How Dangerous are Metal Bodied Powertools?

[Keith 66]

I recently picked up an old Kango hammer, in its case with a pile of chisels. Looked to be in good condition but had obviously been in a damp environment for some time. It dates from around 1956 & still has a Round pin plug on it. Last week I asked my son to check it over & if ok put a new plug on it as we need one for a job in the near future. He started by taking the side panel off the switch & brush assembly. The hall of horrors inside was a death trap. All rubber wiring insulation was like old cheese & the whole lot was heavily corroded.
Heres a photo that speaks for itself. Sometimes its time to call it a day. It has been scrapped.

 

[Rhyolith]

I have bought back ones worse than that. Just replace all the corroded electronics and re-lube the mechanical bits. Nice thing about these old powertools is that they are very rarely beyound repair.

What I have learnt from this thread is how to check what I have done is actaully safe (and has a few safety nets!).

Edit: which reminds me, can someone recommend a cheap multimetre?

 

[Eric The Viking]

Depends what it's for, but for mains testing, personally I'd pick up an old AVO 8 from ebay or similar.

They usually clean up well, and the electronics can be repaired, and they may even be recalibrated (expensively, but AVO are based in Dover, UK, IIRC) but it is _essential_ that they are shipped to you with the selector switches in the off positions: this puts a dead short across the meter coil, which damps the movement and makes it reasonably shockproof. They still need to be packed very well as they don't survive being dropped.

Mine came from ebay, and it's very useful. You do have to remember how it works though, as there's a bit of understanding required. For example the meter coil impedance is usually 2k Ohms, IIRC, not the very high impedance of digital meters. This is good and bad: a digital meter can give false (or at least wildly inaccurate) voltage readings, because it draws almost no current in use. So measuring earth potentials or earth-to-neutral can give you weird values that may not matter at all in practice. They are similarly poor at measuring low resistances. For both these tasks a traditional moving-coil meter (used properly, and that's important!) will give more reliable results, as there will be actual current passing through it.

So if the reason for an odd earth-neutral voltage value is capacitance-induced, your digital meter will possibly lie to you, whereas a multimeter will settle down to a meaningful value.

I'm a bit out-of-date on this, and I'd expect modern Fluke digital meters (for electricians, note!), will probably be spot-on for the purpose, as would the other quality brands. But I can't afford one!

E.

PS: Safety warning: Used incorrectly, all test meters can be dangerous, as you are probably connecting them to live circuits. AVOs have some protection built-in, but it's for the meter, not the human using it.

"If in doubt, don't!" is a good rule of thumb for any electrical testing, and applies particularly to the correct selection of meter ranges. AVOs are excellent but they are also complex and you need to be confident in their use.

 

[Eric The Viking]

PS: There was a version of the AVO8 made with a much higher resistance coil (10k Ohms, IIRC). This is helpful for some measurements and makes it more useful for electronics work, but for electrical testing, probably not so.

They also use batteries that are nowadays unusual - these can be had from RS Components and a few other places (Google is your friend here, probably). The odd ones in the meter should last for years, so not as expensive overall as they might seem. You might also get a couple of 12V car alarm batteries in the same space (haven't tried), but 24V might be OK instead of the 22.5V of the proper thing.

 

[Racers]

I bought an AVO8 many years ago and it is still working fine, I now have about 5 of them as they seen to throw them out at work.

Both low resistance ranges work with the 1.5V C cell.

Pete

 

[Lax Luthier]

That belt sander is a work of art. If you can find a friendly electrician who'll loan you a PAT tester for an hour, it will at least put your mind at ease (or maybe not)
Otherwise, as previous post have already said, replacing old cabling for new rubberised sheathed, a quick check for good earth continuity with a dvm and a fuse with a rating as close to that of the device (or in line rcd) and they should be good for another 50 years.