I'm a bit confused on UL98 vs UL508 switches. Can a UL508 rotary cam switch be used (open transition, ON-OFF-ON) to switch a load between two different supplies? Each supply has a UL489 breaker upstream of the switch. Some of what I have read seems to indicate that UL508 switches are only for motors, other info I have come across seems to indicate this is ok as long as the 508 switch is not the only disconnect.
UL98 vs UL508 switches
- Thread starter Todd0x1
- Start date
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Typically the restriction on switching sources is partly due to the internal construction of the switch. The switches need insulation and arc control to prevent the arc, created by switching a large load, from following the switch contacts and thus creating a source-source fault.
This particular issue is addressed when the switch is tested as a transfer device.
This particular issue is addressed when the switch is tested as a transfer device.
ok thanks. The particular switch in question is a stack of independently enclosed spst contact sets so hopefully that will be acceptable.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
The main regulatory difference between UL98 and UL508 switch use is that a UL508 listed switch cannot be the only “branch disconnecting device” in any circuit, there must be either a UL489 circuit breaker or a UL98 listed device ahead of it somewhere in that branch circuit. So for example if you have a motor starter / MCC unit on a single motor circuit, and all you need is another disconnect within sight of the motor, that last disconnect can be a UL508 listed device. But a UL508 listed disconnect cannot be used AHEAD of fuses as the disconnect, so you cannot build yourself a motor controller that has ONLY a UL508 listed disconnect in it.
Another way to look at it is to think of a UL508 listed disconnect as just a “manual motor controller” with no protective features in it. As such, something else ahead of it must provide the other protective functionality.
Another way to look at it is to think of a UL508 listed disconnect as just a “manual motor controller” with no protective features in it. As such, something else ahead of it must provide the other protective functionality.
Can UL508 switches only be used in motor applications?
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
It depends. A “cam switch” can be UL508 listed as either Category NLRV, which is for motor controllers, or NRNT, which is for “control switches”, but in many cases, both. As a “manual transfer switch” it would need the NRNT listing, but I think you will find that any double throw cam switch sold in the US and listed, will be listed appropriately. The only time they have ONLY the UL508 listing under NLRV is when they are being sold as low cost local motor disconnects.
I can't thank you enough for this info, i didnt even know what to look for. Of course the switches we were looking at are NRLV....ugh...
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Only? Might be worth asking them.
i plan to ask them. when i put the file # in product iq the results only have nrlv. when im back at desk and can log in to iq maybe i can see more details