While replacing a fuse in my Fluke multi-meter I noticed a split in this little yellow 1500V MOV. I thought it exploded from over voltage at some time in its life, as I'm not the first owner. But looking more closely at the split under a microscope it looks very clearly like it was cut on purpose.

Am I correct in my observation? And if so, what's the point of cutting it like that? Is it like a pressure release valve?

 

Gap Cap, Spark Gap Cap. It will conduct electricity at about 1500V. The width of the gap determines the voltage.
They come with or without a capacitor inside.

 

I looked up the schematics and the part is called "Surge Protector 1500V +/- 20%".

So is there just a piece of wire inside the blob? And it shorts over voltage input through a spark?

 

If I recall correctly, these were used on an analog TV’s gun drivers to protect them from possible arcing from the focus voltage of about 5 kV.

It has been a looooooooong time, though.

 

So is there just a piece of wire inside the blob? And it shorts over voltage input through a spark?

Yes.

 

Think of it as a varistor designed for higher-voltage circuits and which won't suddenly turn into a low-ohm resistor.

 

Here is a Gas Discharge tube. Similar but in a tube. See the gap. Can use different types of gasses. To get low voltage they can make the ends radioactive.

 

they can make the ends radioactive.

 

Sorry. Couldn't resist being dumb.

 

Couldn't resist being dumb.

My bottled water has that warning.

 

Not to further derail the thread, but I've seen that warning on a SUV... have a pic in my files somewhere.

 

My bottled water has that warning.

I bought a little bag of wooden dowels at Home Depot. It had this warning.

WARNING: Drilling, sawing, sanding or machining wood products can expose you to wood dust, a substance known to the State of California to cause cancer. Avoid inhaling wood dust or use a dust mask or other safeguards for personal protection. For more information go to www.P65Warnings.ca.gov/wood.

 

Sorry all, I didn't mean to derail this thread.

 

Sorry all, I didn't mean to derail this thread.

NBD. I'm happy my multi-meter is just fine. Now if I could only remember when I blew the 400mA fuse.