How do I calculate the size of an insulator to prevent arcing?

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Need formula for insulation distance at 24 VDC
#1 21676346 13 Aug 2016 15:57

Filip Guzina Filip Guzina

Anonymous

Need formula for insulation distance at 24 VDC
Post #1 21676346 13 Aug 2016 15:57

Hi Everyone, I'm new here.

I'm passing a conductive cable through a metal plate and need to insulate the cable from the plate. Does anybody know or can anybody refer me to a formula or standard by which to calculate the distance from the plate that needs to be insulated to prevent arcing?

I am dealing with a low voltage system, 24VDC 2.5A. It's for a modern LED light fixture.

Cheers and thanks in advance!
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#2 21676347 13 Aug 2016 18:48

richard gabric richard gabric

Anonymous

Post #2
21676347 13 Aug 2016 18:48

A cable has a voltage rating, which relates to the voltage breakdown of the insulating sheath. At your working voltage you don't have to worry about arcing. What you do have to be aware of is cable damage, there are a wide variety of light duty cable glands or bushings available to ensure that the cable passes through the plate with adequate mechanical protection.
Cheers,
Richard.
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#3 21676348 16 Aug 2016 07:58

Filip Guzina Filip Guzina

Anonymous

Post #3
21676348 16 Aug 2016 07:58

Thanks Richard. The cable we are using is unsheathed and is rated for low voltage class 2 circuits, hence the need for an insulating bushing.

I basically need the formula to calculate what distance the arc could travel and make sure the insulating bushing is larger than that.
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Creepage and clearance, not air breakdown
#4 21676349 16 Aug 2016 12:36

richard gabric richard gabric

Anonymous

Creepage and clearance, not air breakdown
Post #4 21676349 16 Aug 2016 12:36

As I said, you don't have to worry about breakdown, figures of around 3000V/mm in air are used as a standard. Treat it as a creepage and clearance issue, see this articles, for example. http://www.frontdoor.biz/HowToPCB/HowToPCB-extra/CreepageandClearance.pdf, there are tables for voltages less than 50 volts.
See https://en.wikipedia.org/wiki/Paschen's_law for some theory.
Hope that helps,
cheers,
Richard
#5 21676350 17 Aug 2016 06:43

Filip Guzina Filip Guzina

Anonymous

Post #5
21676350 17 Aug 2016 06:43

Thanks Richard!
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How do I calculate the size of an insulator to prevent arcing?

How do I calculate the size of an insulator to prevent arcing?

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