Inverter Tripping RCD

I had a search of the forums, but didn't stumble across anything about this.

I have 240v single phase to 240v 3 phase inverters in my workshop, which is powered from the house supply. Lately, the house RCD has begun tripping, sometimes when first powering a motor from the inverter, sometimes when the machine is running. Only one inverter is powering a motor at any time.

I have read that inverters and RCDs are not good companions. Does anyone have any suggestions to cure the problem of the house RCD tripping? The RCD is about 20 yrs old.

I am considering changing the existing RCD to a type B RCD, or replacing the consumer unit with an isolator and RCBO type, but I am not sure if RCBOs suffer the same problem with inverters.

Many thanks for any info,

Rgds,

John

Hi,

I run 2 inverters of the same make on the house supply, again, not using both at the same time and i've not had a problem like this, you have to investigate what the tripping current is on the RCD (i have a seperate RCD in my work shop), it could be an over current or some wires have been crossed somewhere and it's shorting. This could be many possible reasons for this.

Michael W

There's no such thing as a type B RCD. B designates a time/current curve applicable to MCB's. One of your options is to have a professional electrician install a designated circuit for your inverters. He may then use a time delayed RCD of 30mA tripping current, or, depending on how he installs and designs the circuit, he may use an RCD with a greater than 30mA trip current, or in some cases if the circuit is for items of permanently connected equipment and the circuit is for the sole use of a person skilled in the safe use of such, an RCD may, as long as overcurrent protection and effective means of earthing is in place, omit the RCD altogether,.. However, the design and installation methods for the cables are paramount. An electrician who is competent to the 17th edition regs as amended 2015, and not one who pretends he or she is will be able to advise.

The supply to my inverter was professionally installed and on the advice of the inverter supplier is not via an RCD. It has a 20 A breaker and two independent earth connections.

Rick, with all due respect B type RCD's do exist and are used where there is a DC component. With standard AC RCD's they sometimes do not trip if the coil becomes saturated due to the DC component.

See http://www.abb.co.uk/product/ap/seitp329/4bd0ec0528a84420c1256f5500557772.aspx

I would suggest contacting the inverter manufacturer for advice.

Very often inverters has a filter near the input connection

you can switch/unplug this

look in the book for instructions

if the filter is installed it will trip the rcd

Hi John,

99% certain it is an earth leakage which is very common with inverters. I had the same issue on mine a while back, since I was not certified to play with the mains and change the breaker back to an mcb I chose to remove the earth to my inverter.

The supply was earthed, the motor earthed and the inverter plastic, so there was no reason why it needed an earth. After removal it never tripped again confirming it was earth leakage.

The reason it happens is because the filter capacitors negative terminal is grounded, electrolytics can leak current. If your inverter is metal then do not under any circumstances remove the earth, you would have to modify the inverters internals otherwise.

I'd go the way Stuart describes but i have to say I find the whole question of VFD and RCD's baffling when I was working I had lot's of problems with tripping something to do with earth leakage if I remember correctly, but it's just accured to that both my shed and workshop are fed from RCD's and never had a problem

H

Thanks for all the replies Gents, much appreciated. I will digest the knowledge imparted and think about what to do. At least I now am better informed than an hour ago!

Once again, many thanks for your helpful and knowledgable input.

Best regards,

John

John C,

I don't have an inverter in my workshop, but all the various garden services are supplied from the workshop consumer unit; these include two pond pumps which I know to be 'lossy' things anyway each with measurable leakage to earth.

After we had a PV system installed we started getting earth leakage tripping at irregular intervals and our installer rewired the system via its own dedicated circuit. He confirmed that the PV inverter itself produced about 10mA earth leakage and any other stray leakage elsewhere could easily lead to enough to trip the house breaker.

On his advice I later on had our own electrician fit a further earth leakage protected unit in the supply to the workshop, which was, and this is the crucial bit, referenced back to its own local dedicated earth rod so that the house breaker was no longer 'seeing' any leakage on the workshop power supply. The two 'earths' operate completely independent of each other.

End of problem.

Inverters all need a degree of earth leakage loss to work anyway and it may be that you have altered the conditions domestically such that your house breaker is now reading a total loss approaching 30mA.

My electrician convinced me that all is well with my new arrangement, for example the effect of damper soil where the earth rod is installed can be dramatic, just pouring a watering can full round it will make a big difference, and with variable soil conditions it is all a purely relative business anyway.

I hope that provides some food for thought.

Brian

Two things that will help are as follows:

1. Leave filters connected if they are there and either way fitting a separate filter/choke will help. RS part number 219-2791 would probably cover your needs but check the current etc.

2. Ensure you have only one earth point (try searching for "star earth". You want to avoid creating an "earth loop".

You might also want to check you have the drive parameters set properly and also consider a motor side "reactor" which is another filter/choke to smooth out some of the output - it will also help the life of your motor if it is not a specific inverter duty motor.

Mark

From memory, it was the EMC filter that was likely to trip a RCD rather than the inverter itself. I do have a separate EMC filter on my inverter.

More excellent advice - many thanks!

John

Hi Stuart,

your correct, something I overlooked.

I originally thought it was the filter and I was gonna modify it, turned out the filter was all integrated, some ferrites, one capacitor across the output, the rectifier and then the large inverter filter capacitors, nothing to ground apart from these inverter caps. just a common mode filter in my case which is why it could only be the large filters for me.

I have had this problem at work with 2 new inverters (different makes). The company I work for has 2 buildings the 1 with the most recent wiring trips the breakers (motor rated) the other is fine. I was told by both companies that it was the filters. They were removed and the system worked fine in both buildings. I was told that removing the filters could possibly lead to noise affecting sensitive electronics nearby. However in both cases there was a smart relay fitted in each cabinet with the inverter and these have been fine.

Regards.

David.

I've not had an RCD tripping but I have had the welder tripping the MCB. The mains cable from MCB to power socket was quite short (DB was in workshop). The tripping stopped when I put a long extension cable on the welder supply. I don't know why - I've forgotten all the 'tricky electrics" I ever knew.

I also have a digital readout on the mill DRO switching off when I start the mill motor. The mill motor is single phase a with a capacitor. I have a gut feeling the capacitor start motor is causing a spike in the circuit - just a gut feeling, no theory to back it up - so I have just bought a surge protector to see if that will stop the DRO readout switching off.

Sorry if that has diverted the thread a bit, but it was sort of related. It's electrical and a trip!

I have a rule. NEVER trust anything with wires coming out of it. Tricky animals, electrical stuff.

Chris

Thanks all again.

John

The solution to John Cs problem is to have the shed on its own RCD. It may help if the tripping is caused by cumulative earth leaks and at least it wont be a nuisance to the people indoors when it does trip.

I have occasional problems with the RCD tripping when I switch on my 2HP inverter (momentary surge to earth from the RFI filter?)

My MCB frequently trips when I power up my arc welder or 110V site transformer (transformer inrush current)

As with ChrisH, an extension lead helps to alleviate the problems (adds a bit of resistance?)

A small inductor would probably have the same effect, any experts able to comment on this?

Dave

Here are a few cheap suggestions.

I read this on another forum somewhere. Guy had problems RCD trips. Tried various things. Ended up having a look see inside the inverter, saw nothing wrong, but wiggled a lot of internal wires. Hey presto, his problem was cured.

I had an inverter running on the upstairs ring main, controlled on and off via a switched fused spur, which was wired to a 3 pin domestic plug. I had no problems with that set up. A little while ago, I temporarily used the inverter downstairs, and plugged it directly into the mains via a normal 3 pin plug. When I pull the plug, the RCD trips. One time, I pulled the plug out and touched the pins; I got quite a big shock, so there is a fair voltage laying around on the inputs to the VFD when the power supply is removed.

Maybe pull the VFD apart and have a gentle fiddle inside, just to move a few things about (careful of capacitance). Give it a hoover out and a clean. Then try disconnecting all wiring and reconnecting. Maybe try using a different isolation hardware, or a different wiring arrangement (i.e. change something). You never know your luck.

I think the forum also mentioned replacing the RCD as an electrician suggested they wear if they trip frequently.

If you can, try connecting a borrowed good known motor to the VFD and see what happens.

Temporarily move the VFD into the house, plug it in to another circuit, try it out, and see what happens.

Steve

Edited By Steven Vine on 03/04/2016 15:27:23

Edited By Steven Vine on 03/04/2016 15:32:03

Edited By Steven Vine on 03/04/2016 15:38:17

I had to change an inverter on friday on a very large walk in industrial washing machine, I switched the machine off and gave it the obligatory 5 mins then started undoing the three phase wires when I touched the blade of my screw driver, I got a belt from the capacitors.

When we install our inverters we use 3 core + earth, screened cable, the screening is earthed with the earth wire, as the interference can drive the Siemens S7 PLC nuts, maybe its something to do with that.

Martin P