View Full Version : What gauge wire for water heater?

November 5th, 2007, 10:55 AM

I building a new home and would like to run the wiring for the water heater that is about to be installed....

Can someone tell me what gauge wire and what size breaker I need? I dont know what size water heater but I can say that it'll be whatever the standard size is.


November 5th, 2007, 10:59 AM
For a "standard" size water heater you would use 10/2 NM cable or 10ga THHN wire in conduit (2 hot and 1 ground) protected by a 30A double pole breaker (240V).

November 7th, 2007, 10:24 AM
Since this is new install in addition to the 30A breaker does he not also need a local disconnect right at the heater.

November 7th, 2007, 02:09 PM
Good point. Yes if the breaker panel feeding the water heater is not visible from the water heater and within 50 feet. An air conditioning disconnect box is the cheapest thing to use here.

November 8th, 2007, 08:33 PM
This just prompted another thought, same general subject. Must it be a fused disconnect, or just an appropriately rated DPST switch. My A/C unit has fuses in addition to the breaker. Is that because it is a motor-driven device, or is there another reason for a fuse set. Seems like the circuit would be adequately protected against shorts and overloads by just the 30A breaker at the panel.

November 8th, 2007, 10:48 PM
A simple double pole switch, pullout disconnect, or breaker type disconnect are all OK for a water heater. Some look like they have breakers, using a breaker that is just a switch with no overcurrent disconnection.

As long as the branch circuit overcurrent protection device is adequate for the connected applilance, then an unfused switch is OK. It is the darn motors or AC units that demand fuses only that force you into a fused disconnect (most today say fuses or HACR breakers). You would also need a fused/breaker disconnect if the power source was a large feeder that powered a few other things.

November 9th, 2007, 03:00 AM
Let me add one more item related to this matter any time you use the 10-2 NM for water heater useage and have both black and white wire if used for 240 volt useage IMO i really strongly suggest that remark the white wire with marker or something so you know this is a 240 volt instead of 120 volts in case someone did not catch it real quick,

Merci, Marc

November 9th, 2007, 09:56 AM
IMO i really strongly suggest that remark the white wire with marker or something

It's not just "in your opinion", it's code.

November 9th, 2007, 01:10 PM
I really don't understand it though??

If your an electrician your going to recognize a hot white in all the allowed applications and you should be testing for hot in the box. So if a white is incorrectly used as a hot (like in a conduit run) it most likely isn't going to be marked. So I just don't get it.

A person that isn't an electrician isn't going to know whether marked or not. but the code wasn't written for them so I suppose they have there reason......which would be???

November 9th, 2007, 08:51 PM
I think Code notwithstanding, anything we can do to make it just a bit safer for the next guy, whether electrician or DIY homeowner, the better.

Case in point: A buddy was trying to wire in a fan in a cabin that had electric heat (hint) and while a wall was open, found a 12/2 NM wire in just the right place for a tap that seemed to be heading towards some receptacles and thought he would just tap in to a handy run of 120V, white black and ground. And the fan went pffft with hardly one revolution. So I was looking at the wiring being programmed to think ground is bare or green, black or red is hot, 240V is SUPPOSED to be black and red, and white was neutral and basically safe, and just like the fan I too got zapped. Even though we all know that it is perfectly legal to recolor white to black or red, how much more trouble and expense could it be, for those situations when someone might be momentraily distracted, or not at either end of the cable to just run 12/3 for all 240 V runs, so all the colors come out right.

The whole point, I believe, in having mandatory colors to begin with was to make what is connected wrong so out of place and glaringly obvious it would be one more safety factor.

November 9th, 2007, 09:26 PM
A 240 volt device does not require a neutral. The use of 12/2 for the heater is perfectly fine and code compliant.
Anyone with any electrical knowledge would have known that when they turned off a double pole breaker to kill power to the line that it was a 240 volt device they were dealing with.
In Canada we do have available to us a 12/2 cable that has black and red and NO white in it. It is called HEATEX.



November 10th, 2007, 12:42 AM
I'd love to see my inspectors face if I had that red stuff installed with the black and red. I like it..!!!!

November 10th, 2007, 01:02 AM
Hi guys.

sorry i did not get a chace to reply this part i was rather cut off fast with service call and other issue came up so now i am back and will get this matter straghten out

I did not do a good job writeing my last comment on that one sorry about that [ my mind was not full awake that time ]

anyway yes anytime with XX-2 NM if have straght 240 volts yes it have to be remarked to other colours [ not green of course ]

and i used the NCVD [ non concat voltage detector ] also to verify too

useally double pole breaker is a dead give away to indenetify 240 volts but just watch out with the twinner espcally with the GE 1/2 inch breakers they are very nortius for not landing right " legs " on the system.

Merci, Marc

November 11th, 2007, 05:16 PM
Originally posted by Joe: A 240 volt device does not require a neutral.

Can you enlighten us on your comment?


November 11th, 2007, 06:50 PM
Can you enlighten us on your comment?


A 240 volt device like a water heater, compressor or welder uses straight 240 volts. There is no 120 volts used and therefore no neutral conductor required.

November 11th, 2007, 10:14 PM
A 240 volt device like a water heater, compressor or welder uses straight 240 volts. There is no 120 volts used and therefore no neutral conductor required.
OOOOOOOOh Come-on Joe, you didn't say that:smokin:

You said:
A 240 volt device does not require a neutral.

November 11th, 2007, 10:56 PM
A 240 volt device does not require a neutral. A 240/120 volt device does. We are discussing a water heater which is a 240 volt device not a stove or range that is a 240/120 volt device.

November 11th, 2007, 11:33 PM
Good way to clean it up!:rock:

There is another side to this:

-I can say straight 240 all day long, but this doesn't mean that others will understand that some appliances do not require a neutral.

I can post some of what I've read from other sites-where this is an ongoign question. The question being: What is a 240 volt circuit without the neutral.

Many believe a neutral is needed anytime you say 240 (vise versa).

Lets not assume everyone knows what we know, or what we think we know!

In conclusion, good answer! ;)

June 2nd, 2013, 11:40 PM
I looked up this thread through a google search and became intrigued on the subject of a 240v circuit without the neutral.
I have absolutely no formal training whatsoever on how to properly run electrical circuits.
Just seems pretty obvious when ya look at any breaker panel that the two leads off a 240v circuit are both hot., since they both go to the hot side in the panel.
Thanks for the recommendation on the 10/2 and using an old sharpie marker for the next man in a hurry trying to tap into a line but that won't protect the uneducated joe blow attempting to patch into a hidden wire with an illegal enclosed junction box which he would probably attempt to enclose before anyone seen. I like the red and black lead with red insulation rubber myself.
Only reason I am here telling you is so you can do this: go to hardware store and pick up a double breaker if you have available space in your panel.
If you have any 10 gauge wire, hook one side to hot, and the other side to hot as well.
Make sure the ground connection is solid.
Wire the heater.
Enjoy electrically heated water.
Use a god damn disconnect beside the heater for 'safety', if not more importantly, convenience, for if you ever want to turn off the heater without going to another room to access the panel.
Thanks for the help guys.
I'll be wired up in no time now.
Good luck with all your projects and remember sometimes code is a place to start and things can always be way better than average.