Drill causing earth leakage fault - Page 1
Forum section: electronics / general

author: Geoff_S
author_rank: Regular Contributor
timestamp: December 26, 2023, 08:21:50 am
content: Posting this here, since I couldn't find a more suitable forum. Mods, feel free to move if appropriate...I bought a new drill press recently. Plugged it in for the first time and switched it on, and it immediately tripped the circuit breaker.The drill is 1 kW, 240VAC single phase, with a variable speed drive. Other bits of equipment (2HP compressor, the old 1 HP drill press) on the same circuit have never caused any issues.The breaker is an "RCBO" combined circuit breaker and residual current device (Hager AD 820T C20) rated at 20A. When it trips, there is a little flag on the device showing an earth leakage fault. But it is a C curve RCBO, which I think may be sensitive to trippping due to inrush currents.A bit of googling suggests some household items (eg electric hot water heaters) are known for causing nuisance earth leakage trips, but I haven't seen anything about drills or variable speed drives.With the drill unplugged, I checked resistance between the ground pin and the live and neutral pins and measured about 3 MOhms.Interested in thoughts about whether this is just one of those things that can be expected to happen (and maybe solved by using a D curve RCBO), or an indication of an actual fault with the drill ?

author: wofritz
author_rank: Contributor
timestamp: December 26, 2023, 02:03:01 pm
content: Variable sped drives may have noise suppression capacitors to ground causing current leakage. We had a similar problem with a relatively small high efficiency water pump.

author: themadhippy
author_rank: Super Contributor
timestamp: December 26, 2023, 03:08:32 pm
content: Quotethe curve dont matter if its tripping on an earth leakage faultQuotewas that with a multimeter? the test voltage is to low to do a proper insulation testQuotetake the bugger back

author: Kleinstein
author_rank: Super Contributor
timestamp: December 26, 2023, 06:06:27 pm
content: The variable speed drive may cause quite some EMI and this can effect some RCDs, especially those that use an active circuit and when combined with other circuits connected that have capacitance to ground.For a new machine this should normally not happen and chances are the drill press is faulty in some way. A measured 3 Mohm resistance to ground also does no sound right, though technically it shoudl still be in the allowed range.When the motor is variable speed, chances are it would also start slow and thus not have large inrush current. It still depends on the details of the motor and controller.

author: Geoff_S
author_rank: Regular Contributor
timestamp: December 27, 2023, 12:16:26 am
content: Thanks for the comments and suggestions.Resistance was checked with my Fluke 87V - don't have a megger.When I said it tripped while turning on, this was just turning on power to the machine with the main switch, not starting the motor. Is it possible that inrush to the VFD (charging capacitors etc) would trip the RCBO?Quote from: wofritz on December 26, 2023, 02:03:01 pmHow did you resolve this (if at all) ?In any case, have been in touch with the vendor and will see what their response is.

author: uer166
author_rank: Super Contributor
timestamp: December 27, 2023, 02:39:29 am
content: I was about to suggest to use a 30mA RCBO instead of 5mA rated, but seems that is already is 30mA. If it is indeed the residual leakage bit being tripped, then it is a quite severe leak indeed. One way to check is to place a shunt in the PE path and scope the earth current inrush to Y-caps. If so your only solution might be a "high-immunity" type RCBO or high immunity RCCB+ normal MCB.

author: wofritz
author_rank: Contributor
timestamp: December 27, 2023, 08:13:36 am
content: Quote from: Geoff_S on December 27, 2023, 12:16:26 amWe have a number of VFDs and other electronic devices in the installation, and that pump was the straw that broke the camel's back, so we split the circuit in two with separate RCBOs. That pump was specified with up to 3.5 mA earth current by the manufacturer.We analyzed the installation with a Gossen-Metrawatt profitest MTECH+ installation tester and found that the 30mA RCBOs already tripped at 12-15 mA.

author: SeanB
author_rank: Super Contributor
timestamp: December 27, 2023, 11:00:21 am
content: Yes with multiple devices each contributing 5mA of ground current, best to split the loads into groups, and give each one a separate RCD device. I have done this often enough, having loads with enough ground current that there was only around 10mA of margin on the RCD and thus nuisance trips. Separate the breaker to it's own RCD and all was fine, and for the 3 phase boards 3 single phase RCD units, and loads spread over all 3 phases, instead of the original installer putting in one, and calling it all good, on the red phase, meant the other 2 phases were running at almost zero load, but red phase was running at 80A. Balanced loading and got it down to 30A per phase, and a lot cooler running, with all AC loads running off the one row, using 3 bus supply wires, to spread the load. Then 3 RCD devices, and split the socket outlets apart, which was fun to identify the neutral returns, seeing as this board was placed over the old panel and the wiring.

author: f4eru
author_rank: Super Contributor
timestamp: December 29, 2023, 03:53:27 pm
content: QuoteYep. Very often those currents add up, and at some point the total goes over the limit.It can be tricky.I usually measure the earth wire current to find out the contribution of each one (tricky measurement)

author: themadhippy
author_rank: Super Contributor
timestamp: December 29, 2023, 04:11:30 pm
content: QuoteNot tricky at all,you just need the correct test equipment like a sensitive clamp meter

author: jonpaul
author_rank: Super Contributor
timestamp: December 30, 2023, 01:31:42 pm
content: Any mains connected device made in China especially a motor like drill press may have faulty insulation.Check via HyPot earth to phase.Should have very low leakage at 100..2500 VACJon

author: Faringdon
author_rank: Super Contributor
timestamp: December 30, 2023, 09:10:58 pm
content: Does it still trip it when its the only device plugged into that phase?Have you tried putting in an inrush resistor at startup to see if it is inrush that trips it?

author: Geoff_S
author_rank: Regular Contributor
timestamp: December 31, 2023, 03:25:05 am
content: I haven't yet done any further testing. The vendor is away over xmas but has said they will help resolve the problem when they return to work. In the meantime they suggested checking the electrical requirements in the manual, where I've found this little nugget of info (which is pretty much a direct cut n paste from the Siemens SIMATIC V20 manual which is the VFD used in the drill). Certainly indicates that it will draw more than 3.5mA leakage, but not 30mA.However it does make me think the earth fault is due to the type of RCBO used. This is the actual RCBO on our distribution board. I've searched but not found any datasheets for it - seems to be quite old (~20 years). I'm guessing this is a "Type AC" RCD, and per the manual I'll need to change it for a Type A (or possibly Type F according to thishttps://www.electrical-installation.org/enwiki/Types_of_RCDs)?

author: wofritz
author_rank: Contributor
timestamp: December 31, 2023, 09:21:38 am
content: Ha! We have a V20 in our problem circuit as well and I also found that information. Replacing the RCBO with a type F is a quite expensive option so we installed a separate "standard" RCBO only for the V20 and is associated circuitry.IIRC correctly, the V20 had a leakage of about 7-8 mA. I don't know if that's normal though.Also our 30mA RCBOs tripped already at 12-15 mA and with the pump in the circuit it tripped, mostly on transients when some motor started/stopped or similar.

author: Geoff_S
author_rank: Regular Contributor
timestamp: December 31, 2023, 10:19:03 am
content: Ah thanks Wofritz. Interesting. I am getting an electrician to come and have a look at either replaceing the existing RCBO with a Type A, or installing it on a dedicated circuit for the drill.Found an old thread which sounds similar to mine also:https://www.eevblog.com/forum/chat/variable-frequency-drive-tripping-out-the-earth-leakage-in-my-house/

author: Geoff_S
author_rank: Regular Contributor
timestamp: January 01, 2024, 03:47:24 am
content: Cut into an extension cord and did some testing.With earth disconnected (yes, appropriate safey precautions were taken):- drill powered up ok without tripping the RCBO. Open circuit voltage from chassis to PE measured at 118 VAC.- if I then closed the earth circuit via my multimeter, measured about 18 mA residual current (and RCBO did not trip).If I disconnected the drill from power, inserted multimeter (with current peak hold enabled) in the earth circuit and then applied power, the RCBO tripped and the multimeter did not catch the peak. Guess it happens faster than the bandwidth of the multimeter is able to measure.I have an electrician coming to replace the RCBO's with new Type A ones. The existing ones are old (> 20 years) and maybe tripping a bit easier than they should.

author: wofritz
author_rank: Contributor
timestamp: January 01, 2024, 08:50:02 am
content: 18 mA is a lot. Maybe there is something wrong with the drill after all?The standard RCBOs seem to be sensitive to transients if leakage is close to the tripping point. We had our "problem child" tripping when there was something happening on a completely different circuit (like a motor starting or stopping). Funny thing was it mostly tripped exactly one minute after full hour (17:01, 18:01 etc.). We never found out what caused this, may be even outside our installation.I also learned during this process that 30 mA RCBOs are allowed to trip at 15 mA, and that was what ours did (5 year old Eaton). I checked an ABB type and that one tripped at 24 mA. So you may or may not be lucky with your new RCBOs.BTW: Happy new year!

author: uer166
author_rank: Super Contributor
timestamp: January 01, 2024, 11:15:22 am
content: 18mA can be lethal and is probably above the let-go current. Consider replacing or fixing the drill.

author: Geoff_S
author_rank: Regular Contributor
timestamp: January 20, 2024, 12:03:00 am
content: Had an electrician replace the existing RCBO with a new Type A "super immune" RCBO, and the drill now powers up without tripping.https://www.clipsal.com/products/circuit-protection/max9/residual-current-breaker-with-overcurrent-protection-rcbo-1pn-20a-30ma-c-curve-6000a-a-si-mx9r3220sWhether the "super immune" feature is less sensitive to initial spikes, or whether the new breaker just trips at a somewhat higher current than the old breaker (or both) I'll probably never know. But happy that it all seems to be working now.

author: Monkeh
author_rank: Super Contributor
timestamp: January 20, 2024, 02:20:22 pm
content: Quote from: Geoff_S on January 20, 2024, 12:03:00 amThe electrician should have verified the tripping current on the new breaker before he left you with it, and should have checked out the old one as a matter of curiosity before removing it.