# Thread: VFD (?) tripping RCD

1. Left the spindle on for about an hour last night. It was fine. Just been using the lathe for quite a while and no problems there. So the former implies it's not the spindle and the latter implies it's not. That or it's nothing to do with the VFD.

Originally Posted by 2e0poz
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
We do have dinner late ... but not past 11pm when it tripped! So I doubt it's the oven.

Originally Posted by mocha
Bring some power from the house or from next door!
Next door, too many awkward questions like 'What's a CNC Router'!
I'm going to try it once more as normal, then if that fails I'll use an extension lead.

Originally Posted by mocha
The RCCD you point to; 40amp? is it 30 or 100 mA?
30mA ... more is surely not safe?

2. Originally Posted by Jonathan
[*]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.
I would hope so! The IEE recommend (0.1 + cable resistance) ohms earth continuity ,say 0.125 ohms. To get a volt of difference you will need 8 Amps of earth current! If you can, borrow an earth continuity tester and make sure the resistance between parts is less than 0.1 ohm.
[*]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!
Although a potentially unsafe practice this shows no problem. Assuming you are using a digital multimeter as opposed to an old AVO, the input impedance of the meter will be about 10 MΩ. So you are measuring a current of only 18 μA.
something to do with filters in the VFD providing a path to earth - which then trips the RCD
All VFDs produce high levels of RF. In order to comply with the EMC directive they are fitted with RF filters on the mains input. These have relatively high capacitance to earth which results in a high reactive current to earth and can trip RCDs.
Try measuring the leakage current of the VFD on its own. If that is the problem connect it via a separate, lower sensitivity RCD but make sure your earth bonding is good!

Russell.
Last edited by russell; 27-11-2011 at 01:50 PM.

3. Originally Posted by russell

All VFDs produce high levels of RF. In order to comply with the EMC directive they are fitted with RF filters on the mains input.
Russell, are the Chinese spindle / VFD combinations likely to do this too?? I suppose I'm asking if this filter is an "EU" thing or world wide??

4. Originally Posted by mocha
Russell, are the Chinese spindle / VFD combinations likely to do this too?? I suppose I'm asking if this filter is an "EU" thing or world wide??
For anything to be "placed on the market" i.e., sold anywhere in the EU it must comply with all relevant EU directives. It is not a worldwide thing. However for such things to be sold in the USA it must comply with FCC regulations which are basically the same. As that is the largest market for Chinese goods they are likely to comply.

Russell.

5. ## The Following User Says Thank You to russell For This Useful Post:

6. It might help to try and replace the mains rcd, i had the same problem with the house main fuse popping all the time(through the night also) it turns out that after a couple of times the main rcd was too sensative,all fuses are ment to be changed after a couple off trips.(told by an electrition)

7. Update... worked for a long long time running the lathe and coolant pump in parallel (machining stainless). Long enough for the cast iron headstock to warm up a bit.
Failed after about 3 minutes on the router, but this time only the VFD, circuit breaker didn't trip. I just got the 'ELuS' error... I've only had an error before on the VFD when I've been getting a bit carried away on the lathe and overloaded it (so not often).

I'm going to buy another VFD now as I could do with having two anyway as then I can run the lathe and router at the same time. I think I'll get a 3kW one as the lathe plus pump is borderline on the 2.2kW. It will help diagnose the problem, though I hope to have sorted it by then.

Originally Posted by russell
If you can, borrow an earth continuity tester and make sure the resistance between parts is less than 0.1 ohm.
Considering they wouldn't even let me borrow a soldering iron for a couple of hours from Uni, I think there's not much hope of that. Unless there's somewhere else...

Originally Posted by russell
Although a potentially unsafe practice this shows no problem. ... measuring a current of only 18 [FONT=Times New Roman, serif]μA.
Yes DVM, so that's true. I did consider putting a high-ish value resistor from the frame to earth with that test and measuring the voltage across it to see if it will sustain a higher current. Is it worth it?

Originally Posted by russell
Try measuring the leakage current of the VFD on its own. If that is the problem connect it via a separate, lower sensitivity RCD but make sure your earth bonding is good!
I will try that again next weekend. This weekend I only managed to cut one part on the router, and some bits on the lathe

8. Just a thought Jonathan But

Have you checked your water pump and pipes ?? on the router

would it help if I came with my VFD at the weekend to try ??

James

9. Originally Posted by luke11cnc
Have you checked your water pump and pipes ?? on the router
I have checked the integrity of the pipes, but I've not tried running it without the pump as I do not want to risk the spindle.

Originally Posted by luke11cnc
would it help if I came with my VFD at the weekend to try ??
It would help, thank you very much for the offer. However I don't want to risk your VFD as clearly the VFD getting turned off by the breaker is bad for the IGBTs inside it and could well damage or ultimately break them. It's not worth it particularly as your machine is so close to being finished now. Would have finished the parts by now if it wasn't for this.

10. Jonathan,
make sure your RCD is rated at 30mA and NOT 100mA. Around 50mA can kill with the correct fault path through your body, which I think is from your left hand through your body to right foot then to ground.

Ian

11. have you checked for rodent damage ??

as you are away from your work shop in the week rodents will get in and chew cables (just a thought)

has your water pipe got a blockage if a filter is fitted it my be blocked, is the water flowing around your motor ??

James

James

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