3 Phase & Neutral Supply, 3phase Motor.

240v Contactor Coil.

I've only ever connected a Remote Stop between the unit's Stop & the Overload.

Is there a ruling on this. Because I've come across a couple of Motors with the Remote Stops on the Neutral Side of the circuit.

Cheers!

I have not the slightest clue as to your local rules....but would not switching the neutral be in vain, should there be a short between the motor and the switch? A short there would result in a motor you couldn't turn off.

Quite Right renosteinke, unless you hit the Stop on the DOL box itself.

Plus if the overload was siezed in the closed position as well as the short to Earth after the coil & someone was jammed in the machine, the remotes would do nothing.

Thats why I want to know if there is a regulation I can state to my workshop manager, because his attitude is,"They wired it up, so put it back the same way as they had it!" If there is no regulation. I'm going to have to go to the Director & tell him to Phone the Factory concerned to tell their Electrical Foreman my concerns.

Thanks Reno. Another shouting match Tomorrow, I'll let you know the outcome.

As I mentioned if anyone knows of a site I can copy a written regulation from; it'll save a big barny & possibly someones life!

Thanks.

Couldn't you argue on the general rule about single-pole switching in a circuit with one earthed conductor (neutral) having to be in the live side?

The concerns over an earth fault preventing the contactor from releasing are noted here:
http://www.tlc-direct.co.uk/Book/3.2.2.htm



[This message has been edited by pauluk (edited 02-07-2006).]

Thanks Paul,
I went in this morning,the machine in question had gone, so I went into the office & asked if he had notified the customer that I had noticed their wiring wasn't right for the remote Stops. I was expecting an explosion of abuse, but he mumbled something & said that, he was just about to ring them...(aye Rite!!) So I stood there & the manager the other end said,"no problem I'll checkit out right away as we are just about to reinstall it"

No shouting... but a strange silence all day....Looks like I've lost my weekend OT!!

Can you change the coil to a 415v coil??

wouldnt switch the neutral..

Aye that would work, but even on 415V I've only ever added a remote stop in series with the fixed stop & O/L.
The Mach. came in, was over-hauled, wiring tidied (conduit etc). Thisis where I noticed the240V set up, with the remotes. But I was told not touch it as the other company's sparkies had wired it that way.
If we would have built it, it would be ok to do it right. But in this case I suppose the Gaffer's attitude was "They're not paying us to do that!"... At least I've got him to notify them to correct it!

Let's look for a second at what a E-stop or Stop switch is in a circuit.
All the contact does is opens the energising circuit of the Main Contactor.
IE: It drops out the coil, which releases the hold-in contact and de-energises the circuit.
Any Remote Stop will be in Series with the original and as long as things like Voltage Drop are taken into account, you should be OK.
The Neutral really doesn't come into it.

Uppeydog I've seen D.O.L.s that switch the neutral too ! Remote stops should always be wired in series with the overload and emergency stops should always be wired in series with the main contactor coil so as to cut power and control voltage in the system.

The potential is there for a ground fault to render the emergency stop non-functional though.

Assume the control wiring is as follows:

Phase -> Start -> Overload -> Local stop -> Coil -> Emergency stop -> Neutral.

Now imagine a ground fault develops on the line between the coil and the E-stop switch. You would never notice it until you came to use the E-stop, because the local stop would still function just fine.
Of course, you could say that putting the E-stop on the "hot" side of the coil also leaves room for a short to phase to do the same thing, but I would have thought that a ground fault would be the more likely.


[This message has been edited by pauluk (edited 02-10-2006).]

Good one Paul,

That's the lines I was thinking along.
Bearing in mind we are talking about a 240V coil, (one Phase -> Coil -> Neutral) not a 415V coil (L1 Phase -> Coil -> L2 Phase).

So when would a 240V coil be used instead of a 415V coil? As you already have 3Phases to use, & in some instances, if you use a 240v coil, you have to run a Neutral back to the Board anyway, as only 3Phases & Earth
are Supplied.

Would it something to do with safety, ie; less Voltage in wiring running to remote Switches, where operaters of the machine could be working?

It would affect the switch rating. On a 415V coil wired phase-to-phase, when you hit the E-stop switch and open the contactor circuit there will be 415V across its contacts.

Using a 240V coil phase-to-neutral would allow a 250V rated switches to be used instead.

Sorry Paul,
I see your point.
At this point in time there is a LOT of pressure on us PoCo workers here locally and some of us have had that for some months.
My apologies for upsetting this topic,
Mike.