Water heater breaker sizing

[rgallahorn]

Inspected at home today with 2 titan electric continuous water heaters. Specs call out a maximum of a 54 amp draw. Using a common 20% safety factor, my calculations call for ~65 amp breaker sized then to 70.
Is there a logical explanation for the use of a 60 amp breaker and wiring?

[Paul W. Abernathy]

Whos common safety factor are you using....you own? I would have to see the units and the manual to comment any furthur on it. All the ones I have delt with tell you exactly what size breakers to use.....FYI if they want to use 60A breakers and they dont trip...as that is the real concern.

Now.....going higher simply because of building in a safety factor actually DOES not GIVE you any real safety factor as tripping at 60A would be safer than tripping at 70A...but then again if the water heaters are working with 60A and not tripping......I would be fine with it.

[rgallahorn]

Paul,

Installation instruction do not give specifications on breaker or wiring sizing. The do state a max 54 amp draw though. They do reference a 60 amp and #6 awg as being acceptable in Miami tho. I fully understand nuisance tripping is safer that over sizing. In this case would you size wire for 60 or 70 amp?

[Paul W. Abernathy]

I would be fine with the 60A if they are indeed protecting it with a 60A breaker and it is not causing any problems...then I would have no problem with it.

Unless they used romex......all other is going to be more than likely at the 75 degree terminal rating and the conductor at 75 degree is good for 65A.....and technically the ampacity that conductor can carry safely is 75...technically speaking.....but beyond all that....unless it is romex running to it which should be sized at 60 degree anyway.....I would not have a problem with it.

[Greg Fretwell]

You are talking about an "instant" heater? If so it is not a continuous load (3 hours) so you really only have to size for the max load (54a). I would be curious what the real load is.

[Paul W. Abernathy]

yep.....I think the 60A is perfectly fine....

[Marc D. Shunk]

Were these both being used for domestic hot water? If either was for the pool, the breaker must be sized at 125% of nameplate.

[Greg Fretwell]

Resistive pool heater? eeek!

[Paul W. Abernathy]

I would think they are just Whole House units....I have one in my house and I love it. I can take a hot shower forEVER without it getting cold. I can't imagine living without one but mine is larger...lol...

[Brian A. MacNeish]

Originally Posted by pabernathy

I would think they are just Whole House units....I have one in my house and I love it. I can take a hot shower forEVER without it getting cold. I can't imagine living without one but mine is larger...lol...

If it's electric, how many amps does it draw and did you have to incerease the entrance size just for this item?

[Paul W. Abernathy]

Basically my unit has SPECS and the SPECS said what size to use per the manufacturers instructions. If they provide it that is what you use as the intent is to install it via the Manufactures Intent.

As for sizing the service.....basically they give you guidelines on service sizing as well, in my case which I have a 200A service...there is enough diversity in most all homes that this is not a problem.

heck I have had EVERYTHING on in my home and placed a ampmeter on my service and only drawn 138 amps...so remember most service calculations ( standard method ) is oversized anyway as usually Optional methods are quite smaller because it takes into account diversified loads.

[Brian A. MacNeish]

Originally Posted by pabernathy

Basically my unit has SPECS and the SPECS said what size to use per the manufacturers instructions. If they provide it that is what you use as the intent is to install it via the Manufactures Intent.

As for sizing the service.....basically they give you guidelines on service sizing as well, in my case which I have a 200A service...there is enough diversity in most all homes that this is not a problem.

heck I have had EVERYTHING on in my home and placed a ampmeter on my service and only drawn 138 amps...so remember most service calculations ( standard method ) is oversized anyway as usually Optional methods are quite smaller because it takes into account diversified loads.

Yeah! I've heard but never measured that most average sized houses (without electric heat, but electric hot water, stove and drier- common setup here) with 100 amps service only draw 50-60 amps at most on average.

Did the calculations in the past couple of years for (1) an older 6 unit (1 bedroom) apartment building to be renovated by purchaser (the existing newer 200 amp service was still adequate) and (2) a 5 year old 1592 sq ft all-electric split entry bungalow with 100 amp service. The realtor told me it needed a 200 amp service because it had electric heat!! Tried to tell her on site that chances were better than 95% that this met codes. Did the calcs that night and was able to tell her the next morning that if the buyers need more heat, they could add at least another 2 kW, if desired. She said she'd check with an an electrician .......never heard back from her!

I hear this all the time up here and see many way oversized 150 and 200 amp entrances.

[Frank P. Newman]

Originally Posted by pabernathy

As for sizing the service.....basically they give you guidelines on service sizing as well, in my case which I have a 200A service...there is enough diversity in most all homes that this is not a problem.

heck I have had EVERYTHING on in my home and placed a ampmeter on my service and only drawn 138 amps...so remember most service calculations ( standard method ) is oversized anyway as usually Optional methods are quite smaller because it takes into account diversified loads.

Around here the AHJ requires a 400A service for larger homes, even if space and water heating is gas !! So, I have two 200A panels in my basement - have never measured the total maximum load, but imagine it would likely not be much more than 100A even with both A/C untis running. Go Figure !!

[Paul W. Abernathy]

Amazing they would REQUIRE it as a blanket statement....it would more " PROPER" to demand EC's to provide a load/service analysis versus just doing a 400A blanket statement...which tells me they probably don't know how to calculate the loads in the dwellings in the first place....

I got a class on that....lol.......called EXAM PREP....lol

[Frank P. Newman]

That was my argument as well, but to no avail - but that was 15 years ago. At least they did not require me to install the 400A disconnect next to the meter base as I see on the houses of many houses around here, so I won that one.