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Spark plug boot arced through but looked OK

How does insulation break down when it seems to be perfect?

I have a silicone rubber spark plug boot, 4mm thick, that emitted a

0.5" arc to ground, yet it didn't seem to have any tears, cuts, voids, or carbon tracks (arc occurred 0.75" from end). According to:

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the boot should have been able to take roughly 48,000V, and the minimum voltage for a 0.5" arc through air isn't that much outside this range.

I've never had a boot arc through before without visible damage or carbon tracking. The brand of plug wire is Prestolite, 56,000 miles.

Reply to
jamarno
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What magnification did you use on your microscope to inspect the boot?

If the spark did indeed travel through the boot, that is prima facie evidence of either a hole in the boot or a breakdown in the material properties. I bet it is a very small hole.

Reply to
Mark Olson

Sounds to me like it had a manufacturing defect that was just too small to see.

Tim

Reply to
Tim Brown

miles.

boot?

I used a 20X rock inspection microscope.

I tried an old silicone boot in its place and couldn't get any arcing, even though it's a thinner boot and has a few small tears on it (ran a grounded wire around it to create arcs - none). This was an orange boot, so I wonder if the original black boot had an area with an unusually high concentration of carbon black in it.

Reply to
jamarno

This was an orange

A spark plug boot better not have ANY carbon black in it!

Reply to
Steve

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