Instantaneous water heater

[hhsting]

I have 8.31kw 277V single phase tankless instantaneous water heater. FLA is 30A so the breaker should be 30A since it’s non continuous. However plans show 35A. What gives should it not be 30A per code?

 

[Greentagger]

It’s permitted to be 30. The language is shall not be less than 100%. 42210.(A).

 

[infinity]

I don't have the book in front of me but I believe that you're allowed to size the branch circuit up to 150% of the FLA.

 

[augie47]

I don't have the book in front of me but I believe that you're allowed to size the branch circuit up to 150% of the FLA.

Correct, 424.11 150% where over 13.3 amps

 

[Dennis Alwon]

Yes but then the conductor must be sized for the large overcurrent protective device if you use the 150%

 

[Little Bill]

Correct, 424.11 150% where over 13.3 amps

Are you sure that is the correct Article? 424 is for fixed electric space heating.

 

[kwired]

Correct, 424.11 150% where over 13.3 amps

Yes but then the conductor must be sized for the large overcurrent protective device if you use the 150%

Which is part of why a majority of typical 4500 watt tank style WH's get put on 30 amp breaker without that rule they would need to be on 25 amp circuit. Just happens either way they need a 10 AWG conductor on this one.

 

[kwired]

Are you sure that is the correct Article? 424 is for fixed electric space heating.

Didn't pay that close attention, but pretty sure there is rule like this in 422 somewhere.

ADD:
2017: 422.11(F)(3)

 

[augie47]

Typo )or old age, never know).. 422.11

 

[Little Bill]

I'll take typo for $200 Alex

 

[Little Bill]

Didn't pay that close attention, but pretty sure there is rule like this in 422 somewhere.

ADD:
2017: 422.11(F)(3)

That should be (E)3 since the OP's heater is not 48A or more

 

[kwired]

That should be (E)3 since the OP's heater is not 48A or more

Yep, missed that.