Inverter Tripping RCD

[EmgeeParticipant @emgee]

Neutral to earth fault.

Emgee

[JohnFParticipant @johnf59703]

John C , let me say first I am not an electrition and thus have limited knowledge and slightly of topic but it may still be useful. My workshop is run on a sub main from the house consumer into a smaller consumer with RCD & MCB's in place of fuses.

I had a problem with my Tig welder tripping the MCB caused by a high start up load, I spoke to an electrition and he advise to change the MCB from a type B to type C problem cured.

David Laurence, we also had a problem similar to yours, had some cowboy outfit install a new bathroom some years ago and at the time the house was on a hard wired fuse consumer. Some years after we installed a modern unit with MCB, RCD etc suddenly we had a problem—-every time we switched on the extractor fan the RCD tripped, no problems before on the old fused consumer unit!

What the Cowboys had done was wire the fan with a live and earth off the lighting circuit from the pull switch and because there is no neutral in the switch they "pinched" a neutral from the ring main !!

My local spark sorted it very quickly but food for thought, maybe have a qualified electrician look at your wireing?

John F

[davebParticipant @daveb17630]

If you disconnect the earth connection of your EMC filter it means that the EMC filter is no longer doing the job it's meant to do. The filter must have the earth connection in place to work.

Dave

[john swift 1Participant @johnswift1]

for the manufacturer the main function of the EMC filter is to enable them to get CE approval

if you look at page 79 in this manual –

https://inverterdrive.com/file/Commander-SK-Technical-Manual-Data

to enable the inverter to be used with a RCD protected supply

they provide a practical solution in the form of a switch to disconnect the earth connection from the EMC filter

 

 

 

Edited By john swift 1 on 09/04/2016 19:04:41

[MuzzerParticipant @muzzer]

Posted by David lawrence 3 on 09/04/2016 17:04:12:

re RCd tripping, I am at the moment having a new kitchen installed, all the power to the kitchen is off but the main house rcd has tripped 4 times in 1 day due to the plasterer moving the dead ring main wires around in the back boxes, explain that. crashed the computer several times, not so happy. David

As Emgee suggests, you can trip the RCD by creating a path between neutral and ground. Although neutral is grounded back at the substation, there can be a voltage difference (few volts) between the neutral and the ground. That's enough to generate sufficient current to trip the RCD in some situations.

I had problems with RCD tripping a few years back due to neutral-earth shorting although in my case it was worsened by the fact I had a TT installation with no effective protective ground connection. I ended up fitting a proper earth spike. But it was a bit puzzling initially trying to figure out how the RCD could trip with no live anywhere near.

[MuzzerParticipant @muzzer]

Posted by john swift 1 on 09/04/2016 18:34:02:

for the manufacturer the main function of the EMC filter is to enable them to get CE approval

if you look at page 79 in this manual –

https://inverterdrive.com/file/Commander-SK-Technical-Manual-Data

to enable the inverter to be used with a RCD protected supply

they provide a practical solution in the form of a switch to disconnect the earth connection from the EMC filter

Edited By john swift 1 on 09/04/2016 19:04:41

The overall installation still needs to meet the legislated EMC requirements but what they need to achieve that depends very much on the individual installation. As the note says, if the motor shielded cables are relatively long, the supplied (internal) filter may not be sufficient. The actual limits are dependent on the line impedance of the branch.

As far as I'm aware, RCDs are fairly unusual on motor installations. I never saw any in the medium-sized (10-30kW) range and I know that larger drives are designed to tolerate a (single) short from the motor side to ground. That approach allows large installations such as paper mills and steel mills to flag the fault up without bombing out. The last thing you want is one of the drives to trip out when you have paper or steel flying through, trashing not just the product but also potentially some of the plant. I know this from first hand, having worked with GEC / Cegelec when I designed the control power supplies for their Gemdrives (50 – 500kVA, IIRC) some years back.

Murray

[ChrisHParticipant @chrish]

John F – please excuse my ignorance, but what is a type B MCB and a type C MCB and how do they differ?

Are type C MCB's readily available?

Chris

PS I ask as that may be the solution to my requiring a long extension lead to my welder to stop the MCB tripping.

Edited By ChrisH on 09/04/2016 21:09:42

[Nathan SharpeParticipant @nathansharpe19746]

ChrisH.

Class B is best described as SLOW rise (Amps) fast trip, Class C as FAST rise slow trip. So Class C can allow for the initial start current on single phase motors which is generally high but safe. Class C is usually called/remembered as Motor Rated and Class B as Domestic rated. Nathan.

[The Novice EngineerParticipant @thenoviceengineer]

This maybe an old topic but still relevant to keep updated.

I have problems with VFD's [Variable Frequency Drives aka Inverters] tripping RCDs in the workshop . It seems worse with an RFI Filter wired before the VFD [some units have the Filter built in so can't be bypassed.] . In the past I have put the VFD on to a Non RCD protected circuit [Industrial Practice] but with a change of workshop this hasn't been possible [easily!] so I have been looking a bit deeper into the RCD topic

Recently I came across this article that should be of interest. Besides the sales push there is good information The Type F RCD has been specifically developed to cope with Motor inverter drives

**LINK**

So far the target price looks around £150 [compared to ~£25 for a good quality Type A RCD]

Another short article explains some of the difference between the differing Types of Circuit Breakers and RCD's

**LINK**

The other information that I have discovered is that Type AC RCD's should never be used with an Inverter, they are designed for lighting and heater loads.

The Type A RCD should be used, or preferably Type A-APR RCD.

There is also another type recommended called a Time Delay RCD and this is designed to cope with the transient surge typically from an Inverter at power-up. Though these are not easy to find and do come a bit pricy as the ones readily available seem to be 100Amp whole house protection [allowing local downstream RCD's to trip without plunging the whole house into darkness], I'm aiming for a 32 Amp version for the workshop/garage.

Trust this might be useful.

Steve

[Clive HartlandParticipant @clivehartland94829]

When my fuse tripped it was the Micro wave oven! I had everything PAT tested (cost £60.00) The Micro Wave failed the test, dumped and bought a new one and no more problems.

Clive

[Steven VineParticipant @stevenvine79904]

Just to add something to this old thread.

If you are having trouble with VFDs tripping RCDs, then maybe try changing, or redoing, your wiring, as a first port of call.

I had an VFD that was working without problem, when plugged into a socket on the upstairs ring main.

I temporarily used the VFD downstairs, to run a 3 phase motor on a drill press. Every time I switched the power off, the RCD tripped.

I have just moved the drill press to a new location in the downstairs room, put a new extension lead on, and redid the wires between the VFD and motor. I powered the VFD from the same ring main socket as before. The RCD does not trip at all now. Why, I don't know.

HTH

Steve

[Martin ConnellyParticipant @martinconnelly55370]

There can be other things on a circuit that have some leakage to earth. If this existing leakage is below the trip current there will be no problem until you add the straw that breaks the camel's back. Heater elements such as are found in immersion heaters, kettles, ovens and electric hobs can be quite troublesome.

Martin C

[Gary Barnes 2Participant @garybarnes2]

I know this is an old post, but the obvious and safe solution would be to put a 230V isolation transformer between the mains supply and the inverter. The type that are used on building sites are available from RS for under £100 depending on size, which is cheaper than getting an electrician in and swapping circuit breakers. The RCD will not 'see' any leakage to earth through the inverter.

[Oily RagParticipant @oilyrag]

An interesting discussion and one where I have had some experience of in both a factory situation and in a domestic workshop. The former led to a cure for the later!

The factory situation was that we had a small machine shop situated at the far end of the factory (offices and stores) building. We had to extend the wiring from the main CB to the far end of the 'shop' (it only had a single phase circuit at the far end but needed a 3 phase 100 Amp supply for the machinery). The wiring was duly done and immediately we had the CB tripping the whole building off. The electrician immediately said that the problem was the RCB timer value being too short. As you all know the RCB works by measuring current 'in' against current 'out' and if it has to travel a long way the time constant needs extending – he upped it from something like 10 micro sec to 25 micro sec and cured the tripping problem. My house had the same problem with the workshop occasionally tripping the RCB on inverter switch on. A change to the timer constant of the RCB cured the tripping.

Edited By Oily Rag on 21/03/2019 10:46:27

[Robert Atkinson 2Participant @robertatkinson2]

This is an old thread, but it contains a worrying comment from john swift 1

"they provide a practical solution in the form of a switch to disconnect the earth connection from the EMC filter"

You should NEVER, EVER REMOVE THE EARTH from an mains EMC filter for any reason. Doing so will leave the body of the filter (and possibly the entire equipment) "live" and an electric shock hazard.

The manual John linked to describes removing or disconnecting the filter completely (not a good idea as the drive will cause interference and is therefore illegal). However in that manufactures smaller drives this is done by pulling a tab that disconnects the filter.

As suggested by Gary an isolating transformer should prevent the tripping, but it brings it's own issues. The drives are industrial components and should really be installed in a circuit with correctly sized protection. Unfortunately most domestic "part P" electricians (and at least 1 supposed industrial one I've met) don't understand the requirements.

Robert G8RPI

[Barnabas TaylorParticipant @barnabastaylor89961]

Hey guys, sorry to get in on an old thread but I have just taken delivery of a 1.5Kw motor and VFD and I am concerned about tripping problems.

Another forum I came across to do with Electric Vehicle charging had an easy to understand explanation about the differing types of RCDs/MCBs and as far as I understand it, it doesn't matter what sort of MCB I have (So long as it takes the current rating) and it is all to do with the RCD.

Now, I have just had a look on RS and they have RCCBs, type B (Which is what I understand to be the type needed?) and they are horribly expensive, with the cheapest being £488+VAT! This is absurd and I assume I am looking at the wrong parts! Can anyone point me to what I should be buying?

Naturally, I cannot get a sparky out for a job like this in the current climate so I was planning to do it myself, if it is simply a matter of swapping components. I would like to get a professional out to checking the whole workshop wiring system once Covid-19 has buggered off but in the meantime, I want to be able to use my motor!

Ta for any help!

[Steve Skelton 1Participant @steveskelton1]

Hi, you are going to struggle to find one at a reasonable price – I came across this when searching. We have a business selling obsolete electrical control gear and we very rarely come across them.

id-65-2998:dev-c&gclid=CjwKCAjw7LX0BRBiEiwA__gNw3ejZT-uMTXxgyXoU1ZlkIqVIa8yutDq4oPUFsE5rrAdDbPebByruRoCB7EQAvD_BwE”>https://www.rapidonline.com/Schneider-Electric-A9Z51240-40A-Single-Phase-2-Pole-30mA-Type-B-RCD-65-2998?IncVat=1&pdg=pla-340003444795:kwd-340003444795:cmp-757438067:adg-98613163406:crv-428566073244id-65-2998:dev-c&gclid=CjwKCAjw7LX0BRBiEiwA__gNw3ejZT-uMTXxgyXoU1ZlkIqVIa8yutDq4oPUFsE5rrAdDbPebByruRoCB7EQAvD_BwE

Cheers

Steve

[Steve Skelton 1Participant @steveskelton1]

Alternatively Proteus do a slightly lower cost one

**LINK**

Steve

[Steve Skelton 1Participant @steveskelton1]

Last one – on eBay but is not a known brand to me, but much lower cost!

**LINK**

Cheers

[Phil WhitleyParticipant @philwhitley94135]

Ouch, that sounds like a lot, are you looking at a 3 or 4 pole RCD when all you need is a 2 pole one? A brief reading of the backstory on this thread seems to show that the understanding of what the filter does in the VFD is incomplete, it prevents EMI and voltage spikes in both directions, in order to protect the VFD from voltage spikes incoming from the mains supply, which would damage the VFD. It does this using a capacitance bridge type circuit which dumps any spike to earth, and depending on the value of the charge that is dumped, plus any residial leakage from other equipment, you arrive at the above mentioned cumulative leakage to earth, and if the leakage current exceeds the tripping current of the RCD, then it will trip, but it may be that the tripping only occurs when other equipment, lighting etc is in use as well, and the cumulative current is greater than the RCD rating, hence a situation where tripping is intermittent. The easy way to solve this is have a non RCD circuit (MCB protected) for the VFD only, or to protect that circuit with its own 60ma RCD (about £35). The other way, and I would recomend this anyway, is to have all the equipment including the VFD circiuts and equipment, checked (including lighting) for residual leakage. Always make sure that all the metalwork of the machine is earthed to the earth point provided by the supply authority. If an RCD trips, it is either sensing a leakage current beyond its tripping threshold, or it is faulty, there is no arcane magic! What often happens to confuse the unwary is that either a spike is discharged as a pulse large enough to cause tripping, but once discharged, does not reappear for some time, or that other equipment on the same RCD has small amounts of leakage, and the small amount of normal current leakage from the filter in the VFD( in other words, the filter doing what it is designed to do) causes the tripping, and the VFD is blamed for the tripping, whereas the tripping is actually caused by the addition of lots of small leakages from other equipment, and switching on the VFD was the "last straw". Leaving the VFD unprotected from spikes by removing or otherwise disabling the filter means that the first mains spike will destroy it, simply doesnt make sense.

Hope this makes sense, and helps with the problem!

Phil.

Edited By Phil Whitley on 08/04/2020 12:36:03

Edited By Phil Whitley on 08/04/2020 12:38:19

[SillyOldDufferModerator @sillyoldduffer]

Posted by Barnabas Taylor on 08/04/2020 11:37:12:

Hey guys, sorry to get in on an old thread but I have just taken delivery of a 1.5Kw motor and VFD and I am concerned about tripping problems.

…

Have you actually got a tripping problem, or just concerned there might be one?

If the latter, I'd try plugging it into whatever you've got and trying it. No trip = no problem.

Otherwise, it's possible for several small leaks to accumulate enough to trigger a shutdown, even though the devices are all individually OK. (The trip can't tell the difference between a single big fault leak and a combination of small deliberate leaks due to EMC filters as fitted to many household devices.) A new appliance might be the straw that breaks the camels back rather than root cause.

If a new device causes a trip, it's worth unplugging everything else and reconnecting in various combinations. Possibly one or two of them are the big problem, not the new VFD.

I'm reluctant to recommend removing EMC filters – although the radiation is silent and invisible, it's anti-social. Bypassing the RCD with a rusty 6" nail isn't done either!

Dave

[Barnabas TaylorParticipant @barnabastaylor89961]

Cheers Steve, those are a bit more reasonable! It still amazes me why this is not a simple (cheap!) solution. Do most VFD users simply not replace their RCDs? Or do they just pay a huge electrician bill and never mention it when they say VFDs are great? Did I make a huge mistake buying such a thing as I now cannot afford to install it and use it? If I was less conscientious, I would never have even realised I was supposed to worry about such things because it rarely comes up on the knifemaking forums, where VFDs are very common…

I have a further problem because the slightly sketchy electrical set-up to the garage (left over from the previous owner) has the supply coming off the house DB, to a DB in the shed with an RCD to a DB in the garage with simply a breaker and MCBs. I think this means I need to replace both the RCD in the shed DB and the RCD in the house DB which is then a lot of money!

Would it be cheaper to get a man in to rewire the garage to an earth spike? are there problems with such a set-up? I remember my grandfather telling stories of him rigging up his own earth spike from a fence pole when he was about 12… He went on to have a successful career in the power distribution industry!

[Barnabas TaylorParticipant @barnabastaylor89961]

From what I gather from my own research, the problem with a VFD is not so much the earth leakage but that you need an RCD that will protect against more than just an AC current. Hence the silly priced versions.

this how-to blog is very handy but doesn't sold the cost issue!

How-to-Use-Inverter-Drives-with-RDC-Earth-Leakage

 

The type B ones still seem to trip at 30mA so how that helps with VFD leakage trips I am not sure, whether you have to just have them on a separate circuit which is yet more cost!

Edited By Barnabas Taylor on 08/04/2020 12:47:41

[Steve Skelton 1Participant @steveskelton1]

Hi Barnabas,

Yes you are right , it is the DC component that causes the problem. You can use a basic AC type RCD which will trip on a pure AC fault but if the DC component is too high it may not trip. I am not an expert on VFD systems but the same problem can occur with charging systems for electric car charging systems and solar power installations.

It is no consolation for you but the price of Type B RCD's will drop as the demand increases.

I imagine that most people do not fit Type B units – probably from a lack of understanding they fit AC types.

My advice would be to do exactly as the manufacturer recommends as they are the experts but I would have thought that it is only the supply to the VFD that needs the Type B RCD and not the rest of the house.

Steve

[duncan webster 1Participant @duncanwebster1]

When I first got a VFD it was the MCB which kept on tripping, not the RCD. I cured it by fitting a fuse instead, it coped with the inrush current

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