NEC 440.4 and Disconnects

[hvacmonster]

I am working on a project at a school where we are replacing Self-Contained Unit Ventilators (they have hermetic compressors in them). There are multiple units fed from a single circuit so the breaker in the branch panel is larger than the unit nameplate for Maximum Overcurrent Protection since its feed multiple units. Each unit has a non-fused disconnect switch and all branch circuits withing the unit are fused. So the branch circuits for the fan, compressor and low-voltage components are all protected by fuses. One of the electricians is stating that NEC 440.4 requires fused disconnects at each unit since there are multiple units being fed from one circuit. Its too late to add them to the units since the equipment is onsite and the cost to add them now is large. If the code requires them then we'll have to add them but the unit manufacturer is stating they do not believe they are required when reading the code. I am not sure what to do so just looking for some expertise or direction on where to find my answer.

Thanks!

 

[tom baker]

You have answered your own question.
"There are multiple units fed from a single circuit so the breaker in the branch panel is larger than the unit nameplate for Maximum Overcurrent Protection since its feed multiple units."

A typical HVAC outside unit has a nameplate with max overcurrent protection and circuit ampacity. The mfg in the testing and listing process determines the MOP, which is based on the short circuit the unit can with stand.
Can you replace the non fused disconnect with a fused disconnect?
And is the conductor from the main single circuit OCPD sized for that ampacity, or is the conductor sized based on the load, IE big OCPD with smaller conductors to each unit? You may have a code violation there
And consider this. A unit faults, shorts and takes out the main, you lose all the ventilators not just one...
And the mfg stating they do not belive...is that what they know or what they think?
A better design would be a seperate OCPD to a non fused disconnect for each unit