Do I have to get a panel re-approved by UL if I add a UL-recognized component to it?

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BurnabyBeej

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Vancouver, BC, Canada
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E&I Technician
Hi all,

I'm hoping that someone has some experience in this area.

We have built a number of control cabinets with Allen Bradley RIO (remote I/O) racks in them plus other devices and have had them UL approved at great expense. Now that we have the units in the field we've discovered that we would like to add a signal isolator in between the PLC analog output card and a valve actuator. Would this necessitate getting a re-approval? It seems like it would be such a racket if that were true. Add a $200 part and pay $1000+ for a reinspection.

Cheers,

B
 
It is a lot less expensive to have a UL508a shop just build the cabinet for you rather than having a field inspection.

If you don't want to modify the listed cabinet put the isolator in a small junction box outside the listed control panel.
 
There are other testing agencies that can do listing to to UL508A, eg ETL, etc, for much less than UL.
We can’t advise if you need to maintain listing on control panel due to field mods. I may of done some field mods myself…
 
Great answers. Do you think that a UL508A shop can send a representative to the site to make the modification? It's bolted on and wired in to the system right now.

The second option might be the best.

Thanks.
 
BurnabyBeej said:
Great answers. Do you think that a UL508A shop can send a representative to the site to make the modification? It's bolted on and wired in to the system right now.
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The UL508a shop has to perform all work associated with the listed control panel in one of their locations. So they cannot list something they did field work on. You could ship it to them, have them do the changes, apply the sticker and ship it back.

Realistically, who is ever going to notice you added an isolator. Or care.
 
petersonra said:
The UL508a shop has to perform all work associated with the listed control panel in one of their locations. So they cannot list something they did field work on. You could ship it to them, have them do the changes, apply the sticker and ship it back.

Realistically, who is ever going to notice you added an isolator. Or care.
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I agree but the company that we are doing the work for are incredibly OCD about this stuff. :^) I really appreciate your input.
 
tom baker said:
There are other testing agencies that can do listing to to UL508A, eg ETL, etc, for much less than UL.
We can’t advise if you need to maintain listing on control panel due to field mods. I may of done some field mods myself…
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Thanks for your reply, Tom. I'm sure we all have done a few field modifications... As long as I am using proper wiring and fusing, I feel like I'm not adding to a potential hazard.
 
petersonra said:
Just out of curiosity, why did you add the isolator? Such things rarely serve any useful purpose.
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We are using a Flowserve valve actuator for this project and have used about 20 or 25 total (so far) in the field. Lately, we've been having them fail on us and we aren't sure why (And, neither is the factory).

In speaking with a rep from the factory they mentioned that it is absolutely important to isolate the command signal (4 to 20mA) from the power supply (DC Com) or the control circuit board can be irreparably damaged. In most cases, we are controlling the position command signal with an Allen Bradley 1734-OE4C analog output card. I don't know if there is a potential path to DC Com or if there is a lack of isolation between channels on that card so I thought I would install a signal isolator to gain some guaranteed isolation. Adding a second power supply is beyond what we can do with these panels now.
 
BurnabyBeej said:
We are using a Flowserve valve actuator for this project and have used about 20 or 25 total (so far) in the field. Lately, we've been having them fail on us and we aren't sure why (And, neither is the factory).

In speaking with a rep from the factory they mentioned that it is absolutely important to isolate the command signal (4 to 20mA) from the power supply (DC Com) or the control circuit board can be irreparably damaged. In most cases, we are controlling the position command signal with an Allen Bradley 1734-OE4C analog output card. I don't know if there is a potential path to DC Com or if there is a lack of isolation between channels on that card so I thought I would install a signal isolator to gain some guaranteed isolation. Adding a second power supply is beyond what we can do with these panels now.
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sounds like a design flaw to me.

the common on the analog output module is the same as the common on the power supply powering the 1734 rack.
 
Look at AGM electronics products. They make all types of signal converters and isolators, with 7 year warranty. They will have a signal isolator. I have used hundreds of AGM modules, most are custom made to your specs.
 
If all you do is add a signal isolator, it would be low voltage and not critical to the UL listing of the panel (IMHO). If the end user wants to be a stickler for it, just put it in a small can bolted to the side of the panel. The typical rule on UL listing of "panels" is that there are 3 or more devices, including the box itself. So one device in a box usually doesn't need a label (assuming the device itself is listed).

Side note: seeing that you are in Vancouver BC, CSA is a lot less expensive for you to work with in terms of field labeling. I was a UL 508A panel shop in Washington State myself, yet when something had to be listed in the field, I used CSA. UL was typically $15-20k plus travel expenses for a field eval, CSA was just time on the job and travel time, often $5k or less if the project was close to the border. All states in the US that require listing by an NRTL (Nationally Recognized Testing Lab) will accept CSA. In fact CSA has a special listing referred to as CSAUS that means CSA evaluated it to UL standards (and vice versa, UL has C-UL for UL listed products tested to CSA standards). There is a mutual agreement across the border to accept both.
 
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