Author Topic: High voltage ceramic fuses  (Read 4883 times)

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dnix71

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High voltage ceramic fuses
« on: April 16, 2015, 06:27:48 PM »
I have 2 multimeters that I use to indirectly measure 1000v (very low amp) DC power supplies. I cannot find replacement fuses rated 1kv.

What is the real difference between a ceramic glass fuse rated for 250v and the one rated 1000v? Both look the same on the outside.

The meters in question are a Tenma 72-7720 and a Commercial Electric aka "Mastech" MS8260A. The fuse itself says 6FF, the letter H circled and a triangle logo on one end and 1000v 400ma on the other. The fuse is the US standard ceramic glass fuse 1 1/4" x 1/4"

DanG

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Re: High voltage ceramic fuses
« Reply #1 on: April 16, 2015, 11:33:15 PM »
Model 72-7720/72-7725: OPERATING MANUAL
http://www.farnell.com/datasheets/316033.pdf
page 32 says "0.5A. 250V fast type fuse, φ 5x20mm."

XeonPony

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Re: High voltage ceramic fuses
« Reply #2 on: April 17, 2015, 01:21:40 PM »
the difference is the flourosulfat (I think that was the chemical) arc quenching sand that is in them.

It kills any attempt of an arc forming

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dnix71

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Re: High voltage ceramic fuses
« Reply #3 on: April 17, 2015, 08:31:34 PM »
There is discussion in another forum about which multimeters are actually safe and to code. As DanB pointed out, the fuse rating in the booklet is lower than the supposed rating of the device. At 1kv physical separation of components inside to prevent arcing also comes into play.

http://unsafeproducts.eu/2013/11/08/multimeter-%CF%88%CE%B7%CF%86%CE%B9%CE%B1%CE%BA%CE%BF-%CF%80%CE%BF%CE%BB%CF%85%CE%BC%CE%B5%CF%84%CF%81%CE%BF-digital-multimeter/
This looks like my favorite Harbor Freight meter. For $3 I wouldn't trust them around high voltage.

http://www.eevblog.com/forum/reviews/a-list-of-recommended-multimeters/  Meters that are correctly built.
http://www.eevblog.com/forum/testgear/a-list-of-multimeters-that-do-not-appear-to-meet-their-claimed-safety-specs/ Meters that are not correctly designed and built.

Mary B

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dnix71

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Re: High voltage ceramic fuses
« Reply #5 on: April 17, 2015, 10:10:23 PM »
Mary B That's not the one, unfortunately. The fuse in my meters looks like a normal glass ceramic fuse. I am using a 250v 500ma fuse for now.

http://www.amazon.com/Qty-400mA-Fast-Blow-Ceramic-ABC400mA/dp/B004HIGI6Q   This has the correct physical size and amp rating, but it isn't rated for 1kv.

DanG

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Re: High voltage ceramic fuses
« Reply #6 on: April 18, 2015, 12:37:15 AM »
http://tinyurl.com/nqdjx6n  <--- mouser 1kV cartridges and pesky 6.3 x 32mm; the 1/4" x 1-1/4" dimensions...

dnix71

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Re: High voltage ceramic fuses
« Reply #7 on: April 18, 2015, 12:57:06 AM »
Thanks DanG
http://www.newark.com/multi-contact/69-0012/fuse-0-5a-mc-iv/dp/08R6144  Seems to be as close as I can get. I wonder what the total cost would be. $2+ a fuse isn't bad if the shipping is cheap.

Mary B

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Re: High voltage ceramic fuses
« Reply #8 on: April 18, 2015, 05:22:31 PM »
Mouser shipping is usually reasonable if you order enough to fill a small flat rate box. Good time to get crimp on connectors, wire, solder... whatever else the junk box is low on.