hvac overcurrent protection

[DAC8]

I've been noticing lately, in commercial buildings specifically, HVAC contractors have been changing large RTU's with electric heat to gas units that draw a much smaller load. What doesn't sit right with me, is that, the breakers from the old units are left in place and a fuseable disconnect and fuses are installed to accommodate the max fuse rating on the nameplate, to cut cost I'm sure. Example: 200 amp breaker at the gear, 60 amp disconnect with 60 amp fuses. I'm familiar with article 440.22 but it does not specify, weather or not, the 225% is for the entire circuit. Could you please clarify?

 

[ActionDave]

As long as fuse matches the MOCP on the unit I say it's fine. This is area of the code where branch circuit and feeder definitions overlap and there is not a clear interpretation.

 

[Dennis Alwon]

I agree with Dave. The 225% is limited by the fuses so as long as the wires are sized appropriately for the 200 amps then you are good. If the wire from the panel to the disconnect is not rated 200 amps then IMO you have an issue.

 

[peter d]

I agree with the others. From an NEC standpoint, as long as a compliant OCPD is provided in accordance with the nameplate on the unit, you are good to go.

 

[infinity]

I've been noticing lately, in commercial buildings specifically, HVAC contractors have been changing large RTU's with electric heat to gas units that draw a much smaller load. What doesn't sit right with me, is that, the breakers from the old units are left in place and a fuseable disconnect and fuses are installed to accommodate the max fuse rating on the nameplate, to cut cost I'm sure. Example: 200 amp breaker at the gear, 60 amp disconnect with 60 amp fuses. I'm familiar with article 440.22 but it does not specify, weather or not, the 225% is for the entire circuit. Could you please clarify?

Just curious as to how they getting the 200 amp conductors terminated in a 60 amp disconnect? Most 60 amp disconnects I've seen do not have terminals large enough for 200 amp conductors.

Welcome to the Forum.

 

[Dennis Alwon]

Just curious as to how they getting the 200 amp conductors terminated in a 60 amp disconnect? Most 60 amp disconnects I've seen do not have terminals large enough for 200 amp conductors.

Welcome to the Forum.

That was why I asked about the conductors being large enough from the panel to the disconnect. My guess is that the original install may have had a conductor that was sized smaller with a circuit breaker at 225%

 

[infinity]

That was why I asked about the conductors being large enough from the panel to the disconnect. My guess is that the original install may have had a conductor that was sized smaller with a circuit breaker at 225%

Good point.

 

[kwired]

That was why I asked about the conductors being large enough from the panel to the disconnect. My guess is that the original install may have had a conductor that was sized smaller with a circuit breaker at 225%

If the electric heat was the larger load, then the overcurrent device was probably not 225% of total load. But that also means the chance of having 200 amp conductors instead of smaller conductors is greater.

 

[kwired]

I've been noticing lately, in commercial buildings specifically, HVAC contractors have been changing large RTU's with electric heat to gas units that draw a much smaller load. What doesn't sit right with me, is that, the breakers from the old units are left in place and a fuseable disconnect and fuses are installed to accommodate the max fuse rating on the nameplate, to cut cost I'm sure. Example: 200 amp breaker at the gear, 60 amp disconnect with 60 amp fuses. I'm familiar with article 440.22 but it does not specify, weather or not, the 225% is for the entire circuit. Could you please clarify?

What 225%? If this unit has hermatic compressors in it 440 applies anyway.

That said the circuit between the distribution panel and the rooftop disconnect is a feeder. The disconnect to the unit is the branch circuit. If original conductor is too large for the 60 amp disconnect you can tap the feeder and follow rules in 240.21 for feeder taps.

 

[DAC8]

I've been noticing lately, in commercial buildings specifically, HVAC contractors have been changing large RTU's with electric heat to gas units that draw a much smaller load. What doesn't sit right with me, is that, the breakers from the old units are left in place and a fuseable disconnect and fuses are installed to accommodate the max fuse rating on the nameplate, to cut cost I'm sure. Example: 200 amp breaker at the gear, 60 amp disconnect with 60 amp fuses. I'm familiar with article 440.22 but it does not specify, weather or not, the 225% is for the entire circuit. Could you please clarify?

Thanks for the responses guys. I've seen several different attempts to justify this type of installation including tap rules and changing lug sizes in the disconnects. I'm just a stickler for clean installations.