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Old 04-07-2017, 13:48   #1
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Water heater works on generator, but not on shore power

Looking for troubleshooting advice. Our water heater used to work both on shore power as well as on the generator. Last summer, flipping the 'on' switch at the navigation station for the water heater while on shore power would sometimes trip a circuit breaker (sometimes the boat's breaker, sometimes the dock's breaker). Since winter, it has always tripped a breaker. But the water heater continues to work well off the generator. All other boat systems work normally.

What might the problem be? Where would the problem be? And what might be the solution? Thanks!
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Old 04-07-2017, 14:20   #2
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Re: Water heater works on generator, but not on shore power

Could be nothing more then a bad breaker. You would need to check the amp draw when the water heater is on to confirm. If the amps are say around 10-12 amps for a 1200-1400 watt element then the breaker is most likely bad. Not that uncommon.

Could also be bad corroded wiring or a old shore power cord with too high a resistance. If the voltage drops lots when turning on the water heater with shore power (more then a few volts) then most likely the shore cable has corroded wires. which also happens lots.
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Old 05-07-2017, 02:46   #3
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Re: Water heater works on generator, but not on shore power

Greetings and welcome aboard the CF, Heather.
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Old 05-07-2017, 03:23   #4
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Water heater works on generator, but not on shore power

I don't have the experience of troubleshooting a boats systems, but a circuit breaker will trip when there is too much current flowing through it. Since the breaker changes, it's not a bad breaker. It may be a long, high resistance cord making the problem worse, but I doubt it. I think your water heater is getting old and drawing more current than it used to. Changing the element may fix it, replacing the water heater may be a better option depending on funds and whether you consider it a necessity. Also check all connections and joints for corrosion and if you find it, clean it with a wire brush and make sure the connections are nice and tight.
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Old 05-07-2017, 03:48   #5
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Re: Water heater works on generator, but not on shore power

Assuming the power goes through the same breaker regardless of source, I would say the problem must be in what is different between the two power sources. That would be the shore cord and connecors, and the wiring from there to the transfer switch. Shore cord connectors are notorious for arcing and corrosion.
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Old 05-07-2017, 04:00   #6
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Re: Water heater works on generator, but not on shore power

That could be the case, I wouldn't think it would trip the breaker on the boat from a shore cord though.. corrosion was what I was thinking as well.
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Old 05-07-2017, 04:04   #7
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Re: Water heater works on generator, but not on shore power

Another cause could voltage from the dock supply. If you're out near the end of the line you may not be getting full 110-120 volts. As volts go down, amps go up and that can trip a breaker. Easy to check, if a volt meter shows like 90 volts that would be your problem. Good luck getting the marina to fix it.
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Old 05-07-2017, 04:07   #8
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Re: Water heater works on generator, but not on shore power

Voltage drop, I was considering that too. Using a larger gauge extension cord would adjust for that some. What is the length from the power? Do you have a voltmeter to check voltage at the cord?
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Old 05-07-2017, 04:42   #9
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Re: Water heater works on generator, but not on shore power

Volt meter can diagnose all of that. If volts are good at the dock but low on the boat, problems in the cord or boat. Low at the dock outlet, it's the marina's fault and nothing you can do about it.
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Old 05-07-2017, 05:46   #10
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Re: Water heater works on generator, but not on shore power

And if volts are good at the end of the cord, problems in a connection on the boat or the water heater itself.
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Old 05-07-2017, 06:03   #11
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Re: Water heater works on generator, but not on shore power

Suggest (1) removing the element for careful inspection; or (2) carefully measuring the voltage potential of the outer case of the heater.

I suspect the dockside breakers that are tripping are Earth Leakage Circuit Breakers. And they are tripping because the submerged heating element has cracked, allowing water to leak into the element and contact electrically the active wire of the AC that is the heating element.

Some AC is then leaking into the water, possibly going to Earth via the metal case of the heater.

The dockside ELCB is tripping either because it is metering the balance between AC active and neutral, or it is measuring the leakage to Earth.

Your genset is not measuring that imbalnce of active vs neutral oo the leakage to Earth.

If you pull the element, you will likely see a metal element that has a surface crack. And perhaps the element will have expanded at that region of cracking.

That sort of scenario happens with age.

Explore and remedy fast.
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Old 05-07-2017, 06:09   #12
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Re: Water heater works on generator, but not on shore power

Quote:
Originally Posted by Alan Mighty View Post
Suggest (1) removing the element for careful inspection; or (2) carefully measuring the voltage potential of the outer case of the heater.



I suspect the dockside breakers that are tripping are Earth Leakage Circuit Breakers. And they are tripping because the submerged heating element has cracked, allowing water to leak into the element and contact electrically the active wire of the AC.



Some AC is then leaking into the water, possibly going to Earth via the metal case of the heater.



The dockside ELCB is tripping either because it is metering the balance between AC active and neutral, or it is measuring the leakage to Earth.



Your genset is not measuring that imbalnce of active vs neutral oo the leakage to Earth.



If you pull the element, you will likely see a metal element that has a surface crack. And perhaps the element will have expanded at that region of cracking.



That sort of scenario happens with age.



Explore and remedy fast.


100% agree.. except all that stuff about earth.. lol j/k. Here in the USA we call it a ground fault circuit interrupter (GFCI) and we don't say earth, we call it ground. Different strokes for different folks.
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Old 05-07-2017, 08:52   #13
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Re: Water heater works on generator, but not on shore power

Hi and welcome. You dont say where you are but in the US the voltage is 110-120 and in europe its around 230V. If you are in the UK then your lead will be 3 wire which also includes an earth. On shore power you will have pos, neg and earthh. On the boat your earth will be from the generator. Sometimes the earth is bound to the anodes, engine and seacocks. It could be a problem here so the trips go shore pwoered as there is an earth fault but not with the generator. I would reccomend that if you arent confident you get a professional (not somone for another baot unless he is qualified) In the UK all electricians have to be P Qualified. Hope it helps. I cant help much with US power as its lover voltage and higher frequency with different connectors etc. We have an RCD in our fusebox to protect everyone on board, and anyone in the water near us.
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Old 05-07-2017, 09:27   #14
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Re: Water heater works on generator, but not on shore power

Taking a slightly different tack...
What is the water heater coolant circuit connected to? (Usually an engine, but could be the gen I suppose). Is it possible the heater "works on the genset" because whatever engine it's connected to is running at the same time?

If the electric element is burned through (operated when dry?) then I don't see how it would work one way but not the other.
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Old 05-07-2017, 09:40   #15
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Re: Water heater works on generator, but not on shore power

CAREFUL! One difference between your shore power and gen power is how the 120v AC white (neutral) and the ground (green) wires/ circuits are handled. Many boat generators are not always properly wired. There may be a serious fault/ wet insulation inside your water heater electric heating element that your properly wired shore power is correctly responding to by tripping a breaker. So be very careful continuing to run on gen power that might actually be miss-wired and not tripping the safety breaker. Unfortunately, many boats have their 120v AC green ground wire connected inadvertently to their battery - terminal. This happens because many boats have their AC green ground wire connected to the ships ground/ engine block... as is the negative wire from the starter batteries/ ship's battery bank. If the hot water heating element wiring has become damaged or the hot water heater is leaking/ soaking the fiberglass insulation that is in turn providing an electrical path between the now live 'hot' 120v AC wire and the green ground wire... every DC powered device on the boat may not only have 12v DC... but also a floating 120v potential as well. Not only might this be a serious shock hazard it also could cause a serious electrolysis issue anything the gen is running and waterhearer breaker on. While we all like to save $$ and/ or just like to fix things ourselves... this is one of those things that if you are not experienced/ have the proper measurement equipment/ troubleshooting skills... should be left to an expert. In the worst case scenario if your engine, propshaft, prop, all thru-hulls are at 120 AC while the the gen is running and hot water breaker on... anyone in the water touching/ or near them may risk electrocution.
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