I have square D QO panel. I am adding a Stiebel 29 on demand water heater and it calls for (3) 50 amp 240V breakers. Can I add a subpanel that has (3) 50 amp breakers to tie into my existing 200 amp service? If so what gauge copper wire would connect the two and does Square D QO make a 150 amp breaker that will fit within the 200 amp box? Please give me your thoughts. Thanks so much!

You can whatever panels or breakers you like, I doubt the 200 amp service will handle the added load. Before you continue you need to have a load calculation done.

Adding a whole house electric water heater to a 200A service is almost never feasible, nor a good idea. An upgrade to 320/400 is almost always mandatory.
This is something the water heater sellers/dealers like to keep from you.

What is required to upgrade the service to 300 amps from 200 amps and is this expensive? I live in Annapolis Maryland and I am a BGE customer. Thanks so much!

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Originally Posted by dukespence

What is required to upgrade the service to 300 amps from 200 amps and is this expensive?

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A call to two or three reputable electricians to get quotes.


Expensive is a relative term.
IMO to spend potentially $4000-$5000 on a 320/400A service upgrade just to install one of those water heaters is absurd.
What would the monetary recoup time be on an investment like that? :rolleyes:

Ask the dealer of the water heater to provide a return on investment analysis. Could be 2 to 7 years to save what you spend.

Price to do yours could range $2K to $8K, and $8K might not be expensive to you.

Be sure quotes include sizing the service, so far your only guessing on the service size.

tkrussell:

Thanks to you and the others! I had an electrical contractor come out and look at my situation as well as the schematic and load requirements for the Steibel 29 water heater. He proposed to install 3 #6 wires to run to the unit (Steibel says wire must be at least #8). He said he would mount a sub with three 50 amp breakers (Steibel says each of the three elements pull a max of 40amp but they say to use three 50 amp circuits) and that he would then place a 125 amp breaker in my 200 amp service to handle the sub. He seemed to know what he was doing. Does this make sense? What if I get it hooked up and it is too much load drain, what would happen? BGE says that I cannot go to two 200amp services as we are 300 yards from their last bump up or something to that effect and that at most I might get 300 amp total. I appreciate all the assistance from everyone!

What is proposed to connect the heater is fine. Will be up to the installer to be liable for the service to handle this additional load, as the electrician is to insure the service is of sufficient size.

Be sure there is some clause in the contract that they will be held responsible.

Thanks again. If my service does not carry the "load"... How will I know? What signs will tell me that I have a problem? Thanks again!

My omly concern other than my last question is that he wants to hookup (3) 50 amp breakers in the sub and then feed that to the main which will have a 125 amp breaker for the sub. Just seems to me it should be a 150 amp breaker installed but he said it should be fine since each of the three zones is supposed to only draw a max of 40 amps each. Is this correct?

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Originally Posted by dukespence

Thanks again. If my service does not carry the "load"... How will I know? What signs will tell me that I have a problem? Thanks again!

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The sign will be the Main Breaker will trip due to overload.

The Main will be subjected to overload current and heat will be created.

Depending on the age of the service additioanl damage may occur to the service.

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Originally Posted by dukespence

My omly concern other than my last question is that he wants to hookup (3) 50 amp breakers in the sub and then feed that to the main which will have a 125 amp breaker for the sub. Just seems to me it should be a 150 amp breaker installed but he said it should be fine since each of the three zones is supposed to only draw a max of 40 amps each. Is this correct?

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Perhaps I spoke too soon and said the plan was fine, I did not do any calcs to confirm.

The feeder circuit should be rated 125% of this, to arrive at the 150 amp feeder circuit.

The electrician should know this. Perhaps he knows the load will not be all on at once.

If a service load calculation was not done, perhaps you need to find an electrician that will do it to confirm the service can handle this load, and size ths subpanel feeder correctly.

The house is 4 years old. I am going to have another electrical contractor come out and look at it. Thanks!

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Originally Posted by dukespence

The house is 4 years old. I am going to have another electrical contractor come out and look at it. Thanks!

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If you have your heart set on installing this water heater, this is a wise decision.

If you can, please get back with the results.

BE SURE, any quote you get INCLUDES confirming the existing service either can handle the additional load of 120 amps, or increases the size of the existing service.