277 Volt single phase water heater on 240 volts

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G

g-and-h_electric

Senior Member
Location
northern illinois
Occupation
supervising electrician
I have run into a strange situation. The plumbers installed a replacement 80 gallon electric water heater in a single family residence on Friday. they didnt check the model plate (allegedly they did order a 240 Volt unit). Space is tight and this was the only unit that will fir in the space. AO Smith apparently no longer offers a residential unit that will fit ( I checked the website). The unit is not upper lower sequenced, both elements come on on a call for hot water. The elements are 6100W each, with a specified input of 12.2kW input current.

My question is this: By calculation I am at about 20 amp per element at 240 Volts. As I am in the Chicago area and it is "pipe and wire", do we as a group think I can up size the conductors to #8 , the breaker to a 40 or 50, and have the customer have hot water?

FYI: At this minute the homeowner is kinda pissed ( not at me), and I have dropped this in the plumbers lap. Since the shop I work has the plumbing division that installed this unit I am trying to be helpful and not just do the "it isnt my problem, I didnt install it it" routine.

Any thoughts???? (yes I did tell the plumbing supervisor to check and see if the factory has the "normal" 5 kW elements and sequencing t'stat available. and would this be a warrantable and listed modification (I am not putting my license on the line for their mistake))


Howard
 
Upsizing the breaker and wire size will not have any effect on the heat output.
May produce heat. Approximately 12% below rated voltage.
Not correct. Not per nameplate requirements. Not warrantable.
Not your mistake, yet. Have the plumber install correct water heaters or start looking at some transformer options. Yes , it is your license. 2 wrongs dont make a right.
 
The only problems I see with the OP's approach is using the calculated current rather than the nameplate current, and the possibility that the water heater requires a grounded conductor.

Both of those evaluations appear correct to me (re-rating a resistor to lower voltage is easy, and the heating elements and terminal blocks are probably no different) but both of those calls officially need to be made by the manufacturer.

The additional load at the customer home might also be a problem.

I think the approach of getting the supplier to provide approved modifications is the best approach.

Can you temporarily disconnect the upper heating element to get the customer some hot water with the existing circuit?
 
Just of interest, why does USA have such different voltages ? For the EU we all use the same LV at 230Vac which is more in total capacity than all of USA.
 
Besoeker3 said:
Just of interest, why does USA have such different voltages ?
Click to expand...
History and installed base. We can blame Edison for 110 & 220, which were slowly increased to 120 & 240. When wide-spread three-phase came along, well, 208/120 is compatible with the existing 120 equipment. (When the Los Angeles area converted from 50Hz to 60 in the late 1940s, the utility gave customers "475,000 clocks, 380,000 lighting fixtures, and 58,000 refrigerators" to be compatible. Changing from 110 to 220 for utilization equipment would have to have been started decades before that.)
 
infinity said:
Do you not use 3 phase?
Click to expand...
Yes, of course. Most of my work was for industrial systems - steel mills, paper mills, cement works etc......
Typically it was 400/230 Vac but I also used some odd ball units up to 11 kV.
 
Besoeker3 said:
Just of interest, why does USA have such different voltages ?
Click to expand...
120 volt was always used for convenience receptacles, and portable appliances, but the higher voltages could not be standardized the same way.
Besoeker3 said:
Typically (UK 3 phase) was 400/230 Vac
Click to expand...
National standards require some organization to control the captains of industry, which are detrimentally relied upon to run the USA.

The US confederates challenged president Lincoln, Rockefeller & Carnegie controlled the industry during presidents Grant to Roosevelt, and Al Capone ran the commerce until president Hoover, just like the current mobsters run it now.
 
ramsy said:
120 volt was always used for convenience receptacles, and portable appliances, but the higher voltages could not be standardized the same way.

National standards require some organization to control the captains of industry, which are detrimentally relied upon to run the USA.

The US confederates challenged president Lincoln, Rockefeller & Carnegie controlled the industry during presidents Grant to Roosevelt, and Al Capone ran the commerce until president Hoover, just like the current mobsters run it now.
Click to expand...
But we do have the standard for for the EU. It is 230V for domestic use and 400V for industrial. For what its worth, that single standard is larger than the whole of USA
 
Thank you all so far! :) You have confirmed my personal liability concerns. I did see the conversion kits on "supply house. com" They are a definite possibility. There is 1 thing that concerns me.... the info for the water heater shown on their site (which is the one installed) says it is NOT APPROVED for residential use. (https://www.supplyhouse.com/AO-Smit...tric-Water-Heater-Simultaneous-Operation-277V) I dont know if that is because of the 277 V rating or something else.

At this point I am going to let the plumbing foreman and our company owner sort out the following: 1 what was ordered, 2 what was received according to the carton. 3 verifying ( I want it in writing) that we can convert the heater that is onsite.... If it can be converted, upon seeing a parts order and shipping confirmation, I will re-wire what is there as a temp, and complete the conversion upon receipt of the parts. I want NO personal liability for a non approved conversion.


howard
 
g-and-h_electric said:
Thank you all so far! :) You have confirmed my personal liability concerns. I did see the conversion kits on "supply house. com" They are a definite possibility. There is 1 thing that concerns me.... the info for the water heater shown on their site (which is the one installed) says it is NOT APPROVED for residential use. (https://www.supplyhouse.com/AO-Smit...tric-Water-Heater-Simultaneous-Operation-277V) I dont know if that is because of the 277 V rating or something else.

At this point I am going to let the plumbing foreman and our company owner sort out the following: 1 what was ordered, 2 what was received according to the carton. 3 verifying ( I want it in writing) that we can convert the heater that is onsite.... If it can be converted, upon seeing a parts order and shipping confirmation, I will re-wire what is there as a temp, and complete the conversion upon receipt of the parts. I want NO personal liability for a non approved conversion.


howard
Click to expand...
I have seen 277V 'simultaneous' electric resistance water heaters used in residential for this exact reason, funny shaped space and hi-demand for water.
It had two 25A circuits run the the water heater, 10 AWG wire. one circuit for upper element one for lower.
at 240V each element is a 19.1 amp load.

I am not sure what 'approved for residential use' means, it might have to to with the Energy efficency / insulation of the tank.
 
tortuga said:
not sure what 'approved for residential use' means, it might have to to with the Energy efficency / insulation of the tank.
Click to expand...
The 110.3(B) instructions will only apply to municipal building zones designated R1- R5, not commercial zoning with office occupancy.
 
Besoeker3 said:
Yes, of course. Most of my work was for industrial systems - steel mills, paper mills, cement works etc......
Typically it was 400/230 Vac but I also used some odd ball units up to 11 kV.
Click to expand...
So your residential areas there all have 400/230 y 3P transformers?

How about more rural areas, is there a system with only single phase medium voltage primaries coming off a larger 3p circuit?
 
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I think the "not intended for residential" use can be explained here by UL 174 for residential water heaters vs UL 1453 for commercial water heaters. Type "UL 174 vs UL 1453" into Google and hit the AI deeper dive. The UL 174 residential ends at 12kW and maximum thermostat temperate of 171F. The conversion kit gets you below the 12kW. The next UL difference is the thermostat which, on the commercial unit, can go past 171F.
 
I don't see the manufacturer or model mentioned, but I'm sure they have a parts catalog. See what's different and anything that is different is needed if you want to literally go "by the book".

Now if I got it for free because some plumber installed it and it was wrong. And it was going in my building. I'd make it work
 
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