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Wyome
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Given 4500 watt electric water heater, is it legal to install a 20 amp double pole toggle switch to serve as a disconnect? The load should only be 18.75 amps. 30 amp circuit of course. I can't find where in the code it prohibits this.
 

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I'd check the operating manual first. I've seen water heaters with specs calling for a max OCPD of 25A.

The 10/2 (or 10/3) wire size should be fine, though.
 

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Given 4500 watt electric water heater, is it legal to install a 20 amp double pole toggle switch to serve as a disconnect? The load should only be 18.75 amps. 30 amp circuit of course. I can't find where in the code it prohibits this.
I would think that the disconnect could be a dp 20 although I would use a dp 30. Never thought about using a dp 20. I use an a/c disconnect but I have had to use a switch before and it was a dp30. I know with motors the disconnect must be 115% of the load but I don't see that for water heaters
 

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I would think that the disconnect could be a dp 20
Not if the load is 18.75 amps -- unless it's a 100% rated breaker.

210.20 Overcurrent Protection. Branch-circuit conductors and equipment shall be protected by overcurrent protective devices that have a rating or setting that complies with 210.20(A) through (D).

(A) Continuous and Noncontinuous Loads. Where a branch circuit supplies continuous loads or any combination
of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load.

Exception: Where the assembly, including the overcurrent devices protecting the branch circuit(s), is listed for operation at 100 percent of its rating, the ampere rating of the overcurrent device shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.
 

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Not if the load is 18.75 amps -- unless it's a 100% rated breaker.
Correct-- I was thinking a dp switch is rated at 100% but I am not certain
 

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I don't think a water heater runs for three hours straight
No it doesn't but the NEC considers it continuous as stated above but that does not mean the disconnect must be rated at 125%
 

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There is no requirment for a disconnect in Canada but based on the number of times I get asked I think a lot of Canadian Electricians are reading this thread and applying it to Canada.
 

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BTW 210.20 is for overcurrent protective device not a disconnect.
 

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Likely cheaper than a DP switch anyway
Yes but a lot uglier. I have had some areas where I decided a dp sw in the wall was a much cleaner look. It depends on the situation- 99% of the time it is an a/c pullout.
 
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