Electric Tankless water heater

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  #1  
Old 11-03-06, 09:31 PM
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Electric Tankless water heater

I am installing an electric tankless water heater as part of my garage project. The installation instructions (my wife made me read them) say the unit has two elements each requiring 40 Amp double pole breaker disconnects @ the water heater with a 60 Amp double pole breaker at the main sub-panel for the garage. I plan on running 4/2 copper wg from the main sub-panel to the water heater and recoding (black tape) the white wire black. Is this accepatable or do I need 4/3 wg (stuff is expensive!)....Thanks in advance......
 
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  #2  
Old 11-04-06, 02:56 AM
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I would use the 4/2 and tape the white with black or red tape.
 
  #3  
Old 11-04-06, 04:23 AM
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I hope this is an attached garage. If this is a detached garage, you are not allowed to run a sub panel run and two runs for the water heater from the main panel in the house.
 
  #4  
Old 11-04-06, 07:33 AM
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Would you consider providing the make and model of water heater to us? Maybe even the internet link to the manufacturer website? It is always good to know a little about the equipment and its installation requirements.

Roger
 
  #5  
Old 11-05-06, 06:22 PM
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Yes, 4/2 with w/ black tape relabeling the white wire was my plan as well. racraft- This actually is a detached garage but the water heater is off the garage sub-panel not the main house panel. Sorry I wasn't clear....Thanks again
 
  #6  
Old 11-06-06, 01:26 PM
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Is the panel in your garage on a 60A feeder?

Are you now installing _two_ separate 40A branch circuits into this panel for this single boiler? It sounds to me like this single appliance will overload the feeder to your garage panel. Is there anything in the boiler that prevents both circuits from being used at the same time? What is the KW rating of the boiler?

-Jon
 
  #7  
Old 11-07-06, 04:50 AM
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Actually my garge sub-panel is 100 Amp. The Max amp draw from the water heater is 55 Amps when both heaters are in operation @ max. This heater has contrals as well and I will never have these controls all the way up as our climate does not require it. The manufacturere of the Unit is SETS and they recommend at least a 100 Amp sub-panel....Bill
 
  #8  
Old 11-07-06, 05:32 AM
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Then where does the 4/2 come into play?

If the water heater requires 2 40A circuits, each could be on 8/2.

4ga is not sufficient for a 100A feeder; depending upon wiring method you need 3ga or 2ga. Additionally, you probably need a 4 conductor feeder, so that you can separate ground and neutral.

-Jon
 
  #9  
Old 11-07-06, 10:04 AM
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Originally Posted by winnie
Then where does the 4/2 come into play?

If the water heater requires 2 40A circuits, each could be on 8/2. ...
I just reread the OP and this is my question also. I've installed these and the ones I've done have required separate runs of #8 for each circuit.
 
  #10  
Old 11-07-06, 10:53 AM
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The model I have came with a local disconnect breaker box with two 40 Amp 220v breakers. I am running 4/2 to the disconnect box with a 60 Amp breaker (per instructions) in the sub-panel protecting the entire circuit. The feed for my subpanel from my house main is #2 copper w/g....Bill
 
  #11  
Old 11-07-06, 03:38 PM
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How many amps total does the water heater draw according to the name plate?
 
  #12  
Old 11-07-06, 05:06 PM
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50 amps draw
 
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Old 11-08-06, 06:31 PM
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Question

Kind of late now.... Do you have gas available?
 
  #14  
Old 11-10-06, 06:25 PM
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No gas. I guess I am missing something. Is there something wrong with a 60 A breaker protecting 4/2 wiring to (2) 40 A breakers in a local disconnect panel servicing an appliance with max. amperage of 50 A?.......Other than the fact the 4/2 cost me $250 of course......Bill
 
  #15  
Old 11-10-06, 09:01 PM
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I would have thought only #6 was necessary behind the 60A breaker, but you said your instructions say otherwise. While I consider completely unnecessary, I can't really say to ignore them either. If this was a welding machine, I'd be an expert, and know when to ignore a manual.
 
  #16  
Old 11-10-06, 09:33 PM
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I'm sorry maybe I too am missing something. I'm not quite following why you would have two 40 amp circuit breakers after a 60 amp OCPD in the panel. If the instructions say 50 amps total draw then I'm even more confused as 4 awg copper is good for 85 amps if thhn. A tankless isnt generally considered a continuous load like its counter part the whole house electric storage type water heater. So IMO we are missing something, again if you could supply us with the brand name of that heater of yours it would be a great help.

Roger
 
  #17  
Old 11-11-06, 05:55 AM
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Could the OP be confusing 40amp unfused disconnects with breakers? They can look alike.
 
  #18  
Old 11-17-06, 09:57 AM
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Perhaps I can be of some assistance to the OP. I do happen to have an electric tankless that I have used for almost 2 years now and am very happy with it.

Most electric tankless heaters are constructed with separate elements and each element requires its own dedicated circuit. Mine is constructed this way. It has 3 elements, each on a 60A circuit, however the elements themselves are capable of drawing 50A max, for a total cumulative draw of 150A. However even budgeting for an overdraw in each circuit for a total of 180A, my system can still handle it without a problem.

As I understand the OP, he has a heater with 2 elements, each needing its own circuit with a 40A breaker. His subpanel can handle a maximum of 60A. As is the case with my heater, I suspect the maximum draw of each element to be 25A, hence why the OP responded the maximum was 50A. I've noticed many tankless manufacturers tend to overestimate how much capacity they need, most likely to just give themselves a buffer. I have never once, even when I turned the temperature up to the maximum, seen my heater draw a full 150A with my meter watching the circuit the entire time.

What is probably a more important question to ask the OP is what is the estimated GPM water usage that is anticipated in this setup? 1-2GPM? 4+GPM? If, for example, this heater is only going to be providing hot water for a sink, I would not be too concerned. However if he intends to use this for a shower, then some caution should be exercised here as he could find the heater drawing around 20A for each element. This could potentially trip the breakers serving this heater or even possibly the main breaker on the subpanel.

Good luck, and enjoy the new heater.
 
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