I think my electrician ran too small of wire

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Old 12-14-17, 08:30 AM
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I think my electrician ran too small of wire

Hello. I think my electrician didn't run heavy enough wire for a long 20 amp circuit.
From the breaker box he ran #10 Romex for the first leg of the circuit. The first leg runs into an underground 1 inch pvc conduit 122ft into a j-box. From there he ran #12 Romex back underground, in conduit, for another 129 ft into an outdoor GFCI outlet.

All the online calculators make it look like the circuit needs #6 wire for that long of a pull. A 15 amp breaker would probably take care of that circuit for me, but isn't the #10 and #12 wire still way too small? Is the electrician way off base and should I raise a stink about it or am I wrong?
 
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Old 12-14-17, 09:59 AM
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That wire size is OK, no need for #6 wire. Way to big.
 
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Old 12-14-17, 10:33 AM
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Romex® (NM cable) or gray UF cable? Only the gray UF is OK to use outside even in conduit as things always get wet.

A 250' run will have some voltage drop but only significant if near maximum load. Even then most devices operate fine.
 
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Old 12-14-17, 10:58 AM
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In theory, a 12ga cable would potentially be code compliant for a 20A, 360' run to a receptacle.

It depends though on what wattage devices are planned to be used at that receptacle. The wiring would likely be sized differently if you were planning on running a 16A well pump, versus some plug-in landscape lights.
 
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Old 12-14-17, 11:23 AM
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That cable run is really perfect for a 15A load but as mentioned it depends on what you are plugging in.
 
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Old 12-15-17, 05:54 PM
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Short answer: Yes, it is way too small.

The combined run of 122' 10 gauge and 129' 12 gauge will support about ten amps at about 5% voltage drop for 120 volts.

You can draw 20 amps for small resistance heat appliances (hair dryer, coffee maker) and most lights. These are not sensitive to voltage drop. You can draw 16 amps for resistance space heating (80% continuous load rule). For other things including electronics it is an unpredictable make and model idiosyncrasy whether it works or not when drawing upwards of 15 amps total. Tools and other high load motorized devices are likely to have problems with a starting power draw well over 10 amps.
 

Last edited by AllanJ; 12-15-17 at 06:21 PM.
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Old 12-16-17, 04:56 AM
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The combined run of 122' 10 gauge and 129' 12 gauge will support about ten amps at about 5% voltage drop for 120 volts
How can you know this when you do not know the load? I like to use real numbers, not just assume the load will be 16 amps.

@Fastford - what are you planning to use this GFCI for? How much load (watts/amps) will you be putting on it?
 
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Old 12-16-17, 05:08 AM
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As asked, what is the anticipated load the wire was sized for?

If for a few post lamps or security lights and camera it would be just fine.
If a garage or shed with lights and a few power tools it would not be fine.

What's going to be at the end of the run?
 
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Old 12-16-17, 06:19 AM
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A question from a beginner - as a matter of good practice, shouldn’t the cable always be sized to the maximum ampacity of the breaker protecting it? Although 12 guage cable may suite the needs of the OP, a homeowner down the road may have greater requirements and he may not know the size cable servicing the receptacles . Again ,just looking to learn.
 
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Old 12-16-17, 06:39 AM
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Good in concept Jack, but the future cannot always be known or economically feasible for the current owner. If the future owner needs more they can install it. The code does not require futureproofing.
 
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Old 12-16-17, 01:29 PM
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I think Jack's point is that a future homeowner could see the #10 cable at the panel and assume he can increase the breaker size to 30A. In a long run application like this one..... a larger cable size is needed to reduce voltage drop. I put a P-Touch label right on the wire where it enters the breaker stating to "protect at 20A maximum".
 
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Old 12-18-17, 09:15 AM
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Thanks for your answers. I am building a shop out by that outlet. I want to run a DeWalt metal cutoff saw that is 4hp / 15 amp. I also forsee using a homeowner size portable air compressor and a ShopVac. I have been running my DeWalt cutoff saw off of my portable generator, but was hoping to use the new outlet.
 
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Old 12-18-17, 10:42 AM
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Forgot to mention. The 10 gauge wire is in an orange sheath and the 12 gauge is in a yellow sheath. I can't see enough of it be able to read what's on it. I'm just familiar with the gray coating as being outdoor wire. The electrician told me this orange and yellow wire is rated for underground and wet conditions. Is he right or pulling my leg?
 
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Old 12-18-17, 10:48 AM
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He is not correct. Those are for inside usage in dry areas only.
 
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Old 12-18-17, 01:13 PM
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Is your electrician licensed? Or is he a handyman? Nothing wrong with being a handyman but a licensed electrician would KNOW that type NM cable cannot be used in any place other than a permanently dry location. Conduit, when installed outside or buried is NOT a dry location regardless of how carefully it was threaded or glued.

If he IS a licensed electrician, did he "pull a permit" for the work and did he get it inspected? If not, you need to report him to the building department before he does something that could be lethal.
 
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Old 12-18-17, 04:25 PM
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Yes, he is a licensed electrician. No, there is no permit. This part of Texas is kind of loose about that out here in the country. 20 years ago, I was an electricians helper. On this project, I did everything but pull the wire and do the final hookup. I wanted an electrician to come do that and verify my work. I wish now that I had just done it myself. I expected he would run THHN or THWN. It never occurred to me that he'd run Romex since that's not how we did it when I was a helper.

My big question is if the half 10 gauge and half 12 gauge, 250 foot circuit will run my 15 amp chop saw like it's supposed to or will it damage it?
 
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Old 12-18-17, 05:10 PM
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At that distance your power tools MAY have a starting issue, They require a lot more amperage to start then run. It's that starting load that may be your issue. You won't be able to run a heavy appliance and start another one.

Did you tell him what this circuit was going to be used for ?
 
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Old 12-18-17, 05:27 PM
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I go along with Allen in post #6. Using this VD calculator (Voltage Drop Calculator) and assuming the entire run in #10 and at 120 volts supply the VD with a 15 ampere load would be 7.5% or 9 volts leaving a voltage at the tool under load of 111 volts. If you run the calculator using #12 it works out to be a VD of 12% or 14.4 volts leaving 105.6 volts at the tool under load. Actual VD will be approximately in the middle due to using both sizes of wire. (I also calculated the individual VD per leg/run and the end result came out as 107.6 volts terminal at the tool under loaded conditions.)

Those are some pretty steep voltage drops to be using with a motor-driven tool. Performance WILL be less than rated and the motor WILL overheat if used continuously. The other issue is that the specification on your saw, i.e. 4 horsepower and 15 amperes are misleading. Multiplying 120 volts by 15 amperes gives 1,800 watts. Divide that by 746 watts (one electrical horsepower) and you get 2.41 horsepower. Multiply that by the motor efficiency, say 80%, and you get 1.93 mechanical horsepower. It is obvious that the saw is vastly overrated in terms of horsepower, just like most consumer air compressors. To actually achieve 4 horsepower would require approximately 30 amperes at 120 volts.

Now remember, those calculations are ONLY for the saw. Add in the compressor and lighting and it goes even higher. I am, of course, ASSUMING the voltage being 120 since no mention was made of running a three-wire 240/120 circuit.

Bottom line, yeah, the wiring is too small for the anticipated load as well as any future increase in load.

Added: The saw is probably using a universal motor and will start okay since the load is minimal. However, when actually sawing it could very well go into an overload condition and the amperage draw will soar. It is almost a sure bet the compressor will have trouble starting.
 

Last edited by Furd; 12-18-17 at 05:31 PM. Reason: Response to Pete's posting.
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Old 12-18-17, 09:08 PM
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You guys have helped me a bunch. Now I need to confront him again. He got kind of hot with me before. I want to pay him for the bit of work he did that was right, but his wiring came up short. He already told me the wire was rated for underground and wet conditions and that he wasn't pulling it out.

What size and type wire would you recommend that I run for this circuit? The most I can see running is the 15 amp chopsaw with a LED worklight and small radio
 
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Old 12-19-17, 03:57 AM
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You want to run individual conductors, type THWN or dual-rated THHN/THWN. I would recommend nothing smaller than #8 but as you calculated in the first post #6 would be best.

A little story to illustrate the problem. I used to volunteer at an historical museum where 120 volt convenience receptacles were few and far between. The director bought a high priced industrial vacuum cleaner and some 100 foot extension cords. Unfortunately, the extension cords were only 16 gauge. Anyway, she was using the vacuum for a long period of time and it quit, She found the motor housing too hot to touch and after letting out some choice words she eventually took the machine to a repair shop that told her the motor was burnt out. When she found out the repair cost she said she would never again buy an expensive vacuum cleaner.

Well, when she told me that and also told me about cheap a** electric weed trimmers burning up I told her about the problems of voltage drop from using too small a gauge extension cords. Then I got a spool of 10/3 type SOOW cable and made up some fifty foot and a one hundred foot extension cords. The extension cords are very heavy but they don't cause motor burn-outs.
 
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Old 12-19-17, 11:51 AM
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If you're looking at #8 or #6 copper that's a breakpoint where I'd switch over to aluminum on price. I'd have to run the numbers on your conduit size to see what's possible, but you're at a price point where a single 20A circuit with #6 copper is going to be about the same price as a 50A or 60A 240V subpanel with aluminum. If you're thinking of going that way we can help you look into the possibility more.
 
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Old 12-19-17, 11:52 AM
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He already told me the wire was rated for underground and wet conditions
You can tell for yourself if you can find a part of the sheathing with writing on it. You should see "UF" printed on it for 'underground feeder'. NM is non-metallic, which is not rated for outdoor/underground usage. Even if you have to dig up a foot or two to find the labeling, it's probably worthwhile to be 100% sure either way.

Earlier this year I ran across a spool of white 14/2 cable which I assumed to be NM. Started using it, and quickly realized when stripping it it was white UF. Sure enough - clear as day, it was printed on the sheathing. I decided I did NOT want to spend the extra time wiring a basement full of recessed lights with UF.
 
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Old 12-19-17, 07:43 PM
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You don't need to read the writing or imprinting on the cable sheath, just look at the end of the cable. If the individual wires are surrounded by plastic, making it difficult to extremely difficult to strip, it is type UF. If the wires have a paper filler around them it is type NM. ONLY type UF is acceptable in outside or buried conduit.
 
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