OCPD

[FaradayFF]

Greetings, All -

I have a scenario where we're replacing an AHU consisting of fan unit and electric heater, mounted in a duct. Unfortunately, the breakers protecting the existing circuits to the existing AHU are legacy, and it would be difficult to procure them if we wanted to change them out. Is there anything in the NEC that would allow me to keep the existing branch breakers and mount the properly sized OCPD for the AHU locally to the AHU, like a fused disconnect?

Thank you,
EE

 

[Little Bill]

If the conductors for the existing are the correct size for the new equipment and also the existing breakers, I don't see a problem with local OCPD. If the breakers are in good shape & proper size, why would you change them?

 

[GoldDigger]

If the existing branch breakers are propery sized to protect the wiring toward the AHU and the new AHU has a maximum OCPD size lower than the size of the existing breaker, there is no reason not to put the correct OCPD closer to the new AHU. You should also note whether the new AHU specifies a maximum OCPD or the more limiting maximum fuse size. I have not seen any labeling that requires the use of a breaker.

 

[FaradayFF]

I think this plays favorably in regards to the requirement of having local disconnect switch. A properly sized fuse can act as an overcurrent protection for the motor and as a disconnect.

 

[Eddie702]

It's done all the time.

Someone changes a roof top unit and most of the older units required a higher MCA and MOCP than the new units for two reasons. The new units are higher efficiency and the older units had 1 or 2 large compressors and the newer unis have 3, 4 or more smaller compressor. No need for a new feader and breaker just fuse it down