Inverter Tripping RCD

this is like a post I answered in this thread on cnczone -

**LINK**

if you look at post 20 reference is made to the 28mA earth leakage due to the VFD's EMC filter and how to disable it

see page 79 in this inverter drive manual : -

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

john

Edited By john swift 1 on 03/04/2016 16:23:36

Thanks again Gents, more good info. I shall report the results of any changes, John.

For what its worth.

Our house wiring is still on hard wired fuses. (we avoid blowing them!)

The workshop is fed through an RCD from a 13 Amp socket. The shop is wired with a ringmain, and the VFD is fed through a filtered socket on that ring. Since installation in late 2003, the RCD has never tripped, (My problem is stopping SHMBO switching off , by mistake, the socket that feeds it) nor is any interference fed back into the house wiring, judged by the behaviour of TVs and radios.

Howard

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

Neutral to earth fault.

Emgee

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

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

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

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.

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

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

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.

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

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

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

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

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.

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

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

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!