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UL98 versus UL508 disconnect

UL98 versus UL508 disconnect

UL98 versus UL508 disconnect


I am trying to design an Industrial Control Panel that will replace an older Control Panel that is currently being used in a machine control application. I have posted a few questions related to this project, but I thought this topic is different enough that it might be worthy of its own thread.

A previous thread I started in the hope of determining whether I should fuse my main disconnect resulted in me learning that the type of disconnect I had in mind was not suitable for use as the Main Disconnect in an Industrial Control Panel according to UL guidelines. Realizing my ignorance on UL guidelines, I started reading UL508A. I got up to the section covering disconnects, and figured I would start trying to find a 3-pole disconnect rated for 80 amps that is UL508A compliant. I seemed to reach a dead end with my usual supplier, so I figured I'd call Automation Direct. I figured I'd still consider both fusible and non-fusible disconnects. I found out that they have an 80 amp non-fusible disconnect that is UL508 compliant (I'm not sure about UL508A). When I asked about a fusible disconnect, the closest they could offer was one that is UL98 compliant rather than UL508.

Googling UL98 vs UL508 made me think that UL98 devices might be "better" or "safer" than UL508 devices, but they are usually larger or more expensive. (Please correct me if I am wrong). Before I look too seriously at one or the other, I am hoping someone here might be able to give me a push in the right direction.

Considering that I am designing an Industrial Control Panel for a machine control application, and that I hope to be as compliant as possible with regulatory authorities in the USA, should I be looking for a UL98 compliant disconnect or a UL508 compliant disconnect. And should I be concerned about the distinction between UL508 and UL508A compliance?

Any advice will be greatly appreciated.

Thanks in advance,

RE: UL98 versus UL508 disconnect

Thank you FacEngrPE,

That makes it clear that I should use a UL98 disconnect for the main disconnect in my control panel. I appreciate your help!

Best regards,

RE: UL98 versus UL508 disconnect

It's actually simpler than that.
UL98 can be EITHER the Main or the Branch disconnect, "Branch" being defined as the LAST device before the load.
UL508 can ONLY be a Branch disconnect, meaning there MUST be a UL 98 fused disconnect ahead of it (or a UL489 circuit breaker). So they (UL508) can be the LOCAL disconnect right at the motor, but not the MAIN disconnect for a panel.

But also, the PANEL must have an SCCR rating that is commensurate with he Available Fault Current where it is going to be installed. Any non-fused disconnect is never going to have an SCCR of greater than 10kA, which for most industrial installations is far too low to be useful. So a Main disconnect in a panel almost always will need to be fused, and that will necessitate a UL98 rated device.

And just for your edification:
UL508 is generically the standard addressing industrial controls.
UL508A is the standard for assembling control panels.
UL508C is the standard for listing components.

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: UL98 versus UL508 disconnect

Thank you jraef,

That is a big help. I am in the process of trying to pick out a UL 98 disconnect, most likely fusible.

When I started working on this project, I was originally hoping to find a side mounted disconnect. I thought this might leave more space in inside my enclosure for the other components I'll need.

So far in my short time of looking into this, all of the UL 98 disconnects I have found are what I would consider "front-mounted", where the main body of the disconnect gets mounted on the rear wall of your enclosure (or on a panel that is mounted on the rear wall of your enclosure), and there is a shaft that couples the main body of the disconnect to a handle that is installed on the enclosure door.

Looking back, I think all of the side mounted disconnects I have seen in the past are more similar to the UL 508 type that can only be used as a branch or local disconnect for a motor.

I'll continue trying to find a few options, but if you tell me that it is unlikely that I will find a UL 98 side-mounted disconnect, I won't waste my time.

Thanks again for all your help.

Best regards,

RE: UL98 versus UL508 disconnect

Because UL98 disconnects are usually fused, side mounted versions become a challenge for locating the fuses in a way that permits easy access, as well as being able to interlock with the enclosure door AND allow the disconnect to be capable of being engaged with the door open, without the need for a tool (this is a requirement of NFPA79). The best way to do it is to use what's called a "flange mount disconnect", but that requires an enclosure that has a wide flange on one side, typically pre-punched with the mounting arrangement for a particular brand of disconnect switch.

This is one style;

I personally prefer the ones that use a flexible cable operating mechanism, because it gives the freedom to mount the disconnect5 mechanism without worrying about proper lineup;

There is a French mfr called Socomec that makes a rotary disconnect with a side operating handle option. That product line is brand-labeled by a lot of the other major players in the disconnect market. It only goes up to 200A though with the side operating option, I don't know how big you needed. Their website does not do justice to the side operation option, but if you dig into the mounting instruction manuals you will find it.

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: UL98 versus UL508 disconnect

Thanks Jraef,

I actually stumbled across those Socomec disconnects when I was searching for UL 98 disconnects on Automation Direct. I would need a 60 amp disconnect (which I will likely fuse for 50 amps) for the panel I'll be building first, and a 100 amp disconnect (which I will likely fuse for 80 amps) for the panel I'll be building second. For the 60 amp version, photos and product literature make me think that what Schneider Electric calls the GS2GU3N is likely the same part.

Not having the disconnect handle on the enclosure door would definitely make it easier for me to fit the other components I'll need on the enclosure door. I just have one more question.

With the handle on the enclosure door, a tool would be required to open the door with power on. I put the handle on the side, one would be able to open the door while powered without using a tool (unless I took other measures to prevent this). It seems like this would sacrifice some kind of rating, wouldn't it?

Thanks again for all your help.

Best regards,

RE: UL98 versus UL508 disconnect

I'd have to look to make sure, but I'm pretty sure some kind of handle to door interlock is required, and it either can be or has to be bypass-able using a tool.

RE: UL98 versus UL508 disconnect

It's been a long time but he panels that I remember needed a tool, usually a screwdriver, to open the door with the switch closed.
When the door was open, the switch could be closed without the use of a tool.

Ohm's law
Not just a good idea;
It's the LAW!

RE: UL98 versus UL508 disconnect

No absolutely you need a tool to unlock the door if the handle is in the On position, it’s part of the UL98 requirements for any style of disconnect.

In addition, NFPA-79 Standard for Industrial Controls requires that when the door is open, the disconnect must have a way to operate the mechanism WITHOUT a tool. The flange mount disconnects satisfy that inherently, the through-door type must have a special added interior handle mechanism to meet this requirement, often sold as an “NFPA-79 accessory handle” that you pay extra for.

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

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