Hot water heater and wiring

November 3, 2018 9:49 AM

I just removed an old (rusted) 30-gallon electric water heater and put a new heater in its place. However, this new model has the electric connections on top rather than in the front, and the wire is about a foot too short.

The specs of the two heaters are the same. Is it going to be necessary to rewire from the breaker (which I can't do), or could a junction box extend the wires to the heater? Mostly, I wonder if anyone has dealt with similar situations with large, hard-wired appliances and has advice (or can recommend sites with good advice).

I want to be safe and would also like to have hot water again.

posted by Francolin to Home & Garden (22 answers total)

There's no reason you can't install a junction box and another length of the correct gauge wire, assuming you do the splices properly. I don't think there's any expectation of a continuous run of wire with no splices, splices shouldn't degrade the current carrying capacity of the wire in any way. You aren't allowed to "bury" a junction box...the cover must be accessible, just don't fully close it up inside a wall and you'll be good to go.
posted by Larry David Syndrome at 10:00 AM on November 3, 2018 [3 favorites]

I agree with LDS. Mount a junction box to the wall and use BX conduit as needed.
posted by humboldt32 at 10:36 AM on November 3, 2018 [1 favorite]

So long as your splice is contained within a properly mounted (and covered) box, you should be fine in terms of passing code enforcement inspection.

You'll also want to make sure the existing wire is in fact copper. If it's aluminum you'll need noox and special fittings at the splice unless you like house fires. (And even then, I wouldn't leave it in my house on a 30+ amp circuit, but I've personally seen the problems inherent in aluminum indoor wiring)
posted by wierdo at 10:59 AM on November 3, 2018

Oh and just to be clear, by covered I meant "with the correct cover plate installed on the junction box," not "covered under drywall or otherwise inaccessible." That latter reading would not be code compliant in any US or Canadian jurisdiction I'm aware of.
posted by wierdo at 11:02 AM on November 3, 2018 [2 favorites]

There's nothing inherently wrong with aluminum wiring, assuming it's installed correctly. Most service drops use aluminium.
posted by humboldt32 at 11:35 AM on November 3, 2018

In addition to the above (junction box, proper cover, accessible), make sure you use the same or lower (thicker) gauge wire in your extension as was in the original wiring.
posted by true at 11:58 AM on November 3, 2018

No, you use the appropriately sized wire, based on the draw, the type of wire, and the size of the breaker. The size of the current wire has nothing to with nothing.
posted by humboldt32 at 12:18 PM on November 3, 2018

Response by poster: Thanks to everyone. Today I've been to the local hardware store, but without knowing the gauge. Tomorrow, after I take that information in, I will install the junction box. I guess I thought things would be more complicated, and everything about replacing this water heater has been so fraught with stress that I assumed the worst.

Thanks again.
posted by Francolin at 12:46 PM on November 3, 2018

While this can certainly be done, there are right and wrong ways to do it. Make sure you know how to do it correctly before you start.
posted by Anticipation Of A New Lover's Arrival, The at 1:16 PM on November 3, 2018 [1 favorite]

Regarding the size of the wire - yes, to be strictly correct you should use the appropriate size wire based on all the variables mentioned, all the way back to the box. What I should have said is "assuming the current installation is correct and to code (meaning that the wire has been sized appropriately), use the same gauge of wire or lower". If the existing wire isn't sufficient, using correctly sized wire for your extension without replacing the entire run back to the box won't make it materially safer.
posted by true at 2:22 PM on November 3, 2018 [1 favorite]

In the U.S. most water heaters up to 50 gallons are either 4500 watts or 5500 watts. If you divide by 240 volts you get 18.75 amps and 22.91 amps, respectively. But water heaters are considered continuous loads which means they can be on for more than three hours at a time. This means that the circuit must be uprated by 125%. (Equivalently, the circuit breaker must be derated to 80%.)

So the 4500 watt and 5500 watt heaters require circuits of 18.75 * 1.25 = 23.4 amps and 22.91 * 1.25 = 28.6 amps, respectively. Since both of these are above 20 amps, a 30 amp circuit is required.

Rarely, some small 30-gal heaters will be rated 3800 watts which works out to a 20-amp circuit, but most water heaters in U.S. homes are on 30-amp circuits. 30-amps circuits require a 30-amp breaker and number 10 gauge cable.

Also note that electric water heaters are sometimes advertised as having dual 4500/4500 heating elements. This does not mean you need twice the current. The upper and lower elements are wired and switched such that only one element is on at a time. The lower element is only on when the top of the heater is hot and the upper element turns off. Since heat rises and hot water to the faucets is removed from the top of the heater, the upper element allows you to draw hot water for a longer period. The lower element heats the cold water in the bottom of the tank only when the top is already hot.
posted by JackFlash at 3:21 PM on November 3, 2018 [2 favorites]

If your junction box is metal it should be grounded.
posted by Raybun at 8:24 PM on November 3, 2018

There's nothing inherently wrong with aluminum wiring, assuming it's installed correctly. Most service drops use aluminium.

Service drops are neither indoor nor installed by amateurs. There's a reason aluminium isn't typically allowed in residential construction any longer. Even pros messed it up enough that it was a big thing in the 70s. Thankfully, it's highly unlikely OP will be dealing with aluminium wire, so getting a good connection with properly sized and installed wire nuts shouldn't be an issue.

BTW, Francolin, do yourself a favor and get actual lineman's pliers if you don't already have them. Being made for the purpose, handling largish gauge wire is much easier with them than random adjustable pliers or worse, with nothing but your fingers and a screwdriver.
posted by wierdo at 11:00 AM on November 4, 2018

Response by poster: I did it -- I grounded it, I took care with all the connections, and everything works and nothing blew out. The plumbing (with CPVC) was harder, only because I began with a hacksaw and not a pipe cutter -- that was a waste of hours. I finished that this morning and did the electric tonight.

I used 12 gauge (copper) wire to connect to 10 at the circuit breaker. The heater was 4500 watts, as was the one it replaced. The people at the hardware stores I visited many times in the last few days were very helpful, as were you, so thanks. I just got to take a shower, and I feel very happier than I have in a while.

Wierdo, those pliers would have been really useful in the last steps of twisting the connected wires into place -- the needlenose pliers I used kept slipping.
posted by Francolin at 5:49 PM on November 5, 2018

Response by poster: So happy I said "very happier," even.
posted by Francolin at 6:10 PM on November 5, 2018

Wait, what? You "used 12 gauge wire to connect to 10 at the circuit breaker." This is worded a little oddly, perhaps I've misunderstood you, but I hope you realize that 12 gauge wire is thinner than 10 gauge wire and is rated for less current. If the existing run is 10 gauge, you should replace whatever length of 12 gauge cable you added with 10 gauge for safety reasons.
posted by Larry David Syndrome at 7:14 PM on November 5, 2018

Response by poster: Oh no. Two different people said the 12 with the 10 was fine -- it's only two feet. I asked specifically about this, and was told it would be OK for the purpose. But it doesn't make sense, does it? I'll change it tomorrow.
posted by Francolin at 7:34 PM on November 5, 2018 [1 favorite]

If it's 90C THHN type wire, it's not an immediate hazard, but you should rectify the situation before closing everything up and calling it good. It helps that the actual draw is well within the ampacity of basically any 12 gauge wire. Problem is, a 30A breaker is too large to protect it if a short circuit were to occur.

That particular wire is normally 30A rated anyway (which is why people told you it's fine, as it is for the vast majority of 30A circuits, just not those that require derating) and such a short run only increases the total resistance by a relatively small amount, making the fire hazard low relative to common miswiring I've seen over the years. It is important you replace it with the proper gauge wire relatively soon, however, as it could have insurance implications. I'm only saying there's no need to skip work or forgo voting to fix it this very instant.
posted by wierdo at 1:20 PM on November 6, 2018

Come to think of it, if the 12 gauge section is in open air it may even be code compliant in some jurisdictions the way it is. Some codes adjust the derating rules depending on whether the wire is in a closed cavity, surrounded with insulation, etc. Given the relatively small expense, I'd still upsize the wire even if it is compliant with your local electrical code.
posted by wierdo at 1:27 PM on November 6, 2018

Response by poster: Last night, after I read Larry David Syndrome's comment, I shut the heater off at the breaker. I removed the 12 gauge this afternoon and replaced it with 10 gauge. (I voted, too.)

So, everything seems fine -- water's hot again, all the wire is orange, nothing's leaking.

Thank you all again, especially Larry David Syndrome . (And wierdo, for your calming words.)
posted by Francolin at 2:54 PM on November 6, 2018

Hope I didn't send you in to a panic, but now it's right and you don't have to worry. 12 gauge wire should never be connected to a breaker rated over 20A per the NEC... (you'll see a little asterisk in wire ampacity tables noting this.)
posted by Larry David Syndrome at 7:24 PM on November 6, 2018

Response by poster: No panic (I just flipped off the breaker), and thank you very much for helping me. You prevented serious problems, and I am so glad you said something.
posted by Francolin at 7:50 AM on November 7, 2018