Warning Signs

Hindsight is so much clearer than precognition I must say.

Back when I got my Nova lathe, I mentioned I was getting some small shocks from it.  Annoyances really.  I raised it with the Australian supplier, and that didn’t raise any warning flags either.  As it happened, I saw some tweets from Teknatool (the manufacturer) recently which promoted me to get in contact again, and they immediately responded. That was pretty impressive.

Back to earlier: in hindsight, I, or the supplier should have taken more notice of those little shocks.  You shouldn’t get shocks from an earthed machine.  I know that.  They should have.  But for some reason, I didn’t, and it went through to the keeper.

So fast forward to the present.  As soon as Teknatool heard, they got straight into contact with me, even to the extent of one of their senior engineers ringing me directly from New Zealand to get more information, and to help problem solve it.  Impressive.

Now back in time again, I had tested just how much current was passing from the lathe to the shed (and therefore what was giving me a jolt).  Now if only I had instead tested the earth at the same time, a big red flag would have gone up.  The machine was not earthed.  It is not a double insulated machine (and many of those don’t even have an earth pin): it needs a functioning earth.

I’m not criticising Teknatool / Nova here.  As I will show in the following photos, it is so easy for it to happen.  Perhaps Teknatool should actually glue the earth wire to the earth pin.  Perhaps the tester in the Chinese plant wasn’t as diligent as he should have been.  Who knows, but at some stage in transportation of the lathe, the connector came off the earth, and the tool became dangerous.

Other manufacturers could just as easily experience exactly the same problem.  And all it takes is a very quick check with a multimeter to ensure there is continuity between the earth pin on the flex, and part of the tool itself.

If it wasn’t for an idiosyncrasy of the DVR motor that caused the slight jolt I was feeling when I happened to touch the lathe and the shed (or another tool), I would never have known to even test if the earth was connected.  In the workplace, we regularly (annually) get everything tested and tagged.  Rare to do that at home!

I happen to have access to an actual megger meter so I was able to take the test one step further than simply testing the earth, and that there is no continuity between active and neutral, active and earth and neutral and earth. (All can be done with a mulitmeter.)

Under the specific guidance of the company engineer, I removed the cover from the lathe.

Before

After

Bit dusty in there!  Before going any further, and it is a bit dusty, check out the awesome indexing wheel! (Sorry about the image quality – iPhone rushed shot)

Once the cover was off, time to work out where the issue is.

Well there’s your problem!  The earth wire from the chassis connection point to the back of the plug is not connected. Once I fitted it, it was obviously tight enough that it shouldn’t have come off easily.  A Chinese Friday on the Superbowl weekend perhaps?

Whatever the reason, this demonstrates that we tend to trust a tool that is new is right, especially when it works without actually checking for ourselves.  I am not condoning opening each new tool to check the wiring inside, but a simple check with a multimeter that the earth is working correctly before plugging it into the shed for the first time is simple, quick, and could potentially highlight a problem easily missed otherwise.

It is a shame basic PATs (portable appliance testers) are so expensive (around $1000).  There is no justification for them to be this much, after all they are not much more than a glorified multimeter, and a basic multimeter can be picked up for $30.  They do test other things – namely the quality of the insulation, but it shouldn’t cost an additional $970 to achieve that!

What I suggest is get yourself a basic multimeter and actually test the earth of your machines.  You may want to consider actually getting one of those testing and tagging guys to visit the shed and test and tag your machines.  Not sure what they charge at street rates – at my work I bring in external companies, and they charge between $2.20/test and $2.80.   If you consider how many tests your shed would represent, that is a pretty small number, and therefore a pretty cheap annual check that everything is still as it should be.

In this case I did have the megger meter, so ran a proper earth and insulation test. 2 ticks, 2 passes.

After all, insulation ages and cracks, rats & mice can eat through insulation, wires inside your cables can flex and break, machines vibrate, and nuts holding earthing straps on can come loose, and we do play with things that can cut cables, or have sharp edges and break a cable pulled over said edge.

Whatever the mode of failure, the older the shed, the longer it has been since things were checked, the higher the chance that something important could have been nicked, cut, snapped, worked free or perished.

Food for thought?

One Response

  1. Did you blow/suck the dust out?

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