Machine Disconnect for Type Z Purge

[fifty60]

I have a type Z purged enclosure. Can I mount a standard rotary disconnect inside of this enclosure, given that I can maintain the positive pressure after mounting the rotary handle on the enclosre door? I have mostly worked with Type X purged enclosures that require that the all the electronics inside of the enclosure to shut down if the door to the enclosure is opened. Type Z purge does not have that requirement.

I would think that it would be best to have the disconnect inside of an explosion proof enclosure because in the worst possible scenario you would want to be able to disconnect the machine from the supply.

I do not see anything in NFPA 496 that says you have to have the disconnect in an explosion proof enclosure. Is this only a requirement for Type X purge?

 

[petersonra]

The disconnect mechanism is not there for anything having to do with a worst case. It is there to shut off the power to isolate something so you can work on it safely. That is all it is used for.

 

[fifty60]

Yes, very much understood. I know with type X purge I have seen a disconnect, power supplies, and a contactor, all inside of an explosion proof enclosure. The reasoning is because this portion of the installation is powered up before any purging and pressurization can happen.

I believe where this comes from is UL 496 4.4.3 it says that "all pressurizing system components energized in the absence of the protective gas shall be identified for the classification that would exist in the absence of the pressurizing system".

In the Type X purge systems I am familiar with, the interlocking system (ie a contactor) was located in an explosion proof enclosure. The equipment disconnect and a 480VAC to 110VAC transformer was also in the explosion proof enclosure.

I believe the only requirement is found in 4.4.3 referenced above.