Compliance Tip: Non-Compliant Spacings
Have you ever had non-compliant spacings? This is also called Creepage and Clearances. Call it what you want, when you don’t have the right distance between certain parts (see below), you need to take action.
- Uninsulated live parts and accessible dead metal
- Uninsulated live parts of opposite polarity
- Uninsulated live parts of different voltages
The key word is “uninsulated”. So, an obvious option is to insulate it. With what? There are many different insulators that can be used. Some common insulators that don’t need further evaluation are Mica or Ceramic. These are rigid insulators and work well between live parts and metal enclosures. Vulcanized Fiber is a more flexible insulator. Fish paper is also commonly used. GE and many others make a variety of Silicones and flexible polymers to provide proper insulation as well. Most Standards require the insulator to be a minimum 0.7mm thick. Be sure to check the Standard you’re using and if it’s a UL Recognized Component be sure to follow the C of As (Conditions of Acceptability).
For traces on circuit boards, some other options are to cut a slot in the board between the non-compliant area (Air is an insulator). How thick the slot needs to be depends on the requirements in the Standard. This may not be a long term fix, but certainly will get you into production while you’re doing a new layout on the board. Some Standards allow the non-compliant spacing if under a shorted condition, there’s no increased risk of shock or fire.
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Medical Device & Manufacturing
February 11-13, Anaheim, CA
International Housewares Show
March 15-18, Chicago, IL
ISPCE 2014
IEEE Sypmosium on Product Compliance Engineering
May 5-7, San Jose, CA
Lightfair 2014
June 1-5, Las Vegas, NV
Recent Successes
During our preliminary construction evaluation, a client had non-compliant creepage on a PWB. Orders were pending getting NRTL and of course they needed to ship asap. As noted above, we cut an appropriate slot in the board for a quick fix to get him Certified. The client shipped on time and saved the order. The board is being laid out correctly now.
A new client decided to use our services for NRTL management only (i.e.; no preliminary evaluation work). He had orders pending NRTL and didn’t want to spend the extra money to be sure it would pass. The NRTL got backlogged and 8 weeks later delivered a laundry list of non-compliant items. The client was unable to fix all the problems in time, missed the order and lost a new account. Consider using Design For Safety Approval™ on your next project to avoid costly delays.