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UL 508 Questions

UL 508 Questions

UL 508 Questions

To All,

   I've spent some time the last few days poring over the UL508 standard for industrial control equipment and am left with some questions.  My company has for some time been getting our equipment tested to UL61010-1 safety standard for electrical equipment for measurement, control, and laboratory use.  Our controls are designed to control our own machines that are typically installed in industrial factories.

   Recently, we have sold a project where the customer requested a UL508A approved panel.  Since our devices are not UL508 approved, UL508A calls for them to be wired through a GFCI.  The problem is that our equipment is designed with RF suppression to earth, the leakage from which trips the GFCI.  As such, we're looking into getting our equipment UL508 certified which would remove the requirement for GFCIs.

   My question is this:  what category within UL508 would our product fall into?  Our product includes both a CPU with programmable features, outputs, inputs, etc. as well as a DC motor drive board that drives the motor on our machine.  My suspicion is that it would fall under the heading of "programmable controllers" since categories like "combination motor controller" seem to be referring mainly to just fancy motor-starter relays and not closed-loop drive systems.  On the other hand, it also seems like "programmable controller" refers mainly to PLC-type functionality.  Can anyone shed any light on my situation and where I should be looking within the spec to find what's applicable to our equipment?

   Thanks in advance.  

RE: UL 508 Questions

You could just hire a panel shop that is UL-certified package your equipment up for you and then they can get the necessary certification and apply the UL508 label to the panel.  That's kind of the whole point of UL508, as I recall.

Or talk directly with UL.  They'll be happy to help you spend your money.


If you're selling equipment in the NW (OR,WA), the UL508 label is a big issue with local inspectors.  


RE: UL 508 Questions


  Thanks for your suggestions.  I understand what you're saying, but I think it's born of some of the confusion that UL has created with their spec numbering system.  The standard that covers "Industrial Control Panels" is UL508A, whereas the standard that covers "Industrial Control EQUIPMENT" is UL508.  UL508A basically describes how to combine UL508 certified "equipment" into a "panel" in such a way as to make the panel safe.  It has a section that covers what to do when something to go in the panel is NOT UL508 certified.  In that case, it calls for adding a UL certified GFCI to add some operator safety.  The problem is, our devices won't run through a GFCI.

  Our only way around this issue is to actually GET our device tested to UL508, and then it could be added to a UL508A panel WITHOUT the gfi's.  Currently the UL panel house will ONLY certify the panel if our equipment is powered through the GFCI.

  What I'm trying to do is get familiar with the UL508 standard to make sure our equipment will comply with it before we send it off for testing (failing and then revising/retesting is an expensive proposition).  We have previously had ourselves tested to UL61010-1 which is very similar, but I wanted to clarify the original points I mentioned to get a better understand of 508.

  Again, thanks for your help and I still welcome other comments on the topic.

RE: UL 508 Questions

UL 508 is a maze of a spec to work through, with different sections that pertain to different parts of the application.  For example, there is a section related to the PCBs, there is a section related to terminal spacing, wire spacing, etc.  To make things worse, there are even other UL standards that apply to these areas that can be even be used in lieu of 508.  For example, if you have a PCB with 600Vac on it, I believe that 508 calls for about .500" between conductors (traces) of opposite polarity.  However, if you apply conformal coating, or even solder mask, you alter the so called pollution degree that the board will be operated in, which (dramatically) lowers the spacing requirements.

It sounds to me  like you will need to contact UL for advice.  Your contact for your 61010-1 testing can probably steer you towards a good person.  The unfortunate aspect is that depending on who you work with, working with UL can either be a pleasant experience or an aggravation to end all others.

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