by ericmark »
Sat May 28, 2016 11:22 pm
It is hard for me when I was taught from around 4 years old how to play with electricity. First lesson was I stuck two 6 volt bulbs across my electric train track, all was good until one failed and I replaced it with one of a different wattage.
My dad replaced the bulb for me as he said he had not taught me about wattage and resistance, but when the second one went I was told buy it myself I should have listened more carefully.
The problem with multi-meters is they test resistance with low current and low voltage, with mains stuff we (if we follow regulations) measure low ohms with at least 200 mA and high ohms or insulation with 500 volt.
The test in the video was one of the few where the ohm range of the multi-meter is good enough. Most meters have a continuity buzzer, but in real terms one could just as easy use a door bell, in fact we still call it belling out cables to find out which is which.
How he got the meter to stick to the wall I don't know? But that is a major problem using two leads and holding the meter at the same time you need three hands.
The other problem with multi-meters is selecting the wrong range. I wanted to do "A" digital photography it would cost over £100 but if I did three "A" levels then only £10 for all three so I did two other "A" levels picked what I thought would be easy so Physics and Maths. In the physics students were given multi-meters to measure volts and amps and you would not believe how many fuses were blown as they tried to measure volts with meter still on the amps range and these were "Advanced Level Students" would not like to see those at ordinary level?
With the 12 volt power supply all it did was blow the fuse, however with mains the same mistake can cause ionisation of the atmosphere which to put into layman's language is a big bang. Does not happen every time the error is made, but it is the electricians worse fear, and why we wear PPE when testing live circuits.
One way to ensure you never leave the meter on the amps range in error is not to have a wired amp range, the clamp-on ammeter does not require you to disconnect the wire to measure amps, it also has a volts range, and often frequency and ohms as well. The clamp to measure amps is also handy to hang the meter from something when your using it for other ranges.
One thing you need to watch is most cheap meter will measure mains, but the leads provided with the meter are not suitable. GN 38 (General Notice) lays out what the leads should have, this includes only 1 mm of metal showing, have fuses built into leads, having finger guards to stop your hand slipping down the leads, and a double insulated plug to go into the meter.
At around 14 I bought my pride and joy an AVO multi-minor. It cost a fortune to my mind around £15 which was a weeks wages in 1965. I fried it leaving it on the amps range. So I was no different, it taught me always to leave meter set to high volts range.
When my son started I lent him my AVO Mk8 back in 1982 that was £200 worth of meter, but it had all sorts of safety bits, cheaper meters just let out expensive blue smoke. Latter I got him a clamp-on meter like I used. Now he is also an electrical engineer. But early years back in 1992 I was glad I had fitted RCD protection to all circuits as he tripped them quite a few times when he was studying to become a Radio Ham.
My dad was a power station technical supervisor, my father-in-law electrical project director, my son-in-law studied electrical engineering in Turkey, the other one is into computers, so it is hard to recall a time when we did not know how to work with electric. I was taught keep one hand behind your back, it was an old method to reduce the effect of electric shock.
Hope you have watched your videos and now know how to use it?
