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  1. #1
    [Edit - sorry this has ended up being a very long post. Wanted to mention everything so that everyone doesn't reply saying to do something I've already done!]
    "
    Refrained from posting this yesterday afternoon when the problem started as I expected to have found what's wrong by now. Sadly that's not the case.

    In short RCD has started tripping when I run the router.

    It's happened 4 times this weekend, all on the same aluminium part. Today and yesterday the machine ran for roughly half an hour then the main 40A breaker for the workshop went (switching off everything including the lights which is a bit annoying). Yesterday when that happened I switched everything back on, zeroed it ... lasted about 30 seconds and tripped again. Then I tried to start again, but found the parallel port on that computer is now broken :cry: Switched to backup computer, all seemed fine after running for a couple of minutes then bang... electric went again. By that time it was past midnight and I'd spent about 5 hours trying to cut a simple Z-axis plate, so I left it. Tried again today, same again ... worked for about half an hour then tripped ... then worked for 10 mins without tripping which was enough to finish that part. At least the cutter survived every time. Spindle was left at 185Hz throughout ... not getting hot either.

    The RCD trips at a seemingly mundane time - not when the VFD is turned on, or when the current changes quickly or anything like that.

    Things I've tried, all of which made no difference:


    • After the first fault I measured the voltage between machine frame/spindle at various points and earth. Less than a volt AC and DC in all cases. Machine frame and spindle are both earthed.
    • Measured the voltage above with the spindle running, same result. If I disconnect the earth wire I get 180VAC between frame and earth...so I didn't do that for long!
    • Measured voltage as above between everything I could reach with the meter with the spindle running and touching the aluminium it was cutting.
    • Switched of all non essential appliances - i.e. left air compressor, heater and de-humidifier off. So just stepper drivers, spindle, computer+monitor and lights. It has only tripped with the router on, never without so it must be the router or something related.
    • Connected the earth wires a bit more securely.
    • Cleared about 5kg of aluminium swarf, made by the router, off the floor. Though it might be conducting or something...yes I was desperate!
    • Searching on google.
    • I've not changed anything since last weekend and the weekend before when the machine was fine. Even using the same cutter and same aluminium!
    • Measured current to earth ... negligible reading.
    • Measured insulation resistance from the 3 phase wires to earth (spindle body). It's high, megaohms.


    I've heard and read before that you shouldn't use an RCD with a VFD, but mine's been working fine for almost a year now with one so I didn't worry about it. How could it suddenly be causing a problem. I don't really want to just bypass it without knowing why it's tripping and without good reason.

    Maybe the VFD is on it's last legs? Hope not...bit worried about starting again as whatever the fault is appears to have already killed one computer which is quite impressive seeing as it's optically isolated!

    Really want to get this sorted soon as I've got parts that need cutting asap.

    Left my oscilloscope at uni, so if it's not sorted by next weekend I'll bring it back to aid diagnosis - might pick up something the multimeter wont.

    I'll go and make some bits on the lathe now, which I power from the same VFD (got a big switch to swap them over). Hope it works.
    Last edited by Jonathan; 26-11-2011 at 11:38 PM.

  2. #2
    I've had a fair amount of bacardi and coke but will try to help. First thing is never to disconnect and earth conductor with the main supply still live. This is a very easy way to kill yourself and wont really tell you much. Do you have a 40 amp mcb and seperate rcd or is it a combined rcd and mcb? It doesnt take alot to trip a 30mA rcd, apart from 30mA a dodgy computer power supply or filter unit could do it. Does the protection trip with only the router,vfd and the computer/ cnc running? Can you run the vfd and router on its own without the cnc controller? If it still trips this way and doesnt trip when you use your lathe then it could be the spindle motor. You will need an insulation tester to check the windings. A multimeter wont find any high resistance faults.
    Ran out of bacardi now:cry:

  3. #3
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 8 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,831. Received thanks 192 times, giving thanks to others 5 times.
    I know it's not the most ideal way to test, but ammeter in the earth wires to see if there's any measureable leakage?

    Should at least be able to isolate if it's the VFD, or motor causing problems.

  4. #4
    Quote Originally Posted by Web Goblin View Post
    First thing is never to disconnect and earth conductor with the main supply still live. This is a very easy way to kill yourself and wont really tell you much.
    I know ... I was getting a bit desperate thinking if doing that still got no reading then it implies something's wrong with my earth or my meter. I kept one hand in pocket whilst doing that for obvious reasons. Isolated the supply, connected the meter etc ... switched it on, saw the voltage and switched it off straight away. You're right of course I probably shouldn't have done it.

    Quote Originally Posted by Web Goblin View Post
    Do you have a 40 amp mcb and seperate rcd or is it a combined rcd and mcb?
    To be precise, It's one of these, which is what trips every time:
    http://www.europacomponents.com/prod...%206KA&pso_id=

    6A one of these for lighting, and 32A for the ring main.
    http://www.europacomponents.com/prod...20Curvepso_id=

    Armored cable up the garden (maybe 20 meters) from house to workshop.

    Quote Originally Posted by Web Goblin View Post
    a dodgy computer power supply
    Using a different computer after the first one just broke, and it's not likely that they're both dodgy.

    Quote Originally Posted by Web Goblin View Post
    Does the protection trip with only the router,vfd and the computer/ cnc running?
    Yes - but it's only happened whilst cutting.

    Quote Originally Posted by Web Goblin View Post
    Can you run the vfd and router on its own without the cnc controller?
    Started just that as soon as I read your post ... nothing interesting has happened yet.

    Quote Originally Posted by Web Goblin View Post
    You will need an insulation tester to check the windings. A multimeter wont find any high resistance faults.
    Ahh, I suppose a multimeter doesn't test at anywhere near a high enough voltage.

    Seeing as it only happens after the machine *has been* on for a while that implies something is accumulating, then setting it off. So what could that be, charge, heat...? Maybe the spindle insulation is breaking down once it's been on for a while and causing it to trip. I really hope not as those things are not cheap.

  5. #5
    Quote Originally Posted by m_c View Post
    I know it's not the most ideal way to test, but ammeter in the earth wires to see if there's any measureable leakage?

    Should at least be able to isolate if it's the VFD, or motor causing problems.
    I did that, second to last bullet point. But thanks anyway...

    If the problem persists I could try putting a shunt resistor in the earth wire and leaving the oscilloscope (DSO) monitoring it. Set the trigger to whatever voltage corresponds to say 10mA, or just under 30mA (something like that) and see what I get when it trips.

  6. #6
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 8 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,831. Received thanks 192 times, giving thanks to others 5 times.
    Ah, you did mention that (I've been helping a mate move house today, so am currently a bit tired!).

    I'd be more inclined to try it with an ammeter, as that way things are still tied to earth, and give a better idea if it's something slowly building to tripping point, or something causing a more sudden spike. Of course an oscilloscope would be better, but you may as well try with what tools you've got to hand first.

  7. #7
    Quote Originally Posted by m_c View Post
    I'd be more inclined to try it with an ammeter, as that way things are still tied to earth, and give a better idea if it's something slowly building to tripping point, or something causing a more sudden spike. Of course an oscilloscope would be better, but you may as well try with what tools you've got to hand first.
    I have so far only tried it with the ammeter. Oscilloscope (http://uk.farnell.com/gw-instek/gds-...our/dp/1563796) goes down to 2mV/div ... so I could in theory use an about 0.5ohm resistor and it'd still show 30mA.

    Spindle is still running ... that's been over half an hour. Only difference I suppose is it's now running unloaded, so not going to heat up much unless I restrict the cooling. Not going to try that as I'm a fan of non destructive analysis!
    Last edited by Jonathan; 27-11-2011 at 12:55 AM.

  8. #8
    Assuming you haven't overlooked anything or missed something in the tests you have already done... It sounds similar to a problem I had with radios some years ago. ...

    Bring some power from the house or from next door! but bypassing the RCD unit, with a standalone RCD if necessary, (but if you are happy to have a hand in your pocket while disconnecting earths you probably wont want to! lol)

    Try plugging each of the suspect items; the VFD? into the extension lead with everything else plugged into the main RCD, as soon as it stops dying or the problem disappears you have the suspect device cornered for further investigation

    or... find a way of removing DC from the AC line back to the RCD, or split board supply??

    The RCCD you point to; 40amp? is it 30 or 100 mA?
    Last edited by mocha; 27-11-2011 at 01:54 AM.

  9. #9
    NB70's Avatar
    Lives in Swansea, United Kingdom. Last Activity: 3 Days Ago Has been a member for 8-9 years. Has a total post count of 44. Received thanks 5 times, giving thanks to others 3 times.
    Jonathan,
    there's been discussion about this recently on the EMC2 mailing list - something to do with filters in the VFD providing a path to earth - which then trips the RCD. So it might not be a fault per se, just the way the VFD is designed to work. I know Andy Pugh and others experienced this issue (and hopefully solved it). He frequents the EMC2 forum - it might be worth asking a question over there:

    Link: EMC2 forums

    Nathan
    Sorry Jonathan just re-read your post properly - since your set up was working fine for a year this is unlikely to be the cause
    Last edited by NB70; 27-11-2011 at 10:44 AM. Reason: Read the original post properly

  10. #10
    I thought i should give you an experience i suffer from which may help?

    50% of the time i switch my lathe on i trip the main breaker. This is because of the in rush of current to the 2kw inverter controlling the lathe (tested this by switching inverter on before applying breaker and all ok).

    When the lathe is running it will trip out the main breaker, took ages to work out why. The reason for this is because the oven is on in the house, when the temp on the oven gets to a certain point the temperature control causes an earth problem (expansion). A known issue with a lot of ovens if you google it

    To fix my issue when i get time is to run new armored cable i bought to the workshop. I shall connect it to a type 'D' RCBO to the none RCD side of the consumer unit in the house and use type'D' mcb's in the consumer unit of the workshop.

    If the misses is really lucky i might get a new temp control for the cooker ;-)

    In short look for other items that are on for a while as the problem may not happen until warmed up? i appreciate what your going through as it too was a long time for me to find my issue. For the time being i can work round it so no rush.
    If the nagging gets really bad......Get a bigger shed:naughty:

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