Melted water heater elements

[loren]

An interesting problem. On a residential hot water heater the lower element has burned out every four months for the last two years. The owner saved the elements and showed them to me. The outside jacket had melted away, leaving a drip of copper on the end of the burn.
Obviously when the element shuts off water gets into the center of the element and the when it starts again this water boils and blows large tares in the length of the element.
I have seen them blow apart before but never melted. Water should suck the heat away two fast to allow it to melt, let along drip copper.
Specifics:
Water Heater
60 gallon
(2) 4500 watt elements
(2) thermostats (one for each element)
240 Volts

Supply Power:
Voltage: 246
Current: 24 Amps (when both elements are working)
Cold to Hot time: 1 hour 10 min.
Wire Size: #10 Copper
Breaker: 30 Amp

Other than the element size I find nothing to question.
My theory is that the element is getting hot enough to create a boiling water effect around it or part of it. This allows the element to over heat because it is like being in an air pocket.

What do you think?

Loren
Expert Electrical Services

 

[Dennis Alwon]

Here is what I bet your problem is. You need a new water heater because the bottom of the tank is filled with mineral deposits and the element is no longer sitting in water which makes it burn out quickly. I am surprised that it last that long.

My guess is the water is from a well with no treatment of the water.

 

[LawnGuyLandSparky]

I say the thermostat is defective or not resting directly against the tank wall.

 

[haskindm]

I believe Dennis is on the right path here. I have seen this many times. The lower part of the tank gets filled with mineral deposits and scale and the element is no longer in contact with water. Often they will burn out almost instantaneously.

 

[got_nailed]

I will say Dennis is right. The bottom is full of sediment and there is no water circulation on the bottom to keep the element from over heating.

As far as both elements running at the same time I don?t know of many brands that do that. Most of the time the bottom element will be on till the water in the top of the tank gets cool then the top turns on and the bottom turns off. If both elements do run at the same time then it should be on a 40 + amp breaker (I think not my line of work).

I will say that the owner needs to get a new water heater and do a monthly drain of the tank of about 30 to 40 gallons out of the bottom of the tank. This will make the water heater last longer.

Specifics:
Water Heater
60 gallon
(2) 4500 watt elements
(2) thermostats (one for each element)
240 Volts

Supply Power:
Voltage: 246
Current: 24 Amps (when both elements are working)
Cold to Hot time: 1 hour 10 min.
Wire Size: #10 Copper
Breaker: 30 Amp

Loren
Expert Electrical Services

I?m doing my math at 220 not 246
(2) 4500 elements 4500 x 2 = 9000 / 220 = 40.9 amps.
How do you get 24 amps with both elements working?
4500 one element / 220 = 20.45 amps
Breaker size is 30 amps when both elements are working?

The top thermostat should let the bottom thermostat run as long as it is up to temp (this is why it should be set a few degrees hotter than the bottom). When the top is up to temp the bottom one can work when needed.

I do think it is time to call a plumber to let them work on this.

*** I work on mostly low voltage DC stuff. if my math is off I would love to know how to do it right.

 

[charlie b]

got_nailed has a good point about the breaker and conductor sizes. There is an inconsistency in your numbers. If the water heater really has two elements at 4500 watts each, then a #10 and a 30 amp breaker are undersized. Are you certain that it doesn't have two elements that add up to a total of 4500 watts (i.e., 2250 watts each)?

 

[LawnGuyLandSparky]

2 element water heaters do not run both simultaniously. The top element's t-stat is really a single pole, double throw switch. If the top element thermostat is satisfied (meaning, the water at the top of the tank, which will be drawn off first) then it's t-stat bypasses one leg to the lower t-stats. This will allow the lower t-stat to heat the new, colder, lower, incoming water.

Both elements were not meant to operate simultaniously.

The upper element only activates when about 75% or more of the tank is cold, and you're almost out of hot water. This way the heater can appear to recover more quickly, by keeping the top 10% hot.

 

[iwire]

2 element water heaters do not run both simultaneously.

Lets qualify that with most do not run simultaneously.:smile:

I have wired electric water heaters that did have more then one element running at the same time.

There where however commercial water heaters.

 

[Gregg Harris]

Your water heater should be non-simultaneous, using only one 4500 watt element at a time. Your measurements indicate a 6k element. Did you supply the element or customer? Sediment or dry fire are your primary causes for element failure. Four month life span is quite short,high sediment level,and 6k element equals melt down. hope this helps.

 

[LarryFine]

It's easy enough to determine form the nameplate. If it reads "upper element - 4500 watts, lower element - 4500 watts, total - 4500 watts" then they do not run simultaneously.

 

[loren]

Answers

Answers

Answer 1 The water is only two years old
Answer 2 The thermostat is tight against the tank and a recording meter on the panel showed that the thermostat does come on and shut off.
Answer 3 I drained the tank completely. Filled it back up with cold water and than started the heating process. The nominal voltage is 246 with a peak of 249 volts. I admit that I didn?t do the math before now. I calculate it as a little over 18 amps for one which would still over load the breaker. I didn?t check the size of the upper element I just assumed that the two were the same.
Answer 4 The label on the tank does say 4500 upper and lower.
Answer 5 The Upper thermostat is a a double throw stat. When the upper is on the lower is off. (I had never look at that before)
Answer 6 I didn?t look for sediment because of the age of the hot water heater. I will do that.

Thanks for the ideas and help

 

[got_nailed]

If you go back turn off the power and the cold water feed. Put a hose on the bottom of the tank and open it up. Turn the cold water feed beck on to the tank and see how much junk comes out of the tank.

They do make elements that will not burn out as fast that you should put install to get this off your back and walk away. I would get a high $$ top of the line ?sandhog? or stainless element for the bottom. If you do toss a different element in the tank feel around in the tank to see how much buildup there is. To keep it off you for when it blows in a few months tell them they need to drain off part of the tank every month to flush out the sediment.

IMO this is a plumber?s job.

As far as the sediment I have seen a tank fill half way up with sediment in 6 months.

 

[ptonsparky]

Crud in the bottom can be cleaned out with a wet/dry vac and piece of 1/2" emt bent at a 30 degree. Shove EMT in the lower element hole and enjoy the day. I have to do it at my house every couple years & have done it for customers as long as they know upfront it is time consuming. Water softner is the long term solution.

 

[got_nailed]

The warranty calls for a monthly flushing of the tank. I would think that it is there for a reason. Yes you will get a build up with flushing the tank depending on your water but it will keep the build up low.

 

[dereckbc]

I got the perfect solution any sparky should know. Get rid of that slow and money wasting electric water heater and get GAS. You will never go back to electric. Take it one step further, get one or two gas tankless water heater. Best decision I ever made when I built my last home.

 

[LawnGuyLandSparky]

I got the perfect solution any sparky should know. Get rid of that slow and money wasting electric water heater and get GAS. You will never go back to electric. Take it one step further, get one or two gas tankless water heater. Best decision I ever made when I built my last home.

I think the only people in the country still using electric water heaters are those who don't have municipal gas, are on hydropower at an insanely low Kwh rate of .05 cents (Until National Grid buys them out) or don't have any need for a gas or oil based central heating system to piggyback off of. Of course there's always the strip malls etc where venting is impractical and there's not much of a demand for hot water.

 

[480sparky]

Most bottom-dollar tract home builders use electric water heaters. They're cheaper than installing gas one. They don't care how much they cost to operate.

 

[dereckbc]

I think the only people in the country still using electric water heaters are those who don't have municipal gas, are on hydropower at an insanely low Kwh rate of .05 cents (Until National Grid buys them out) or don't have any need for a gas or oil based central heating system to piggyback off of. Of course there's always the strip malls etc where venting is impractical and there's not much of a demand for hot water.

You have not been to Texas. Very few new developments have NG, TXU has their hands in developers pockets by giving them all the infrastructure for free if they agree not to instal gas lines in their developments. I had to look for a long time for a lot to build in the DFW area that had NG.

TX is one of the derugulated states, however there is only one producer and they control all pricing of all the electric bought and sold in TX. TX is not on the US grid every since the infamous black out of the 60's in NYC. TXU rules in TX with some of the highest electric rates and lowest generation cost in the US. I pay 15 per KWH, while my neighbors across the Red River in OK pay 6-cents from OG&E.

 

[sparky59]

sediment gets my vote.