water heater / step down transformer

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JDB3

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San Antonio, Texas
A plumber friend call this afternoon about a 125 gallon single 240 volt water heater that they installed. This water heater has taps so that it may be hooked up for 208 or 240 volt. The manufacture rep. said that the taps are hooked up properly for 240 volts.
The water heater is feed from a 240 volt 30 amp power source, which is feed from a step down transformer. The water heater has 2 4500 watt elements that do not work simultaneously. The water heater has 2 30 amp fuses built into it (I was told that they are time delay fuses).
The water heater will work fine when they leave, but in a week or so, a fuse will blow.
I was told that the customer also has had trouble with the A/C system.
Any thoughts ? :unsure:
Thanks,
 
Is the transformer large enough?

Is the ac fed off the same transformer?

You have about a 19 am load on the water heater

I would check the taps, and the wiring and put an amprobe on it.

Maybe 1 element is bad and when the bad element gets powered it trips the fuse. Then the heater cools down and switches to the other element and works ok
 
Perhaps the upper thermostat is defective and it's allowing both heating elements to be turned ON at the same time, but only on an intermittent and/or momentary basis when it results in a blown fuse.

You might also put a clamp meter around both line conductors to see if you can read any current on the most sensitive scale, which would indicate leakage and perhaps a defective element. Although such leakage itself is not likely to blow a fuse, it could be indicative of a failing element.
 
How can you change "taps" for 208 or 240-volt operation without changing heating elements? I'd like to see that wiring diagram.
(but even connecting a 4500-watt/208-volt (9.6 Ω) heating element to 240 volts shouldn't blow a 30-amp fuse)
 
LarryFine said:
I'd guess only the control circuit transformer has multi-voltage taps.
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That’s what I’m thinking too, but why have a contactor on what seems to be a basic water heater, other than the larger gallon capacity? I troubleshot one last year that was 480 volt, which I could understand the contactor. Brand new, but wouldn’t heat. Found the main thermostat bad and replaced it. What was odd, is the control circuit was 480, which energized the 480/120 transformer to pull in the contactor. The thermostats were only rated 250 volt, which is probably why it failed so quick.
 
He now says that he was incorrect, it is a step-up transformer to 240 volts. The top element was drawing 25 to 28 amps & after a bit, jumped an amp or two. Why would a 4500 heating element draw so much? Sure sounds like a power supply issue.
 
So
JDB3 said:
He now says that he was incorrect, it is a step-up transformer to 240 volts. The top element was drawing 25 to 28 amps & after a bit, jumped an amp or two. Why would a 4500 heating element draw so much? Sure sounds like a power supply issue.
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Sounds like he energized the water heater before it was full, and all the air bleed off, and damaged the heating element, that or a bad element from the factory. I’ve seen them turn into a pretzel and twist up when they do that.
 
Would a bad element cause an increase in amperage?
Maybe if it is grounded?
I dont know alot about water heaters I can only tell you if an element is bad. But Not why its bad or how it went bad...
 
qcroanoke said:
Would a bad element cause an increase in amperage?
Maybe if it is grounded?
I dont know alot about water heaters I can only tell you if an element is bad. But Not why its bad or how it went bad...
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They twist up and short out, but sometimes it doesn’t clear, it just short circuits partially. It is a series resistance, and that resistance is lowered where it touched together.
 
JDB3 said:
... it is a step-up transformer to 240 volts. The top element was drawing 25 to 28 amps ... Why would a 4500 heating element draw so much? ...
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A 4500-watt, 208-volt element will (nominally) draw 25 amps at 240 volts.

Is the transformer output actually 240 volts, or a smidgen high?
If the heating element's resistance has a negative temperature coefficient, the current will go up as it heats up.
If there's a lot of crud on the heating element, its temperature will be a lot higher than it was designed to be, and if it has a NTC, ...

I'm still a little unclear about why there are fuses inside the water heater. I'd certainly like to see that wiring diagram.

I would be very tempted to start over from scratch, install heating elements that match the building's supply voltage, and get rid of the transformer.
 
JDB3 said:
He now says that he was incorrect, it is a step-up transformer to 240 volts. The top element was drawing 25 to 28 amps & after a bit, jumped an amp or two. Why would a 4500 heating element draw so much? Sure sounds like a power supply issue.
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A buck/boost transformer would be the only logical one to use, so was this from the factory? Or was added for quicker heating? As another poster said, if it was using 208 elements, and the voltage was boosted, then that would explain the higher amperage.
 
If a heating element distorts, it might crack the ceramic coating and leak current into the water.
 
hillbilly1 said:
They twist up and short out, but sometimes it doesn’t clear, it just short circuits partially. It is a series resistance, and that resistance is lowered where it touched together.
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usually won't last long before they burn/corrode "open" though.
 
hillbilly1 said:
A buck/boost transformer would be the only logical one to use, so was this from the factory? Or was added for quicker heating? As another poster said, if it was using 208 elements, and the voltage was boosted, then that would explain the higher amperage.
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Or was boosted to higher than 240? But to get kind of current OP was talking you would need to boost to 300 or a little more on a 4500 W 240 volt heating element.
 
kwired said:
Or was boosted to higher than 240? But to get kind of current OP was talking you would need to boost to 300 or a little more on a 4500 W 240 volt heating element.
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Another poster had mentioned the possibility that the heating element was 208. Being a 125 gallon water heater, it’s possible it’s a commercial unit, and may be 208 single phase originally. Not enough information given yet to determine anything.
 
hillbilly1 said:
Another poster had mentioned the possibility that the heating element was 208. Being a 125 gallon water heater, it’s possible it’s a commercial unit, and may be 208 single phase originally. Not enough information given yet to determine anything.
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Maybe, but seems more likely to use a 6000 watt @ 240 volt heater element on 208 if you want outcome close to 4500 watts, or to swap element match supply voltage on any commonly found water heater elements instead of installing a buck boost transformer.
 
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