Water heater overcurrent protection

[curious101]

Hello,
If I have a 6kW, 208V, single phase water heater, shall the overcurrent protection be 40A-2P or 45A-2P?
Thanks!

 

[LarryFine]

6000/208 x 1.25 = 36a, so 40a is plenty.

 

[curious101]

Yes, thank you! That's what I thought. For some reason, some people apply the 1.25 even after the first 1.25. Just looked it up in NEC 2020, 422.13; it says that the breaker can't be smaller than 125 percent of the rating of the water heater, but it doesn't say there is any limitation to be higher than the 125 percent. Thanks again! Have a great day!

 

[augie47]

To be a little more precise, 422.13 simply notes the branch circuit for such water heaters is considered a continuous load. The over-current selection would be governed by 422.11 which would allow your 45 amp breaker if desired.

 

[curious101]

Thank you so much! It's always appreciated when the right NEC section is pointed out! Perfect!

 

[infinity]

6000/208 x 1.25 = 36a, so 40a is plenty.

Yes 40 amps is plenty and as Augie stated a 45 amp circuit would be permitted. This HWH would run forever on a 30 amp circuit.

 

[curious101]

Thank you!

 

[Dennis Alwon]

The overcurrent protective device can be 150% of the load based on 422.11(E) which is what Gus stated. It also allows next size up so 45 is okay

 

[Dennis Alwon]

A discussion I had with someone was over whether the overcurrent protective device could be large than the conductor. For instance, the nec allows 125% for continuous load but for overcurrent protective device it allows 150%. If you use the 150% they were saying you could still use the 125% wire size which may not be good for the 150 amp overcurrent protective device . There is no overload protection here so IMO the wire size may have to be increased if you use the 150% for the overcurrent protective device . Do you agree?

 

[infinity]

A discussion I had with someone was over whether the overcurrent protective device could be large than the conductor. For instance, the nec allows 125% for continuous load but for overcurrent protective device it allows 150%. If you use the 150% they were saying you could still use the 125% wire size which may not be good for the 150 amp overcurrent protective device . There is no overload protection here so IMO the wire size may have to be increased if you use the 150% for the overcurrent protective device . Do you agree?

I agree. You're sizing the branch circuit at up to 150% so the conductor size has to be greater than or equal to the OCPD size.

 

[GoldDigger]

The biggest exception to this is specifically for motor circuits where the overload protection for the wire is provided by the overcurrent device for the motor. The wire needs to be able to carry that trip current (or that current plus non-motor loads in the case of appliances.)

 

[Dennis Alwon]

I agree. You're sizing the branch circuit at up to 150% so the conductor size has to be greater than or equal to the OCPD size.

The biggest exception to this is specifically for motor circuits where the overload protection for the wire is provided by the overcurrent device for the motor. The wire needs to be able to carry that trip current (or that current plus non-motor loads in the case of appliances.)

I must have argued my case for 30 minutes. It seemed like he was stuck on the 150% meaning the overcurrent protective device not the wire. I think he finally agreed, sort of....haha

 

[infinity]

I must have argued my case for 30 minutes. It seemed like he was stuck on the 150% meaning the overcurrent protective device not the wire. I think he finally agreed, sort of....haha

You were correct and he wasn't. As Digger said for a motor circuit the OCPD is only providing short circuit and ground fault protection so the rule is different.