Variable Frequency Drive tripping out the earth leakage in my house.

[AllTheGearNoIdea]

 I’m not sure if we have in UK electricians in the house but I need some advice.

I have just bought a new milling machine and it uses a variable frequency drive. Anyway when I switch it on it takes out the earth leakage breaker in the consumer unit. I have used VFDs in the past in industrial application and I’m aware they have some quite large filter capacitor and I’m guessing that’s my problem.

My test bench with a stack of Marconi analyser and computer sometimes trip them out a few times a month.  But this machine just trips instantly.

Desperate to try my new machine I’m running via an isolation transformer and it works fine but the transformer really underrated 750VA for 1.5VA machine.

Assuming the machines not faulty what are my options can a less sensitive RCBO be installed or should I just buy a bigger isolation transformer.

I have a PAT tester is this likely to damage anything like the VFD. What’s the easiest way to measure earth leakage or get to the bottom of what’s tripping.

Any advice welcome.

[Zero999]

If a larger transformer is not practical. The only advice I have is get it permanently wired in, preferably by an electrician, on a separate circuit to everything else, with a 100mA RCD.

[AllTheGearNoIdea]

Yes I don’t think it will be practical to wire in a new circuit. I am getting a quote for a large isolation transformer.

[jmsc_02]

When I was working in the elevator field the solution to that common problem in places where a VFD was installed is by replace the breaker by another called as "high immunity" (I don't remember the exact name).

[jmsc_02]

Note: some VFD has a little stick where you can decouple gnd and work isolated. We usually do this at the office (not industrial installation) when a test involving vfds is needed

[SeanB]

You might also look into installing the line reactor in the supply, which does a good job of increasing line inductance, and as well as taming the diode input current spikes it also has a big side effect of reducing leakage current through the RF filter capacitors to ground. As well install a big inrush limiter, either a capable NTC thermistor ( with 1.5kVA will be big) or just a  power wire wound resistor and a contactor to short it out instead after a 2 second time delay.

[AllTheGearNoIdea]

Thanks for comments the line reactor sounds interesting. I don’t think the time delay will work or the  NTC as the VFD is switched in out of circuit via a main contractor  interlock with the main guard. I’m thinking a large isolation transformer is the way to go as that how I have it work. It’s likely that the transformer itself is going to need some inrush protection, although I have specified a low inrush in my enquiry to a supplier.

I am guessing I need to determine if it is current inrush or the earth leakage.

[fourtytwo42]

I think you are following the right path (isolating trafo), the problem is it is an industrial drive that is also very noisy so it has large Y capacitors causing the leakage problem, of course they are designed not to trigger 100mA industrial rcd's. However residential rcd's are normally 30mA at most hence the tripping. You dont say if your consumer unit has individual circuit rcd's or there is just one on the incoming grid supply (as is often the case in rural installations).
The other problem you may encounter using industrial equipment in a residential area is complaints about tv and in particular broadband inteferance and you may have to fit additional line filtering to counter that!

[AllTheGearNoIdea]

I was just watching a big Clive YouTube Video with him using a current clamp meter to trace these RCB type proplems.  So I have order the same sensitive clamp meter to do some checks.  The machine also has a forced air cooling motor and a transformer. I think I will disconnect the VFD an double check if it still trips.  It could be a duff motor or mains transformer and I need to be sure I’m not masking a real problem using the isolation transformer.

I’m not exactly sure what’s installed in my consumer unit. I have one large consumer unit but it has two large breakers that look like main switches.  When the unit trips the lights in the house stay on but the sockets go off.  The machine is installed in my garage and the supply is a spur from the kitchen plug socket circuit I think.  The house installation is relatively modern about 20 years old.

Just had a look at the consumer unit and the device that is tripping is marked as an earth leakage device.

Many thanks for the comments and advice all are appreciated.

[fourtytwo42]

Just had a look at the consumer unit and the device that is tripping is marked as an earth leakage device.

So my guess is this is a combined 30AMCB and 30mA RCD, can you take a picture of it and post it ?

Cheaper than expensive test gear buy a 30AMCB without RCD for TEST ONLY and see if it still trips.......

[Edison]

When switching off the shield when using the inverter, it can (if otherwise work) mostly lead to an EMI filter.

[Kjelt]

I have the same issue with a small 3-phase machine.
Some suggestions:
-give the machine its own rcb, remember that the current unit already has many mA's leakage from your fridge, washer, tv etc etc, so it only has perhaps a margin of 20mA's left from the 30.

-use a ssr with zero phase switch on , you get less "spike" noise which also could cause the ecb to trip.

-check the mains filter. In industrial machines they dont give a hoot about leakage currents. I replaced my original mains filter for a 0,5mA low leakage Schurter, lowered the tripping margin significantly.

Then normally with modern vfds they recommend special classB rcb's but those cost over €500 and probably won't solve your problem. They are only less sensitive for the higher frequency distortions.

Good luck and keep us updated.

[Edison]

Just remember that - residual currents are summed
If the protector is in the common circuit with the other device, leakage may occur on another device, when the last leakage machine is connected, activation occurs.
If you do not sensitive enough ammeters Use with caution equivalent circuit.
Disconnect the GND in the device connector - connect the disconnected wire to the mAmeter, connect the second lead of the meter to the wire N the device will be grounded to N and will not switch off the protection. The replacement wiring will only work if it is not connected to an external GND. After the measurement, return everything to the correct terminals !!!

:idea: I do not know what the standards say about you, but in CZ - each circuit is a separate protector (due to the price someone gives a central = fault)
Circuit 230V combined fuseprotector or fuse + protector
Circuit 400V fuse + protector   ( for 400V combined protector is not )

[Edison]

Yes I don’t think it will be practical to wire in a new circuit. I am getting a quote for a large isolation transformer.

the value protector determines  of the environment, not a user  

[capt bullshot]

For lab use, we usually remove the Y filter caps from the VFDs (at the place where I do work, and for lab use only).
There's another not recommended way: isolate the VFD from earth and connect neutral to it's earth.

Note, either way breaks with some rules, so I clearly didn't recommend that ...

[AllTheGearNoIdea]

Thanks for all the comments and suggestions. I’m going to speak to the supplier Warco on Monday and see how helpful they are feeling.   I’m going to unplug all the other equipment in the house to reduce the other residual earth currents from any other equipment as my rcbo could be on the edge of tripping.

I guess I should also just try disconnecting the VFD as there quite a few other motors on the machine. The Vfd and forced air fan both come in together from the main contactor so either could be at fault.  But the filters on the VFD look most likely to me.

Thanks again I will keep you all posted with my progress.

Regards Chris

[Vtile]

Mathematical expression of the situation described above.
VFD + RCD = Problems

[Edison]

Mathematical expression of the situation described above.
VFD + RCD = Problems

YES 

[FrankE]

Is it wired into an isolator or plugged into a 13A socket?
If the latter have you tried it in a filtered socket eg K1816 WHI
The mitigation for circuits supplying equipment having high leakage current eg SMPSs in BS7671 is more about induced voltage, bigger cables 4mmsq for a ring main, dual earths and in more technical environments an earth grid with .

 As someone pointed out leakage currents are additive. At tower blocks the leakage currents I used to measure on the main earthing conductor were in the 10s of Amps.

Could you fit an inlet filter?

[Electro Detective]

...I have a PAT tester is this likely to damage anything like the VFD.

What’s the easiest way to measure earth leakage or get to the bottom of what’s tripping.

Whatever you do mate, DO NOT do any insulation tests on the VFD via your PAT tester or any megger, or you will be starting another thread here   


If it's easy to get into, I'd be having a quick look inside the VFD for any grounding issues and correct A/N polarity, and the stuff mentioned by members above

You could try disconnecting everything in the premises and see if the VFD causes earth leakage trips   

Also consider that the earth leakage device may be degraded if it's old and or weathered,
just changed out both of mine after 14?  years, both were suss,
the new ones pass every external leakage test I can throw at them, the old ones fail intermittently   

Perhaps try powering VFD through a 25 to 50 metre long rolled up extension cord to soften the turn on, might save cash on a transformer 
(Warning: urban myth backyarder jerry rig alert!) 

[AllTheGearNoIdea]

I spoke to the machine supplier  today and they were not unhelpful but clearly new a lot less about domestic installation and VFDs than I do. They just said that it worked fine when tested at the factory and said it should be run off a 16 amp supply and it’s design for industrial use. I said if that’s the case why is it supplied with a 3 pin 13 amp UK plug.

So yes is just plugged into a socket. The sales sheet says it can be run from a domestic supply. But apparently not one that RCD protected as all new domestic installations are.   I do need to pull the lid of my consumer unit at the weekend  and check the standing residual earth leakage.

When I said PAT test I wasn’t suggesting insulation resistant test. The pat tester  I have shows earth leakage by default. However switching the machine on takes out the breaker so disables the PAT tester. However thanks for the warning that’s a good thing.

So I ordered a 3KVA isolation transformer as the machine is working from a 750VA at the moment.   I am a little concerned that this could be masking a real earth fault and I need to investigate this a bit further.

My other concern is that if I do ever get a real live to earth fault in the future that the circuit breaker won’t trip as it will no longer be referenced to earth. I am wondering if should connct one of the secondary winding to earth and neutral conductor?

My house is PMA so I don’t have a real earth anyway as the  earth is bonded to the incoming neutral conductor.

I think the idea of the long extension lead to reduce inrush is a good idea. If I can actually power the machine up I can measure the residual earth current and disconnect VFD and cooling fan.

Thanks again for all your comments it’s been helpful. I’m going to investigate further at the weekend as I cannot keep put the wife in darkness every 5 minutes. 



Best regards Chris

[AllTheGearNoIdea]

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I was thinking about something similar to this. The reason im considering bonding the neutral to earth on the secondary of the isolation transformer is so that a real earth fault on the machine will clear the circuit breaker.

Does anyone have any thoughts on this.

Regards Chris

[AllTheGearNoIdea]

Just spoken with the distributor for the inverter  in the UK and they were very helpful.  There is a RFI link that can be cut taking the filter capacitors out of circuit.   This sound like the best plan rather than messing about  with isolation transformers.   Should have spoken with those guys first.

I will have a look at this next weekend and report back regarding if it works.

Regards Chris

[Kjelt]

Add your own low leakage filter or you will be jamming the neighbourhood 

[sibeen]

There is a RFI link that can be cut taking the filter capacitors out of circuit.   

Dear sweet WTF. Lets cut out the circuitry that lets the unit comply with IEC regulations for RFI and EMI

Or perhaps you could look into RCDs that are especially manufactured for just this problem. Look up type F & B RCDs. F generally for single phase VFDs and the B and B+ models for three phase industrial machines.

[FrankE]

Just remember that - residual currents are summed

I swapped out every MCB for an RCBO to prevent nuisance tripping, each room on it's own ring main and put the fridge and washing machine on their own circuits to reduce the consequences of ring mains being down.

My Iso-Tech ILCM is unfortunately in the 'repair someday' box and it was bloody handy when it was a working unit. When it worked I had an IEC lead with a section of sheath stripped from mid cord to measure earth leakage from units with IEC inlets.

Could you borrow a CT to plug into a multimeter, a PA tester or an earth leakage clamp meter?

It's a good idea to have separate circuit for your bench (with isolating transformer and emergency stop) and workshop equipment.

[AllTheGearNoIdea]

There is a RFI link that can be cut taking the filter capacitors out of circuit.   

Dear sweet WTF. Lets cut out the circuitry that lets the unit comply with IEC regulations for RFI and EMI

Or perhaps you could look into RCDs that are especially manufactured for just this problem. Look up type F & B RCDs. F generally for single phase VFDs and the B and B+ models for three phase industrial machines.

Dont see the point in looking at RCDs that are not allowed for domestic installations.   Im not loosing much sleep over the EMI for a machine that  going to be run for a only a few minutes at a time every few months or so.  I would rather have a safe installation.

Chris

[AllTheGearNoIdea]

Just remember that - residual currents are summed

I swapped out every MCB for an RCBO to prevent nuisance tripping, each room on it's own ring main and put the fridge and washing machine on their own circuits to reduce the consequences of ring mains being down.

My Iso-Tech ILCM is unfortunately in the 'repair someday' box and it was bloody handy when it was a working unit. When it worked I had an IEC lead with a section of sheath stripped from mid cord to measure earth leakage from units with IEC inlets.

Could you borrow a CT to plug into a multimeter, a PA tester or an earth leakage clamp meter?

It's a good idea to have separate circuit for your bench (with isolating transformer and emergency stop) and workshop equipment.

Hi frank

Thanks for the commnet, I do already have an isolated bench in my electrical shop but this is for the garage where i have a  new single phase milling machine using a VFD.  I have ordered a sensitive clamp meter and I am waiting for it to arrive. I am going to investigate the standing leakage current for my installation as it could already be high and the machine start up is just pushing it beyond the limit  of 30mA. Im also going to borrow a installation tester to check out what its actually tripping at.

Many Thanks Regards Chris

[Zero999]

[imghttp://][/img]

I was thinking about something similar to this. The reason im considering bonding the neutral to earth on the secondary of the isolation transformer is so that a real earth fault on the machine will clear the circuit breaker.

Does anyone have any thoughts on this.

Regards Chris

The only issue with that is, it voids any protection against shock, given by the isolation transformer and you then have a circuit which is not protected by an RCD or isolation transformer.

Instead, you could install a leakage current monitoring system to warn you if there's an earth fault.

[AllTheGearNoIdea]

Hi the circuit does show an RCD on the secondary side of the isolation transformer. That’s why the neutral  is strapped to the earth conductor.  But I cannot say I am happy with any of these arrangements.

I thought I had hit gold with my previous post about disconnecting the RFI filter on the drive but on close inspection I cannot find the link.  It could have already been cut at the factory or I may have the wrong model of VFD. Unfortunately the model number is obscured by a transformer that cannot be removed without removing the whole panel back plate. Bloody annoying.

I did however spend an hour investigating tonight. I disconnect all the various circuits that are pulled in by the main contactor including the VFD.  I then put them back one by one and power cycled the machine.

Well much to my surprise I found that it’s not just the VFD Tripping the RCB. The main spindle motor has a auxiliary mains powered fan for forced air cooling at low speeds.  When I connected this fan the RCB tripped out about 40 percent of the time at switch on and about 40 percent at switch off. 20 percent of the time it was OK.  Well this is a first for me, the RCB Tripping when the load is disconnected ?

With the fan motor disconnected I did a 500 volt insulation resistance test on the motor and it passed at nearly 1 Gig Ohm.  I also powered the motor with the neutral disconnected and the live connected and  this should have tripped the RCD if there was a real earth fault but it did not trip the RCD.  I’m starting to think it is an issue with a spike but this is a relatively small motor so would not have expected this caused a trip.

I also plug transformer based welders and welding inverters into this supply these don’t trip the RCB so I’m really at a loss.

It’s annoying I cannot power the machine up off the RCB protected supply without Tripping  so I am unable to make measurement. Running via a transformer hides any potential fault so again cannot make a ground reference measurement.

I’m starting to think I should run the machine off my petrol generator. I’m assuming that neutral and earth are the same point on a generator  but I can at least get some real measurement without the RCB tripping out constantly.  Or strap neutral of the secondary to the machine earth pin for testing. It’s no longer  acting as an isolation transformer but this should be fine fo testing.

[calexanian]

I have had this problem myself. I tracked it down to RFI down the mains line. I re bundled the motor leads in metallic conduit and warped the line cord a few times in a ferrite and made a common mode choke. That fixed it. VFD's are bassically little low frequency radio amplifiers and the high frequency/relatively high current has a way of getting into things and causing problems.

[Edison]

Equivalent circuit for measuring

[Electro Detective]

I'm not sure if an AC leakage clamp meter will show much, especially if the issue is high frequency based or chopped or distorted waveform/s via cabling bleed kicking all over the shop

There may even be a freaky DC component in there too 

Even the better big dollar AC clamp meters might extend from 2khz and stretch to 10khz,
most roll off at 500hz to 2k, they are really geared for 50/60/400hz apps afaik

A cable break current measurement with a 100khz AC bandwidth multimeter might be a better way to go,
even a Fluke 87V may not cut it, it rolls off at 14 to 20khz  and your issues may be at 40 to 70 khz 


The transformer is obviously killing off the generated leakage nasties because it's a LF device for starters, coupled with the isolation/magnetic/air decoupling factor 

Not sure how a generator would cope with such a VFD load btw, especially if the gen has onboard regulator and cutoff electronics, so 'try before you buy' 


If you don't find an issue with the VFD itself or a safe workaround, I'd be going the way I do it for -temperamental- devices

I plug them into a properly rated isolation transformer with FULL ground/earthing on the input and output and the metal box chassis and transformer body,

and check that the central earth/ground bonding point isn't a halfassed job done with flimsy washers/screws/bolts,
squashed on to the paint or powder coating by some Friday afternoon manufacturing process from across the the ocean...  

and transformer OUTPUT neutral and earth ground tied together


Most MIS-LABELED so called 'isolation transformers' come wired this way anyway, aka 'medical isolation transformer' labels etc
so all you have to do is open the box and verify for yourself visually
and or do it the easy way with a good multimeter on Ohms continuity check (not buzzer) if the box is rivetted/pita to get into.
Naturally you do all this with the tranny in the ON position and disconnected from the death mains!   

Basically if the earth/ground reads ok everywhere expected, and the transformer neutral and earth/ground read as connected 'zero ohms',
you should be good to go and 100% legit,
no DIY hackery or isolation guesswork and prayer required     

With a transformer wired this way you also have the option (recommended) to plug the VFD into a portable RCD/GFCI (and maybe a MCB too) and into the transformers output,
and if it trips due to a mishap, your earth leakage device upstream at the switchboard won't know or care
You can also use the TEST button on the portable RCD/GFCI to ensure the function works

otherwise... it's oscilloscope time, with all the pita 'proper procedures' to suss out safely wth is going on where...
without taking out the scope    or zapping the already frustrated VFD owner...   

[Zero999]

Hi the circuit does show an RCD on the secondary side of the isolation transformer. That’s why the neutral  is strapped to the earth conductor.  But I cannot say I am happy with any of these arrangements.

Sorry, I missed that, but adding the RCD after the transfromer would just move the nuisance tripping elsewhere. I suppose at least it's not the whole house being taken out, so it's an advantage.

And the correct term for the equipment to detect insulation failure, in a circuit powered off an isolation transformer is an insulation monitoring device.

I thought I had hit gold with my previous post about disconnecting the RFI filter on the drive but on close inspection I cannot find the link.  It could have already been cut at the factory or I may have the wrong model of VFD. Unfortunately the model number is obscured by a transformer that cannot be removed without removing the whole panel back plate. Bloody annoying.

I did however spend an hour investigating tonight. I disconnect all the various circuits that are pulled in by the main contactor including the VFD.  I then put them back one by one and power cycled the machine.

Well much to my surprise I found that it’s not just the VFD Tripping the RCB. The main spindle motor has a auxiliary mains powered fan for forced air cooling at low speeds.  When I connected this fan the RCB tripped out about 40 percent of the time at switch on and about 40 percent at switch off. 20 percent of the time it was OK.  Well this is a first for me, the RCB Tripping when the load is disconnected ?

With the fan motor disconnected I did a 500 volt insulation resistance test on the motor and it passed at nearly 1 Gig Ohm.  I also powered the motor with the neutral disconnected and the live connected and  this should have tripped the RCD if there was a real earth fault but it did not trip the RCD.  I’m starting to think it is an issue with a spike but this is a relatively small motor so would not have expected this caused a trip.

I also plug transformer based welders and welding inverters into this supply these don’t trip the RCB so I’m really at a loss.

It’s annoying I cannot power the machine up off the RCB protected supply without Tripping  so I am unable to make measurement. Running via a transformer hides any potential fault so again cannot make a ground reference measurement.

I’m starting to think I should run the machine off my petrol generator. I’m assuming that neutral and earth are the same point on a generator  but I can at least get some real measurement without the RCB tripping out constantly.  Or strap neutral of the secondary to the machine earth pin for testing. It’s no longer  acting as an isolation transformer but this should be fine fo testing.

I know I'm probably clutching at straws here. What sort of motor does the cooling fan use? Is it brushed? Does it have a filter capacitor which is leaking AC current to earth and tripping the RCD? Or perhaps it's EMI which is interfering with the RCD, causing it to trip?

[Elasia]

I might be lambasted for this but I've also had to deal with this issue working on projects out of the house with similar motors.

Put the motor on a dedicated circuit with proper grounding and circuit protection just like in a commercial / industrial setting and toss the resi rcd.  Problem solved.  When you go to move.. remove the extra feature so the locals don't bust your balls.  I got an entire lab in my basement of gear that would just eat a rcd/gfcis lunch for breakfast.

Yes they provide great value at protecting a nation of darwins at large but in some specific use cases they are just garbage.  Newer models are getting better though at dealing with current inrush and voltage spikes since you can get ones with microprocessors in them now that can figure out if its real or just another motor.

[sibeen]

There is a RFI link that can be cut taking the filter capacitors out of circuit.   

Dear sweet WTF. Lets cut out the circuitry that lets the unit comply with IEC regulations for RFI and EMI

Or perhaps you could look into RCDs that are especially manufactured for just this problem. Look up type F & B RCDs. F generally for single phase VFDs and the B and B+ models for three phase industrial machines.

Dont see the point in looking at RCDs that are not allowed for domestic installations.   Im not loosing much sleep over the EMI for a machine that  going to be run for a only a few minutes at a time every few months or so.  I would rather have a safe installation.

Chris

I will be the first to admit that I don't work with domestic situations, nor do I live in your jurisdiction, but I'm wondering why a type F RCDO isn't suitable for a domestic installation. I've had a very brief flick through AS/NZS 61009.1:2015 "Residual current operated circuitbreakers with integral overcurrent protection for household and similar uses (RCBOs)" and cannot find anything that precludes the use of a type F. AS/NZS 61009.1 is reproduced from IEC 61009-1 with some national modifications added.

[fubar.gr]

VFDs can also cause the opposite problem: preventing RCD from tripping.

This is due to the DC component they inject into the power lines. The current transformer in the RCD saturates and won't trip should a genuine ground leakage appear.

The solution to this is to use B type RCDs instead of the most common AC type. They are expensive though

[AllTheGearNoIdea]

Just a couple of comments.

The machine is in an outbuilding about 20m from the house. My house is a TN-C-S I have no earth conductor coming into my house. The earth wire going to my power sockets is actually is actually connected to the neutral where the power supply comes into my home. Now this is a crap system has lots of issues and is done to save the utility company a few bucks is copper wire back to the utility transformer.

Now my understanding of the regulations is that plug socket have to be RCB protected  in the U.K.

It’s doubly important that if you have a outhouse away from the main property that this supply  is RCB protected.

The supply to the outhouse is a spur from the plug sockets in the kitchen.

So it’s probably not practical or allowed within the regulation to have plug sockets in my outhouse that are not RCB protected. This rules out rewiring or putting in a dedicated supply as it would still have to be derived from the rcb.

A few post mention changing the rcb. I’m not and expert regarding these however for a domestic application the maximum trip current is 30mA the Tripping time is also defined. So although other RCB may be available they may not be useable for a domestic installation in the UK.

If your an electrician in the U.K.  perhaps you could advise

Many thanks

[capt bullshot]

That's a bad situation for you, alas.

From the technical side, it is clear that this setup won't work if you obeye the laws and regulations ...
Another clear thing is, neither law nor regulations can override laws of physics, but laws of physics won't even care about any law or regulation.
So my advice would be to follow law of physics to get your setup working, or to have a real safe (in the sense of laws and regulations) outhouse, since there won't be any dangerous moving parts there ...

BTW, the power distribution system you describe is quite the same here in Germany, there's no separate earth wire within the Low Voltage Distribution network.
And the yearly increased requirements from law and regulations bring up quite a lot of  here too.

So either you are forced to obeye these regulations (e.g. because you're working in a company and no one is willing to take responsibility) and do some  stuff to get your stuff up and running, or you just choose to take responsibilty for yourself and ignore parts of the regulations ...

[sibeen]

The machine is in an outbuilding about 20m from the house. My house is a TN-C-S I have no earth conductor coming into my house. The earth wire going to my power sockets is actually is actually connected to the neutral where the power supply comes into my home. Now this is a crap system has lots of issues and is done to save the utility company a few bucks is copper wire back to the utility transformer.

Just a quick note on that. It's not a crap system. It's a multiple Earth Neutral (MEN) design which is used all around the world. At the switchboard the neutral and the earth are combined. In the UK they use the plumbing piping or such to form the bond to earth. In Australia we are much more civilised and require that a dedicated earth stake be installed for each domestic premises

A few post mention changing the rcb. I’m not and expert regarding these however for a domestic application the maximum trip current is 30mA the Tripping time is also defined. So although other RCB may be available they may not be useable for a domestic installation in the UK.

This is why I mentioned the type F RCD in my original post. These are made for a domestic application with the type B and B+ for industrial/commercial. They are designed to tolerate the high frequency noise components that things like VFDs put out. They also comply with the 30 mA tripping and can be selected with different tripping current to suit the type of cable that you are feeding.

[Kjelt]

The machine is in an outbuilding about 20m from the house. My house is a TN-C-S I have no earth conductor coming into my house.

I am not uk qualified.
If allowed I would replace the powercables to your building. Starting from where the mains enter the main house you create a special power group with only a large safety fuse (20A or so) use very thick cable (6mm² or so) to cut the losses.
In the outbuilding this cable gets its own cabinet and create a new seperate ground (should be struck and tested). From that basis you can continue properly distributing power with seperate groups and rcb to each machine.

[sibeen]

kjelt, I was going to suggest that but I'm not sure what the rules are in the UK for that. In Australia you can do as you suggest, run a supply to a new board and form a new MEN point at the new distribution board. The RCBO would then be installed in the new switchboard to run the GPOs within the building.

[Kjelt]

In Holland they loosened the rules such that the owner is responsible after the main switch.
That means you got to stick to the rules or if fire breaks out the insurance company might not pay out but it gives lot of room to do what you need.

[AllTheGearNoIdea]

Hi Sibean

Thanks for the heads up on the F type RCBO I will ask an electrician for some advice on this.

Regarding the TN-C-S. I disagree on that it is a crap system with no avantages but saving a few bucks in copper. Its dangerous and has many flaws. I girl was killed in the UK only 1 week ago after touching an outside tap.  It looks like the property had a neuttal fault.  Im also a radio ham TN-C-S is a nightmare as you cannot easily ground outside equipment as you have potential fault cuurrent paths down Coax cables etc.

I think I need to investigate a bit further. I know a currently clamp wont be fast enough to catch the high speed transients etc but it will show a normal earth leakage fault and can discount this as the problem.  If it look to be purely just a transient issue there are measure that can be taken.

Chris 

[Elasia]

Hi Sibean

Thanks for the heads up on the F type RCBO I will ask an electrician for some advice on this.

Regarding the TN-C-S. I disagree on that it is a crap system with no avantages but saving a few bucks in copper. Its dangerous and has many flaws. I girl was killed in the UK only 1 week ago after touching an outside tap.  It looks like the property had a neuttal fault.  Im also a radio ham TN-C-S is a nightmare as you cannot easily ground outside equipment as you have potential fault cuurrent paths down Coax cables etc.

I think I need to investigate a bit further. I know a currently clamp wont be fast enough to catch the high speed transients etc but it will show a normal earth leakage fault and can discount this as the problem.  If it look to be purely just a transient issue there are measure that can be taken.

Chris

I use a I think its either 6 or 4 gauge ground spike at my main panel drove in deep into the ground... not having a spike ... ehhhhh

[AllTheGearNoIdea]

OK this is what I am suggesting for my isolation transformer wiring.  I know its not giving isolation to ground but is this safe to use ?

Note i would probably link the primary and scondary earths

[Elasia]

Why not just get an industrial rcd made for inverters with the higher mA and call it a day if your going that route?  Your just tossing money if you ask me.. you would just need a dedicated circuit to your main panel and avoid all your normal house wiring then wire your rcd in and the motor after it

Also I'd highly recommend a ground spike at your main panel with a proper ground bar... then that bar gets tied to your neutral in your panel usually with a high gauge bond wire.

[AllTheGearNoIdea]

Well I think if the above circuit works safely its my cheapest option.  Just bought a 3Kva isolation transformer for £98 and the 100mA RCB for secondry for   £18.    So In theory I get to run my machine safely without modifying the house wiring.   For very little money.

Chris

[AllTheGearNoIdea]

Wired up the transformer today all working 

[Kjelt]

Do test the rcb with a resistor leaking 35mA to gnd see if it trips.

[AllTheGearNoIdea]

Do test the rcb with a resistor leaking 35mA to gnd see if it trips.

It will be 100mA now as I have installed a 100ma RCB on the output from the issolation transformer.  I think my fluke tester will display the trip current and the time delay.

Thanks Regards Chris

[Kjelt]

That means it is not safe.
35mA through the heart is critical, 100mA is instantenously death.

[Zero999]

That means it is not safe.
35mA through the heart is critical, 100mA is instantenously death.

It's unlikely though and a 100mA RCD is still better than no RCD at all.

The risk of electric shock on fixed machinery is fairly low, compared to portable devices with a flexible power cord, which as far as I'm aware, is why RCDs are not mandatory on machinery in workshops. 100mA RCDs are commonly used in industrial situations, as protection against fire, more than shock, although it will provide some protection against the latter.

[Kjelt]

He could have tried a 35mA first, as stated earlier the leakages in the rest of the house are now isolated so it could have worked.

[Zero999]

He could have tried a 35mA first, as stated earlier the leakages in the rest of the house are now isolated so it could have worked.

I agree, except I've never seen a 35mA RCD, 30mA is the usual value.

[Kjelt]

Ah yeah 30mA it is.

[AllTheGearNoIdea]

 Ok the clamp meter arrived today. I’m getting around 14mA at the mains lead and 10 mA at the VFD. There a few other fan motors and filter accounting for the other 4mA.  Also likely some measurement errors  as the clamps sensitive to position and adjacent metalwork.

Just googling the subject states that VFDs leak 20mA upwards.

Your correct I could have tried a 30mA RCD and perhaps I will. But let’s not get carried away, I grew up before RCDs were common and managed to survive. These mainly serve to protect the average very stupid user that decides to pick up the cord just cut by the hover mower.

Regards Chris

[Kjelt]

You know what I realized, if there is standard 20mA leaking that should be considered the zero state.
A RCB should have a nilling or delta knob to set this leakage as normal and ignore it, eg only trip if an additional 30mA leaks.
These things are too dumb to be really usefull in such cases.

[AllTheGearNoIdea]

Looks like I will be trying the 30mA RCD as that is what arrived in the post today. I did order the 100mA

[Electro Detective]

So far so good    

I reckon VFD may be fine with a 30ma RCD because the transformer should block all any recycling nasties going up and down the line/s causing issues

FWIW a good quality '30ma' labelled RCD should trip anywhere (depending on ambient conditions)  between 22ma and 27ma in zero and 180 degree testing, or a real world trip   

If 30ma is a fail, better to have a 100ma RCD than no RCD

I have one packed in a box somewhere    just in case, or as a future upstream RCD at the switchboard before the main breaker/isolator if ever needed


Doesn't hurt to own one, and not cheap or easy to get when you need one 
 

[AllTheGearNoIdea]

Well all up and running now with the 30mA RCD. Did my first cut with the new milling machine today, cutting a window for the RCD in a plastic box. The new VFD is much better having to constantly change those drive belts.

[Kjelt]

That is excellent news, so the 30mA does not trip? 

[Edison]

what I said, she wants to measure and not guess 

[AllTheGearNoIdea]

Here is a link to my first go on the new milling machine. I show some of the leakage current issues and the isolation transformer solution. Not completely happy with the earthing arrangement and would be happy for any comments etc. Not sure if I should have connected in the domestic earth connection.  The VFD information is about 8:51 in as many people won’t be interested in the machine part.

Thanks Regards Chris

https://youtu.be/F82FMSPw38o

[Jeroen3]

That a cool machine. I'm sure you can put it to good use.

Not completely happy with the earthing arrangement and would be happy for any comments etc.

I'd be unhappy with this way as well. But it runs for now. I have seen bad things happen when running VFD's from low impedance sources, they can't do load steps really well. But you won't be making those anyway. VFD's are really designed to run on the grid, those that are not are marine approved (and not affordable). And even then there are many problems.

If I would buy such machine, I would install (or have installed) a RCD-less socket in the workshop or a higher rated one that is VFD compatible*. Preferably with an other type of plug.
CEE 16A for example (the blue one).

*This is important, I'm actually in the process of developing an automated tester for RCD's, and VFDs create such high frequency and distorted leakage current, often also DC, that normal type A and AC RCD's refuse to trip if their coil is saturated with DC or this distorted current. Testing some units on the shelf shown that you could have seconds with up to 3A DC leakage before they would trip.
This problem can also occur with bad PFC power supplies... So something to think about.

[AllTheGearNoIdea]

Hello jeroen

Thanks for the comments. I did actually order a 100mA RCD for my power converter box but it was a 30mA version that turned up in the post.  I would have liked to have run directly off the mains but there was just no easy way to defeat the RCD in the consumer unit and still be compliant with the U.K. regulation.  The drive manufacturers say there is a link that can be cut to remove the filter capacitor and that was also an option. I guess I’m just going to have to try it and see how I go. These VFDs have really come down in price so not the end of the world if it pops.

Yes I’m aware of desensitisation Of breaker. I work in the rail industry and we still have some traction system that use DC and also tram system running from DC and it can be a real problem.  Network Rail specify the use of dc immune breakers in such applications and these are really expensive. Still not quite a big an issue of the cathodic erosion of steel structure and steel reinforcement bars.

Good look with the test gear be very interesting to see it when you have it done.

Chris

[Jeroen3]

there was just no easy way to defeat the RCD in the consumer unit and still be compliant with the U.K. regulation.

Over here, you can screw around all you like. No third party will ever validate what you do, until injury or you sell the place.

Good look with the test gear be very interesting to see it when you have it done.

Yeah, unfortunately some things stay proprietary.

[Kjelt]

Very nice machine Chris. 
Great you got it running.
I haven't used my vfd since for the drillpress but soon will use another chinese vfd for my cnc machine.
No one of the many tens that use these vfds on the cnc forum has complained about their ecb tripping, so I guess there are vfds that don't leak as much.
Searching for mains netfilters from Schurter I also found out that there are filters esp three stage ones that leak more than 20mA and there are ones with two stages that leak <0,5mA.

The ecbs fit for vfd cost over €500 so this might be two cheaper future ways to tackle it although Jeroen is right they might not trip while they should in case of vfds, difficult dilemma.

[AllTheGearNoIdea]

Yes having the VFD really makes a great improvement. Found that if you get resonant chatter of the tool you can slow down the cutting speed but also sometimes just increasing the speed helps. The ease of doing this on the fly as opposed to belt changing for speed control is a massive bonus.
Thanks

Regards Chris