Water Heater Wattage

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mkgrady

Senior Member
Location
Massachusetts
I need to wire a 40 gallon water heater and can't find a wattage rating any where. It is a Ruud PE2S40-2. Even the Ruud website is no help. 40 Gallon seems small so i'm wondering if it will need a typical 240 volt 30 amp circuit. The only electrical spec I can find is that it needs 240 volts. Seems ridiculous that I can't find the wattage.
 
G

G._S._Ohm

Senior Member
Location
DC area
Measure the element resistance. P = V^2/R so it's P = 57600/R
Another way is to use the recovery time. 330 lbs of water heated 70 degrees F in one hour is 23,000 BTU = 6800W.
 
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renosteinke

renosteinke

Senior Member
Location
NE Arkansas
Really ... all this fuss over a few watts?

I have a completely different 30-gal heater, and it uses a 240v 30A circuit. I can't imagine your going wrong with that.

"Worst case" is that you spend an extra $10 on wire and a 2-pole breaker. Chump change.
 
kwired

kwired

Electron manager
Location
NE Nebraska
I would think it would be pretty rare if you ran 10 AWG conductor and later found out it would not be able to be used.

Can't recall ever seeing a "household tank style" water heater that was not 4500 watts (or less) that was smaller than 60 - 80 gallon. If it happens to be 120 volt it is probably no more than 2000 watts - so 10 AWG is still going to work.
 
J

John120/240

Senior Member
Location
Olathe, Kansas
kwired said:
I would think it would be pretty rare if you ran 10 AWG conductor and later found out it would not be able to be used.

Can't recall ever seeing a "household tank style" water heater that was not 4500 watts (or less) that was smaller than 60 - 80 gallon. If it happens to be 120 volt it is probably no more than 2000 watts - so 10 AWG is still going to work.
Click to expand...

kwired has nailed it

I just looked at Whrilpool, 40 gal electric has two 4500 watt elements
 
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Gregg Harris

Senior Member
Location
Virginia
Occupation
Electrical,HVAC, Technical Trainer
(E) Single Non-motor-Operated Appliance. If the branch circuit supplies a single non-motor-operated appliance, the rating of overcurrent protection shall comply with the following:

  1. Not exceed that marked on the appliance.
  2. Not exceed 20 amperes if the overcurrent protection rating is not marked and the appliance is rated 13.3 amperes or less; or
  3. Not exceed 150 percent of the appliance rated current if the overcurrent protection rating is not marked and the appliance is rated over 13.3 amperes. Where 150 percent of the appliance rating does not correspond to a standard overcurrent device ampere rating, the next higher standard rating shall be permitted.
4500 watts = 18.75 amps

18.75 X 1.25 = 23.44

18.75 X 1.5 + 28.125

28.125 = maximum over current device would be 30 amp fuse or breaker
 
kwired

kwired

Electron manager
Location
NE Nebraska
Gregg Harris said:
(E) Single Non-motor-Operated Appliance. If the branch circuit supplies a single non-motor-operated appliance, the rating of overcurrent protection shall comply with the following:
  1. Not exceed that marked on the appliance.
  2. Not exceed 20 amperes if the overcurrent protection rating is not marked and the appliance is rated 13.3 amperes or less; or
  3. Not exceed 150 percent of the appliance rated current if the overcurrent protection rating is not marked and the appliance is rated over 13.3 amperes. Where 150 percent of the appliance rating does not correspond to a standard overcurrent device ampere rating, the next higher standard rating shall be permitted.
4500 watts = 18.75 amps

18.75 X 1.25 = 23.44

18.75 X 1.5 + 28.125

28.125 = maximum over current device would be 30 amp fuse or breaker
Click to expand...

My understanding is OP is "roughing in" a cable at this time and does not have the exact specification of the unit. He is not as concerned at this point about overcurrent protection as he is with "minimum conductor ampacity" needed. He could, if he wishes, install a 75 amp conductor, and still protect it at 30 amps later if the appliance rating calls for 30 amp max overcurrent protection. It is harder to install a 30 amp conductor now and find out later it should have been at least 35 amps.
 
david luchini

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
kwired said:
My understanding is OP is "roughing in" a cable at this time and does not have the exact specification of the unit.
Click to expand...

mkgrady said:
I need to wire a 40 gallon water heater and can't find a wattage rating any where. It is a Ruud PE2S40-2. Even the Ruud website is no help.
Click to expand...

The OP has the spec on the unit, just couldn't find a wattage on the Ruud website.

I think he just didn't look hard enough. The spec sheet on the Ruud website shows two 4500W elements - non-simultaneous operation, as Hv&Lv pointed out.
 
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mkgrady

Senior Member
Location
Massachusetts
kwired said:
My understanding is OP is "roughing in" a cable at this time and does not have the exact specification of the unit. He is not as concerned at this point about overcurrent protection as he is with "minimum conductor ampacity" needed. He could, if he wishes, install a 75 amp conductor, and still protect it at 30 amps later if the appliance rating calls for 30 amp max overcurrent protection. It is harder to install a 30 amp conductor now and find out later it should have been at least 35 amps.
Click to expand...

Bingo
 
kwired

kwired

Electron manager
Location
NE Nebraska
david luchini said:
The OP has the spec on the unit, just couldn't find a wattage on the Ruud website.

I think he just didn't look hard enough. The spec sheet on the Ruud website shows two 4500W elements - non-simultaneous operation, as Hv&Lv pointed out.
Click to expand...

He maybe didn't look hard enough, but since he didn't find what he was looking for he came here for suggestions.

Add: I guess he had a specification that consisted of a model number, but did not have/find specifications he was looking for that apply to that model.
 
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mkgrady

Senior Member
Location
Massachusetts
kwired said:
:slaphead: I never clicked on the link, until now.:slaphead:
Click to expand...

I had already clicked on the link and determined that wattage was not on the chart. Silly me I should have looked closer but I had already determined that it wasn't there the first time I looked. Thanks for all the responses
 
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