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Topic Title: DOL Starter - Single Phase
Topic Summary: Correct wiring?
Created On: 26 August 2008 05:09 PM
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 26 August 2008 05:09 PM
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andrewmac

Posts: 237
Joined: 14 April 2004

Gents,

The connections for a single phase motor, controlled by a DOL starter are giving me problems.
Well, its one connection in particular.

My question(s):
1. Why is there a link wire between Terminals 3 & 6?
2. Why cant the connection go straight from Terminal 6 to the motor?

In summary:

Terminal 1 - Neutral
Terminal 3 - Linked to 6
Terminal 5 - Live


Terminal 2 - Neutral
Terminal 4 - Live

Thanks, as always
 26 August 2008 05:14 PM
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Avatar for rocknroll.
rocknroll

Posts: 8838
Joined: 03 October 2005

1. Why is there a link wire between Terminals 3 & 6?


So that all three poles are monitored for overcurrent, it is considered good practice

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------

Edited: 26 August 2008 at 05:14 PM by rocknroll
 26 August 2008 05:22 PM
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andrewmac

Posts: 237
Joined: 14 April 2004

Thanks RnR for the speddy reply.

Its only single pole - so its ok to wire the output to 2 & 4 then?
 26 August 2008 05:45 PM
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rocknroll

Posts: 8838
Joined: 03 October 2005

Here is a wiring diagram for a single phase DOL starter that may help you.

http://www.memonline.com/circuitdiagrams.html

MEM seem to use L1 for the N and L3 for the L, other manufacturers use L1 for L and L3 for N but it doesnt matter whether the control circuit runs via the neutral or live

In your case after drawing it out it looks like 2 (N) & 4(L)

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------

Edited: 26 August 2008 at 05:54 PM by rocknroll
 26 August 2008 07:37 PM
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zeeper

Posts: 1409
Joined: 11 July 2008

Dont forget that there are two windings in a single phase motor. the run winding and the start winding, the start winding is normally connected to the supply and a capacitor. when the motor hits a certain speed a switch inside the motor disconnects the start winding. the connection of the supply to the motor is normally on the underside of the motor terminal lid lol.doesnt matter which way round you connect it it will only rotate in one direction.if the capcitor isnt connected the motor will just hmmm and not rotate.
 27 August 2008 09:45 AM
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andrewmac

Posts: 237
Joined: 14 April 2004

Thanks again.

After wiring as suggested the motor did not start.
However, on connecting Terminal 6 directly to the motor, it started.

Any suggestions?
 27 August 2008 11:12 AM
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rocknroll

Posts: 8838
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If its wired as per your OP then both 4 and 6 are live when the contacts close, using 6 for the motor you are not monitoring all poles for overload.

See my sketch

http://groups.msn.com/SparkyRe...ShowPhoto&PhotoID=123

Good practice states that all poles of the overload should be monitored for it to be effective, hence the reason why a link is used in a dol starter for a single phase motor

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 27 August 2008 12:18 PM
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OMS

Posts: 19623
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doesnt matter which way round you connect it it will only rotate in one direction.if the capcitor isnt connected the motor will just hmmm and not rotate.


You can change direction of rotation of a capacitor start capacitor run single phase motor if you swap the start winding over

Regards

OMS

-------------------------
Failure is always an option
 27 August 2008 12:26 PM
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andrewmac

Posts: 237
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Thanks for your time and effort and drawing!

If all poles are not used is it necessary to in clude the link?

thanks again!
 27 August 2008 12:40 PM
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OMS

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Usually yes because the O/L module is normally a 3 pole unit and as RnR has said (repeatedly) that it is best practice to ensure all poles run through the O/L device.

Essentially all you are doing is taking the output from one pole of the run contactor and rerouting via the unused pole when in single phase mode to effectively give you two output poles but three monitored poles.

Regards

OMS

-------------------------
Failure is always an option
 27 August 2008 12:50 PM
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andrewmac

Posts: 237
Joined: 14 April 2004

Thanks again for your patience.

Yes, RnR has een very helpful and has stated that it is good practice.

I am asking why it is considered good practice to monitor something that is not being used?
 27 August 2008 12:59 PM
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pnorton

Posts: 402
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Using all 3 poles when connecting a single phase motor is a bit more than good practice!

These thermally operated overload modules are usually made to detect an uneven load across the 3 poles (assume loosing a phase on a 3 phase motor) as well as just overload. So if you fail to use all 3 poles when connecting a single phase motor you are likely to get "nuisance tripping".

By putting in the link, you are wiring 2 poles in series so ensuring current passes through all 3 sets of thermal devices and the module sees a balanced load on all poles.

Hope that helps.

Paul

-------------------------
The body is now decrepit but the mind is still active - just!
 27 August 2008 01:07 PM
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rocknroll

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If all poles are not used is it necessary to include the link?


Think about what I said " Good practice states that all poles of the overload should be monitored for it to be effective, hence the reason why a link is used in a dol starter for a single phase motor".

This is a decision I cannot make for you,

what is good practice?
if the manufacturer supplied a link fitted and something happened would altering the specification make a difference?
if only two thirds of the overload is monitored would that affect the operation?

So convention tells you to wire up a DOL with a link, but if you want to buck convention and be a rebel thats your choice, 'hey man' everyone loves a rebel

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 27 August 2008 01:08 PM
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OMS

Posts: 19623
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Can't argue with that - although you would need specific knowledge of the type of overload present to determine if it needs a balanced current flow for reliabale operation or not.

If it comprises a number of independant devices acting on a common trip bar (think oil dashpot magnetic trips and thermal bi-metal trips) as opposed to a "detection module" performing a variety of functions including phase failure or phase balancing

Regards

OMS

-------------------------
Failure is always an option
 27 August 2008 01:25 PM
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rocknroll

Posts: 8838
Joined: 03 October 2005

I dont disagree with what PN says but I have to say I am more in line with OMS, basically that is why I avoided that theory and emphasised the conventional link method which should cover-all scenarios.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 27 August 2008 02:09 PM
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OMS

Posts: 19623
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dont disagree with what PN says but I have to say I am more in line with OMS


Thats cos you are old enough to remember oil dashpot trips

OMS

-------------------------
Failure is always an option
 27 August 2008 02:49 PM
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rocknroll

Posts: 8838
Joined: 03 October 2005

How retro is this, I still have a tin of dashpot oil, 4 pint can in my garage, probably still has around 2 and a half pints left, most of it was used in the SU carburettors on my Mini Cooper a lot of moons ago

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------

Edited: 27 August 2008 at 02:50 PM by rocknroll
 27 August 2008 02:58 PM
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Avatar for OMS.
OMS

Posts: 19623
Joined: 23 March 2004

most of it was used in the SU carburettors on my Mini Cooper a lot of moons ago


I was a Webber man myself - DCD's with the air intakes protruding into the cockpit through the dash - not funny when you had the occasional "backfire" but probably no more dangerous than driving everywhere at a ton plus invincible in the cooper shell c/w rollcage, bucket seats and minilites all round.

OMS

-------------------------
Failure is always an option
 27 August 2008 03:13 PM
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rocknroll

Posts: 8838
Joined: 03 October 2005

Ah! the Weber and the associated manifold was a valuable commodity them days, my problem was using 3 in 1 oil putting your foot down to the floor at traffic lights the pistons came up to fast and flooded the engine, tried engine oil but borrowed a tin of dashpot oil from work (must take it back) worked a treat, I bet you were one of those who used to cruise the high street get up a bit of speed then turn the engine off and back on again 'bang' frightening the old dears played havoc with your exhaust.

Those were the days.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 27 August 2008 03:18 PM
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pnorton

Posts: 402
Joined: 16 September 2005

Originally posted by: OMS

dont disagree with what PN says but I have to say I am more in line with OMS




Thats cos you are old enough to remember oil dashpot trips



OMS


Ah dashpots. I was always told they were the "Rolls Royce" of motor overload protection - but then, we were otherwise using the old MEM starters - you know, the ones where you could see the bi-metal strips and the heater element.

But then we started to use the MEM modular type of starter (methinks this must be about 30 years ago). Remember taking an overload unit apart and saw the very cleverly designed system of levers and "floating" elements which allowed for the detection of a loss of a phase.

All of a sudden dashpots were then considered inferior.

I reckon I could give you two a few years Could have got my bus-pass in 2005.

Have fun.

Paul

-------------------------
The body is now decrepit but the mind is still active - just!
IET » Wiring and the regulations » DOL Starter - Single Phase

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