Manufacturer vs NEC

[Butta Dawg]

I have a contractor installing a water heater. The link provided here shows the specific one.

QR Code

www.wh1.co

I took a look at the nameplate rating. It states 208v/240v, and at 240v, it requires 25A. (Really 25.4 or some decimal) regardless, I said at 125% of that would be 31.25A, were looking at #8's and a 40A breaker. But the manufacturer states on the name plate, max breaker to be used, 30A. For me, follow the NEC. But the contractor states they've done 100s of these on 30A breakers and #10s. I'm concerned, and they already installed it

 

[LarryFine]

I would use #10 on 30a with no hesitation.

 

[Eddie702]

From your link both the install manual and the spec sheet say to use a 30-amp circuit. Don't know about the nameplate.

 

[ramsy]

I'm concerned, and they already installed it

Look at Table 310.16. See insulation types limited to 60C; everything else for #10cu is good for 35A @ 75C.

 

[infinity]

Look at Table 310.16. See insulation types limited to 60C; everything else for #10cu is good for 35A @ 75C.

I don't see how you can use #10 AWG for a 35 amp circuit for a water heater due to 240.4(D)(7).

 

[roger]

IMO I would go with 110.3(B)

 

[infinity]

I took a look at the nameplate rating

Can you post a photo of the nameplate?

 

[ramsy]

I don't see how you can use #10 AWG for a 35 amp circuit for a water heater due to 240.4(D)(7).

The circuit breaker only sees a 25.4A load, per post #1 nameplate, even after 125% is applied.

 

[infinity]

The circuit breaker only sees a 25.4A load, per nameplate, even after 125% is applied.

How does that override the limits of 240.4(D)(7) for this type of load?

240.4(D) Small Conductors.
Unless specifically permitted in 240.4(E) or (G), the overcurrent protection shall not exceed that required by (D)(1) through (D)(7) after any correction factors for ambient temperature and number of conductors have been applied.

240.4(D)(7) 10 AWG Copper.
30 amperes

 

[NEC Inspector]

Go with the manufacturer. A smaller breaker is safer, and if it caused constant nuisance trips, they would not have that in their install manual.

 

[ramsy]

240.4(D)(7) 10 AWG Copper.
30 amperes

I believe 24A is less than 30A, unless I’m doing something wrong.

 

[infinity]

I believe 24A is less than 30A, unless I’m doing something wrong.

everything else for #10cu is good for 35A @ 75C.

My point is that you cannot protect the #10 conductors at 35 amps.

 

[ramsy]

My point is that you cannot protect the #10 conductors at 35 amps.

Looks like 422.13 wont let me size breaker to nameplate 24A.

If breaker & wire must be sized 125% of water heater rating, then code wont agree with MFG instructions. A discrepancy of 1 Amp over 30.

 

[jes25]

I highly doubt the manufacturer instructions from a reputable company like AO Smith and NEC are in conflict. I would like to see the actual nameplate for the WH

 

[Little Bill]

Maybe the fact the WH is a heat pump type causes it to go under the rules for compressors. Meaning they can use a larger breaker for smaller conductors. MCA & Max breaker

 

[Butta Dawg]

Apologies, I took a closer look today than the other day. I had to pick up my daughter and glanced at the name plate for seconds before I had to leave while they worked on it. Looks like the working load without a locked rotor is 21.03 amps. 4500watt element=18.75 + 1.78A compressor + .05A fan x125% is 26.28A.

The locked rotor situation of 11A would trip the breaker, which is the reasonable course of action.

Interesting conversation my lack of prior information caused though. Appreciate the help everyone

 

[Eddie702]

As I said above. The MFG spec sheet and the install manual say to use a "30 amp circuit"

 

[jaggedben]

Apologies, I took a closer look today than the other day. I had to pick up my daughter and glanced at the name plate for seconds before I had to leave while they worked on it. Looks like the working load without a locked rotor is 21.03 amps. 4500watt element=18.75 + 1.78A compressor + .05A fan x125% is 26.28A.

The locked rotor situation of 11A would trip the breaker, which is the reasonable course of action.

Interesting conversation my lack of prior information caused though. Appreciate the help everyone

I was going to say, 25.8 on the label is the minimum circuit amps, not the actual load. Your calculation is off, you evidently put 0.5 instead of 0.05 for the fan. When corrected that calc comes to 25.8A (rounded off). So now you see that the 25.8A min circuit ampacity already includes the NEC required 125% factor.

It's never going to use that much continuously anyway! It has a thermostat! It's rarely if ever going to use the 4500W element! And who takes 3 hour showers?! But I digress...

 

[augie47]

I was going to say, 25.8 on the label is the minimum circuit amps, not the actual load. Your calculation is off, you evidently put 0.5 instead of 0.05 for the fan. When corrected that calc comes to 25.8A (rounded off). So now you see that the 25.8A min circuit ampacity already includes the NEC required 125% factor.

It's never going to use that much continuously anyway! It has a thermostat! It's rarely if ever going to use the 4500W element! And who takes 3 hour showers?! But I digress...

agree...
it never hurts to check but when the manufacturer gives you MCA & MOCP that's the only numbers you need to take int account.

 

[infinity]

Apologies, I took a closer look today than the other day. I had to pick up my daughter and glanced at the name plate for seconds before I had to leave while they worked on it. Looks like the working load without a locked rotor is 21.03 amps. 4500watt element=18.75 + 1.78A compressor + .05A fan x125% is 26.28A.

The locked rotor doesn't mean much. If using 208 volts then you'll need a 23.6 amp condcutor or with 240 volts you'll need a 25.8 amp conductor. In either case the max overcurrent device would be 30 amps.