Water Heater OCP

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So the consensus is that this water heater is permitted to be supplied by a 2-pole 30 amp CB due to 422.11(E)(3)? That's the way I read it. Sounds like he should cancel the order for the 440 CB's. :rolleyes:
 
William1978 said:
What size OCP are the rest of you putting on a water heater in a dewelling that has a total connected load of 3500w @ 208?
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I looked for a 208-volt single-phase rated water heater and didn't find one. I also looked in the Grainger catalouge for 208-volt replacement elements and didn't see one. I am currently under the influence, but I believe I did a reasonable search.

This begs the questions:

Is this a true 3500 watt unit at 208-volts?

If not, is it a 3500 watt unit at 240-volts?
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William1978 said:
Now that you said that it refreshed my memory and its 3500w @ 240v and 3380w @ 208v
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unless I missed my math, that would be 4500 @240 = 3380 @ 208, a common element
which would take us back to a 25 amp max
3380/208x1.5=24.375
 
My interpretation is:

3380 @ 208= 16.25A

422.10(A) requires a continuously loaded appliance to be no less than 125% of the marked rating. 422.13 confirms a hot water heater is continuously loaded.

Therefore:

16.25 x 125%= 20.3A so a 25 is acceptable

If you still use the 3380 as the rating @ 208 then apply 422.11(E)(3) then:

16.25 x 150%= 24.4A so 25 is acceptable and required. No 30A on this circuit with the 3380 rating @ 208. If you use 3500W then that is another story and 30A is OK

Bottom line. What does the data plate actually say?
 
Just went out to the truck to look at my notes and the element is 3380w @ 208v, and I don't know what the wattage is at 240v.
 
William1978 said:
Just went out to the truck to look at my notes and the element is 3380w @ 208v, and I don't know what the wattage is at 240v.
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Who cares if it does not show 240. It is installed in a 208 system.

In that case. No smaller than 25A and no larger than 25A.

30A is a no go @ 3380W
 
Ok, help me out here!! I just do NOT see how you can say a MAX of 25 amp breaker is allowed on a that 3380w water, or a 3500w water heater, unless the instructions specify a max in ocp. So long as the cicuit/wire is big enough whats the problem?? Ive read the NEC 2005 422.10 (A) AND 422.11(f)(3)

AS for the continuous loads calculations are at least for 3 hours, does this water heater really be HEATING for 3 hours straight. Mine doesn't do that, heats for a while (2 at the most) then stops (depending on the temperture you set it at). Help me out here??
 
Water heaters are considered continuous loads because 422.13 says so.

3380 W @ 208 volts would be
4500 W @ 240 volts
 
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brother said:
Thanks for the info!! I had missed that. But im still confused with the max ocp, is there another article ive missed in the NEC 2005??
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Actually there was a math error in that original post. I corrected it. The answer for 240 volts is 4500 watts not 3900. :smile:
 
hardworkingstiff said:
I looked for a 208-volt single-phase rated water heater and didn't find one. I also looked in the Grainger catalouge for 208-volt replacement elements and didn't see one. I am currently under the influence, but I believe I did a reasonable search.

This begs the questions:

Is this a true 3500 watt unit at 208-volts?

If not, is it a 3500 watt unit at 240-volts?
​
Click to expand...

hardworkingstiff said:
<deleted>

Edit: Oops, my bad. Sorry Pierre. I was confused. It seems that William is the AHJ rep.
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OK buddy time to put down the key board and show us your license and registration, may be a citation for PWI. :D
 
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