On-demand water heater

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frofro19

Senior Member
Location
VA.
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Master Electrician
Ran into a situation at a church where the 17 kw on-demand water heater was switched out for a 14 kw heater. The original heater was on 2 double 40 amp breakers and the new heater was calling for one double pole 60 amp breaker. It was hooked up splitting the 2 elements by using the existing wire on 2 double 40 amp breakers. I advised it should be on one 60 amp breaker. I wasn't sure if both elements in an on-demand come on at the same time or not. Is there any issue leaving like it is, or should I tell them it needs to be changed? If one breaker trips, then all the currect, (58 amps) would be on the other breaker which should cause it to trip as well.
 
What is the voltage at the church? Is it 3 phase or single phase? At what voltage is the water heater rated 14kw?
 
What is the voltage at the church? Is it 3 phase or single phase? At what voltage is the water heater rated 14kw?
Pretty sure it's 120/240 single phase at the church. I believe the name plate stated 208/240. I contacted the pastor and told him I would change it out for him.
 
Likely needs to be rewired as well. You can’t parallel 8s!
The panel is next to the water heater so I told him it would be an easy fix to run the correct wire of 6 Cu on a 60 amp breaker. Told them I would donate all materias and labor to do it correctly.
 
Pretty sure it's 120/240 single phase at the church. I believe the name plate stated 208/240. I contacted the pastor and told him I would change it out for him.
If the nameplate is 208/240 then the wattage is different at the different voltages. For instance if the water heater is 14kw at 240 v then you have 14kw. If the voltage is 208 then the wattage of the element would be about 75% of 14000 or 10,500 watts.

If it is 14kw at 208V then it will be18,666 watts at 240v
 
If the nameplate is 208/240 then the wattage is different at the different voltages. For instance if the water heater is 14kw at 240 v then you have 14kw. If the voltage is 208 then the wattage of the element would be about 75% of 14000 or 10,500 watts.

If it is 14kw at 208V then it will be18,666 watts at 240v
It's my understanding that it's 14kw based on 240 volts.(I could be wrong). I'll take a closer look when I change it out.
 
If the heater is designed for a single 60 amp circuit then that is what needs to be used. Leaving it as is with 2-40 amp circuits is not an option.
 
Thread got me thinking along this line of reasoning. I am NOT a code guru.

Of course, the code does NOT allow parallel 8 AWG, the reasoning being the probability that 2 parallel on the same OCPD could allow unequal currents and overheating.
Now, with a 40A OCPD on each 8 AWG, what is the problem? Worst case scenario is if one is half again as long it might end up tripping both breakers, but length probably within 5%.
What would be the specific code section (other than not doing EXACTLY what the mfg install sheet says) that would not allow such a hookup? This is assuming you DO label the load as being fed from 2 sources.

This is analogous to feeding one critical load from 2 separate panels, as done for clean room fans, critical hospital loads, and such. All labeled per code of course.
 
Thread got me thinking along this line of reasoning. I am NOT a code guru.

Of course, the code does NOT allow parallel 8 AWG, the reasoning being the probability that 2 parallel on the same OCPD could allow unequal currents and overheating.
Now, with a 40A OCPD on each 8 AWG, what is the problem? Worst case scenario is if one is half again as long it might end up tripping both breakers, but length probably within 5%.
What would be the specific code section (other than not doing EXACTLY what the mfg install sheet says) that would not allow such a hookup? This is assuming you DO label the load as being fed from 2 sources.

This is analogous to feeding one critical load from 2 separate panels, as done for clean room fans, critical hospital loads, and such. All labeled per code of course.
The only issue I see is whether the manufacturer gives instructions for separating the heater load into two independent circuits, not necessarily in phase. Unauthorized mods to the equipment should not be allowed by the inspector if he becomes aware of it. If he passes it you may still have liabilty if problems arise.
 
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