UL508 UL508A Opening for monitor

[gwooster]

We are changing to LCD monitors in the machine tools we manufacture. UL is saying that the opening for the monitor must have a polycarbonate cover with a 5VA flammability rating.

1. Is he correct?
2. Any way to get around this?
3. Anyone have any experience with this.

Our plastics vendor indicates that 5VA material is hard to get in small quantities (we would use about 1000 12"x12" covers in a year) and very pricey.

 

[buzzp]

I would suspect he is if he is from UL. Do you have a copy of the standard? I do not have one where I am at now. Is this really listed under UL508?
There are additives that can be added to the material to increase the flammability rating. However, in your case this may not be an option.
Get a copy of the standard and read up on it. If it really is listed on UL508 then I suspect there are other alternatives. Is the LCD in a rated enclosure (3R, 4, 12)?

 

[gwooster]

Yes, he is a field engineer with UL.
UL 508A section 23 covers observtion windows. 23.3 says an observation window must be polycabonate, 1/8" thick minimum, and have a 5VA flammability rating.
We design our own cabinets and our entire machine is UL listed.
If we do not comply with the specifics of 23.3 then testing under UL 508 is required and that will be ugly.
The real question is "Is this really a observation window?"
After all, our CRTs are glass and a glass observation window cannot be more than 4" in any dimension according to UL508A 23.2.

Does anyone know of UL508 or 508A exceptions for monitors (CRT or LCD)?

 

[buzzp]

UL508A is for the controls, etc that may make up the panel. If you do not use listed or recognized components for your UL508 panel, then this does not mean it will not pass but testing will be required as you indicated. What does UL508 say about observation windows?
So your inspector or UL rep is saying you need to comply with UL508A for your display on the panel or conduct testing on the display according to UL508? Strange, I always heard of them requiring testing on panels period. No matter if you used all recognized/listed parts or not. The "system" still needs to be tested as a complete system not bits and pieces. Your not listing your display to UL508A unless your planning on selling just the display. You need UL on the whole panel so UL508 is the standard to use. Perhaps 508 refers to a section in 508A for the displays.
Your monitor will be internal to your panel? If so, and UL508 section refers to UL508A for observation windows then there likely is no way around it. The window should resist the same things as the steel that makes up the panel, hence the 5VA rating.
I know I rambled a bit but maybe some of this will help you. Good luck. Maybe locate the monitor outside of the panel? I suppose it will be in too nasty an environment for that.

 

[gwooster]

UL508 sends me to UL508A which sends me to UL746C for the required test.
Loacting the LCD panel outside the electrical elclosure would require another enclosure (more bucks and assembly time).
So, I am about to do the 5 inch flame test to see if we have a snowball's chance. (Let's see: an 1/8" snowball subjected to a 5 inch flame for 5 seconds five times with 5 seconds in between.) Pray for me.

 

[buzzp]

Hehe. I do not believe there is any way around this unless its not part of the panel. Good luck.

 

[alexit]

I misread this the first time. You are installing an LCD panel in the machine enclosure? The device you install does meet UL for its category, but you need a polycarbonate cover in addition to the device's inherent electrical insulation?

I could understand the polyshield for physical security (machine tools have the possibility to throw broken tools and such) but you could also cover the REAR (inside the enclosure) with sheet metal to protect against a breach of the guards.

Did the UL inspector give any reasoning why the UL rated LCD monitor isn't electrically stable enough? What if you hung it on the outside of the enclosure (surface mount) does he still require the polycarbonate shield?

Sorry to come in late, I just wanted to confirm this...

Thanks,
Alex

 

[REDDOG]

What is the rating of the enclosure you are seeking.. NEMA 1,12,4x,..?

 

[gwooster]

To Alexit and Reddog:
The problem with the LCD panel (monitor) is that it has no UL ratings at all. None of them do apparently. Therefore UL considers the opening for the LCD panel to be a 14" square opening in the cabinet and requires a viewing window.
Hanginf the LCD panel on the outside of the cabinet or putting a metal shield on the inside are not economically feasible alternatives.
As far as the rating of the enclosure is concerned: Since these are our cabinets that go on our machines there is no NEMA rating required. We are strictly dealing with UL508 and UL508A.

gwooster

p.s. We have selected a V-0 rated polycarbonate (GE Lexan 9600) and it passes the 5 inch flame test.