I need to run a long circuit out to a stock tank heater in a pasture. This is a 120V, 20 Amp line. Due to length, 4 AWG is called for to hold voltage drop within 3%.

The panel where the circuit will originate is a Siemens G2040. It appears that the 15A and 20A circuit breakers for this panel only accept a maximum size of 6 AWG.

Is it safe to run a short 2 to 4 ft length of 6 AWG wire and connect that to the 4 AWG wire?

-- Update - please see my answer below.

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    What does code have to say about clipping a few of the strands off so that it does fit? Surly that'd be preferable to a splice which would be worse IMO, and effectively do the same thing? But it probably says no to both, and you should be installing a sub panel, as the first would be blatantly against code (?), and the latter against the device's specifications. – Mazura Dec 5 '16 at 4:22
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    A properly made splice should have absolutely no voltage loss, no excess heating at the splice, and last for decades. – Jim Stewart Dec 5 '16 at 12:27
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    Any reason you can't downsize the circuit to 15A? You're not giving the livestock hot showers, so it's probably a fairly low-current device on the order of a few amps. – isherwood Dec 5 '16 at 16:08
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    Assuming a stranded 4 AWG, I doubt if there is any benefit in 2 to 4 ft of 6 AWG connected to long run of 4 AWG versus cutting out a few strands of the 4 AWG for the 20 AMP breaker. Neither of which sound that good an idea, but the 2nd one is simpler. – chux Dec 5 '16 at 22:12
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    @Mazura: I would definitely not clip away part of the wire. That would be virtually impossible for someone to identify later on and might lead to a fire-hazard if the wire is reused and assumed to be 4 AWG. – Hank Dec 5 '16 at 23:23

Why not bring the 4 AWG all the way into the panel and splice it there. If you are using a 20-A breaker, then you could use 6, 10 or 12 AWG to go to the breaker. The neutral and ground of the 4 AWG cable could be connected without splices if the neutral and ground bars would accept 4 AWG.

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    I may be wrong, but I'm pretty sure it's not code to split in the panel. Wires entering the panel should go directly to their breakers. A panel is not a junction box. – mickeyf Dec 6 '16 at 13:36

I would go to 240V power instead of thick wire

First I would contact the manufacturer of the heater and see if they make a 240V version instead of 120V. Then I would run it as a 240V circuit instead of 120V, at what is typically half the amps.

When you double the voltage and halve the amps, useful power is the same, but you reduce losses by a factor of 4. Which means you can go down 6-8 sizes in wire on a long run like this. Plug it into a voltage drop calculator and you'll see.

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    If you already have a 120-V heater that you want to keep, you could run 240 to the tank and use a 240-to-120 step-down transformer before the heater. – Jim Stewart Dec 5 '16 at 12:22
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    If the heater is a heavy, expensive, commercial grade unit, it's quite likely that the manufacturer has designed the unit so it can be reconfigured from 120V to 240V. I would suggest to consult with the factory. – Harper Dec 5 '16 at 15:11

I don't see a problem with your proposal and I can't think of why it would be a code violation, but if you do it you might try to mark both ends of the 4AWG wire as being part of a 20amp circuit. You don't want someone to find it years from now and think it is 4 AWG all the way back to the panel.

Another option is to set up a sub-panel at the remote location and then run your 120V circuits from there. A 60-amp double breaker should have no trouble taking 4 AWG and that would give you some flexibility in the future.


You might have a tough time finding these - but a "pin terminal" at the circuit breaker end would probably work. The end of terminal is much smaller than the wire it terminates. I've used these on several similar occasions. See the image here ->


You'd also need a proper way to compress it. You could likely rent a compression tool with a bit of searching.

[EDIT] Barring that, I would use a butt-splice of some type (or if that's too hard to find, use a split-bolt) inside the electrical panel just far enough down that the #6 has plenty of room to bend and flex. Say within a foot or so of the breaker.

[EDIT2] I would advise against using a blue wirenut unless you are experienced splicing large wires of dissimilar size. The problem is that the larger of the two wires tends to hog the spring inside the splice, and you'll be looking at a potential for a burned up wirenut in a few years. If you do decide to go this route, then be sure after you splice to hold the wirenut firmly while you tug on each wire separately to make sure the splice "took".


I think you're doing something wrong here. Either your math is bad, or you have the world's largest water heater that's about a mile from your house.

I don't remember the last time I saw a 120VAC water heater; they aren't exactly common.

6 awg is used for electric stoves @ 50amp, which is more than you describe. 6 awg is also used for water heaters (240vac @50amp) 8 awg is used for 240vac clothes driers @ 30amp

My water heater has dual 5500w elements, which consume just shy of 50amp, and that's the biggest one they sell at the big box store.

Also remember that a 120VAC appliance does not need exactly 120VAC. Fluctuations at your local neighborhood transformer can drop that as low as 110VAC.

In a normal-sized house, you don't generally need to worry about voltage drop on a/c lines. For example, in my house, my line voltage is 120VAC in order to compensate for any possible drop on-premise. My shed has an underground run 300' from the house and measures at 110VAC, which is perfect.

Edit -- now I understand the problem more completely. Instead of putting the 20 amp breaker in your panel, put a 50 amp in there and run a daughter box at the remote site with a separate 20amp breaker. RV panels are great for this [http://www.menards.com/main/electrical/circuit-protection-distribution/rv-panels/120-240-volt-20-amp-gfci-rv-power-outlet-plus-50-amp-with-breakers/p-1444427371346-c-6440.htm?tid=8800702129165764672]

  • You get 50 amps at the remote site! Plug in a welder too!
  • A 50 amp breaker takes a 4awg wire just fine
  • No splices in the panel
  • No voltage drop
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    A 1500W tank heater 500 feet away is not at all unreasonable on a farm. Those conditions cause a 3% voltage drop for the OP. – Bryan Boettcher Dec 5 '16 at 18:18
  • As alluded by insta, the consideration here is voltage drop, not amperage. You are absolutely correct that the wiring is large from a pure amperage standpoint. But depending on the distance to use, it's (at least potentially) right on the money voltage drop wise. – Chris Parker Dec 6 '16 at 16:55
  • See, I didn't see it was a stock tank heater. Stock tank heaters don't care about voltage drop; they are not sensitive electronics. I've seen stock tank heaters run with 12awg dropcords for 500 feet. Yes the voltage drops over the distance, but again, tank heaters don't care. They'll just get hotter. – W. Smith Dec 6 '16 at 20:40

If it's a standard stock tank heater, there's little reason to keep the voltage within 3%. 10% would be sufficient, and if you have such little margin that you really need that 3% or better, then you should probably use a more powerful stock tank heater and give yourself a reasonable margin.

The correct way to do this is to set up a sub panel with larger breakers nearer to the stock tank, and put the 20A breaker in there with smaller wire and the appropriate breaker. You'd still have the same 4awg run, but you'd connect it with 40A breakers which should fit the 4awg wire.

Whether you run the full 240 or a single 120 is up to you, but 120 should take less wiring, but if you're going to the trouble of laying 4awg wire such a long distance anyway you might as well future proof the installation and lay in the full 240.


Thanks to everyone for your comments and help. For those of you who might not be aware of what I was referring to please see, for example, this drain plug heater which screws into the drain plug of a livestock watering tank. Since these sit out in the open air (looking at 10 deg F tomorrow night), they can pull a lot of current.

I used the Southwire voltage drop calculator to come up with the 4 awg. A local electrical supply store clerk scoffed at the result, and wanted to sell me 10 awg but i am confident that i need the 4 awg to keep voltage drop within guidelines.

If I had done some better pre-planning I could have designed in a remote panel and a 240 volt leg to reduce wire costs but that will have to be a lesson learned!

From everything I have read, given the design requirements, a short section of smaller diameter wire from the breaker that is spliced to the 4 awg will have almost no measurable affect on voltage drop across the run, and this will be my solution.

thanks again!


  • This is really an oversized comment-set, not an answer – ThreePhaseEel Dec 6 '16 at 1:43
  • You really didn't need to keep the voltage to within 3% of the panel voltage for that product, but if the wire is already installed then it's not worth debating at this point. Glad you found a solution! – Adam Davis Dec 6 '16 at 1:52

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