Strange fault ML7

[Haydn CallowParticipant @haydncallow19480]

Hi, have had a ML7 for a few weeks now….very occasionally when I switch it on it trips the house RCD……but it now in the last 2 days it trips every time I switch to FORWARD….When I switch to REVERSE it works fine….the lathe was a refurbished one with new motor (3/4 HP) and new switch….(the switch is a fairly cheap one in a green plastic case)

I have released all the belts so no load being applied

where should I start to find the fault ?
thanks

Edited By Haydn Callow on 22/08/2022 20:32:53

[Haydn CallowParticipant @haydncallow19480]

Tripping RCD

[Swarf, Mostly!Participant @swarfmostly]

Good evening, Haydn,

I suggest that, before delving into very technical test equipment, you disconnect your lathe from the electricity supply and then perform a very careful visual inspection. It's surprising what the Mk. 1 eyeball can find if given its opportunity.

The nature of the symptoms you describe suggest that you should be looking for illicit contacts between wires rather than for loose connections, though connections that are SO loose that they can make illicit contact are sometimes encountered.

I repeat: perform the checks I have suggested ONLY after the system is definitely isolated from the mains supply.

If the Mk. 1 eyeball finds nothing, then you may need the help of test equipment, initially a good multimeter.

Best regards,

Swarf, Mostly!

[Haydn CallowParticipant @haydncallow19480]

Thanks for that……I have looked as best I can, everything within the switch looks good and tight….this is a refurbished ML7 and the guy who supplied seems to have done a good careful job…

[EmgeeParticipant @emgee]

Hi Haydn

Probably best for you to seek the help of a friend with electrical knowledge to have a look for you, they may even have an insulation tester to trace the fault, unless of course it turns out to be intermittent in which case it will be more difficult to find.

From what youv'e said the fault seems to be on the motor feed live supply, check that at all positions for leakage to earth problems.

As said by Swarf make sure the power lead is disconnected from the socket before venturing into the electrical boxes.

Emgee

Having just read your latest post you could contact the supplier of the lathe, he may offer some help/advice.

Edited By Emgee on 22/08/2022 20:55:33

[old martParticipant @oldmart]

Fine swarf can get into motors and cause earth faults before the big bang.

[noel shelleyParticipant @noelshelley55608]

Is it dropping the RCD or an MCB. You make reference to THE HOUSE, is it on a long feed to a shed ? A fault in the reversing switch ? One direction is causing a problem with the centrifugal switch in the motor. Just a few thoughts ! where are you in the UK ? Noel.

[Haydn CallowParticipant @haydncallow19480]

I’m pretty sure Swarf is not the problem as I have built a shield around the motor. I have contacted the supplier and a new switch is on the way. I will swap the switches and and see if that resolves the issue.
I have read that these switches should not be used to switch power on, is it better to set the direction of rotation first then turn power on via a separate switch (even the socket switch )

[Clive Brown 1Participant @clivebrown1]

Since the fault only occurs with the switch in the "forward" position, I'd see the switch or its wired connections as prime suspect.

Incidentally, take care when switching a Myford into reverse. the chuck can uhscrew with startling effect.

[Haydn CallowParticipant @haydncallow19480]

It’s tripping the RCD so half the house goes down….the wire to the shed is about 25ft but armoured cable professionally fitted. I am in Somerset TA11 7NB… the lathe has been working well for some weeks after when first fitted tripping the MCB a few times which I put down to a new motor running in .

[Haydn CallowParticipant @haydncallow19480]

Clive Brown, thanks, I’m hoping a new switch will fix things….I suppose with these switches you get what you pay for.

[noel shelleyParticipant @noelshelley55608]

Mostly these switches are a way of changing direction of rotation NOT starting or stopping the motor. In an ideal world there would be a direct on line starter with overload, set correctly AND a reversing switch. Select rotation THEN start with the DOL. Noel

[Haydn CallowParticipant @haydncallow19480]

Noel, DOL ??

[Haydn CallowParticipant @haydncallow19480]

Got it, direct online

[old martParticipant @oldmart]

I found a link, it may be us**LINK**eful.

[SillyOldDufferModerator @sillyoldduffer]

Take it logically and trust nothing! Off the cuff:

Is it an RCD or a Circuit Breaker. Can you provide details of what's exactly in the consumer unit

Does an Mains tester illuminate correctly in the workshop on all the sockets? I was thinking one like this

but I see technology has moved on, only slightly more expensive:

Probably not, but could be the wiring to the shed or within it. Does the RCD pop if something else with a beefy motor like a vacuum cleaner is substituted for the lathe? Try several times/ Any other hint of trouble in the shed such as lights flickering etc. Do the lights flicker or dim when the motor first starts to turn?

Is anything else electrical fixed to the lathe such as a machine light? If so remove and disconnect it, and try again.

Just to be sure, is the lathe fitted with a single phase motor or a three-phase motor and VFD?

Probably not, but open up the plug and check the wires inside are OK and on the correct terminal. Follow the wires into the lathe and make sure they connect soundly in the lathe too. Look at all the connections between the switch and motor. Check for damage wherever wires have any opportunity to chafe ot touch the metalwork. If the wiring has been recently replaced, it's possible the insulation was nicked with a knife or damaged during installation.

Is the shed damp or the could the lathe be wet in any way?

If the motor runs completely OK in reverse, and only pops in forward, it suggests the motor is OK, and the fault lies in the switch or in the forward wiring between switch and motor. I agree with Hayden that the switch is the most likely suspect. Reversing switches aren't meant to switch the motor on and off and it can damage them; it may not be rated for UK voltage; or there's debris inside. Not unknown for too-cheap switches to contain bits or for bits to fall off when the switch is operated.

Good hunting!

Dave

[Haydn CallowParticipant @haydncallow19480]

Silly old duffer, thanks for the thoughtful reply, the motor is single phase, I have other hefty machines in the shed and they don’t cause problems….I’m betting on the switch. Will keep you all informed.

thanks again

[duncan webster 1Participant @duncanwebster1]

I had a motor once which tripped the RCD on start up, turned out to be arcing from the centrifugal switch to ground. Can't see how this would be dependant on direction tho'

[MacolmParticipant @macolm]

To trip a simple RCD (one that does not include overload protection), it needs something to contact the frame (which is earth connected). The symptoms described suggest a spurious contact at or near that end of the start winding that connects to live at forward, and to neutral at reverse. This could indeed be a fault in the switch, but equally could be a chafed wire touching frame, and so on.

I would suggest you try to find the fault before simply disturbing everything to change the switch. It is all too easy to temporally dislodge the fault only for it to return a month or three later.

[Haydn CallowParticipant @haydncallow19480]

It’s the RCD that trips

[Dave HalfordParticipant @davehalford22513]

Are you using the reverser switch for the on/off as well?

It's very easy to arc the contacts if you do, which deposits metal nearby and gives you a earth leakage issue.

[Haydn CallowParticipant @haydncallow19480]

Dave, yes I have been……I’m fitting a new switch and putting a DOL in the mains lead before the selector switch.

[Haydn CallowParticipant @haydncallow19480]

Well ! New switch arrived, very excited this morning, very carefully took photos of the old switch wiring positions and fitted the new switch…..really really excited now….big switch on and ???? BINGO, exact same fault as before, ran lovely in reverse but tripped the main RCD when switching to forward………phoned the supplier of the lathe ( it was supplied with a new motor and switch a month ago.) All he could understandably offer was for me to send the motor back and he will fix it or send another…so, spent a hour removing the lathe from its bench and removed the motor…I examined all the wiring and took the cover plate off the rear of the motor……everything looked neat and tidy with no obvious faults……so the motor and switch are now packed in a box ready for the Post Office to collect tomorrow….16 kg large parcel only £12.60 including collection from our house…

more to follow, I will keep you informed.

[Haydn CallowParticipant @haydncallow19480]

With ref to this post….when I am up and running again, I have a dol switch ready to fit. Newlec 240 volt….do I just put in the mains wire to the Forward Off Reverse selector switch ? Then in future select direction of rotation and use the dol to provide power ?
thanks

[noel shelleyParticipant @noelshelley55608]

Haydn, If the DOL has overload then you need to set this to the Full Load amps as stated on the motor data plate. This means the DOL must have a current rating to suit the motor. The coil in the DOL is 240 V ? Most DOLs are intended for 3 Phase and it was considered a good idea to use all 3 thermal heaters , so live would be in, cross linked to the second and out whilst the neutral would be in and out. Then the live and neutral would go to the FNR switch and onto the motor. If you take ME then look for an article called " smoke signals" about 2 years ago and some of this will become clear.. ALWAYS select direction on the FNR switch first, then start with the DOL. NEVER throw the the FNR into the other direction unless the motor is at rest. Good Luck. Noel

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