DIYnot
Local | Network
   DIYnot > Forums
Local | Network
DIYnot Network Local DIYnot Network Local  
  Forum IndexForum Index     RulesRules    HelpHelp     Join FREERegister Free     About CookiesCookies     SearchSearch     LoginLogin 

3phase and neutral

Goto page 1, 2  Next
 
Post new topic   Reply to topic    DIYnot.com Forum Index > Electrics UK
Search this topic :: View previous topic :: View next topic  
Author Message
Christhescott

from United Kingdom

Joined: 21 Feb 2010
Posts: 51
Location: Aberdeen,
United Kingdom
Thanked: 2 times

PostPosted: Thu Nov 25, 2010 10:46 pm Reply with quote

Hi, Im looking for some connection diagrams/pictures of 3phase and neutral motor start/stop connections, would anyone in here have any links I could have a look at? I have tried google with little avail.

Thankyou!
Back to top
 Alert Moderators

If you do not want to see this advert, click here to login or if you are new click here to join free.
ban-all-sheds

from United Kingdom

Joined: 27 Aug 2003
Posts: 46282
Location: London,
United Kingdom
Thanked: 1666 times

PostPosted: Thu Nov 25, 2010 10:54 pm Reply with quote

I don't think that 3-Ph motors have a neutral do they?

There might be one to the controls, but not to the actual motor.
Back to top
 Alert Moderators
Spark123

from United Kingdom

Joined: 02 Jun 2005
Posts: 14171
Location: Cumbria,
United Kingdom
Thanked: 396 times

PostPosted: Fri Nov 26, 2010 12:09 am Reply with quote

As the motor is a ballanced 3 phase load there is no need for a neutral, however a neutral may be used in the control side if it is 230v. The control side may be any voltage sufficient to drive a contactor i.e. common size contactors I come across are 24v, 48v, 110v, 230v and 400v.
What type of motor control are you talking about, direct on line (DOL)? If so there is a similar diagram here:

As you don't need the neutral ignore the neutral contact at the bottom, the normally closed contacts on the left hand side are stop buttons.
Back to top
 Alert Moderators
IJWS15

from United Kingdom

Joined: 18 Oct 2006
Posts: 1256
Location: Staffordshire,
United Kingdom
Thanked: 37 times

PostPosted: Fri Nov 26, 2010 8:52 am Reply with quote

Try googling delta star wiring
Back to top
 Alert Moderators
bernardgreen

from United Kingdom

Joined: 03 Nov 2006
Posts: 10174
Location: Bedfordshire,
United Kingdom
Thanked: 754 times

PostPosted: Fri Nov 26, 2010 9:15 am Reply with quote

ban-all-sheds wrote:
I don't think that 3-Ph motors have a neutral do they?


Some motors that run in Star mode do have a "neutral" connection to the star point. Its purposes more often than not is provide a means to detect faults and /or unbalances in the three phase windings while the motor is running.
Back to top
 Alert Moderators
Christhescott

from United Kingdom

Joined: 21 Feb 2010
Posts: 51
Location: Aberdeen,
United Kingdom
Thanked: 2 times

PostPosted: Fri Nov 26, 2010 7:17 pm Reply with quote

Yes its a DOl starter. The manual says It needs a neutral, I can't remember off the top of my head what its for but I think its an air brake. Aswell as the 3 cables going away to the motor it has a two core flex. Its a second hand machine and it looks like the starter is not standard. I wanted a picture as Im not sure if the neutral should go into the top and through the contactor aswell as the 3 phase supply.
Back to top
 Alert Moderators
PrinceofDarkness

from United Kingdom

Joined: 01 Jan 2006
Posts: 611
Location: London,
United Kingdom
Thanked: 62 times

PostPosted: Fri Nov 26, 2010 7:45 pm Reply with quote

"Some motors that run in Star mode do have a "neutral" connection to the star point"...................




I'd like you to give me an example of such a motor, 'bernard', where the star link is connected to the supply neutral. I've been dealing with rotating machines since the early 60's and I've never come across such a ridiculous situation as that. Don't you realise the implications of doing such a thing?

It's certainly true in some circumstances that a lead is taken from the star position of the motor terminal block for monitoring purposes - but that type of connection is never connected to the supply neutral.

Getting back to the O/P: I'd say that the DOL starter needs a neutral simply because the hold-in coil is 230 Volt - as they often are. But this doesn't mean that that neutral has to be taken to the motor itself......


Lucia.
Back to top
 Alert Moderators
ELZ4742

from United Kingdom

Joined: 22 Jan 2007
Posts: 557
Location: Oxford,
United Kingdom
Thanked: 16 times

PostPosted: Fri Nov 26, 2010 7:53 pm Reply with quote

A three phase motor does not need a neutral because it has two 'phase' leads running it at any given point in time. The electricity comes in on one phase lead and goes out on the other phase lead.
Back to top
 Alert Moderators
PrinceofDarkness

from United Kingdom

Joined: 01 Jan 2006
Posts: 611
Location: London,
United Kingdom
Thanked: 62 times

PostPosted: Fri Nov 26, 2010 8:16 pm Reply with quote

The O/P, Chris-the-Scot, hasn't actually implied that the motor itself needs a neutral. He's surely on about the control circuit of the starter and perhaps, the wiring of remote start/stop buttons.

This seems to me to be a bog-standard arrangement, and I'm rather surprised that he can't find any 'Googlese' for such a plain task.


Lucia.
Back to top
 Alert Moderators
Christhescott

from United Kingdom

Joined: 21 Feb 2010
Posts: 51
Location: Aberdeen,
United Kingdom
Thanked: 2 times

PostPosted: Fri Nov 26, 2010 10:49 pm Reply with quote

PrinceofDarkness wrote:
"Some motors that run in Star mode do have a "neutral" connection to the star point"...................




I'd like you to give me an example of such a motor, 'bernard', where the star link is connected to the supply neutral. I've been dealing with rotating machines since the early 60's and I've never come across such a ridiculous situation as that. Don't you realise the implications of doing such a thing?

It's certainly true in some circumstances that a lead is taken from the star position of the motor terminal block for monitoring purposes - but that type of connection is never connected to the supply neutral.

Getting back to the O/P: I'd say that the DOL starter needs a neutral simply because the hold-in coil is 230 Volt - as they often are. But this doesn't mean that that neutral has to be taken to the motor itself......


Lucia.


Thanks for your help. As you can tell Im not as familier as I would like to be with motor control. I dont think the neutral is for the coil, I think the neutral is for something to do with dust extraction and I think the saw motor will work without the neutral connected. The neutral does not go to the motor itself but it is terminated inside the starter.
Back to top
 Alert Moderators
ban-all-sheds

from United Kingdom

Joined: 27 Aug 2003
Posts: 46282
Location: London,
United Kingdom
Thanked: 1666 times

PostPosted: Sat Nov 27, 2010 8:51 am Reply with quote

Christhescott wrote:
I think the neutral is for something to do with dust extraction.

Could be a single-phase extractor.

I believe that sometimes motors have single-phase anti-condensation heaters.

Or as others have also said, single-phase components in the control systems.
Back to top
 Alert Moderators
bernardgreen

from United Kingdom

Joined: 03 Nov 2006
Posts: 10174
Location: Bedfordshire,
United Kingdom
Thanked: 754 times

PostPosted: Sat Nov 27, 2010 9:55 am Reply with quote

PrinceofDarkness wrote:
I'd like you to give me an example of such a motor, 'bernard', where the star link is connected to the supply neutral. I've been dealing with rotating machines since the early 60's and I've never come across such a ridiculous situation as that. Don't you realise the implications of doing such a thing?,


I cannot remember the manufacturers part numbers of the motors I have seen with the star point bought out as a monitoring access for the control system. Hence the " and " round the word neutral.

Quote:
but that type of connection is never connected to the supply neutral.
I didn't say it was.

I can recall one production line where the 4 or 5 main conveyor drive motors did have their star points commoned up but not connected to the main neutral supply. Something to do with reducing slip to an acceptable level.
Back to top
 Alert Moderators
mikhailfaradayski

from United Kingdom

Joined: 21 Jul 2009
Posts: 1677
Location: Derby,
United Kingdom
Thanked: 86 times

PostPosted: Sat Nov 27, 2010 10:36 am Reply with quote

Chris-T-S,

as others have said, the neutral is most probably required for the coil in the start/stop gubbins.

It may also be the case that the 2 core flex you refer to is a thermistor or other thermal device. If it is (which you need to find out) then it should be included in the control wiring
Back to top
 Alert Moderators
sparkyy

from United Kingdom

Joined: 10 May 2008
Posts: 24
Location: Aberdeen,
United Kingdom
Thanked: 3 times

PostPosted: Sat Nov 27, 2010 3:26 pm Reply with quote

The two core flex is probably a thermistor which should be incorporated into the stop circuit. It's purpose is to stop the motor if it overheats.
Back to top
 Alert Moderators
ricicle

from United Kingdom

Joined: 14 Sep 2006
Posts: 6295
Location: Gloucestershire,
United Kingdom
Thanked: 374 times

PostPosted: Sat Nov 27, 2010 4:29 pm Reply with quote

sparkyy wrote:
The two core flex is probably a thermistor which should be incorporated into the stop circuit.


Via a suitable thermistor relay.....
Back to top
 Alert Moderators
Search this topic :: View previous topic :: View next topic  
Post new topic   Reply to topic    DIYnot.com Forum Index > Electrics UK All times are GMT
Goto page 1, 2  Next
Page 1 of 2

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
Similar Topics   Replies   Views   Posted 
3phase lighting and shared neutral 51 2560 Sun Sep 13, 2009 8:20 pm
new 3phase supply but only 2 working? 6 320 Thu Jun 23, 2011 8:51 pm
Electric setup 3phase with pics and diagram question 10 660 Mon Apr 18, 2011 8:13 pm
How to wire 2N 400V appliance to 3phase mains 2 140 Sun Aug 14, 2011 12:16 pm
3Phase Fryer connection 8 220 Sun Dec 18, 2011 7:50 pm


 
DIYnot
Find an Expert | Find a Supplier | Search DIYnot.com
Network | Advertising | Newsletter
DIY | DIY How To | @home | DIY Wiki | DIY Forum
By using this site you agree to our Terms of Service / Disclaimer.
Please read our Privacy Policy. Copyright © 2000-2014 DIYnot Limited.