Wall electrics

Can anyone help with my electricity box on the wall please?. I have a circuit breaker for the sockets that my Myford S7 and milling machine are plugged into.

They both have inverters and if the Myford it is plugged in (but not running) when I switch on the Bridgeport milling machine it triggers the circuit breaker on the wall.

If I unplug the Myford the Bridgeport works no problem and vice versa.

I suspect I need an operated circuit breaker?

Inverters often have quite a lot of earth leakage, is it an earth leakage device that is tripping rather than a plain circuit breaker?

Mike

My inverter (Mitsubishi fr-a024-1.5k) specifies that it cannot me connect to a circuit breaker (for the reasons Mike mentioned).

If you breaker is a type AC then it's no good for use with an inverter, point your research towards type A or B, also look in to the effects of fitting a single phase EMC filter which may or may not help.

Sorry, I'm not an electrician, my dad is and he "sorted it" within 20 minutes and the above is what I picked up along the way. I'm not sure what's relevant to you and what bits just confused me along the way.

You can even get a Type C MCB if you need a really "slow" trip. However, as Mike says, you'd need to clarify if it is actually the RCD (earth leakage) or the MCB (overcurrent) breaker that is tripping.

I used to get the RCD tripping out occasionally when I switched my lathe inverter on, plunging the workshop into darkness. I also used to have problems with my old 50Hz TIG welder tripping out the main 63A MCB. I ended up making a soft starter for the welder and running the lighting from a non-RCD feed. The other equipment ran from a std 32A MCB.

Transformers are prone to occasional saturation at turn-on due to remanence in the laminations. It all depends when you turn them off and turn them on again in terms of the phase angle. Probably not the issue here but it's another form of nuisance tripping that may be encountered.

Murray

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Bring back wire fuses, earth rods and good 'earthy' lead water and gas pipes I say.!

Nick

It sounds very much like this is a residual current breaker problem. The EMI filter in the mains feed to the inverters have shunt capacitors to earth, so they generate an earth leakage which the breaker detects. Probably because there are two machines the amount of leakage is close to the trip value. You could try running both machines through the same filter, should be no problem as long as you only use one at a time.

A few years ago I had a problem with a group of sockets in my computer room tripping the RCD intermittently. I had wired the group of sockets on the front of the bench via a fused spur switch which was in a convenient position to switch off all of the equipment in the room. (This was just fed from a single 13 amp plug.) Sometimes when the switch on the spur box was switched on the house RCD would trip but this never happened when individual computers etc. were switched on. I had a theory that what was happening was that the live pole of the double pole switch might close a few milliseconds before the neutral pole. This would mean that the two capacitors in the filter (One between live and neutral and one between neutral and earth.) would be in series between live and earth. This would cause a leakage current via the capacitors until the neutral pole of the switch made contact. I shorted out the neutral pole of the switch and this solved the problem. If the switch on the machines is double pole switch AND is before the filter this may explain what is happening. This is only relevant if it is an RCD that is tripping and not am MCB. The OP has still not clarified this point.

Les.

That's a very odd design of filter. EMI filters for mains input are usually symmetrical, One capacitor between live and neutral, one from neutral to earth, and one from live to earth.

It is not a good idea to bridge the neutral pole of the switch. There is no guarantee that the "neutral" doesn't carry a dangerous voltage, for example as a result of an earth fault at the substation, not to mention faulty house wiring.

Russell.

Hi Russell,
I agree that it is not good practice to use a single pole switch but it illustrates my theory. The symmetrical filters you describe were common before the use of RCDs was common but there seems to be a move towards the design I described to reduce the leakage to earth.

Les.

Sorry chaps , the arrowed switch in the pic is the one that trips. And thanks.

I checked out all my electric wiring in house and workshops a couple of days ago, because I suspected false signals or spike of some sort was affecting electronic controls. I checked every socket and the connections, found one or two that needed a tightening. Checked earth etc. using a cheap plug-in tester and had loads of " no earth" faults on the sockets. To cut a long story short after about two days I found that one of the sockets had no connection to earth. This is a well known British make, the small metal strip that formed the earth connection was missing, presumably from new. Luckily the socket was mainly used for double -insulated tools. I suppose what I am saying is always check everything, even the very unlikely. BTW the false signals seem to have stopped as well.

Filters may look symetrical but to the asymmetrical mains there is always an earth current bias live to ground versus neutral to ground.

Martin

Capnahab. The switch in your picture is an RCBO which is a residual current device with overload protection. Basically it looks like the earth leakage value is excessive when you use more than one inverter at once. As it's a C class time/current curve breaker I would venture to say that if it was overcurrent causing the trip, then it would trip with a bit of a bang. If it just clicks off without a bang then it most probably is earth current leakage. This RCBO is rated at 30 milliamp trip current but in practice most trip before that magnitude of current is attained, in fact some are out at 15 or 16 milliamps which is the reason for nuisance tripping. Most however are out between 19 and 27 milliamps earth leakage and inverters are notorious for earth leakage currents which by their nature and magnitude are not detrimental but are sufficient to trip the safety device.

Rick