Water heater overcurrent protection

[rlqdot]

I am designing a project with a 45Kw 120 gallon tank-type water heater operating at 208 V - 3 P. Article 422.13 says I have to consider it a continuous load. The FLA is 125 amps, and 125% of FLA is 156.25, so I believe I need a 175 amp circuit breaker (next standard size above 156.25 amps), with 2/0 THHN copper conductors for the branch circuit.

However, when I refer to article 422.11(F)(3), it seems to limit me to nothing larger than 150 amps for overcurrent protection on water heater branch circuits.

Can anyone clarify for me what the correct limitations are on this circuit?

 

[augie47]

Note that there are different requirements depending on the type water heater (instant vs storage vs ASME tank, etc).
The limitations are on the branch circuit protective devices so you could install separate branch circuits not exceeding the limits or your 175 amp feeder to supply individual overcurrent devices at the unit.

(Most of the large units I have seen have factory internal fusing)

 

[rlqdot]

Note that there are different requirements depending on the type water heater (instant vs storage vs ASME tank, etc).
The limitations are on the branch circuit protective devices so you could install separate branch circuits not exceeding the limits or your 175 amp feeder to supply individual overcurrent devices at the unit.

it is a storage tank heater with single point connection (internal protection provided by manufacturer so that no single heating element exceeds 40 amps - nine separate 5 Kw elements). I am assuming it is an ASME tank, but will check with my Plumbing designer ... if it is not ASME, do I simply ignore 422.11(F)(3) and use 175 amp circuit breaker with 2/0 copper THHN?

 

[infinity]

The way I read it a single circuit brought to the HWH can exceed 150 amps.

(3) Water Heaters and Steam Boilers. Resistance-type
immersion electric heating elements shall be permitted to
be subdivided into circuits not exceeding 120 amperes and
protected at not more than 150 amperes as follows:
(1) Where contained in ASME-rated and stamped vessels
(2) Where included in listed instantaneous water heaters
(3) Where installed in low-pressure water heater tanks or
open-outlet water heater vessels

 

[rlqdot]

The way I read it a single circuit brought to the HWH can exceed 150 amps.

(3) Water Heaters and Steam Boilers. Resistance-type
immersion electric heating elements shall be permitted to
be subdivided into circuits not exceeding 120 amperes and
protected at not more than 150 amperes as follows:
(1) Where contained in ASME-rated and stamped vessels
(2) Where included in listed instantaneous water heaters
(3) Where installed in low-pressure water heater tanks or
open-outlet water heater vessels

THANKS - now I see it ... this code section is saying that the circuits INSIDE the heater can be protected at more than 40 amps if the conditions are met! I was reading it as though the code section was dealing with the branch circuit TO the heater. Duh.

 

[infinity]

THANKS - now I see it ... this code section is saying that the circuits INSIDE the heater can be protected at more than 40 amps if the conditions are met! I was reading it as though the code section was dealing with the branch circuit TO the heater. Duh.

Yes if you're bringing a single 175 amp branch circuit to the unit you are not subdividing circuits.