Three phase water heater with simultaneous heating elements

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Greg1707

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Alexandria, VA
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Business owner Electrical contractor
I got a call from a salon owner. She had a three phase water heater replaced last year. The heater cannot keep up with demand. A technician was sent out from the installer. He informed her the heating elements should be changed so they operate simultaneously. He would not make the change and recommended calling an electrician. (this sounds really lame to me!)

Here is the setup.
Name plate: 4,500 watts
3 phase 20 amp breaker (not sure about voltage) 10/3 cable

According to the instructions only one wire needs to be moved in the control panel to change setup to simultaneous operation.

Is this it? Is there anything more to consider?
 
What is the rated voltage of heater and the applied voltage? If both are 208 for single element operation at 208 volts you're looking at 4500/208/1.73=12.5 amps. Two 4500 watt elements on a 20 amp circuit would not work.
 
Sounds odd to me but you should double check name plate voltage vs applied voltage as mentioned above. A 240V rated heater running on 208 will be drastically down on power.
 
fastline said:
Sounds odd to me but you should double check name plate voltage vs applied voltage as mentioned above. A 240V rated heater running on 208 will be drastically down on power.
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I will confirm voltage. The only number I saw on the name plate was 4,500 watts. Do I assume that both heating elements are 4,500 watts--which would mean a total usage of 9,000 watts?
 
fastline said:
Sounds odd to me but you should double check name plate voltage vs applied voltage as mentioned above. A 240V rated heater running on 208 will be drastically down on power.
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Often the elements can be replaced to change voltage. Some even have a jumper for that purpose.
Adding a second circuit to enable simultaneous use of the two heating elements (the electrician part :) )
might or might not be cost effective, depending on the difficulty.
 
A single 4500W element designed for 208V would draw 4500W/208V = 21.6A. If the elements in there now are designed for 240V, then their resistance is 240/208 = 1.154 times higher than that needed for 4500W at 208V. So the higher resistance and lower voltage reduces the current to 21.6A x (208/240)² = 16.2A. So I suspect they are actually 240V elements running on 208V if the 20A breaker isn't tripping as presently configured. And then a single element would only be dissipating 208V x 16.2A = 3370W, making the customer unhappy.
If both elements are running at the same time then the line conductor connected to both elements would draw 1.73 times higher current than each element, or 1.73 x 21.6A = 37.4A. And even with the lower current draw of 240V elements, 1.73 x 16.2A = 28.0A and so the 10/3 would be a concern for continuous loads.
 
synchro said:
A single 4500W element designed for 208V would draw 4500W/208V = 21.6A. If the elements in there now are designed for 240V, then their resistance is 240/208 = 1.154 times higher than that needed for 4500W at 208V. So the higher resistance and lower voltage reduces the current to 21.6A x (208/240)² = 16.2A. So I suspect they are actually 240V elements running on 208V if the 20A breaker isn't tripping as presently configured. And then a single element would only be dissipating 208V x 16.2A = 3370W, making the customer unhappy.
If both elements are running at the same time then the line conductor connected to both elements would draw 1.73 times higher current than each element, or 1.73 x 21.6A = 37.4A. And even with the lower current draw of 240V elements, 1.73 x 16.2A = 28.0A and so the 10/3 would be a concern for continuous loads.
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You're calculations are for 1Ø these heaters are 3Ø.
 
Im still trying to figure out where the original post said 240V...
only after the voltage is known are any calculations needed..
 
We need more info. Is it a 3ph heater or just a 3ph supply?

We don't know which of the above posts apply to the situation.
 
The customer is complaining of insufficient hot water.

According to another thread, having two heating elements will not solve this problem. Two elements will heat the water faster but will not provide additional capacity. The solution to the problem is to have a larger or an additional water heater to increase capacity.

If this is the case. One would need to consider the cost benefit ratio of modifying the existing setup or adding a new circuit and additional water heater?
 
Greg1707 said:
The customer is complaining of insufficient hot water.

According to another thread, having two heating elements will not solve this problem. Two elements will heat the water faster but will not provide additional capacity. The solution to the problem is to have a larger or an additional water heater to increase capacity.

If this is the case. One would need to consider the cost benefit ratio of modifying the existing setup or adding a new circuit and additional water heater?
Click to expand...

Exactly which tells me either the unit isn't big enough for the demand or is not working correctly.

If demand has not changed significantly and it once did keep up - then something has probably failed. Could have lost an element, lost a voltage on an input lead, malfunctioning control...
 
kwired said:
Exactly which tells me either the unit isn't big enough for the demand or is not working correctly.

If demand has not changed significantly and it once did keep up - then something has probably failed. Could have lost an element, lost a voltage on an input lead, malfunctioning control...
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The salon has had great success and has added additional work stations.
 
Greg1707 said:
The salon has had great success and has added additional work stations.
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How many work stations we talking about and how large of a storage tank does the water heater have? A typical 4500 watt unit with 80 or 120 gallon tank would likely wash a lot of heads before running out of reserve, if 50 gallon or less I can see it may not last too long if there is a lot of demand.

The fact it is three phase doesn't mean much other than it is easier to balance load on the source, 4500 watts heats the same amount of water the same number of degrees regardless of number of phases or voltage. Larger tank however gives you longer lasting reserve .
 
Sounds like a single phase water heater was installed to replace the three phase one. Three phase ones usually have 3 kw increments, and are usually single stage (one thermostat controlling multiple contactors) That is probably why they don't have the capacity. The three phase one was probably a 9 kw unit, with all three elements on when the thermostat calls for heat.
 
Greg1707 said:
The customer is complaining of insufficient hot water.

According to another thread, having two heating elements will not solve this problem. Two elements will heat the water faster but will not provide additional capacity. The solution to the problem is to have a larger or an additional water heater to increase capacity.

If this is the case. One would need to consider the cost benefit ratio of modifying the existing setup or adding a new circuit and additional water heater?
Click to expand...
Running two elements can cut in half the recharge time, or alternately double the recharge rate. If you can get the recharge rate up to match the usage rate in gallons per hour you will have enough hot water.
Depending on the rate at which they use hot water and the number of hours of use per day, increasing the size of the water heater (storage capacity) may not help either, just delay the time when the hot water runs out.
 
hillbilly1 said:
Sounds like a single phase water heater was installed to replace the three phase one. Three phase ones usually have 3 kw increments, and are usually single stage (one thermostat controlling multiple contactors) That is probably why they don't have the capacity. The three phase one was probably a 9 kw unit, with all three elements on when the thermostat calls for heat.
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X2

Roger
 
GoldDigger said:
... Depending on the rate at which they use hot water and the number of hours of use per day, increasing the size of the water heater (storage capacity) may not help either, just delay the time when the hot water runs out. ...
Click to expand...
Hear, here.
The size of the storage tank influences only the first-hour rating. To "solve" this problem with a bigger tank would require a tank so big that its first-hour rating was sufficient for an entire day's service. (plus enough recovery rate to fully recover overnight)

Wouldn't a three-phase water heater have three heating elements?
 
drcampbell said:
Hear, here.
The size of the storage tank influences only the first-hour rating. To "solve" this problem with a bigger tank would require a tank so big that its first-hour rating was sufficient for an entire day's service. (plus enough recovery rate to fully recover overnight)

Wouldn't a three-phase water heater have three heating elements?
Click to expand...
Don't know what is common, but wouldn't necessarily have to. For balanced loading it kind of needs to have some multiple of three of equal rating, but could also have just two elements connected in open delta fashion.
 
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