Cheap DVM with believable CAT rating ?

[dglcomp]

A picture of the inside my unit, fuses are ceramic types, being the next size down from a normal plug fuse (5x20?), both are rated for 300V.
No isolation slots between the inputs but they are widely spaced apart on the PCB.

[G.Castle]

Thats a Parkside PDM300.

Pretty decent cheapo meter, they are only rated for 300 volts so aren't really meant for prodding around in HV environments.

Edit: cat rating of 1kV for the leads, which is a separate issue to the protection in the meter, (the meter warns you if you exceed the voltage rating).

[stuarth]

So is that the Lidl conventional DMM with a CAT III 300V rating? That would be consistent with 300V rated fuses to protect the current ranges.

My Metrix MX1 has a CAT III 600V rating, and uses slightly larger 1 1/4 inch ceramic fuses (and two pairs of back to back diodes as a clamp) to protect the current ranges. It use PTCs (4 of them) to protect the voltage and resistance ranges. I notice your meter has a PTC marked on the board.

A clamp meter doesn’t have conventional current ranges (with a low internal resistance path) to need fuse protection, so may not have an internal fuse. This is where independent test/certification houses come into play.

A quick word to our younger listeners about glass fuses. A glass fuse may not break a high current, say 10s of Amps, because the fuse wire vaporises, deposits itself on the inside of the glass tube and continues to to conduct, the glass gets hot and also conducts, then at best you have a blob of molten glass in a plastic box in the palm of your hand. Not nice. A ceramic fuse can break currents of 1000s of Amps, and must be used where low impedance paths and energetic power sources are involved. That’s why the fuse in a UK mains plug is ceramic.

Stuart

[G.Castle]

Good point about those glass fuses people have lost their eyesight when one of those has been used in ignorance and one has ruptured in their face.

DC ratings are not usually stated on generic fuses but IME they should be, as it is far less likely the arc caused by a ruptured fuse will extinguish on DC at quite low votages.

People will use cheap fuses found 'on line' to replace those in multimeters, very often they have poor operating characteristics or no sand filling. Don't present a meter for repair with one in, they won't entertain you.

There's a reason why Fluke spare fuses are expensive.

On the issue of safety to the user, the Parkside meter does have a very robust case and I'm sure if used within their ratings are perfectly OK: using any equipment outside its specifications isn't under the control of the manufacturer, they are not duty bound to protect against 'Stupidity'

[stuarth]

I don’t think you need an expensive fuse for CAT III 300V environment, ie downstream of the consumer unit in a conventional single phase domestic installation. Effectively, the 13A sockets are in that environment, and the fuse in the plug should break the connection if someone chops through the flex close to the plug. Anything you can do with your meter is unlikely to be lower resistance than a pair of side cutters through the flex. Of course a reassuringly expensive fuse may be, well, reassuring, but on 240V house wiring a BS1362 fuse will do the job.

If the meter is rated for CAT IV, then the impedance of the supply could be much lower, the short circuit currents correspondingly higher, and the fuses more expensive. CAT IV is on the incoming supply to your house, or a significant industrial/commercial installation, which I suspect very few of us are involved in, and those that are should fully understand the risks and equipment requirements.

From the responses to this thread (thanks everyone), I think my cheap but TUV certified meter should be safe on house wiring, isn’t an eye watering loss if it gets stolen or left on the car roof, and I don’t need to lash out on a Fluke. My Proskit meter, with glass fuses and who knows what other problems, is probably not safe on house wiring, despite having CAT III 500V printed on the front panel, and best just used for bench and low voltage work (as are many older meters!). If I ever stray into the other side of the consumer unit (not likely) I’ll consider a CAT IV rated meter (with a believable rating).

Stuart