Zapped by my lathe

[quantumeer]

While merrily screwcutting on my mini lathe this afternoon, one hand on the handwheels, one on the electrical controls, I was treated to a healthy zap of mains electricity.  It didn't last long, because it tripped the RCCB through which I power it.  However, I was moved to express a modicum of surprise, and reflected that RCCBs were a good thing if one did not want to fry like an electric pickle (e.g.

).

I take a pretty dim view of stuff that tries to kill me, so a rapid investigation ensued.  Anyone with a lathe having an electrical control panel like this might do well to check for similar dangerous construction.



Note the metal switch handle, and aluminium panel (with worn paint). 

Internally, there is no attempt to earth the metal parts, and take a look at the lower blue wire soldered to the speed pot:


How close is that to the metalwork of the switch?  Much too close.  The pointer below shows where a tiny movement of either switch or pot can put a zapworthy voltage on the switch frame, and thus on both the switch handle and the metal panel.


Yow!  So now I have not only to correct the slapdash wiring, but I think also check the electronics, as it doesn't seem right any more.

Mark

[awemawson]

Mark,

I'm sure if you bring this to the attention of Roger Warren at Warco he will be as horrified as you are and do something to rectify the problem. He is an honourable businessman in my experience.

[trevoratxtal]

Mark Without the trip you could have been dead.
The worst kind of electric shock is across the heart,
arm to arm, or arm to opposite leg.
Now retired Electrical/Mechanical engineer, have received many shocks over the years, but due to the one hand rule, ( one hand in your pocket ) I survived all but one without injury.
That one was while at the top of a ladder adjusting an aerial one hand on the element one on the metal pole.
My father an avid fiddler plugged in the coax cable to an old type TV ( live metal no isolators but bleed resistors only)
He nearly killed his eldest Son, as I fell 12 feet landing on my head.
I have been a MAD MODDER ever since.
Mark you are lucky and I wish you well, the design of you lathe electrics is very poor and must be corrected, the manufacturers and distributors have a duty of care so do follow it up.
Most of all a big thank you for bringing it to our attention so others can be spared the shock.

Regards
Trev

[Stilldrillin]

Food for thought Mark, Trev! 

My speed control has loosened, and is beginning to rotate in use....... 

Time for investigation. TODAY!! 

David D

[BillTodd]

if the lathe was bought in  the uk, you should contact trading standards now!

there is no way a CE marked device, properly earthed  (3 pin plug) should give you a shock. It should have either tripped your house RCD as soon as power was applied or blown the plug fuse .

there is a serious flaw in both the wiring insulation (that mains wiring should be sleeved) and the earthing of the machine (it would fail a  PAT test).

report it. before someone is killed.


bill

[awemawson]

It's a Warco - Warren Machine Tools in Guildford - as I said in post #2 get in touch with Roger Warren asap

[BaronJ]

While merrily screwcutting on my mini lathe this afternoon, one hand on the handwheels, one on the electrical controls, I was treated to a healthy zap of mains electricity.  It didn't last long, because it tripped the RCCB through which I power it.  However, I was moved to express a modicum of surprise, and reflected that RCCBs were a good thing if one did not want to fry like an electric pickle (e.g.

).

I take a pretty dim view of stuff that tries to kill me, so a rapid investigation ensued.  Anyone with a lathe having an electrical control panel like this might do well to check for similar dangerous construction.



Note the metal switch handle, and aluminium panel (with worn paint). 

Internally, there is no attempt to earth the metal parts, and take a look at the lower blue wire soldered to the speed pot:


How close is that to the metalwork of the switch?  Much too close.  The pointer below shows where a tiny movement of either switch or pot can put a zapworthy voltage on the switch frame, and thus on both the switch handle and the metal panel.


Yow!  So now I have not only to correct the slapdash wiring, but I think also check the electronics, as it doesn't seem right any more.

Mark

Hello Mark,

You were lucky !  At least the ELCB saved you from any worse.

When I got my mill one of the things I specifically checked for was that it was properly earthed.  It wasn't !  Though unlike yours, on mine the earth wire simply hung in mid air.  It wasn't connected to anything.  There was an earth screw with a tag on it but nothing else.

You need to report that problem to the supplier double quick.  You may prevent someone from getting electrocuted.

[lordedmond]

The only way you could have had a belt from that setup would be if the metal cover over the electronics was not bonded to the frame and the earth conductor PE is bonded to the main casting


The speed pot wire would have been at a logic level vac not at mains vac

I would look further into to root cause of the fault

And double check the bonding of all the loose bits of metalwork

Stuart

FWIW I had one of those lathes that after one week used to start up by itself and run in reverse if you moved the chuck , to give credit were its due Warco took it back and refunded without any problems, yes I could have fixed it but it was not right so it was return to sender

[quantumeer]

Thanks for all your concern.  I'll see what Warco have to say.

Just to sort out the technical bits:

The only way you could have had a belt from that setup would be if the metal cover over the electronics was not bonded to the frame and the earth conductor PE is bonded to the main casting

Metal cover? It's  plastic, so no bonding possible there.  I can confirm the earth on the casting is fine ;)

The speed pot wire would have been at a logic level vac not at mains vac

Nope, the pot sits at something like half-wave rectified mains potential, by design.  The electronic design is actually pretty reasonable; the implementation on mine was incompetent.  Not unlike the mechanics, really.

Mark

[lordedmond]

Mark

All I can say then is that they have altered the design over the years mine had a metal cover and the logic board was of an early design and was not the USA ones

Sorry for the error but I was quoting from my unit

If it is plastic and the switches and pot are at the level you state then they should be on a bonded plate because they are not classed as double insulated as should all metal parts to conform with CE mark. Is it a true mark or one of the look alike ones with the centre of the E not quite the correct length

Hope Warco do right for you


Stuart

[zimma]

The speed pot wire would have been at a logic level vac not at mains vac

Nope, the pot sits at something like half-wave rectified mains potential, by design.  The electronic design is actually pretty reasonable; the implementation on mine was incompetent.  Not unlike the mechanics, really.

Mark

I'll second that one. My KBCC-225R motor controller has the speed pot at mains potential. I found out the hard way. I suspect most DC controllers operate in the same way. I wonder if the person wiring them up just assumes that they are at logic level, and not mains level, and therefore just solder up any old wire without putting any protection in (As i did before i found out).

[hopefuldave]

The "CE" markings on Chinese lathes refer to "China Export", not what you'd expect...
The majority of Chinese lathes are electrically unsafe, for instance the Wanko WM series and it's ilk run the mains input through the chuck guard and belt cover "safety" microswitches which are rated at a lower current than the lathe motor draws, mains cables with high resistances (particularly the earth, regrettably), the RFI filters aren't unearthed so they radiate unacceptable levels of interference.
The CE marking is stipulated to only be applied to equipment that exemplifies "best practice" which doesn't come with building down to a price rather than up to a standard.

Don't get me started on duplicated 'test certificates' with identical measurements on a whole batch of lathes....

[quantumeer]

I guess it's time for a conclusion.  On the good side, Warco were very efficient at exchanging the dodgy control box for a new one, despite the original being a decade old. No arguments, no delays.

On the bad side, their new box is constructed almost identically to the old one, which is fine until the controls work loose.  Oh, and a terminal had come unriveted from the emergency stop switch.   So before installing the new box, I repaired it, installed an antirotation locking ring to the reversing switch, earthed the exposed metal, and put an insulating partition in the obvious place.  It works fine.

Overall, I am content with what I got from Warco, but it is disappointing that their communications (and indeed the replacement box they supplied) showed little concern or awareness of what they are doing, beyond shipping boxes.

Picture time (new box).  Can you see how far I had to rotate the switch to make its lever live?


The moral of this story is to look on the electrics of these cheap machines with the same suspicion as the mechanics, reputable importer or not.  And fit an RCD.

[Meldonmech]

Hi

      Thank you for bringing this topic to the attention of the members, anyone having this type of control on their Mini Lathe or other machine, should have them checked out by a qualified electrical engineer. You cannot afford to operate machinery that has suspect electrical faults. Keep safe, keep alive.

                                                                        Cheers David