Commercial Water Heater Overcurrent Protection

[A-1Sparky]

I've got a 120KW water heater with a nameplate load of 144 amps. The elements are individually fused at 60 amps. The main feed is 2/0 THHN fused at 200 amps. I'm wondering if the 200 amp fusing is code compliant based on the nameplate load and the 2/0 conductors. Because the 2/0s are rated for 175 amps and the elements are individually fused, I think the installation is fine. However, is it code compliant?

 

[david luchini]

I think this violates 240.4. The 2/0 is not properly protected at 200A.

If the load is considered continuous, the the 2/0 also violates 422.10(A).

 

[A-1Sparky]

So, can I fuse this at 175 amps and be compliant?

 

[A-1Sparky]

Or does the OCP have to be sized at 125% of continuous load? If so, I'd have to stay with the 200Amp fuses and upsize to 3/0. Is that correct? Thanks.

 

[david luchini]

Or does the OCP have to be sized at 125% of continuous load? If so, I'd have to stay with the 200Amp fuses and upsize to 3/0. Is that correct? Thanks.

See 422.13. If this is a storage type water heater with 120 gallons or less, then you'd have to size it as a continuous load and increase the circuit conductors to 3/0.

If this is a storage type water heater with more than 120 gallons, or if it is an instantaneous type water heater, you could reduce the fuses to 175A.

 

[A-1Sparky]

It's an instantaneous type, so 175 amp fuses it is! Thanks, David.