Water Heater - Continuous Load???

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ramdiesel3500

Senior Member
Location
Bloomington IN
Okay, I came across a 4.5KW residential water heater the other day (50 gallon unit). It was fed by a 2P20A breaker. Has worked flawless for several years. First one I have ever seen. My knee jerk reaction was to say it needed to be fed with #10AWG on a 2P30A. However, I was informed that it is NOT a continuous load and therefore is okay at a draw of 18.75 amps. Is this correct???
 

jimkaki

Member
Re: Water Heater - Continuous Load???

Did you pull the covers and check the element rating? We run across a few 20 amp #12 ckts feeds for water heaters where the elements have been changed to 3000 watts. We do the same and change out the 4500 watt elements to 3000 watt.
Best Wishes J.Lockard
 

bphgravity

Senior Member
Location
Florida
Re: Water Heater - Continuous Load???

I don't think a water heater is truly a continuous load per definition. The same goes for fixed electrical space-heating. However both are "considered" as such per the NEC.
 

RUWired

Senior Member
Location
Pa.
Re: Water Heater - Continuous Load???

ramdiesel3500,
article 422.13 requires a branch circuit rating of not less than 125% of the nameplate rating.your 18.75 amps @125% = 23.43 amps requiring #10 awg wire.overcurrent protection is 422.11 ,shall not exceed 150% if not marked and over 13.3 amps. which would be 18.75 x 150%= 28.125 amps.(next higher =30) but only needs to meet the minimum 18.75 amps (20 amp breaker),although call backs can be expected depending on ciruit length and voltage. The big key is to use the 10 awg wire.

Rick
 

mdshunk

Senior Member
Location
Right here.
Re: Water Heater - Continuous Load???

It's hard to find water heaters that will be okay on old, existing 20 amp circuits. Some construction types, and resulting finish materials make it difficult (or nearly impossible) to replace the #12 water heater circuit with a #10. As a result, I see that some plumbers are installing their normal water heater, and changing out the elements to lower wattage ones at the time of installation. When doing service changes, when I find a #12, 20 amp water heater circuit present at the panel, I generally pull the element covers off the water heater to see what I'm working with.
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
Re: Water Heater - Continuous Load???

Rick, welcome to the forum! :)

Originally posted by RUWired:
... but only needs to meet the minimum 18.75 amps (20 amp breaker),although call backs can be expected depending on ciruit length and voltage. The big key is to use the 10 awg wire.
The rating of the branch circuit is determined by the breaker. Therefore, 422.13 requires the 30 amp breaker, not a 20. ;)
 

mario

Senior Member
Location
Alaska
Re: Water Heater - Continuous Load???

I recently finished roughing my son's house and it has a 40 gal 4.5kw water heater ... my standard is #10 and a 2p30 but when I hooked up inside the heater, the name plate called for a 20 amp breaker !! I don't remember the exact wording (son's out of town and can't get in to read it again) but it said something about the internal wiring was sized for 20 amp breaker !! as I said I have #10 but am using a 2p20 ... when I get a chance I will go back and read the plate and get back on with the explanation ... M
 

jimwalker

Senior Member
Location
TAMPA FLORIDA
Re: Water Heater - Continuous Load???

Whe have used 2 pole 30's for as long as i been wiring.What could posabbly go wrong that this would be a problem ? Using a 2 pole 20 is just asking for a service call.
 

RUWired

Senior Member
Location
Pa.
Re: Water Heater - Continuous Load???

George,These forums get you to think,read and interpret. Don't get me wrong ,i would also use a 30 amp breaker. 422.13 is calling for minimum branch circuit conductors,(10 awg). 422.11(e)3 is calling for maximum protection of those conductors,(30 amp).210.20 (a) states that overcurrent protection shall not be less than the noncontinuous ,(18.75), or 125% of the continuous load.Article 100 definitions states continuous loads as 3hr or more.So the question comes back to ramdiesels question is it continuous or not.if it is, then 30 amp breaker would be the minimum.
Rick
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: Water Heater - Continuous Load???

Originally posted by RUWired:
George,These forums get you to think,read and interpret. Don't get me wrong ,i would also use a 30 amp breaker. 422.13 is calling for minimum branch circuit conductors,(10 awg).
Not quite Rick.

2002 NEC
422.13 Storage-Type Water Heaters.
A branch circuit supplying a fixed storage-type water heater that has a capacity of 450 L (120 gal) or less shall have a rating not less than 125 percent of the nameplate rating of the water heater.
422.13 requires the branch circuit to be 125%, not just the conductors.

The rating of a branch circuit is as George mentioned determined by the overcurrent device.

[ February 05, 2006, 06:45 PM: Message edited by: iwire ]
 

RUWired

Senior Member
Location
Pa.
Re: Water Heater - Continuous Load???

Bob,article 100 definition, branch circuit are the circuit conductors between the overcurrent device and the outlet.I know it sounds as if it there talking about breaker but, branch circuit is the conductors.
Rick
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: Water Heater - Continuous Load???

Originally posted by RUWired:
Bob,article 100 definition, branch circuit are the circuit conductors between the overcurrent device and the outlet.I know it sounds as if it there talking about breaker but, branch circuit is the conductors.
Rick
Rick I can not agree with your interpretation.

210.3 Rating.
Branch circuits recognized by this article shall be rated in accordance with the maximum permitted ampere rating or setting of the overcurrent device. The rating for other than individual branch circuits shall be 15, 20, 30, 40, and 50 amperes. Where conductors of higher ampacity are used for any reason, the ampere rating or setting of the specified overcurrent device shall determine the circuit rating.
I respectfully suggest you reconsider your position. :)
 

RUWired

Senior Member
Location
Pa.
Re: Water Heater - Continuous Load???

Bob,i enjoy a good debate,i hope there is no animosity.The opening to 210.3 states that the circuit shall be classified as the maximum being allowed.422.11(e)3 says over 13.3 and not marked,your allowed to go to a maxiumum of 150%.so this would be a mandatory 30 amp breaker.I take back the part that i said about 18.75 amps (20 amp)being the minimum.I read it as if i could make what i wanted up to 150%, but 210.3 says that i have to make it 150%.Just so that we are on the same page ,the second part of 210.3 says , even if we wanted to run #8 wire,itwould still be classified as a 30 amp circuit.
Rick
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: Water Heater - Continuous Load???

Originally posted by RUWired:
Bob,i enjoy a good debate,i hope there is no animosity.
None at all, debate is what we do here. :)

By the way welcome to the forum.

I will get back to this.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Re: Water Heater - Continuous Load???

Originally posted by RUWired: overcurrent protection is 422.11 ,shall not exceed 150% if not marked and over 13.3 amps. which would be 18.75 x 150%= 28.125 amps.(next higher =30) but only needs to meet the minimum 18.75 amps (20 amp breaker)
No. It has to meet the minimum 18.75 times 125%, or a minimum of a 25 amp branch circuit rating (i.e., 25 amp breaker) and a minimum #10 wire.

I include the 125% factor for the following reason:

Run a load of laundry using the "hot/warm" setting. When it's done, run the dishwasher. Half an hour or so later, take a bath (or as we said in the Navy, a "Hollywood shower"). With the size of water heaters commonly seen in households, it is not unreasonable to expect the heating elements to be on for three hours or more. I think that is why the 2005 NEC made this point unmistakably clear. It explicitly states that such a water heater shall be considered a continuous load.
 

RUWired

Senior Member
Location
Pa.
Re: Water Heater - Continuous Load???

Yes Charlie, I misspoke when i said the minimum 20 amps.The 150% i was referring to is the up to maximum allowed for waterheaters not marked with data as to amperage.the 125% being the minimum.
Rick
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
Re: Water Heater - Continuous Load???

I think Rick is onto something.

At first glance, 422.13 appears to conflict with 422.11(E).

One calls for a circuit rating of the appliance rating plus 50%, the other calls for the appliance rating plus 25%. They result in two different OCPD's.

Rick, I maintain that the branch circuit rating is determined by the branch circuit overcurrent protective device, as Bob referenced in 240.3. But what that breaker minimum is does appear to be in question. :confused:
 
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