and expecting no more than a 5% maximum drop.

Here is the link to the calculator site so you can change whatever variables you want: Online Wire Size Calculators & Tables

Note that when the voltage drops below around 108 (in a 120volt circuit) or 216 (in a 240 volt circuit), things like motors start burning out much faster.
 
Bill Crowell said:
I'm sorry, DesertRat, but I don't think 4 gauge wire is nearly large enough for a 100-amp current draw over the distance involved.
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You are correct. #2 would be more suitable, Cu=115A @ 75C, #2 Al=90A @ 75C. I would run #2 CU for myself. Good catch--------:)
Our L & I inspectors rate the connectors @ 75C so calcs @ 90C fail inspection for us.
 
Wow, glad I asked, thanks for all the help! I'm hoping to get this done sometime this summer, but I'm going to keep my eyes open for a decent price on the cable. I'll probably stick with aluminum, but also agree that it's better to have 'overkill' and go with a larger size.

Thanks again
 
bighammer said:
Wow, glad I asked, thanks for all the help! I'm hoping to get this done sometime this summer, but I'm going to keep my eyes open for a decent price on the cable. I'll probably stick with aluminum, but also agree that it's better to have 'overkill' and go with a larger size.

Thanks again
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IMG_1561.PNG

Use some Penetrox on the ends of the aluminum wire or you could have a fire in the future as some corrosion builds on the wire surface at the end connectors.
 
68gtxman said:
View attachment 1715042223
Use some Penetrox on the ends of the aluminum wire or you could have a fire in the future as some corrosion builds on the wire surface at the end connectors.
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I had to run a new underground service to my house. I bought it from my electrical supplier. won`t hurt to go a little oversize, but might make it harder to hook up. you don`t need any convertors for 110. take it off one side of the 220 . A bout 40 yrs ago, I took the power for the outlets off one side, and the power for the lights off the other side of my 220, in my garage. w/ a 50amp breaker, I can weld , run my lathe , or mig welder w/ the lights on, no problem.
 
famous bob said:
I had to run a new underground service to my house. I bought it from my electrical supplier. won`t hurt to go a little oversize, but might make it harder to hook up. you don`t need any convertors for 110. take it off one side of the 220 . A bout 40 yrs ago, I took the power for the outlets off one side, and the power for the lights off the other side of my 220, in my garage. w/ a 50amp breaker, I can weld , run my lathe , or mig welder w/ the lights on, no problem.
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Yes, famousbob, you can do it that way but it creates a shock hazard not to use the neutral wire in addition to the ground wire on 110 service. You've got to take each leg of the 110 paired with the neutral, not with the ground, in order to meet the code.
 
Bill Crowell said:
Yes, famousbob, you can do it that way but it creates a shock hazard not to use the neutral wire in addition to the ground wire on 110 service. You've got to take each leg of the 110 paired with the neutral, not with the ground, in order to meet the code.
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Don`t remember , but no problems w/ any shock or grounds. neutral and grounds were used at time of hook up.
 
famous bob said:
Don`t remember , but no problems w/ any shock or grounds. neutral and grounds were used at time of hook up.
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Hmm, well then, if you wired it according to code, famous bob, I think maybe you raised a straw man.

Why it creates a shock hazard not to use the neutral line on 110:

Imagine that you are operating an electric drill with a steel case, and the drill's motor winding burns up and shorts to ground. Basically your body is connected in parallel with the current from the short that is trying to flow to ground, and both the neutral and the ground are at close to ground potential. Anything you can do to decrease the resistance to ground means that less of the current will be flowing through you. Remember that the ground wire is connected to the earth at the service entry, near the meter, by a copper-plated ground rod, while the neutral is grounded via the electric utility system's internal ground, through the center tap of the pole transformer. Therefore the utility service's internal ground tends to be of somewhat higher resistance than the earth ground at the service entry. With a separate ground wire, and with the case of the drill connected to it rather than the neutral, more of the short current is drawn to ground than would be the case if the neutral were used for ground, and therefore less of the current passes through you before the breaker pops.

"Ask him what time it is, and he'll tell you how to make a watch!" - Jane Wyman, on her former husband Ronald Reagan.
 
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I'm not sure he SAID he didn't use the neutral. A floating neutral not only creates a shock hazard it will quickly show up or damage electrics. If you have, say just one 100w lamp burning on leg, and a big load, say, a stove burner or 110 electric heater, the lamp will get very bright and MAY blow out. Replace the lamp with a TV, radio, computer, and you can get expensive.

Subpanels can be a tricky deal. It pays to check local AND US code and do it right.

Some places (I don't remember "our old well" and I mean OLD) you could get by with two legs and a neutral, then ground the box with a second ground stake AT the well house. Not sure you can do that anymore.

Neutral and ground are "the same thing" at only one point.........where the main service comes into the main box. You have a three wire service, with the main box grounded by a rod. The box, the rod, and the service drop neutral / ground are all bonded at that point ONLY. From then on, the neutral is treated as "insulated," even though tied to the box.

Another danger is crap like old commercial buildings, where you might find, say, a small 1 1/2 or 2 ton (24000 BTU) AC unit, 240 single phase, no neutral as no 120V is used. The conduit might have been used as ground. "Now" 20-30--60 years later, after remodel, damage to building, who knows, the conduit might be damaged or loose, BREAKING THE path to ground. VERY dangerous. Now, with a poor ground at the AC unit (example) and no or poor ground, a leakage from say, the compressor, blower, or control transformer to the unit ground WILL CREATE a possibly lethal condition.

This situation would have been made safer by a SEPARATE green wire ground run in the conduit.
 
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