Switching power supplies tripping GFCI

[Rachie5272]

I built a four axis CNC machine, where each motor driver has its own integral SMPS (Zeta 4 driver).  For the most part it works great, but it keeps tripping the GFCI.  A bit of detective work reveals each driver leaks about 1 mA to ground, and the computer running everything leaks about 0.5 mA.  I'm in the US where nearly all GFCIs trip at 5 mA ±1 mA, so it's not surprising I'm having trouble with it.

What can I do to solve this?  I don't know where to get a GFCI with a higher trip current, if it's even labelled.  Do GFCI circuit breakers have a higher limit?

I'd simply remove the GFCI, but I think it's required by the electrical code.  The machine is technically in a garage, despite being a finished space which has never held a car.

[uncle_bob]

Hi

Put it on an isolation transformer.

Bob

[tautech]

Thinking 2 possible reasons. 

Faulty X/Y rated caps in the PSU.
High neutral return currents relative to the size of cabling used and related to the distance back to the neutral/earth bonding link. In NZ that's at our POE switchboard and at submain distribution boards too. If in an out-building there's usually another earth rod as well.

[Ian.M]

This is what you get for running machine tools on a domestic grade supply.  I strongly suspect you have used 120V Zeta 4 drives.  If you'd used 240V Zeta 4-240 drives, on a North American 240V circuit, their line filters and stray capacitance to ground would be reasonably well balanced, cancelling out most of the earth leakage.

Talk to a good local electrician.  Have the make and model of your distribution board and the wire gague of the circuit to the 'garage' outlet handy.

[wraper]

I'm in the US where nearly all GFCIs trip at 5 mA ±1 mA, so it's not surprising I'm having trouble with it.

You have such options:
1) Replace GFCI with one with higher current rating.
2) Remove Y caps prom PSUs and use only one set of them externally before PSUs.
3) Replace Y caps in PSUs with some which have about 2x lower capacitance.

[Rachie5272]

A higher current GFCI would be great.  Where can I find one?  I've been searching for hours with no success.

[NiHaoMike]

Some AFCIs have high threshold GFCI functionality built in. Of course, then there's a possible problem of noise tripping it...

[Ian.M]

You wont be able to find a higher trip current GFCI that meets the NEC code requirements for a domestic installation as class B GFCIs no longer comply.
See http://www.ecmag.com/section/codes-standards/special-purpose-gfcis

[jitter]

5 mA? Really? We use 30 mA residential (as of 2005), and even then a lightning strike in the vicinity might trip them.
Don't you get nuiscance tripping all the time with only 5 mA GFCI, even without the CNC machine?

[Jeroen3]

You are most likely allowed to get an higher current gfci and make your cnc a permanent installation. Using a higher current industrial plug or permanent wiring.
Aks a local electrician.

I see that 5mA are in-socket GFCI for single personal appliance safety. You have those in europe as well for garden equipment. You can't run multiple equipment on those.

[uncle_bob]

Hi

All of the rules on what you can and can't do in a situation like this are local rules. What I can do in this town may be different than what you can do in the next town over. Either you get involved directly with the local codes office (not recommended) or spend the (maybe) $100 on having a licensed electrician take care of it.

Bob

[Photon939]

5 mA? Really? We use 30 mA residential (as of 2005), and even then a lightning strike in the vicinity might trip them.
Don't you get nuiscance tripping all the time with only 5 mA GFCI, even without the CNC machine?

It's usually never a problem unless you get some borderline faulty equipment. Even then most (older) houses in USA that I've seen use the GFCI outlets that protect one 15/20A circuit instead of one giant GFCI breaker in the power panel. That way a GFCI trip only turns off one circuit.

[jitter]

GFCIs/RCDs are limited to maximum of 4 circuits over here. That could mean one GFCI in a somewhat older house, more modern houses will need more than one.

[uncle_bob]

GFCIs/RCDs are limited to maximum of 4 circuits over here. That could mean one GFCI in a somewhat older house, more modern houses will need more than one.

Hi

In most areas here, there are parts of the house that require protection. Most of the circuits do not get a GFCI on them. Areas where water and electricity are likely to mix are the main targets (kitchen, bathroom, garage, outdoor outlets).

Bob

[Jeroen3]

Freedom Electricity Regulations are inconceivably unsafe if you ask me.
No gfci? They are mandator, all nen 1010. How many death by electrocition and fires due to electrical failure do you have over there?

[uncle_bob]

Freedom Electricity Regulations are inconceivably unsafe if you ask me.
No gfci? They are mandator, all nen 1010. How many death by electrocition and fires due to electrical failure do you have over there?

Hi

I have never heard of a problem associated with the in ceiling lighting and washer dryer type loads that are the majority of what is unprotected.

Bob

[steverino]

I'm not 100% sure about this, but if you make the plug dedicated to the cnc machine, I don't believe it has to be GFCI rated because of the garage location.  You might have to swap it for a non duplex receptacle for it to be considered dedicated.  If it were me, I'd swap it out without worry.

[jitter]

Freedom Electricity Regulations are inconceivably unsafe if you ask me.
No gfci? They are mandator, all nen 1010. How many death by electrocition and fires due to electrical failure do you have over there?

Hi

I have never heard of a problem associated with the in ceiling lighting and washer dryer type loads that are the majority of what is unprotected.

Bob

Neither have I, but that doesn't mean these sort of things don't happen. Rules and regulations usually only come after things go wrong. We may try to put them in place to prevent accidents (think of drones righ now), but not until serious accidents start to happen for real will people actually feel the need.

[uncle_bob]

Freedom Electricity Regulations are inconceivably unsafe if you ask me.
No gfci? They are mandator, all nen 1010. How many death by electrocition and fires due to electrical failure do you have over there?

Hi

I have never heard of a problem associated with the in ceiling lighting and washer dryer type loads that are the majority of what is unprotected.

Bob

Neither have I, but that doesn't mean these sort of things don't happen. Rules and regulations usually only come after things go wrong. We may try to put them in place to prevent accidents (think of drones righ now), but not until serious accidents start to happen for real will people actually feel the need.

Hi

Upgrading 200 million electrical systems for problems that never happen does indeed cost money. If that money could save more lives spent another way ... it's not a rational thing to do.

Bob

[jitter]

That's not how they do it. New regulations come into effect on new stuff and renovations.
I'm sitting here in an apartment, built late 1950s. It has a distribution box with two fuses. Yes, that's it (apart from the parts that are from the utility company such as the meter and the main fuse).
Now, a new apartment would probably get at least 4 circuit breakers, a RCD and a master switch.

[poorchava]

In the apartament which we are renting right now, there are 7 fuses + 1 RCD for the entire apartment. All fuses are 10A rated with the exception of the one for ceiling lights which have 6A one due to part of the wiring being old aluminum stuff.

As for the leakage, check all the caps between earth lead and anything else. 1mA of leakage is very high (that's an insulation resistance of less than 0.5 megaohm which is very low.

Sent from my HTC One M8s using Tapatalk.

[Siwastaja]

The fact that 5mA GFCIs are used outside some special (think about medical) cases is news to me. In Europe, it's always 30mA, and for a good reason, it gives just as good protection but is actually usable (so it can be used, not bypassed). 5mA GFCI sounds paranoid, and unusable as 5mA leakage quickly adds up from completely normal number of perfectly normal equipment, like a few computers. "False positives" is always a real safety issue in any safety system, because it will lead to people bypassing them in one way or another. Completely unusable and broken electrical system is not something people agree with...

So, you should fix your broken electrical installation first (by installing a proper 30mA GFCI), because your CNC equipment is most likely perfectly ok.

It's hard to believe that local electrical code requires this. If it does, your options are to move somewhere else, where they have heard about this great thing called "electricity" and it can be used legally; or to break the law.

Sidestepping the issue by modifying the equipment can be a real safety or EMC issue, causing actual problems. So here we see again how false security works against real security.

[Monkeh]

The fact that 5mA GFCIs are used outside some special (think about medical) cases is news to me. In Europe, it's always 30mA, and for a good reason, it gives just as good protection but is actually usable (so it can be used, not bypassed). 5mA GFCI sounds paranoid, and unusable as 5mA leakage quickly adds up from completely normal number of perfectly normal equipment, like a few computers. "False positives" is always a real safety issue in any safety system, because it will lead to people bypassing them in one way or another. Completely unusable and broken electrical system is not something people agree with...

So, you should fix your broken electrical installation first (by installing a proper 30mA GFCI), because your CNC equipment is most likely perfectly ok.

It's hard to believe that local electrical code requires this. If it does, your options are to move somewhere else, where they have heard about this great thing called "electricity" and it can be used legally; or to break the law.

Sidestepping the issue by modifying the equipment can be a real safety or EMC issue, causing actual problems. So here we see again how false security works against real security.

A 'proper' 30mA unit is not appropriate under the code in the US. The installation is not broken. Your preconceptions may be..

[wraper]

In the apartament which we are renting right now, there are 7 fuses + 1 RCD for the entire apartment. All fuses are 10A rated with the exception of the one for ceiling lights which have 6A one due to part of the wiring being old aluminum stuff.

As for the leakage, check all the caps between earth lead and anything else. 1mA of leakage is very high (that's an insulation resistance of less than 0.5 megaohm which is very low.

Sent from my HTC One M8s using Tapatalk.

1mA leakage is not very high. You can expect 0.5+ mA leakage current from computer PSU. 0.15-0.3 mA leakage is what I usually see from double insulated power plugs (which are not even grounded). My bench (PC+Monitors+test equipment) equipment together produces around 5mA leakage as measured few years ago. Should be more now as there are more equipment.

[SeanB]

As it is the USA can you not simply have 4 separate GFCI outlets next to each other, feeding the CNC using 4 separate power leads.. Supply cable is rated to supply the 20A load of 4 outlets with a 20A breaker, but the GFCI is spread out so each power supply only has a small share of the load.

USA has GFCI at point of use, not like the rest of the planet at point of supply. Thus they have 5mA units, as the leakage from a single point is less likely to add up with a single load, while the 30mA is driven more by the need to protect an entire section of a dwelling or business including the wiring in the walls and the outlets themselves from leakage.

Thus in the USA you can retrofit a GFCI onto DCC rubber wiring even if it has a leakage current of 20mA without tripping, the leakage is upstream. Do that elsewhere and it will trip almost immediately from the leakage current.

[Photon939]

As it is the USA can you not simply have 4 separate GFCI outlets next to each other, feeding the CNC using 4 separate power leads.. Supply cable is rated to supply the 20A load of 4 outlets with a 20A breaker, but the GFCI is spread out so each power supply only has a small share of the load.

USA has GFCI at point of use, not like the rest of the planet at point of supply. Thus they have 5mA units, as the leakage from a single point is less likely to add up with a single load, while the 30mA is driven more by the need to protect an entire section of a dwelling or business including the wiring in the walls and the outlets themselves from leakage.

Thus in the USA you can retrofit a GFCI onto DCC rubber wiring even if it has a leakage current of 20mA without tripping, the leakage is upstream. Do that elsewhere and it will trip almost immediately from the leakage current.

Usually one GFCI is placed at the first outlet in the circuit to be protected, then the outgoing wiring is protected. It would be very expensive to install one GFCI outlet for every place you wanted an outlet in a kitchen/shed/bathroom/etc. Not that you can't buy GFCI circuit breakers here, they're just less common.

[Rachie5272]

I took a closer look inside one of the motor drivers, and found something interesting.  It actually has two Y capacitors in parallel, located at opposite ends of a big heatsink.  A rather unusual design.

Each one is a Wima FKP1, rated "0,022", which I presume is 22 nF.  Would it make sense to simply remove one of the capacitors, or should I replace them both with something smaller?

Are 30 mA GFCI breakers common in the US?  It's hard to find trip current ratings online.

[Ian.M]

You could import a 30mA trip current 3 pole DIN rail mounting RCD intended for 230V use.  They trip on current imbalance so the voltage difference wouldn't matter.  Wire it so the two phases the test button is across are L1 and L2 to give the correct 230V across the test button.  It wouldn't be US code compliant so get your tame electrician to provide a non-GFCI protected NEMA 14-30 dryer outlet, and put your RCD in a DIN rail box on the machine so it plugs in by a flex cord.   You'll also want MCBs for over-current protection.  Balance the loads of the drives and the PC across the two phases.

[Richard Head]

A Wima FKP1 capacitor is not  Y-cap rated. It's a metalized polypropylene snubber capacitor. Wima has a range of Y-capacitors but FKP1 is not part of the range.
The Wima Y-caps are normally metalized paper, although they too have some issues.

[Siwastaja]

A Wima FKP1 capacitor is not  Y-cap rated. It's a metalized polypropylene snubber capacitor. Wima has a range of Y-capacitors but FKP1 is not part of the range.
The Wima Y-caps are normally metalized paper, although they too have some issues.

.... and finally, we can see where the broken electrical code with false sense of fake security actually leads to:

people start considering the modification of properly designed, safe and working equipment, which is subject to real safety standards, and as we can see, it is not always easy, as we already have a misidentification of a safety-critical component here. If the actual Y cap is going to be replaced with another cap that is misidentified as an Y cap, like this cap was, it will be an actual death trap then.

EU has most likely the most strict attitudes towards safety in the world (even if hindered by excess bureaucracy), and we see absolutely no issue with 30mA GFCI here. This is based on actual research on the safety. Sure, 5mA would be even safer. 0 mA would be extremely safe, all electricity related incidents drop to zero when we stop using electricity! ... Unless we start counting all the accidents that result in from bypassing the "safety" devices, modifying carefully designed equipment to "pass" (easiest way is to remove the earth connection), or setting houses on fire when downgrading from the light bulb to a candle.

5mA (+/-1mA, so really 4 mA) just doesn't work; the OP's case is a perfect example why. If the electrical "safety" protection device gives false positives on perfectly good equipment and cuts the power, the "protection" is broken and needs to be fixed. Of course we can talk about fixing attitudes, but that won't fix the problem of not having electricity due to the "protection". We can go on masturbating at our great attitudes in the candle light and then we can ride horses to work, it's going to be so safe!

[Rachie5272]

I misidentified the capacitor as Y because it's being used as a Y: it couples a high voltage circuit to chassis ground.  I wouldn't call it well designed equipment.  Replacing this capacitor with a proper Y could only improve safety.  When I get time, I'll remove one of the capacitors and see how it affects leakage.  Then I'll go about finding proper replacements.

Edit:
I removed a capacitor, and the ground leakage dropped by half.  So, it's clearly being used as a Y.  I ordered replacements with half the capacitance, and I'll be sending an email to the manufacturer about not using proper safety rated components.

[Rachie5272]

I finally got around to replacing the capacitors with proper Y safety ratings.  Each motor driver now leaks 0.25 mA to ground, for a total of 1.5 mA on the circuit.  And it still trips the GFCI.

The GFCI only trips when multiple motors are spinning at once.  Maybe a surge leakage is causing it to trip.  I haven't tried measuring when the motors are in motion.  Any more ideas?  I'm about ready to remove the GFCI entirely.

Oh, and the manufacturer never responded about the improper capacitors.  I'm not terribly surprised.

[Jeroen3]

RCD's are allowed to trip anywhere between 0.35 to 1.4 In for (EU) type A, or might not function reliably at all with high frequency currents.
I'd suggest you find out the type you have now, and replace it for one that does support your application.

[rstofer]

Freedom Electricity Regulations are inconceivably unsafe if you ask me.
No gfci? They are mandator, all nen 1010. How many death by electrocition and fires due to electrical failure do you have over there?

We have over 200 electrocutions per year even after using GFCIs for decades.  This is probably because the laws aren't retroactive.
https://www.nema.org/Products/Documents/NEMA-GFCI-2012-Field-Representative-Presentation.pdf

There is no 'higher' GFCI device, UL only lists Class A for residential use and the trip characteristics are firmly established at 6 mA
http://www.csemag.com/single-article/ul-s-new-gfci-classes/89c8746cdc4a7fd8a3cb93f1d51ba57a.html

Installing an isolation transformer can be workable BUT...  The safety ground must be carried through because, in general, all exposed non-current-carrying metallic components are to be grounded.  The machine frame, the CPU case, etc.  Plastic stuff like monitors may not need to be grounded if they have no exposed non-current-carrying components.  Double insulated tools are also an exception.

We don't tend to use GFCI breakers because, in general, they will be farther from the load and long cable runs also have leakage.  So, maybe we cable half way to the first GFCI outlet and then cable to the downstream protected outlets.  It's not unusual for the GFCI receptacle to be in a bathroom and also protecting the garage and patio outlets.

One would have to parse the NEC quite carefully to see if a dedicated outlet for a specific machine tool could be excluded.  Understanding that the device is a receptacle and the machine could be hard-wired might allow for the machine to not be on a GFCI.  It's crappy hand tools held in-hand while standing in a bucket of water that they're trying to protect.

To hard-wire a machine tool, it probably has to be made 'permanent'.  This generally involves just bolting it to the floor.

Don't take my word for it, all Codes are subject to interpretation by "The Authority Having Jurisdiction".

[Siwastaja]

Just install (or have installed by authorized electrician) a single outlet without GFCI. At least in EU electrical code (considered strict), this is valid and everyday stuff for some equipment - for example, freezers!

An industrial device with too much leakage is a perfectly valid reason to have that particular load outside of the GFCI - this is done all the time. It doesn't make it particularly unsafe - properly done, installations are safe even without the GFCI, which is a relatively new safety device. And you'd still have it there for all the other loads, which is great, because you can carefully inspect that single load, but bad things could happen with outlets that can have any random thing connected.

[Rachie5272]

My meter read no change in leakage when the motors were running, but it probably wouldn't see high frequency spikes anyway.

I think I'll just make a single non-GFCI outlet for the motors.