RTU Disconnects

scnkapc

Member
First, picture this: 1000 amp main switch gear. Breaker in that gear feeding and panel. Panel feeding and disconnect mounted to the RTU on the roof of a gymnasium.
Name plate on RTU states: Maximun Fuse or HACR Breaker size: 30.

Now here is the question:
The breaker in the gear protects the feeder going to the panel, right?
The breaker in the panel protects the feeder going to the disconnect mounted on the RTU, right?
The disconnect mounted to the RTU protects the circuit wires to the components within the RTU itself, right?

So when the Unit Name Plate states that this RTU must be protected with : Max. Fuse Size or HACR breaker 30 amp, does the disconnect on the RTU have to be a fusible disconnect? Or does the breaker that is in the panel feeding the disconnect, that has HACR rating, sufficient?

It is my understanding the the disconnect mounted on or adjacent to must have fuses or house the HACR breaker. Not the remote location panel 2-stories down inside a closed.

Please clarify with code references.
 

scnkapc

Member
So you're saying that a knife blade disconnect is fine. No fuses or breaker is need at the diconnect? You're saying the the breaker in the panel is good enough.
 

jwelectric

Senior Member
Location
North Carolina
If the conductors are sized no smaller than the minimum conductor size and the overcurrent is sized no larger than the maximum overcurrent listed on the unit then the disconnect on the roof can be a non-fused disconnect.

There is no need for the second overcurrent device on the roof. Being that there is no requirement for this second overcurrent device there is no code section stating this.
The only code reference will be in Part II of 440. 440.14 will require that a disconnect be within sight of the unit but Part III of 440 does not require the overcurrent device to be within site of the unit.
 

augie47

Moderator
Staff member
Location
Tennessee
So you're saying that a knife blade disconnect is fine. No fuses or breaker is need at the diconnect? You're saying the the breaker in the panel is good enough.
Yes, a non-fuse disconnect, properly rated, is sufficient.
The requirement is that you have the nameplate required protection ahead of the unit..at any location.
 
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