# Is there an electrican in the house? (technical Q) **URL:** \ **Category:** Factual Questions\ **Created:** [July 27, 2002, 10:43pm UTC](https://boards.straightdope.com/t/is-there-an-electrican-in-the-house-technical-q/121169 "2002-07-27T22:43:49Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [July 27, 2002, 10:43pm UTC](https://boards.straightdope.com/t/is-there-an-electrican-in-the-house-technical-q/121169/1 "2002-07-27T22:43:49Z")
I am revamping my back yard and installing a patio(now) and spa later. As part of this I will have an electrican upgrade my panel service to 200A. (the panel upgrade will be later during the spa installation, I don’t have an electrican yet.) As part of the general upgrade I want to get rid of the overhead wires that supply power to my garage. I want to run the wires underground under the patio I am installing NOW. I have spoken to several people and from what I understand the conduit needs to be at least 18" deep and steel when it comes out of the ground. Being a take no chances kind of guy I will put it about 24" down under grade. Now in the garage I have a chance to get a free air compessor (Whoo Hoo) it runs on 220 and draws 7.5A. I have a freezer that draws 5A, flourcent lights (6 eight foot 40W?) and a security light. Plus the usual assortment of electrical outlets. My plan is to run a 220 circuit (30A if I can or 20 otherwise) put a sub panel in the garage hardwire the compressor, split the lights and freezer onto 1 circuit, and the security light and plugs on the other 110 circuit. I have gotten conflicting information about wire size and what amount of power I can get through a particular size wire. It is 100 feet from my panel to where the compressor will sit. This includes bends, up down turns and all that. So my question is can I run 4 #10 wires for either a 20A or 30A circuit? If the answer is no, what size wire do I need to run. Is there a website I can refer to for this type of info? I have been having zero luck so far. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [July 27, 2002, 10:45pm UTC](https://boards.straightdope.com/t/is-there-an-electrican-in-the-house-technical-q/121169/2 "2002-07-27T22:45:52Z")
In case I did not make myself clear (not uncommon with me) the garage only has a 15A 110 circuit now. As this circuit is shared with stuff int he house, I will terminate the overhead run. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [July 27, 2002, 11:42pm UTC](https://boards.straightdope.com/t/is-there-an-electrican-in-the-house-technical-q/121169/3 "2002-07-27T23:42:55Z")
If your electrician is a licensed contractor he will have all the information needed on the electrical code in your area. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [July 27, 2002, 11:54pm UTC](https://boards.straightdope.com/t/is-there-an-electrican-in-the-house-technical-q/121169/4 "2002-07-27T23:54:04Z")
> [@](#): > > \*Originally posted by David Simmons \* > \*\*If your electrician is a licensed contractor he will have all the information needed on the electrical code in your area. \*\* Perhaps you missed this line in my post > [@](#): > > (the panel upgrade will be later during the spa installation, I don’t have an electrican yet.) ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [July 28, 2002, 12:43am UTC](https://boards.straightdope.com/t/is-there-an-electrican-in-the-house-technical-q/121169/5 "2002-07-28T00:43:40Z")
```auto CIRCULAR MAX MICRO AWG MILS AMPS OHM / FT 16 2580 11.3 4087.7 14 4110 15.6 2566.0 12 6530 21.4 1615.0 10 10400 29.5 1014.1 8 16500 40.6 639.2 6 26300 56.0 401.0 ``` that should make it easy to calculate voltage drop as a function of length. Or do I have to do that too? 😉 ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [July 28, 2002, 1:03am UTC](https://boards.straightdope.com/t/is-there-an-electrican-in-the-house-technical-q/121169/6 "2002-07-28T01:03:30Z")
12 AWG is rated for 20 amps, while 10 AWG is rated for 30 amps. However, that’s a _safety_ rating, not a performance rating. When making long runs, you should increase the gage of the wire. As an example, I recently installed a 220 VAC / 40 A air conditioner. Normally a person would use 8 AWG wire for 40 amps, but I used 6 AWG due to the long run (130 feet). _Why increase the size of wire for long runs?_ Because wire resistance is proportional to wire length. More length = more resistance = more voltage drop = less power. To overcome this problem on long runs, conductors with larger cross-sectional area are used, which lowers the linear resistance. This is especially important for devices with high start-up currents, such as motors. _At what length should you increase the wire gage?_ I don’t know; you’ll have to check the NEC and/or your local codes. But 100 feet sounds like a pretty long run, and I would feel more comfortable using a larger wire gage. Hell, I’d probably just go ahead and use the next size larger even if it were not a long run, just for insurance. Besides, it won’t really cost you that much more $$. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [July 28, 2002, 1:32am UTC](https://boards.straightdope.com/t/is-there-an-electrican-in-the-house-technical-q/121169/7 "2002-07-28T01:32:02Z")
OK, I’m back. Assume #10 AWG, 30 A, 200 ft (double the distance) the voltage drop is: 30_200_1014/10^6 = 6 volts. Sounds good to me. Especially since that will not be the steady load. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [July 28, 2002, 2:19am UTC](https://boards.straightdope.com/t/is-there-an-electrican-in-the-house-technical-q/121169/8 "2002-07-28T02:19:49Z")
> [@](#): > > \*Originally posted by Rick \* > \*\* > > Perhaps you missed this line in my post > > \*\* No, Rick, I didn’t miss the line. My only point is that if you are going to have a licensed electrician do the job he will want you to tell him exactly what you want, including possible future expansion or extension, and he will then configure the system in accordance with local electrical code requirements and for good performance. He, and he alone, will be held responsible for the safety and performance of the system and if he has any smarts, he will want it done the way he knows it should be. And I suspect he won’t be thrilled to be told, "Well, someone on the internet, whose qualifications I don’t know anything about, said this was the way to do it. ---
**Author:** ![casdave](https://avatars.discourse-cdn.com/v4/letter/c/c6cbf5/32.png) [@casdave](https://boards.straightdope.com/u/casdave)\ **Post date:** [July 28, 2002, 11:09am UTC](https://boards.straightdope.com/t/is-there-an-electrican-in-the-house-technical-q/121169/9 "2002-07-28T11:09:57Z")
Here is my suggestion. When you decide to install an underground conduit, use the pvc water pipe rather than the proper electrical conduit. It costs around the same but is far tougher, do not put any fixed bends in it or the cable will not pull through easily. I know this means you will have upward bends of a large radius but its not unmanageable. When you install your pipe make sure you feed a length of drawline through it first, whilst the pipe is straight and, leave this inside your pipe with the ends out side of it. Pick a goodly sized pipe, at least 32mm, that’s about 1"and 3/8ths. If you are going to do this then you might as well install a water supply as well, if there isn’t one there already. Doing this will allow you to pull the cable out if necessary too. If I were you I’d also run some telephone cable down there and some intruder alarm cable, even if you are not going to use it just yet, it may well come in useful at a later date. If you use a power breaker, RCD in the UK but you Americans have differant names for them, these trip very fast and it means you can use a slightly thinner wire(but I guess there is little point if you are doing it yourself) If you plan on doing any welding then power breakers have a habit of tripping out, so you may not want to use one in such a case. I you are going to carry out welding then your earth will need to be very good, and you might either wish to try one gauge thicker wire(the earth wires are generally thinner than the main conductors) . The other option would be to install an earthing rod nearby and conect to both the earth wire from your house and also to this. ---
**Author:** ![casdave](https://avatars.discourse-cdn.com/v4/letter/c/c6cbf5/32.png) [@casdave](https://boards.straightdope.com/u/casdave)\ **Post date:** [July 28, 2002, 11:12am UTC](https://boards.straightdope.com/t/is-there-an-electrican-in-the-house-technical-q/121169/10 "2002-07-28T11:12:38Z")
…er reading that about putting in a water pipe, it looks almost like I mean put water through the pipe you would use as an electrical conduit. What I meant to say was… Since you are already putting in a trench for the electrical conduit, then it makes sense to also lay a water pipe in the same trench. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [July 28, 2002, 2:52pm UTC](https://boards.straightdope.com/t/is-there-an-electrican-in-the-house-technical-q/121169/11 "2002-07-28T14:52:10Z")
> [@](#): > > \*Originally posted by sailor \* > \*\*OK, I’m back. Assume #10 AWG, 30 A, 200 ft (double the distance) > > the voltage drop is: 30_200_1014/10^6 = 6 volts. > > Sounds good to me. Especially since that will not be the steady load. \*\* Upgrading to 8 AWG (from 10 AWG) will give you a 0.9% increase in voltage and 1.9% increase in power (assuming an 8 ohm load at 240 VAC). So I agree; it’s not that much of an improvement. However, if it were me, I would upgrade to 8 AWG anyway, just in case I wanted to change the service to 40 A in the future… ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [July 28, 2002, 3:22pm UTC](https://boards.straightdope.com/t/is-there-an-electrican-in-the-house-technical-q/121169/12 "2002-07-28T15:22:57Z")
> [@](#): > > \*Originally posted by casdave \* > \*\*When you decide to install an underground conduit, use the pvc water pipe rather than the proper electrical conduit. > \*\* **No!** There’s a color code in the U.S. that _must_ be followed for plastic pipes: Gray PVC is used for electrical cables, white is used for water, and yellow is used for gas. This is (obviously) for identification; you don’t want a plumber cutting into (what he believes is) a water pipe and have it turn out to be 220 VAC. Use _gray_ plastic conduit for electrical runs… ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [July 28, 2002, 3:26pm UTC](https://boards.straightdope.com/t/is-there-an-electrican-in-the-house-technical-q/121169/13 "2002-07-28T15:26:49Z")
\>\> if it were me, I would upgrade to 8 AWG anyway, just in case I wanted to change the service to 40 A in the future Well, he started off by saying he could do with 20A but 30 would be better. By that reckoning you can go up as high as your pocket allows. ---
**Author:** ![Running\_with\_Scissors](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Running\_with\_Scissors](https://boards.straightdope.com/u/Running_with_Scissors)\ **Post date:** [July 29, 2002, 6:48pm UTC](https://boards.straightdope.com/t/is-there-an-electrican-in-the-house-technical-q/121169/14 "2002-07-29T18:48:02Z")
I just started researching spas. If you’re going to be connecting one up to this circuit at a later time, I’d recomment **at least** a 40 amp, two-phase (i.e 220V) circuit. That’s just for the spa itself (some of them require this much power, some less). Adding on other appliances (like that compressor) will require more power. A 50A circuit will **probably** be enough, although you run the risk of blowing a breaker if the freezer and compressor start up at the same time while the hot tub’s heating elements are on. It’s up to you to determine how likely that occurence is. [Here’s an example](http://www.savannahspas.com/install1.html) of a hot tub that requires 40 amps/220 V. Cheaper to do it right now than change it out later. Wire is cheap, labor is expensive. ---
**Author:** ![NurseCarmen](https://avatars.discourse-cdn.com/v4/letter/n/5daacb/32.png) [@NurseCarmen](https://boards.straightdope.com/u/NurseCarmen)\ **Post date:** [July 29, 2002, 8:13pm UTC](https://boards.straightdope.com/t/is-there-an-electrican-in-the-house-technical-q/121169/15 "2002-07-29T20:13:21Z")
> [@](#): > > \*Originally posted by Crafter\_Man \* > \*\* > **No!** There’s a color code in the U.S. that _must_ be followed for plastic pipes: Gray PVC is used for electrical cables, white is used for water, and yellow is used for gas. This is (obviously) for identification; you don’t want a plumber cutting into (what he believes is) a water pipe and have it turn out to be 220 VAC. > > Use _gray_ plastic conduit for electrical runs… \*\* Thank you Crafter\_Man. Let me just reiterate, NO! You should also call your local power/gas/etc. company to check your yard for buried nasties. Most states have just one number you call, and they come out and paint your grass and plant little flags. Don’t just assume that because it is your back yard, there will be no buried dangers lurking below the grass. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [July 29, 2002, 8:38pm UTC](https://boards.straightdope.com/t/is-there-an-electrican-in-the-house-technical-q/121169/16 "2002-07-29T20:38:55Z")
> [@](#): > > \*Originally posted by NurseCarmen \* > \*\*You should also call your local power/gas/etc. company to check your yard for buried nasties. Most states have just one number you call, and they come out and paint your grass and plant little flags. Don’t just assume that because it is your back yard, there will be no buried dangers lurking below the grass. \*\* So true. I installed central AC last year, and decided to locate the compressor unit 70 feet from the house. I (obviously) needed to dig a trench, so I rented one of those big, gas engine-operated “trencher” tools. I started up the engine, and _just before digging_, I thought, “Hmmm, I better evaluate this situation… I wonder if there are any utility lines buried down there?” I surveyed the situation, and realized the trench would intersect **four** things: 1. The 220 VAC mains 2. The gas line (from propane tank) 3. Telephone line 4. Water line (from well) “Better not use the trencher!” I said. So I returned the trencher (which they charged me for anyway) and ended up digging the entire length of the trench w/ a hand shovel. I ran into everything except the water line, which is not surprising since it was buried below the frost line. Thankfully I didn’t break anything.