VFD Tripping an RCD

Morning all,

I was going to post this in my build log thread, but thought I'd put it here, as its more appropriate.

Anyway, I have made some good progress with my machine and was going to run a quick test yesterday on a simple job to mark a centre point and then 4 6mm "dowel" holes for a double sided job I have some stock for.

Switched on the VFD (one of the 2.2Kw jobs from Chai) and was immediately plunged into darkness. Groped about for a torch/inspection lamp and reset the RCD (30mAmp) coming into my workshop (it has its own consumer unit, so the main house was unaffected). Thought to myself "may just have been a fluke" so tried again and the RCD tripped again. Its not an overload/short as the VFD has its own MCB and is the only thing on that circuit.

Check my wiring and also fitted the filter I bought from Arc Euro last week, just in case, but every time I switch power to it I get the same result.

So I'm a bit stumped (I read Jonathan's thread, but his seemed to be a dodgy wire and I have good continuity on all my wiring).

Unless anyone has any suggestions I'm thinking the VFD may have "bought the farm" during its long period of idleness, so will likely grab a new one from ebay. Other than that I'm then looking at the RCD itself and perhaps running a completely new circuit or a different RCD rating.

Cheers


Chris

I sometimes get this with my ABB ACS355 drive, it says in the manual that for single phase input models you need a Type A RCD also make sure your supply and motor cables do not run side by side. The drive may have an internal EMC filter, this can cause a leakage current to earth, in some drives it can be disconnected. It's usually best to disconnect all the VFD wiring other than the supply cables and try to energise from there, then begin to reconnect and retest as you go.

When I had that problem it turned out to be a problem with the earth wire, so double check that you've got the earth wire from the spindle body connected to the VFD and that point connected to earth. Also earth the machine frame to the same point.

Thanks guys,

Some more things to check......

It's to do with the filter caps.

I'm guessing you're switching it with a double pole switch?
Try just switching the live wire, and see if things power up without any issues.

If the drive has stood a while then the DC link capacitors may need to be 'reformed', this is how to do it on an ABB drive

Guide for capacitor reforming

I also says in the manual;
"WARNING! Disconnect the EMC filter when installing the drive on an IT system (an ungrounded power supply or a high-resistance-grounded[over 30ohms] power system), otherwise the system will be connected to ground potential through the EMC filter capacitors. This may cause danger or damage the drive. Disconnect the internal EMC filter when installing the drive on a corner-grounded TN system, otherwise the drive will be damaged. NOTE: When the internal EMC filter is disconnected, the drive is not EMC compatible without an external filter"

It's unlikely you suffer from this problem but maybe you are fed from a local transformer ?. A friend of mine had a local transformer just for his property and RCD's tripped all the time.

Interesting suggestion re capacitor reforming.

I reckon it's worth bringing the VFD into the house and testing it alone on a different circuit.

Maybe an issue with the earth to workshop.

Good reasons to move the lights off the RCD.

Ok I will just get the 100 ohm 500 W resistor out of my box:highly_amused:

Quote:

---

Originally Posted by Clive S

Ok I will just get the 100 ohm 500 W resistor out of my box:highly_amused:

---

You could hook it up as a workshop heater when your done reforming your caps.

Never thought about that: could also feed the solar panels into it :whistle:

They used that because it's a common size for the braking resistor.

Hi!
Did you manage to solve your issues?
What was the outcome?

Wow - this was a long time ago.

If I remember correctly I switched out the type B RCD for a Type C to stop the issue and it hasn't tripped since.

depending on the make of VFD
you have you may find the EMI filter required to get the CE mark for sale in the EU has a removable jumper to break the filters earth connection to stop the normal (for EMI filters) leakage current from tripping the RCD

john