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Black Forest
05-05-2010, 03:31 PM
Somewhere in the electrical system of my 58 year old mill I have a problem with the coolant circuit. If I flip the switch to turn on the coolant pump the breaker trips. I pulled the pump and connected it directly to three phase power and it runs fine. The pump is three phase. On the pump label it says 220/360 volts. According to the schematic (I think) the factory is running it with 360 volts the same as the main motor.

Accessing the electrical box on top of the main motor( that is where all the power comes off of) is next to impossible to get to without pulling the main motor.

Can anyone tell from the drawing how the switch works to turn on the coolant pump?
http://i853.photobucket.com/albums/ab91/burnandreturn/wiring.jpg

Alistair Hosie
05-05-2010, 03:37 PM
Make sure the breaker is rated to accept the pumps capacity.I have just completely been educated into how these things work as I am changing a static transwave convertor to rotary and it keeps blowing the trip switch seems anything with a motor in it needs type c or d tripswitches rcbo's not domestic b types things may well be different in other countries so beware.I just bought a complete new consumer unit for my shop because of this.Alistair

Black Forest
05-05-2010, 03:44 PM
Alistair, The breaker is ok I think because the main motor runs fine. The breaker trips even if the main motor is not running.

dr pepper
05-05-2010, 03:47 PM
Ok then,
Power comes in from 3 phase to the device marked HS which I presume stands for haupschalter - main isolator, then goes through what probably is a control fuse SA, then goes through what looks like the on/off/direction switch, or maybe a spindle on/off and pump on/off switch, then through whats looks like 2 limit switches first KS then AK not sure what these are, and finally power goes through the contactor/overload assy .
The first thing I would do is megger (insulation test) the pump motor, when you ran it on the bench was it earthed?, try it again with the earth connected, if the fuse blows then the pumps dead (down to earth), watch out as the case may be live.
The next thing I'd check is the contactor/overload assy for the pump, measure the resistance of the operating coil, you should get around 1K ohm, sometimes these go short circuit.
Then if that doesnt show anything check the wiring with the megger especially around the devices Ks and MK, maybe coolant and crud has collected somewhere causing a short, I've even seen bits of swarf jammed in contacts.
When you said the breaker trips, do you mean an MCB or an earth leakage device or an RCD.

Black Forest
05-05-2010, 03:54 PM
Funny you should mention the earth ground. When I first got the mill two weeks ago When I connected the earth ground in the connection box and turned on the main motor the breaker would trip. If I leave the earth ground unconnected the mill runs fine. The mill casing and all is not hot! I thought there must be a short somewhere but doesn't seem to be.

dr pepper
05-05-2010, 03:58 PM
I suggest, for safety that you investigate the cause of the trip, running a mill with no earth is highly unreccomended.
If you can run the pump motor and the spindle motor direct of 3 phase with the earth connected, then the motors are ok, the issue is within the controls.
If for some reason theres a fault in the wiring, and it sounds like there is, then if the mill is not earthed you may find suddenly that the mill and everything in contact with it is live.
If the casing is not live as you say, then there may not be a dead short, more of a leakage, this is still iffy, maybe coolant has got into the pumps windings and created a leakage to earth.

Black Forest
05-05-2010, 03:58 PM
This is the bottom half of the schematic.
http://i853.photobucket.com/albums/ab91/burnandreturn/wiring2.jpg

Black Forest
05-05-2010, 04:02 PM
I know it is dangerous and I have a electrician coming tomorrow to try and find the short. I hope he is a small man because there is not much room in there!

dr pepper
05-05-2010, 04:04 PM
Ok then, looks like KS is the collant on/off switch, and AK is part of the emergency stop.
Its good that you have drafted someone in to look, the first thing he'll do is connect the earth.

Black Forest
05-05-2010, 04:06 PM
I like plumbing better. If you have a leak you just get wet, not dead!

MaxHeadRoom
05-05-2010, 04:24 PM
Alistair, The breaker is ok I think because the main motor runs fine. The breaker trips even if the main motor is not running.

It appears your control circuit is from neutral (star point?) and phase T.
As mentioned, get your electrician to megger all the phases and motors to ground after the disconnect.
I would also ensure the star point is grounded together with the neutral.
Max.

dr pepper
05-05-2010, 04:33 PM
Lectric is not so bad, if you know the basics your ok.

doctor demo
05-05-2010, 08:39 PM
I like plumbing better. If you have a leak you just get wet, not dead!
Unless the leak is over the electric panel :eek: .

Steve

JoeFin
05-05-2010, 08:55 PM
It is (A)"Load Side of the Coolant Contactor, (B) the Wires from the Contactor to the Coolant motor - terminal strip included, or (C) the coil in the contactor itself. You don't show a control transformer on the schematic so I'm thinking you have all 240v contactor coils in your control - I'm thinking the contactor coil myself is the problem - but that is purely speculative

I suspect that for 2 reasons

You said you took the motor out, connected it and it ran fine. - OK you eliminated the motor

It doesn't trip while the spindle motor is running - only when you hit the coolant switch. So you eliminated the wiring leading up to the contactor.

MaxHeadRoom
05-05-2010, 10:06 PM
The control common is referenced to T phase so if Mp is the star point of 380v then the control voltage is ~220v Mp set up as the neutral.
Max.

JoeFin
05-05-2010, 10:42 PM
The control common is referenced to T phase so if Mp is the star point of 380v then the control voltage is ~220v Mp set up as the neutral.
Max.

Thanks - I neglected to look at your location in your post. I get 3 guess to let the magic smoke out the bottle - right Mr. Geinee

I'm still leaning towards the contactor coil

Should be easy enough to check with a multimeter. You'll have to disconnect the coil wire and read across the coil's resistance to ground. Compare readings to the known working coil of the spindle motor

dr pepper
05-06-2010, 09:09 AM
Yep I'm thinking the coil too.
However one comment about the motor being eliminated, I dont think it is, that is untill it has been run with the earth connected, I've sen motors run but are down to earth.
Doesnt really matter so much now as mr forest has called in the elektriker.

Black Forest
05-06-2010, 11:59 AM
The electrician didn't show up today. Of course the wife told him it wasn't an emergency.....that he could come when he had time.........When I found out this little tidbit of information I quickly educated the wife in my assignment of priorities. The main reason the electrician is coming is to replace a blown circuit breaker in the panel for my shop. I have 220 but not 360 which I need to proceed with the troubleshooting of my mill's electrical woes.

Dr Stan
05-06-2010, 01:11 PM
The electrician didn't show up today. Of course the wife told him it wasn't an emergency.....that he could come when he had time.........When I found out this little tidbit of information I quickly educated the wife in my assignment of priorities.

Ah yes, wives, girl friends, significant others, etc. The "thing" that connects all men across all ethnic, political, religious, age, philosophical, and any other descriptors one can determine. :D

reggie_obe
05-06-2010, 04:00 PM
Disconnect the leads to the coolant motor, energize the collant circuit. Does the breaker trip? Earth the machine and retest. Does it trip now? If it doesn't, attach three lamps of suitable voltage, on the output side of the contactor, between each pair of phases of the contactor and repeat. This eliminates all the wiring up to the coolant pump itself.

Black Forest
05-07-2010, 02:49 PM
The electrician came today and replaced the circuit breaker in the panel. But he had no time to help me with my mill. So I started disconnecting wires. But I am confused. I don't understand how this electrical wiring works. The wire I connected to the neutral wire coming off the main power supply is connected to the frame of the mill. Can the neutral also act as a ground? And is this why if I connect the earth ground to the frame of the mill also, the breaker trips? The mill runs if I connect L1, L2, L3 and the blue neutral to the mill. And is this why I was not electrocuted when I touched the mill?

MaxHeadRoom
05-07-2010, 04:02 PM
There should only be one point where the neutral is connected to ground, If you have a three phase transformer with a star or wye secondary, the star point (Mp) is normally set up as a local neutral, this point would be connected to to the service ground at the transformer right at the star point, this is the only point that neutral and ground should be in contact.
It sounds as though that is what you are saying, the star point is connected to the frame of the machine, if so this is normal.
The neutral would be also fed from this point ONLY!
And now the transformer secondary is referenced to ground, any ground leakage on the three phase fed equipment will cause the breaker to trip.
So it goes back to your original problem, that you appear to have an earth leakage on one of the phases.
If you disconnect the star point from ground, the machine may not fault, but you stand the chance of shock from any metal object on the machine due to leakage currents.
Max.

Black Forest
05-07-2010, 04:13 PM
I mentioned earlier that I know nothing about electrical systems. What is a "star point"? Secondly what transformer are you referring too? As far as I know there are no transformers on this machine.

MaxHeadRoom
05-07-2010, 04:50 PM
I am just going by your schematic, Where is the 3 phases (R.S.T.) coming from now?
The print shows Mp as a neutral, which normally would be the star point of a supply transformer or service.
See fig (a) of 14.2
http://www.itacanet.org/eng/elec/edu/pt14.pdf
The secondary is in the shape of a star and the common point is the neutral.
This is where the control voltage for the contactors etc appear to originate, between T phase and Mp (neutral).
This "star" or neutral point would normally be connected to Earth Ground.
I just noticed you are located in Germany, so you may have a system similar to other parts of Europe where the star point is grounded at some remote distribution transformer only, so the opportunity to remove the neutral from ground is not possible. All else applies.
It may pay to get some more local help as someone with a high voltage megger should find the problem swiftly.
Max.

Black Forest
05-07-2010, 05:00 PM
the three phase is coming from my shop service panel.

MaxHeadRoom
05-07-2010, 05:14 PM
. Can the neutral also act as a ground? And is this why if I connect the earth ground to the frame of the mill also, the breaker trips?

See my edit to the last post.
You obviously have a ground fault on the machine, so you really need someone with equipment such as a megger and proceed with logical fault finding to find the ground.
Otherwise it is hit and miss trouble shooting.
Max.

Black Forest
05-07-2010, 05:22 PM
Tomorrow I will connect the spindle motor direct with L1,L2,L3 and earth ground and see if that trips the breaker. The breaker is a ground fault breaker on the service panel. The electrician did say today that this machine was built before they had ground fault breakers and if just one little piece of metal chip got wrong it could be enough to trip the ground fault breaker.

MaxHeadRoom
05-07-2010, 07:59 PM
That explains a few things, Earth Leakage or Ground Fault breakers trip on very little ground current.
This is why something like a megger may be needed to pin point a ground path that only shows up when a high voltage is impressed on the offending circuit.
For example moisture, coolant etc.
Max.

JoeFin
05-07-2010, 09:24 PM
That explains a few things, Earth Leakage or Ground Fault breakers trip on very little ground current.
This is why something like a megger may be needed to pin point a ground path that only shows up when a high voltage is impressed on the offending circuit.
For example moisture, coolant etc.
Max.

Max - the OP already eliminated the spindle motor


The breaker is ok I think because the main motor runs fine. The breaker trips even if the main motor is not running.

He also similarly eliminated the coolant pump as well by wiring it directly to an outlet.

Interesting idea - thinking his mis-wiring the nuetral to the machine would be the cause of the problem. So far I have not seen it addressed "Is the machine wired with 3 or 4 wires to the outlet/wall".

I tried looking it up but could find any thing on the German Electrical distribution for commercial shops. We're all guessing 380 'Y' connected distribution. My point is if BlackForrest had landed the neutral to the machine ground and it was a significant problem he would certainly know about it every time he walked up and touched the machine.

I would like to explain to him how to test the coils of the contactor because that is where I think his problem is

MaxHeadRoom
05-07-2010, 11:19 PM
I suspect it may be the same distribution as the UK, where whether residential or industrial, three phase and star grounded neutral distribution is used, just that for residential one phase and the neutral is taken in and industrial all three phases and the neutral is used.
Max.

J Tiers
05-08-2010, 12:41 AM
I very much suspect that there may be NO FAULT with the machine whatever......

The key words are the ground fault breaker..... With two motors, and a large capacitance to ground, it may be that enough capacitive ground current flows to trip it.

Normally three-phase tends to cancel leakage, but there is also the matter of some single-phase contactors with associated wiring, which will NOT be balanced. Their capacitive ground current may trip the ground fault breaker.

There is , I believe, a dual rating for those....... A home rating, which is rather sensitive, and an industrial rating, which allows perhaps 10x more current to flow.... The industrial is not so much for personal protection, as for the protection of equipment....

As that is definitely industrial equipment, made in an earlier time when ground currents were not considered, the breaker you have may simply be too sensitive to ground current.

Of course, there may also be excess leakage current...... it would be wise to have that checked.

I am also not clear on the wiring......

Normally, there would be 3 "live" wires, and in your case, a neutral, (which does eventually lead to earth ground). But the frame of the equipment should be connected to a green/yellow striped wire which is solidly earthed. The neutral should NOT be connected to any part of the frame of the equipment. The earth connection of the neutral is made elsewhere in the wiring, and you should never make another such connection yourself.

Black Forest
05-08-2010, 07:08 AM
Thanks to J Teirs and NickMueller my problem is solved. The old German wiring of this 58 year old machine had the neutral wire connected to the frame of the machine. By disconnecting the neutral from the frame and connecting the earth ground to the machine everything works now.

It only took Nick calling me and telling this dumb horse trainer how to wire it exactly.

Thank you all for your help!

Black Forest
05-08-2010, 08:42 AM
I did have a problem with the electrical coming into the machine. The neutral should have been disconnected from the frame by the former owner in order to have the earth ground connected and the machine safe to operate.

But the coolant pump never had a problem. The only thing wrong was a hidden contact switch that closed the circuit to the coolant pump. This switch would normally be closed when the spindle lever was engaged. It was out of alignment mechanically and so it did not close and complete the circuit. When I moved it into the correct position everything worked fine.

At least now I know a lot more about my machine than I did when I started to "fix" it!!

MuellerNick
05-08-2010, 11:09 AM
The earth connection of the neutral is made elsewhere in the wiring, and you should never make another such connection yourself.

That statement is right.
But maybe it can be misunderstood:
The only place neutral is connected to PE is in (or before) the fuse-box (howsitcalled? Where all the fuses of your house are). There's only one person having to deal with that, and that's your electrician. No one else! You never ever have to make a connection between N and PE.
As soon as there is a connection between N and PE behind the RCD, it will trip.

I wrote that just for clarification, not contradiction.

I didn't notice that thread. Only after BlackForrest phoned be, I got aware of it.

Nick