Hey Guys, I’m wiring a Bosch electric tankless water heater at my cabin and I’m not sure which double pole breakers to buy. This is what it calls for:
2 x 240V AC
Amperage 2 x 40 A
Maximum output 17.25 kW
It’s a Homeline main panel, do I get two double pole breakers that are ganged 20amp breakers or two ganged 40 amp breakers?
Are the 40 amp double poles actually 20 amps on each hot leg?
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Replies
>> .....Amperage 2 x 40 A....<<
That would be a 2 pole breaker -- each pole will be 40A.
Not positive on Homeline, but on Square-D QO style breakers, it would have a single handle, which trips or resets both poles simultaneously, with "40" on the handle.
Edit: reread your OP, 17.25kw - sounds like you need 2, 2 pole 40 amp breakers (breakers same description as above, just need 2 of them).
17.25 kw = 17,250 w = 71.875A @ 240v or 143.75A @ 120v --- so, yes there would be 4 poles involved at 120v per pole.
Jim
Edited 7/28/2009 6:52 pm ET by JTC1
Thanks for the info. I went on the Square D site and tried to determine which Homeline two poles to get. They look like two single poles stuck together with a bracket that reaches across and trips both levers at the same time. Not the single lever that takes up the double space. Wish I could get a picture. Both lever heads read "40" or "20" etc. My concern is if I get the 40 amp 2 pole I'll actually be supplying 80 amps per breaker? Total of 160 amps to my 80amp water heater?
No, the ganged (double-pole) 40A breaker is what you want (two of). It supplies 40A at 240V. Whether it's a single visible lever or two levers with a bar joining them it's still the same.
As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz
>>My concern is if I get the 40 amp 2 pole I'll actually be supplying 80 amps per breaker? Total of 160 amps to my 80amp water heater?<<
No, using 2 - 2 pole, 40A breakers you will be supplying 80A @ 240v which is exactly what the specs call for.
80A @ 240v = 160A @ 120v - the specs you provided indicate 80A @ 240v, fed by two breakers.
Refer to the equation below which shows your heater requires 71.875A @ 240v:
17.25 kw = 17,250 w = 71.875A @ 240v or 143.75A @ 120v --- so, yes there would be 4 poles involved at 120v per pole.
As others have said / warned -- be sure the "cabin" electrical service is up to the task. FYI, typically you would need to be running #8 copper to supply the heater from the breakers when protected at 40A.
JimNever underestimate the value of a sharp pencil or good light.
Also make sure your wire is big enough to handle the load & trip the breaker before the wire melts.
A 40-amp double-pole breaker is 40 amps on each leg.
It sounds, though, as if this water heater requires TWO separate 40A 240V circuits -- 80A total. So you need TWO separate double-pole 40 amp breakers.
Note that many "cabins" are likely only wired for 100-150A total (and I'm sure that there are more than a few that are only wired for 60A), so 80A is a heck of a lot of juice. Unless the main breaker is --at least-- 150A I wouldn't advise installing this unit. (And you may find that the panel won't support two 40A double-pole breakers anyway.)
Here is a link to the Bosch electirc tankless water heaters manuals webpage:
http://www.boschhotwater.com/HelpfulResources/BrochuresManuals/tabid/354/Default.aspx
Whcih model are you installing?
Below is an example of what specs might look like:
***Note that for the model in this example, they are calling for 3 double-pole 40 breakers with a total of six # 8 conductors and a ground. Also note that for this particular model they recommend 200 amp service. Again, I'm not sure which model you actually have.
Bosch RP27PT Powerstream Pro Electric Tankless Water Heater Specifications:
• Efficiency - 94%
• Weight - 22 lbs.
• Dimensions - 15¼" x 15½" x 4½"
• Water Fittings - ¾" male NPT
• Volts - 240
• Kilowatts - 26.85kWh
• Amps -
o US: 120 (3 x 40 amps)*
o CANADA: 120 (1 x 120 amps)**
• Wire Size -
o US: 8 gauge (6 conductors & ground)
o CANADA: 2 gauge (2 conductors & ground)**
• Phase - Single
• Minimum Flow Rate at Given Temperature Rise -
o 45ºF Rise 4.0 gpm***
o 50ºF Rise 3.7 gpm
o 60ºF Rise 3.0 gpm
o 70ºF Rise 2.6 gpm
o 80ºF Rise 2.2 gpm
Average ground water temperature in the United States is 55ºF.
NOTE: The unit will not provide an output temperature above 131ºF.
* Minimum recommended service for the RP27PT is 200 amps
** In Canada unit must be wired to a single breaker. AE Canada Kit required and included. Always check local codes.
*** gpm = Gallons Per Minute
Details and Features
"Preach the Gospel at all times; if necessary, use words." - St. Francis of Assisi
No, I didn't vote for him; but he IS my president. I pray for the his safety, and the safety of his family every day. And I pray that he makes wise decisions.
Edited 7/29/2009 7:02 am ET by SteveInCleveland
Edited 7/29/2009 7:02 am ET by SteveInCleveland
Edited 7/29/2009 7:03 am ET by SteveInCleveland
Thanks Steve,I've got a refurbed AE 115 which takes the two double pole 40's. It draws 17.25 kw = 17,250 w = 71.875A and I'm mounting it two feet from the main panel.So with the unit set on max it shouldn't draw more than 72A which leaves me 28A to play with in the 100 amp panel. It's not ideal and it may not work but I'm going to give it a shot. Bringing in more amps to a remote location wouldn't be worth it. A smaller tankless electric just wouldn't cut it.The plan is to power down the AC or the Furnace and go with minimum fluorescent lights in the 600 sqft place while taking showers. We only use the place 30-40 nights a year.I wonder if I can swap the 100A main breaker for a 125A or a 150A if need be. How would I judge what the drops are bringing in? Wire size?
One issue with electric tankless is that since they draw large amounts of current there is considerable voltage drop issues. This means you will more than likely experience dimming of lights. What may compounds the problem is that you may be many many feet from the supply transformer.
You can not increase the size of the main breaker beyond that of the service entrance conductors that supply your panel.
I don't want to be a nay sayer but there have been many people who thought electric tankless would be a good idea then ripped them out when it didn't work.
There are articles on line with regard to sizing electric service with electric tankless, a search may help decide if you really want to do it.
<!----><!----> <!---->
MODEL<!----><!---->
AE115<!----><!---->
<!----> <!---->
Efficiency<!----><!---->
90%<!----><!---->
<!----> <!---->
Weight<!----><!---->
20 lbs.<!----><!---->
<!----> <!---->
Dimensions<!----><!---->
15½"x15¼"x4½"<!----><!---->
<!----> <!---->
Water Fittings<!----><!---->
¾" male NPT<!----><!---->
<!----> <!---->
Volts<!----><!---->
240/208v<!----><!---->
<!----> <!---->
Kilowatts<!----><!---->
17.25/13 kW<!----><!---->
<!----> <!---->
Amps*<!----><!---->
80<!----><!----><!---->US<!----><!---->: 2x40 ampsCAN: 1x80 amps<!----><!---->
<!----> <!---->
Wire Size<!----><!---->
US: minimum #8 AWG(4 conductors & ground)<!----><!---->Canada<!----><!---->**: minimum #4 AWG(2 conductors & ground)<!----><!---->
I'd recommend having an electrician assess whether existing supply wiring to the panel can handle a bigger main breaker. I did read that they recommend minimum 150 amp service for your AE115 model. From some of the reconditioned prices I saw online, you could give your current configuration a shot and see how it goes. For a getaway place, it may be fine.
Where are you located? Also noticed they recommend the model AE125 for northern climates. See attached photo chart. But again, for a getaway place, it may be fine.
it said.... NOTE: AE115 is not recommended in climates where average annual ground water temperature is less than 60°F.
"Preach the Gospel at all times; if necessary, use words." - St. Francis of Assisi
No, I didn't vote for him; but he IS my president. I pray for the his safety, and the safety of his family every day. And I pray that he makes wise decisions.