Friend of mine has one of those intermittant problems that drive people nutz. Her hot water heater keeps tripping the breaker, and I can’t figure out why.
The 60-gal tank is relatively new; both elements and thermostats test out good. Power is supplied by a doubly-protected circuit, as far as I can tell. This is an old house with a lot of DIY wiring and re-done stuff in it, so anything is possible.
What I see is a relatively modern 100-amp fuse box in good shape. Wiring to it is all 90ºC plastic-jacketed Romex; none of the old 75º woven sheathed stuff. There is a 20-amp (240v) circuit labeled HW heater, and pulling those fuses shuts it down.
At the tank end of that power, there is a small sub-panel box with a single 20-amp double breaker in it. It is this breaker which keeps tripping. (The fuses do not blow.)
But it doesn’t do it all the time. Naturally….
I checked the whole HW tank electrical system out best I could without tracing every circuit in the entire house to see if anything else could be on that circuit. I did this two weeks ago, found nothing, reset the breaker, and she was good until two days ago.
Now it’s tripping everytime someone uses enough hot water to cause the elements to light up.
She’s owned the house for 10 years and has made no changes to the wiring or service panels in that time. The only thing that has changed since this problem began occuring is that she moved her computer from one room to another. On the theory some goof might have wired a bedroom plug into the HW tank supply circuit at some time in the past, I suggested she keep if turned off to see if the breaker at the HW tank would stop tripping, but it did not.
PS: there is only one feed coming off the local breaker at the tank, and it goes to the tank directly. If there’s anything else on that circuit, it’s tapped into it before that point. (And the walls are urethane foamed, grrr….)
As far as I can tell, we’re down to:
1. Mice chewing the insulation?
2. An intermittently faulty thermostat allowing both heating elements to run at the same time?
3. A faulty breaker?
4. ??
Ideas, anyone?
Dinosaur
How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice….
Replies
Is the tank wired so both elements can come on at once? If so, that's your problem. (Or could be a faulty upper thermostat giving this effect.)
Is the tank wired so both elements can come on at once?
It's been operating correctly since installation; I don't have the exact date but my guess from looks is we're talking a matter of 5 years, ± a few. She doesn't remember.
So if it's wired wrong, it's came from the factory that way. I doubt that happened; plus it has run fine all these years. Whatever happened to cause this, happened without human intervention.
Hmmm. It occurs to me one of the thermostats could have aged just enough to throw the temp adjustment off. But now that methinks of it I can't rememer if it's the upper or the lower T-stat which is supposed to be set just a smidge lower than the other. Damn. CRS strikes again. I don't work on these often enough.Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
What is the label on the WH?
Most of them require #10 wire and THIRTY AMP breakers/fuses.
(Specially seeing that you use those smaller Canadian amps. See tagline)
And there should not be anything else on that circuit. But in old house you never know. Does anything else go out when the fuse blows?
If you have a clamp on amp meter try monitor the current as hot water is drawn.
"Now it's tripping everytime someone uses enough hot water to cause the elements to light up."
I am not up on the ways of elec WH. But I know that one element is used for keep warm and the other for heating "new water". And I believe that it is common for them to be the same size, but one top and one bottom. Forgot which is which.
So most likely the keep warm element comes on several times a day.
So once you verify that you have the right overvoltage protection then either the thermostat is allowing both elements to come on at the same time. Or the element for heating "new water" is shorting out to ground.
Also you might have a breaker that is getting old and weak and tripping at less than rated current. Again a clamp on amp meter will help.
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Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Most of them require #10 wire and THIRTY AMP breakers/fuses.
(Specially seeing that you use those smaller Canadian amps.
Canadian amps aren't smaller; they're metric, so you have to multiply by 3.14159 to find the natural log of the radius of the wattage.
You and McPlumb are both right; the fuses & breaker are 30A, not 20A. I don't know what I was thinking when I typed that.
The tank is a John Wood, 50 Imp. Gal., cascaded type. I do remember once understanding the theory of how a cascaded two-element heater tank works; I no longer remember the sequence of events but it's a bit more complex than keep-warm versus heat-up. IIRC, each element heats the water in its own zone, and they switch off on each other as convection currents inside the tank move the hot water up and new cold comes in at the bottom.
But as Dan mentioned, if both elements fire up at the same time, CLICK! yer outta business.
I don't have a clamp-on amp meter, sigh. I do a relatively small amount of electrical troubleshooting of this sort and never could justify the cost of the tool.Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Water heaters are normally on 30 amp breakers, not 20 amp.
A modern 60 gal W/H probably has 5500w elements (which pull about 22 amps)...it definitely needs a 30 amp 2-pole breaker. But you said the house had old wiring, so perhaps the 20 amp breaker was necessary to protect the existing undersized wiring for the tank. That would be the primary problem. (Fix the undersized wiring, and put in the larger breaker).
Also, both elements can't come on at the same time because, well, they're designed not to. The t-stats are designed for non-simultaneous operation. I don't think this safety is possible to defeat either (if anyone knows how, though, please clue me in). It is, however, possible to mis-wire it so the upper element comes on, and STAYS on until the Over-Limit switch pops, or the relief valve blows, or the tank explodes, which ever comes first.
Obviously, as someone mentioned, you need to check the amperage being pulled while either element is on (if you can get it to stay on). You also need to check for a short to ground. I suspect the upper element has a compromised copper sleeve that causes the short and breaker to trip. The upper element will only come on during a period of high demand, or after a time of non-use. So it's possible that a bad upper element could go unnoticed for some time. W/ power OFF, disconnect one side of the element at a time, and test for continuity btw the screw on the element and the ground. Should be none. Any reading of continuity at all is your culprit. Replace element. And again, the breakers are undersized for this heater.
PS: a la Steven Wright-- If a "hot water heater" is for heating hot water--why do we need them?
Thanks for the reply. I tested both elements for impedance when I looked at it two weeks ago, but neglected to test for shorts to ground on the elements. I've got to pay a visit to her tomorrow evening; I'll check that then and see what turns up.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Look at this. http://www.johnwoodwaterheaters.com/pdfs/TB105.pdfThe upper thermostat is SPDT and removes power from the lower unit.Also I saw that you are suppose to set both thermostats at the same tempature.Here are some trouble shooting thoughts.Run the bottom thermostat down so it will not come on.Then run the top one up and it should turn the top element on. And you shoud measure that the power if off to the bottom circuit. If the breaker trips here (and you have verified that the bottom element is off) then the top element has a short in it.Then move the top one down and the top should go off and you should get power to the bottom element.Then turn the bottom stat up and when the bottom element turns on then the problem is a shorted bottom element.If you ever measure power on both the top and bottom circuit at the same time the top thermostat is bad.All of this assumes that there is no wire shorting out.
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Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Thanks again, Bill. I was over there tonight and took another look at it. It's going to take a dedicated visit to re-troubleshoot this thing some evening this week when I'm not too dead after work. I'll take all your suggestions along in my bag of tricks....
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
First thing to do, after the obvious, is to replace the breaker. They do wear out. Jim
Thanks. I had thought of that and if everything else checks out, that'll be what we try next.Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....