Water Heater OCP

3500 watt water heater 30 amps.

3500/208x1.5=25.24 amps next size up 30 amps

3380 watt water heater 25 amps.

3380/208x1.5=24.38 amps next size up 25 amps.

422.11 (E) (3)

 

3500 watt water heater 30 amps.

3500/208x1.5=25.24 amps next size up 30 amps

3380 watt water heater 25 amps.

3380/208x1.5=24.38 amps next size up 25 amps.

422.11 (E) (3)

Wouldn't you drop the .24? Then it would match a standard overcurrent device ampere rating.

 

Water Heater OCP

Maybe, and I probably would, put in the 25, but I feel an inspector must go by the wording in the code. 25.24 is above 25 and the code allows me to go up to the next standard, I know its splitting hairs but that is what the code says. If I don't have a 25, I'll put in the 30.

220.5 (B) allows the installer to drop a fraction of an amp but does not require it.

 

3500/208 = 16.8269......
16.8269 * 1.5 = 25.24.

Drop the .24 because it's less than .5 and I'd slap a 25A DP breaker in that beeotch.

Just by example if it were 25.6 then a 30A is an option, but a 25A would be ok too.

 

3500/208 = 16.8269......
16.8269 * 1.5 = 25.24.

Drop the .24 because it's less than .5 and I'd slap a 25A DP breaker in that beeotch.

Just by example if it were 25.6 then a 30A is an option, but a 25A would be ok too.

I agree 100%

 

Soo, While Gill and Bill are out running around for your 25A breaker....
I'll slap in a 30A on those 2 # 10s' and be on my way!:thumbsup:

 

Who in the hell is Bill?

 

Its time to watch the Tarhell game. :thumbsup:

 

Tarheel game my butt, I just got home 2 hours ago and just now had time to lay down! Dangit I'm resting up for the competition tomorrow.

 

Why are you guys multiplying by 1.5%?

Isn't it 1.25%?

 

You are right it should be 150% and I think most of us are using that.

 

30 amp, #10 wire. Remember, the OCD protects the wiring, not the device.

 

So if I pulled a #8 wire I could put it on a 50A?

 

I believe the OP is referring to a standard 4500 watt water heater.

At 240 volts, 4500 watts = 18.75 amps. X 1.25=23.4 amps. In this case, I use #10's and a 25 amp breaker.

The same unit operated at 208 volts will consume 3380 watts, and draw 16.25 amps. 16.25 X 1.25 = 20.3. According to 220.5 (B), you're allowed to drop the fraction if it's less than 0.5 In this case I use a 20 amp breaker and #12's.

I was called on this once by a highly respected inspector, and had to provide code references, but I think he already knew the answer, and was just testing me.

Around here, no disconnect is required for anything except an outdoor HVAC unit on residential. On commercial/industrial, you'll need a disconnect if you can't see the panel from the water heater. I usually use the 30 amp pull-out A/C disconnects.

Rob

 

I believe the OP is referring to a standard 4500 watt water heater.
The same unit operated at 208 volts will consume 3380 watts, and draw 16.25 amps. 16.25 X 1.25 = 20.3. According to 220.5 (B), you're allowed to drop the fraction if it's less than 0.5 In this case I use a 20 amp breaker and #12's.

I was called on this once by a highly respected inspector, and had to provide code references, but I think he already knew the answer, and was just testing me.

Micro, I don’t see a problem with how you’re doing it, especially since in this case that .3A is virtually nothing, but as usual, the code seems less than homogenous about this.
Some other less congenial inspector may call you on it again someday, as it could be argued that 422 replaces 220 for appliance branch circuits and the text of 220.5 that allows the dropping of less than .5A for branch circuit and feeder sizing is not mentioned for sizing appliance branch circuits in 422.10.
Also, since according to 422.11[e], the OCP is sized from the rating of the appliance, not the branch circuit, again that .3A would have to remain for minimum sizing of the OCP.
Since you would probably want to go to the next standard size up as allowed by 240.4, you would most likely end up with #10 and 25A OCP for the 208V water heater.
Anyway, keep your sword at the ready just in case.

 

Interesting. I don't use disconnects at HW heaters, but I sort of figure my circuits by using the ampacity of a 30 amp circuit, then build it. Heck, I don't know that I've lately seen a 25 amp double pole breaker, but I sure have seen plenty of 30 amp DP breakers.

 

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The OP also said 3380. This is the wattage of a standard 4500 watt 240 volt element operated at 208 volts.

Rob

 

That is correct. I don't see how the wattage can be different for the same 208 voltage.