3 Phase Tripping

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3 Phase Tripping

This topic has 21 replies, 13 voices, and was last updated 15 February 2012 at 20:44 by ,.

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4 February 2012 at 14:48 #11884
David Parsons 3
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@davidparsons3
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4 February 2012 at 14:48 #83827
David Parsons 3
Participant
@davidparsons3
Hello,

I have the large Myford VME Mill with 3 phase converter. I haven’t used the machine for a couple of years, and now everytime I switch it on it pops the main circuit breaker to my whole house. I must have tried it 4 times on the trot, and everytime it pops the main switch.

Any suggestions people ?

Many kind thanks.
4 February 2012 at 15:05 #83828
Jeff Dayman
Participant
@jeffdayman43397
Hi David,

A few things you might check with power cable disconnected:

-rotate spindle and motor by hand – make sure everything rotates easily.

-test by rotating and watching the belt run and make sure that any V belts do not have “flat spots” or “hard set” areas. Some V belts will stay supple for years, others harden up quickly if not used.

-open switch box and junction box covers and look for water, bugs, mice droppings, or corrosion. To be thorough, remove each screw or spade terminal one at a time and clean with a brass brush and contact cleaner, and examine each wire. (Replace each cleaned terminal one at a time immediately after cleaning, so you don’t risk wiring things the wrong way.) If you find any green/blue corrosion, clean it or replace the wire.

-if the machine has any potientiometers or rotary switches, operate each of them full range many times to clear any corrosion on the contacts.

If the main breaker still pops when plugging in/switching on there is likely a fault in the motor or wires somewhere (again may be mice or bug damage)

Good luck JD

Edited By Jeff Dayman on 04/02/2012 15:07:33
4 February 2012 at 15:16 #83829
David Parsons 3
Participant
@davidparsons3
Hi JD,

Thanks for that advice, I’ve checked inside the box and everything still looks new, certainly no mice or spiders etc.
I’ve also checked the plugs for signs of damage, and they all look fine.

To clarify. It’s not when I turn the motor on, it happens when I flick the switch on the wall, which is a 13 amp plug. This plug works fine with other appliances.

Bless Myford, they always used quality items and components. The gubbins inside the 3 phase box seem to be from a reputable company, so I will try contacting them Monday morning.

I was wondering more if this was a known fault, or if there is a reset button I should be aware of etc etc etc.

Many kind thanks.

David

Edited By David Parsons 3 on 04/02/2012 15:18:02
4 February 2012 at 15:23 #83831
Les Jones 1
Participant
@lesjones1
Hi David,

By the term “main breaker” do you mean en RCD device (Which detects leakage to ground.) or a circuit breaker which trips with too much current. It is more likely to be an RCD as before they were fitted the main switch was normally just a switch which did not trip under fault conditions. If it is an RCD device tripping moisture is a likely cause. By switching on do you mean switching on the power to the inverter or pressing the start button ?

I now see that you have answered some of my questions before I has first posted my reply.

There will not be any kind of reset button that would clear this type of fault, To isolate this sort of fault you really need an insulation tester. If the leakage to ground is severe you may be able to fault find using a digital multimeter as these read quite high resistance values.

The first test to do is to measure the resistance between the earth pin on the plug and the live pin on the plug then repeat the measurement between the earth pin and the neutral pin. Reply with these two readings and it may be possible to suggest a fault finding procedure. Any further information would also help such as a wiring diagram and is there a mains filter before the inverter.

Les.

Edited By Les Jones 1 on 04/02/2012 15:40:18
4 February 2012 at 15:33 #83833
David Parsons 3
Participant
@davidparsons3
Hi Les,

I mean the main fuse box in my house. Trip switches I call them. It pops the main one, so everything I own turns off. I’ve just checked, and it has RCD written on it.

The problem happens when I switch the inverter on. I plug the whole machine into the socket on the wall, turn the socket on, and POP !

Moisture shouldn’t be a factor. The machine has been moved recently, but has always been in a good quality garage that is dry, although often very cold.

Many kind thanks.

David
4 February 2012 at 15:43 #83836
Les Jones 1
Participant
@lesjones1
Hi David,

When the machine was working was it fed from the same consumer unit. (The thing where the main switch is located ?

Les.
4 February 2012 at 16:39 #83839
David Parsons 3
Participant
@davidparsons3
Hi Les,

No, it was at a completely different address.

However, it is still plugged into a 13 amp socket just the same.

I know RCD’s can ‘trip’ just from a spike. Could this be the problem? Too much power too quickly?

David
4 February 2012 at 16:52 #83840
Les Jones 1
Participant
@lesjones1
Hi David,

Did the address where the mill worked have an RCD or just a main switch ?

False tripping of RCD’s is not just “too much power too quickly” Sometimes very inductive loads can cause false tripping. Another cause can be the way the mains filters used on some products is designed. Before looking for causes like this I suggest checking to make sure there is no resistive path between live or neutral and earth.

Les.
4 February 2012 at 16:53 #83842
Swarf, Mostly!
Participant
@swarfmostly
Hi there, David,

Was it running from an RCD-protected circuit at the previous address?

Best regards,

Swarf, Mostly!
4 February 2012 at 20:43 #83870
John Haine
Participant
@johnhaine32865
It may be because you have a mains filter at the input to the inverter. This will place capacitors between the live and neutral conductors and earth. When power is applied some current passes through these capacitors and the RCD can’t tell the difference between this and a “real” earth leakage. This is a known problem that is pointed out about using inverters with filters. To prevent it you probably need a less sensitive RCD or remove the mains filter. If there is a filter in place you could try removing it before you plug in to see if it fixes the problem – you could even run the machine but beware that RFI may leak down the mains.
4 February 2012 at 20:48 #83873
Ken Johnston
Participant
@kenjohnston10955
Dave,

It’s your RCD. You will have to bypass it . The demand from your inverter at switch-on is popping it.

I found the same problem when I moved houses and put in a RCD protected consumer unit.

Had to put in a switch-fuse unit in parallel with the consumer unit. I then found that the inverter manual pointed out just that problem.

Regards.
4 February 2012 at 21:03 #83875
frank brown
Participant
@frankbrown22225
RCDs come in different sensitivities, there should be a 100mA one associated with the input isolator, this is to protect EVERYTHING against a live to earth fault. Then there should be a 30mA one on one half of the distribution box to protect PERSONEL against electric shock, such as outside power points etc.

A 30 mA one fitted to protect every thing is a very chancy affair as they can easily be tripped by external grid switching. Happened to us in S. Hampshire on Friday evenings about 1730 as the factories reduced their load the grid was switched about causing the trip to go.

Outside buildings should be fed via the unprotected side of the mains dist. board and the appropriate RCD fitted at the external end, so a machine fault can be reset locally and not plunge the house in to darkness.

Frank
4 February 2012 at 21:23 #83877
martin perman 1
Participant
@martinperman1
G entlemen,

I install very large walk in industrial washing machines which have 3 phase pumps driven by single phase inverters, we specify to the customer, from memory, a C class 300mA RCD otherwise everytime the machine is turned on it takes a phase out when the inverter powers up.

Martin P
4 February 2012 at 22:22 #83881
Neil Greenaway
Participant
@neilgreenaway71611
Hi There,

I have had problems running inverters from an RCD protected supply – some inverters can “generate” earth leakages due to the electronic design internally, and this can be as much as 20mA. With other electronic devices in a domestic scenario (e.g.washing machines) also generating small currents to earth this can push the current to earth beyond the 30mA leakage current to earth that the RCD monitors and isolates supply in the event of levels above the limit. The 20mA value stated above was found in a siemens micromaster manual for an inverter I have, but other makes may be more or less. Siemens state only one inverter per RCD as the 30mA limit would not be adequate to run more than one inverter with each having leakage currents of 20mA or more.

This could be part of the problem. If you had a split load consumer unit you could feed the machine from an MCB or fused supply on the unprotected side of the consumer unit.

Hope this helps.

Neil
4 February 2012 at 22:34 #83887
Neil Greenaway
Participant
@neilgreenaway71611
Sorry – I forgot to add – for test purposes only you could remove the earth connection from the inverter to see if that will permit the thing to run without tripping the RCD. I say this is purely for test purposes only. If it runs and doesnt trip the RCD then you know that there may be leakage currents being generated.

Lastly I know there can with some manufacturers be startup procedures to follow for inverters that havent been used in some time – this is so as to not cause damage to capacitors etc that havent been used in some time – eg 2 years+.

Thanks,

Neil
5 February 2012 at 21:36 #83991
Jon
Participant
@jon
I have the same problems with numerous stuff. Usually a mig welder on very low amperage will trip RCD, likewise a 5KW inverter ok until any machine is powered up on hard start. The inverter packed up after 1 1/2hrs use cost me £650 last year, so had to fork out for 7.5KW £1100.

Change RCD as said above to a C type.

Having done that i can bang up the amperage on welder, so far never tripped. The only prob i get now is the 7.5kw inverter tripping the RCCD at in oprtune times, could be 3 times in 1/4hr or once in two weeks.
5 February 2012 at 22:04 #83997
confused.eng
Participant
@confused-eng
RCD fitted in consumer units are generally 30mA. This means that a poxy 30mA (0.03 A) is all that is needed to trip the thing.

If you have lots of other electrical equipment especially electronic equipment (computers, video, Hi-Fi etc) these can leak current down the earth connection and when this increases above 30mA then things go pop. If everything else is switched of and just the inverter is powered up does this work?

Some RCD have very low tripping currents, 20-30mA, which can cause problems if a few things operate at the same time.

RCD’s have various tripping currents, eg 30mA, 50mA, 100mA, 300mA. The 30mA things are fitted to protect against electric shock, the higher value ones are to protect property.

RCD’s also have a Voltage/Current detection type, whether they detect AC, DC or both, most fitted will only detect AC leakage.

The Type ‘C’ refered to by Jon is the Circuit Breaker, most houses have Type ‘B’ fitted as these are more sensitive. Type ‘C’ allow a larger overload for a short duration and Type ‘D’ allow an even bigger on. If your interested there are some pretty graphs in the Wiring Regs that show the tripping characteristics.

A usual culprit for RCD’s tripping is damp in the load, especially if unused and stored in a damp location for some time.

Best thing for workshops is to supply them from a non RCD protected supply and fit RCD’s at sockets used for powertools etc.

Appologies for the length of the reply.

Phil.
15 February 2012 at 16:24 #84832
David Parsons 3
Participant
@davidparsons3
Blimey this is a good forum. Loads of advice and very much appreciated.

My electrician said it is more than likely an earth problem related to the garage,

He came round, fiddled with the wires, bypassed the extension I was using and now everything has been working sweet.

If anyone reading this is having similar problems, as can be seen in the lists, check for a good earth, even if it means running an extension from a neighbour. Also, make sure the fuse box is rigged up for the power you’re using etc.

many kind thanks to all.

David
15 February 2012 at 19:35 #84846
Ian Hewson
Participant
@ianhewson99641
Hi

Not a good idea to run an extension from a neighbouring property,if they are on a different phase of the supply you could end up with 440volts around your workshop.

Earth problems should be solved by a qualified electrician, as you did, poor earths and stray leakage currents are the cause of many accidents and fires.

If you have a poor earth and you “import” next doors unknown earth value, you are asking for trouble.

Ian
15 February 2012 at 20:42 #84853
frank brown
Participant
@frankbrown22225
” My electrician said it is more than likely an earth problem related to the garage” , This sounds extremely vague. When I moved into my “new” shed, I found all the circuit earths were commoned, but not to the armouring of the feed cable or to an earth spike. How do you know your set-up now, is not like my old old one? Sounds very dodgey to me

Frank
15 February 2012 at 20:44 #84855
,
Participant
@nousername29627
I totally agree with Ian – if you have the SLIGHTEST doubt about what you are doing then consult a N.I.C.E.I.C registered electrician. I suggest you do NOT try DIY fixes suggested here – a lot of what has beeen suggested is just plain WRONG!!!

DONT RISK YOUR OWN OR YOUR FAMILY’S LIFE

And no its not costly when you think of the alternative

I have no intention of listing my qualifications here but suffice to say that I am employed in a very senior capacity by a large electricity generating company.

Edited By Kinlet Hall 4936 on 15/02/2012 20:55:45
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