Equipment disconnect

Hello,

If I need a local disconnect/circuit protection to protect 2 packaged air compressors from a main feed, what type of requirements need to be met? UL98 UL 508? I'm assuming it's a "branch circuit" since the facility is supplying the main feed to our skid. Or would it be UL489? Not sure what breaker type is needed. The compressor controls has a motor starter and overload already installed. it all makes my head spin...

dginbuffalo said:

Hello,

If I need a local disconnect/circuit protection to protect 2 packaged air compressors from a main feed, what type of requirements need to be met? UL98 UL 508? I'm assuming it's a "branch circuit" since the facility is supplying the main feed to our skid. Or would it be UL489? Not sure what breaker type is needed. The compressor controls has a motor starter and overload already installed. it all makes my head spin...

Click to expand...

I'm answering this version because your first one didn't show all of the info.

You can only use the UL508 listed disconnects as the last device before the motor, where there is ANOTHER branch Over Current Protection Device somewhere else dedicated to that single circuit. That other branch OCPD can be a UL98 listed fused disconnect or a UL489 listed breaker.

So if you have a dedicated line feeding each individual motor starter coming from a UL98 listed fused disconnect or a UL489 listed CB in a panelboard, then the disconnect you use within sight of the motor can be the cheap little rotary ones in a box with the UL508 labels. But if there is ONE feeder breaker in a panelboard and it is going to a control panel for the compressors that has both mag starters and no individual branch OCPD, then each disconnect will have to be either a breaker or a UL98 listed disconnect anyway, so the UL508 listed versions would be pointless.

If you feel safe in ASSUMING your installer will use a branch device for each one individually, or you want to shift the burden over to them by putting it in the installation instructions to save you a few dollars, that's one strategy. If you want to be safe rather than sorry, use the correct device. If it were me, I'd just use Combination Starters, that takes care of it.