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I hooked up a tankless heater, which draws 66 amps. (it is on a 70 amp breaker). The installation guide says to use 6 gauge wire.

I had a 4-wire circuit of 8 gauge that runs right past the room where heater will be (it went to a range; I have a gas range now). So I took the white and red wires together (paralleled), and put them on one leg. I put the ground wire (10 gauge) and the red wire (8 gauge) together, and put them on the other leg.

Am I correct that this will draw 66 amps? How will it split the current? Will each wire draw 33 amps or will the bigger 8 gauge wire (paralleled with the 10 gauge ground) draw more that the 10 gauge? Either way, I should be OK, correct?

It works fine; I grounded it through the old electric water heater circuit in the room, which had 10 gauge ground (like the 6 gauge cable they said to use.)

  • The way you have stated that the connections were made is a code violation or several violations. The red and black art the hot leads 240V 70A the white is the neutral and the equipment ground is green. 422.11F of the NEC list the maximum breaker size as 60 with the heating elements rated at not more than 48 amps. – Ed Beal Mar 31 '17 at 13:12
  • Well If the unit calls for 6 gauge and I double up 8 gauge that is bigger wire then just the 6 gauge how can that not be ok and even better?? And its still grounded with 10 gauge which is the same as the 6 gauge ground comes with, What am I missing?? – durfman8 Mar 31 '17 at 15:14
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    NEC 422.11.f limits the size of the breakers to electric heating appliances. Heat pumps with supplemental heat packs have this same limitation and require multiple breakers. The way you stated the legs were wired sounds wrong white& red on 1 leg , black ground on the other. This should be fed from a double pole 240v breaker, the black, red are the hot's white is the neutral and the ground is for the equipment ground not a current carrying conductor. So there are multiple code violations. You need to understand how 240v works and the code requirements. – Ed Beal Mar 31 '17 at 15:37
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    @durfman8 Also, you can't simply "double up" on conductors. That situation is called "parallel conductors" and is covered by 310.10(H). You'd need at least 1/0AWG to even consider doing this. – Hari Ganti Mar 31 '17 at 16:41
  • What make and model water heater do you have so we can look it up and tell you what needs to be done. Note a 220v water heater hooked up to 120 may get warm but at 1/2 the voltage it really won't work well if at all. – Ed Beal Mar 31 '17 at 17:09
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I heat S-16 requires a 70 amp breaker (it has internal sub breakers) this unit requires 240v at 66.6 amps. This requires a 240v breaker with L1, L2, neutral, and ground to properly operate using #6 copper according to the rep I talked to. Connecting any other way will not work at the rated 16Kw. (888)818-4328

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  • Ok, that sounds correct from when I checked it out, But Why does that 2foot pig-tail that comes with the unit have both 6&8AWG on it? How can wire be rated for both? Anyvbody have answer for that?? – durfman8 Mar 31 '17 at 18:21
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    The whip that comes pre-mounted on the unit does not follow the same rules as the branch circuit wiring. – Speedy Petey Mar 31 '17 at 19:57
  • I suspect if you check closely with perhaps magnification you will find out it's not both but mangled printing on the wire... It's sometimes hard to differentiate 6 and 8 as stamped on insulation. – Tyson Mar 31 '17 at 20:35
  • I'm not sure what that rep is thinking -- only way you can run 66.7A over 6AWG CU is by using 90degC terminations with the 90degC ampacity entry, and those aren't a thing...4AWG CU is what's needed here to be within the Code ampacity limits. – ThreePhaseEel Mar 31 '17 at 23:53
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Since you mentioned common North American wire gauges, I will give you the facts based on North American code.

From your responses so far, you seem resistant to hearing the facts of Code, and seem to want to argue whether Code makes sense or not. I'm not going to argue something that isn't my decision, so I'm not going to go into the details of "why".

Suffice it to say the people on the Code council are just as interested in saving money as you are, and do not waste your time or money with unnecessary regs. It's there for a reason, even if you don't know it. If the reg seems stupid, an honest search for facts will reveal it is not.

You can't parallel

No, two 8 AWG is not better than a 6 AWG.

Paralleling is allowed in certain heavy industrial applications where wiring is subject to professional management, approval chains and regular inspections. In those cases, you can't mix sizes. And each conductor has its own overcurrent protection. Paralleling requires very special panels made for paralleling. Doing this in a regular service panel creates perfect-storm conditions for a stupid person to blow up the panel.

Hot on a ground wire is out of the question

Putting hot on a ground wire is a no-no. It doesn't have any insulation! You shouldn't be horking together your own insulation. Ordinary wear and tear in the panel can expose that insulation and then kaboom.

Yes, there's an outer cable sheath - but the sheath is there for physical protection, and is not designed for insulation.

Ground needs to come with conductors

On a new installation, grabbing random ground off a different circuit is a no-no. You need to install an appropriate ground wire with your appropriate conductors.

However, there is an exception for retrofitting grounds, i.e. to an installation that had been (legally) done in the past when grounds were not required. In that case, the ground borrowing you did would have been permitted, provided of course that a 10 AWG ground is acceptable on a 70A circuit. I doubt it is.

6 AWG seems a little light for 66.6A

I know the manufacturer says it can use 6 AWG. That doesn't sound right, and since their incentive is to get you to buy it, I don't trust them.

It boils down to the temperature of your terminations. Most wires are rated off the 60C column, where 6 AWG is good for 55A, because of rules in the Electrical Code. If Code allows it and all your terminations are rated for 75C, then you can run 65A on 6 AWG, and a 70A breaker is allowed as the "next size up that's available". A better choice would be 3 AWG AL.

Maybe your heater already splits the heating elements

Many hot water heaters subdivide their heating elements into smaller sections, e.g. two of 33.3A. And then they allow you to supply power to each heating element section separately, e.g. two 40A circuits with 8 AWG. You might check if that's possible.

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  • OK, that does it, know what I am doing this weekend, Going to get new wire and get it fished up threw wall and make it more right, – durfman8 Apr 1 '17 at 1:32
  • Dont know what happen to the post I just did?? Anyways am going to go get the wire I need and stay busy this weekend, really wont be to bad just have to get it up to panel. Dont mean to sound like I argue but I cant understand how the place that makes the heater can put such small wires on the pig tail [and they do get warm] and suppose to be UL listed?? I put them next to the 8 gauge I have and I cant tell any difference?? Like the welder example I made, how can they put such small wires on them to plug into a outlet and it really gets hot but in old days [same welder] – durfman8 Apr 1 '17 at 1:43
  • had a much bigger wire on it and never got hot??? Trying to understand all this seems like the newer regulations or something is not like it use to be??? THANKS – durfman8 Apr 1 '17 at 1:43
  • @durfman8 because they're so short, and good chance they cheated on their UL listing anyway, or are counterfeit units. Consider country of origin and shop of sale. Also it's possible the smaller wire is ground, which is often permissible since hopefully ground will fault for only a second or two before the breaker blows. – Harper - Reinstate Monica Apr 1 '17 at 2:01

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