How did this happen?

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Old 10-09-04, 09:36 PM
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How did this happen?

Customer called on a malfunctioning water heater.


50 gallon electric, checked elements for continuity, checked out fine.


I won't even check to see what thermostat is failing, I replace both to assure customer that my visit is a effective one.



The initial call was because the breaker kept tripping. My assumption was that the reset was failing on the upper thermostat, and the majority of issues such as these lead to thermostat issues.



Put new ones in, 5 minutes it trips again.


I couldn't see the wire leading into the water heater, and I noticed it was a double 20 breaker, nothing conspicuous.

The wire leading into tank was 12-2, wire nut connections tight, nothing to indicate a short other than a possible ground out where they didn't protect the wiring after it leaves the flexible metal conduit.


But when I removed the panels to the water heater, and then confirming the tag, this water heater had 4500 watt upper and lower elements.


The serial tag proved this, along with the fact that this water heater was intended for a mobile home, even though it was installed in a regular stick-framed home.



Tell me, How in the world did a water heater operate on the wrong breaker, the wrong sized wire for 5 years without any trouble until recently?

12-2 wire only supports 3800 watt elements; Home Depot had a great deal of water heater cancellations when they first came to this area since all 4500 watt element water heaters demanded 10-2 wiring along with a 30 amp circuit.


My take on this is this: The plumber I am sure didn't realize that the heater was spec'd for mobile home, since there were no side outlets on the tank, and I am sure that they didn't know it was burning 2 4500 elements. The tank is just a 6 year, nothing special or out of the ordinary.


The wires upon inspection when the panel cover was removed was melted a few inches into breaker, and the breaker was hot to the touch.

This morning I ran 10-2 wiring with a 30 amp breaker in the panel. Customer had hot water before I left.
 
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Old 10-09-04, 09:37 PM
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I am thinking that the breaker failed due to being put to the edge (17-19) on a 20 amp throw, for the reason that the customer mentioned the breaker was humming.


Panel was newly installed when the heater was installed (Square D) 5 years ago, wires were secure in the breaker lugs.
 
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Old 10-09-04, 10:51 PM
hex2k1
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Dunbar although there are certain codes in the nec that dont allow you to use number 12 awg conductors for circuits over 20 amps # 12 awg copper conductors of the insulation specified in table 310.16 do have an allowable ampacity of 30 amps. the fact that the breaker didnt trip is what is concerning. i think that the breaker that failed allowed enough current to flow to the heater to keep it running for so long until it overheated like you described. from my experiance some breakers fail because of the mechanical parts of the breakers. i have seen breakers that fail to trip because the trip is spring loaded and the spring failed. anyhow sometimes when you reset them a couple of times they somehow fix themeselves and start operating correctly. that is what possibly might have happened. once fixed the breaker started operating the way it should so it kept tripping once the load surpassed the 20A rating. some other people might have simpler reasons but this is one i have ran across. just to clarify a breaker like that should always be replaced even if it seems it is operating correctly because you dont know when it is going to fail again.
 
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Old 10-10-04, 04:31 AM
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I am thinking that the breaker failed due to being put to the edge (17-19) on a 20 amp throw, for the reason that the customer mentioned the breaker was humming.
This is exactly the problem.

A little known fact about most circuit breakers: they are only rated for _continuous_ operation at 80% of their trip rating. For many loads, including all loads that are on for more than 3 hours at a time, you are required to use a breaker that is larger than 125% of the load current. If you have a 20A continuous load, you are required to use at least a 25A breaker. And when you use the larger breaker, you are required to use thicker wire so that the breaker properly protects the wire.

A 4500W element at 240V draws about 19A. A 20A breaker would be loaded past its continuous rating. The breaker might or might not trip, depending upon things like ambient temperature and age.

-Jon
 
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Old 10-11-04, 10:36 AM
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Thanks for the follow-up on this matter.


I am sure that the master plumber that installed this heater didn't realize the tank had 4500 watt elements, otherwise he would of ran a heavier gauge wire. (10-2 30 amp circuit)
 
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