Electric water heater question

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olc

Senior Member
Is a tank type electric water heater a "continuous load"?

The real question is - Can a 4500W water heater be connected to an existing 20A, 240V (1ph) circuit? (18.75A?)
 

luckylerado

Senior Member
422.13 Storage-Type Water Heaters
A fixed storage-type water heater that has a capacity of 450 L
(120 gal) or less shall be considered a continuous load for the
purposes of sizing branch circuits.


Also consider that you are assuming 240V when in reality it may measure lower. If it is in reality 220V then your math no longer works.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Is a tank type electric water heater a "continuous load"?

The real question is - Can a 4500W water heater be connected to an existing 20A, 240V (1ph) circuit? (18.75A?)

isn't the continuous load issue only a matter of the conductor ampacity? so could you have a 20A circuit as long as the wires were #10 and the CB was 100% rated? Not like you can find a small 100% rated CB as far as I know.
 

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
I would do 10 AWG conductor 25A OCPD

But the 20Amp OCPD may and will probably hold for short period of time. "short" will be interpreted differently.

The closer the current gets to 20A the faster OCPD will trip. I am sure you know that breakers are rated for 80% of their value. So the 20Amp will hold at 16Amps.
 

bphgravity

Senior Member
Location
Florida
422.10 Branch-Circuit Rating. The branch-circuit rating for an appliance that is a continuous load, other than a motor-operated appliance, shall not be less than 125 percent of the marked rating, or not less than 100 percent of the marked rating if the branch-circuit device and its assembly are listed for continuous loading at 100 percent of its rating.

422.11 Overcurrent Protection. Appliances shall be protected against overcurrent in accordance with 422.11(A) through (G) and 422.10.
(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:
(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.
 

jumper

Senior Member
422.10 Branch-Circuit Rating. The branch-circuit rating for an appliance that is a continuous load, other than a motor-operated appliance, shall not be less than 125 percent of the marked rating, or not less than 100 percent of the marked rating if the branch-circuit device and its assembly are listed for continuous loading at 100 percent of its rating.

422.11 Overcurrent Protection. Appliances shall be protected against overcurrent in accordance with 422.11(A) through (G) and 422.10.
(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:
(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.

Bryan, I think Lucky nailed it with 422.13.
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
422.13 Storage-Type Water Heaters
A fixed storage-type water heater that has a capacity of 450 L
(120 gal) or less shall be considered a continuous load for the
purposes of sizing branch circuits.


Also consider that you are assuming 240V when in reality it may measure lower. If it is in reality 220V then your math no longer works.

Being a resistive load, the current would drop. If 18.75 amps at 240, it would only be 17.19 amps at 220.
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Canada yes, US no.

I think this is one of the silliest rules ever made for resi, but technically the code requires this to be considered continuous.

#10 and a 25 amp breaker would be complaint.
 

olc

Senior Member
422.13 Storage-Type Water Heaters
A fixed storage-type water heater that has a capacity of 450 L
(120 gal) or less shall be considered a continuous load for the
purposes of sizing branch circuits.


Also consider that you are assuming 240V when in reality it may measure lower. If it is in reality 220V then your math no longer works.

Thanks. I was not aware of that paragraph. (I did look for something but did not see it.)

I'm curious where you get 220V?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Is a tank type electric water heater a "continuous load"?

The real question is - Can a 4500W water heater be connected to an existing 20A, 240V (1ph) circuit? (18.75A?)


IMO, you cannot use a 20 amp cir. Minimum overcurrent protective device can be 25 amps but you could also use a 30 however the conductor must be #10.

Look at 422.11 (E) as stated above
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
I would do 10 AWG conductor 25A OCPD

But the 20Amp OCPD may and will probably hold for short period of time. "short" will be interpreted differently.

The closer the current gets to 20A the faster OCPD will trip. I am sure you know that breakers are rated for 80% of their value. So the 20Amp will hold at 16Amps.

A 20A circuit breaker will hold at 20A indefinitely.
 

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
A 20A circuit breaker will hold at 20A indefinitely.

You are referring to 100% rated circuit breaker?

Or you are saying if we have a 20Amp continuous load on 20Amp circuit breaker we don't worry about the 80%rule? because the breaker will hold for more than 3 hours?
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
You are referring to 100% rated circuit breaker?

No

Or you are saying if we have a 20Amp continuous load on 20Amp circuit breaker we don't worry about the 80%rule? because the breaker will hold for more than 3 hours?

No, you can't put a 20A continuous load on a 20A circuit breaker because of 210.20. If you did, the breaker would hold indefinitely, but you'd be violating the Code.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
You are referring to 100% rated circuit breaker?

Or you are saying if we have a 20Amp continuous load on 20Amp circuit breaker we don't worry about the 80%rule? because the breaker will hold for more than 3 hours?
A 20A breaker will carry 20A all day and all night. 80% is just a rule used in certain areas of the code.
 

readydave8

re member
Location
Clarkesville, Georgia
Occupation
electrician
I see a lot of water heaters on 12 gauge-20 amp circuits. Mobile home water heaters often or usually have 3500 watt elements. When HO changes, he buys regular residential type with 4500 watt elements because they are cheaper.

The ones I see usually worked for a few years and then started tripping 20 amp breaker. Usually drawing 18 amps or less.

So why do I run across this average twice a year, 30 amp breaker hardly ever?
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
I see a lot of water heaters on 12 gauge-20 amp circuits. Mobile home water heaters often or usually have 3500 watt elements. When HO changes, he buys regular residential type with 4500 watt elements because they are cheaper.

The ones I see usually worked for a few years and then started tripping 20 amp breaker. Usually drawing 18 amps or less.

So why do I run across this average twice a year, 30 amp breaker hardly ever?

Any other heavy use circuits that are near by?
 
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