RCD / GFCI problems with Meanwell PSUs?

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Muzzer
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RCD / GFCI problems with Meanwell PSUs?

Post by Muzzer »

My first step in commissioning my current conversion (Tree CNC lathe) failed at the first step and a couple of hours in, I've barely moved forward. I used the 2 Meanwell PSUs that came with the Acorn and the ETHER1616. With nothing else connected, closing the isolator trips the 30mA workshop RCD (this is called a GFCI in the US). This happens with either or both PSUs connected up. Lifting either L or N avoids the problem, as does running without the RCD in circuit.

I ran the machine from a 240-240 isolation transformer (output N connected to GND) with a 30mA RCD, to avoid tripping the workshop supply. Same issue (but different RCD doing the tripping).

There's no measurable path to ground from either L or N in the PSUs using a decent quality DVM, as indeed there shouldn't be. Meanwell claim 300VAC / 5 seconds as well as the normal 85-264VAC input range. There are no TVS / MOVs in the circuit and I assume the X and Y caps are approved parts.

Operating it at 120VAC input helped a bit but it still tripped out after a few minutes. I'm back to an isolation transformer (with a grounded chassis and neutral) but it's not what I'd want in the final setup. I have a couple of DIN rail Class II PSUs (ie require no protective ground connection) that I could use in place of these enclosed models but it's not something I was planning - or expecting to be required to do.

I measured the mains voltage at between 250-260VAC today. I can't safely measure it with a scope but I get similar results using 2 different DVMs. That's not unusual here these days but as I say, the PSUs are specc'd and tested (not least by UL, CSA etc) at 264VAC and even 300VAC.

As a former SMPS power supply developer, I have to say I'm puzzled. MW are a reputable company and I'm sure these products generally work well in hundreds of applications.

RCD trips are caused by ground faults or leakage and aren't usually bothered by inrush currents. I run plenty of fairly heavy equipment equipment here in my workshop without a hint of a problem, yet these 35W PSUs are causing havoc.

Has anyone reported similar issues? This would most likely affect installations in the UK, EU and possibly Australia / NZ.
https://www.meanwell.com/webapp/product ... rod=LRS-35
Gary Campbell
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Re: RCD / GFCI problems with Meanwell PSUs?

Post by Gary Campbell »

I always recommend that any CNC machine is on it's own dedicated circuit and that GFCIs are not recommended.
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suntravel
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Re: RCD / GFCI problems with Meanwell PSUs?

Post by suntravel »

I use Type B RCDs, and have no problems here in Germany.

Uwe
Muzzer
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Re: RCD / GFCI problems with Meanwell PSUs?

Post by Muzzer »

Gary Campbell wrote: Fri May 20, 2022 11:40 am I always recommend that any CNC machine is on it's own dedicated circuit and that GFCIs are not recommended.
Here in the UK it's pretty much a requirement to have RCD / GFCI in domestic installations. It might be possible to have a non-RCD spur fitted but it would require the consumer unit (fuse box) to be reconfigured.
suntravel wrote: Fri May 20, 2022 3:37 pm I use Type B RCDs, and have no problems here in Germany.

Uwe
Do you actually mean Type B MCB (over current circuit breaker)? My MCBs didn't trip - just the RCD (ground fault trip).
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Re: RCD / GFCI problems with Meanwell PSUs?

Post by Gary Campbell »

Here in the UK it's pretty much a requirement to have RCD / GFCI in domestic installations. It might be possible to have a non-RCD spur fitted but it would require the consumer unit (fuse box) to be reconfigured
Here too in residential applications. The exception is that appliances that require a dedicated circuit do not require a GFCI. Since very few CNC machines will operate properly on a GFCI, the dedicated circuit is the method of choice.
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Re: RCD / GFCI problems with Meanwell PSUs?

Post by suntravel »

Muzzer
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Re: RCD / GFCI problems with Meanwell PSUs?

Post by Muzzer »

suntravel wrote: Sat May 21, 2022 12:03 am I use these :

https://www.reichelt.de/fehlerstromschu ... X4EALw_wcB

Uwe
Yes, that's basically what I have in my workshop consumer unit (distribution box). I have 2 of them so that only part of the workshop loses power if one trips. Mine are also 30mA but they are each rated at 80A load, followed with a B63 MCB for the outlets.

I have 3 other CNC machines full of VFDs and servos and a large single phase (70Arms) TIG welder and NEVER have an issue with nuisance tripping. Yet when I connect up either of these tiny 35W PSUs, I can't even power them up without tripping. The leakage current is supposed to be limited (and tested) by the UL/CSA/CE approvals, so without deploying more exotic test gear which I don't have at home, it's hard to think of a convincing explanation. Perhaps when I replace them with the DIN rail PSUs, I will take a closer look.

My solution (for now) is to power the machine from an isolation transformer with the neutral grounded and a good protective earth connection to the machine chassis. This won't be bothered by leakage currents, won't trip the main RCD / RCCB and gives the benefits of a dedicated circuit without requiring alterations to the workshop itself. I've now been running them continuously for 24h without issue. Furthermore, I've now got my machine up and running, so progress has been made!
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