STAR/DELTA MOTOR STARTING

Randyleprechaun

Hi,

I need some advice on sizing and placing an overload in a star/delta circuit.

I have my own idea on how and where but just want second opinion.

The motor in question was wired up by me about 2 years ago and was working fine till the other day. it now trips the overload when the delta contactor pulls in.
So here goes.

1. The motors plate shows delta symbol and says 31.5 amps.
2. When I first wired the motor up 2 years ago, it came with an old star/delta starter(intregrated to machine) which I ripped out and replaced with new telemecanique gear.

What I'd like to know is:

• Does this motor definetly require star/delta starter.
• If so, what should the thermal overload be rated at and where should it be placed.

As I said, I have my idea, but I'd like to get other opinions.

If you have any further questions please post them and I will answer.:)

I can't understand how it was working fine for 2 years and now is causing probs:mad:

Thanks

M cebee

hey.

i've been off the industrial maintenance for a good while so had to refresh my memory

http://www.wiringmanual.com/motor039.html

the first schematic is the overload in the 'motor line' and the amps is 0.58 the rated current.

afaik that prob offers the best protection


not sure what the prob is. have you checked the delta contactor?

.G.

The last picture in M cebee's link is how we wired star delta in tech very recently.

The overload should be set for the motors full load current

2011

Does this motor definetly require star/delta starter.

Hard to say if it "definetly" needs one without more details, but it is better to have one than not. What rating is the motor?

It is better as it reduces the starting current to about 1/3 of what it would be starting in delta.

Starting it in star is a bit like starting a car in 1st gear instead of 3rd (and then changing up a gear whaen it goes to delta).

• If so, what should the thermal overload be rated at and where should it be placed.

The overload should be set to the full load current of the motor as superg said.

The overloads normally have adjustment on them. Perhaps you just need to tweak them a bit.

It would be no harm to check a few things with the motor for example:

1) Can it rotate freely?
2) Measure the resistance of the windings. They should all be about the same.
3) Carry out an insulation resistance test (meggar).
4) Has the load changed?

Good luck!

ikb

http://www.wiringmanual.com/motor039.html

What a very useful link. I have an original K.M handbook from the 70s, which I carted around in my toolbag when apprenticed, Have tried to get an updated copy, many times over the years- without success.... The Interweb,... Information at your fingertips.:)
As with Mr C, I am also a long time away from plant maintenance.
Your issue may well be that the thermal O/L are just tired out.
You must first rule out any motor issues.Easiest way is to measure the currents to the motor when running (Line current is ok) All should be even.
If this is the case, Unload the motor, (ie. disconnect whatever from the drive pulley/ shaft) and check again.
It is possible that something on the driven end of the shaft is jamming/ seizing causing the motor to load up.?
DO NOT BE TEMPTED TO UP THE OVERLOAD SETTING.
What size motor is it? (kw/hp).
To be honest,Overloads wear out, are easy to change, and- provided all motor currents are even and within spec- are a good place to start.

ikb

2011 wrote: »

Hard to say if it "definetly" needs one without more details, but it is better to have one than not. What rating is the motor?

It is better as it reduces the starting current to about 1/3 of what it would be starting in delta.


It would be no harm to check a few things with the motor for example:

1) Can it rotate freely?
2) Measure the resistance of the windings. They should all be about the same.
3) Carry out an insulation resistance test (meggar).
4) Has the load changed?

Good luck!

+1...very good advice from 2011.
Lets know how you get on.

M cebee

superg wrote: »

The last picture in M cebee's link is how we wired star delta in tech very recently.

The overload should be set for the motors full load current

for 'motor line' and 'delta circuit' it will be 0.58*FLA


for 'mains supply line' overload protection or a 'motor circuit breaker' it will be 1*FLA

if the overload is sized according to FLA it will be approx 18amp if placed in series with the motor windings(motor line,delta circuit)
they're similar except with 'delta circuit' the overload is out of circuit for starting

Bruthal

If the overload is in the main motor contactor (Q11 in m ceebee diagrams) then it should be set to just over half motor full load amps, as when the motor is running, half will go down this part of the circuit when the motor is running in delta, if it is put into the other contactor (Q15) which closes to change to delta then its also set to just over half of motor full load amps but is not in the circuit until delta change over, so facilitates heavy load or slow start ups. If overload is in main contactor supply then its set to full load amps.

Changing the overload to a new one will probably fix it, but do an amps check on the part of circuit where the overload is, and compare it to the overload setting. If the amps is lower than the setting then new overload needed. If amps is higher then the load on the motor may have changed somehow, maybe by the machinery its driving not as free running as it was, or the motor itself is not running as freely as it was.

probably the overload itself needs replacing though.

Bruthal

superg wrote: »

The last picture in M cebee's link is how we wired star delta in tech very recently.

The overload should be set for the motors full load current

The last picture shows it in the delta change over leg there by the look of it, so it should be set to 0.58 as he said, i would of thought.

Bruthal

plate shows delta symbol and says 31.5 amps.

1. When I first wired the motor up 2 years ago, it came with an old star/delta starter(intregrated to machine) which I ripped out and replaced with new telemecanique gear.

What I'd like to know is:

• Does this motor definetly require star/delta starter.
• If so, what should the thermal overload be rated at and where should it be placed.

As I said, I have my idea, but I'd like to get other opinions.

If you have any further questions please post them and I will answer.:)

I can't understand how it was working fine for 2 years and now is causing probs:mad:

Thanks[/QUOTE]

It would need a star delta starter as it looks in and around a 20kw motor or just above if its 31.5 amps at 400v. Where the thermal overload goes depends on the motor startup required, if its a heavy slow build up to speed then it would be put in the delta contactor that closes when its changing to delta so it is only in the circuit at changeover and set to just over half the full load current. I never done it this way though.
It can be put in the main line contactor and so set to the full load amps, or in the motor line contactor and again set to just over half the full load setting, and in this position as in the main line it will be in the circuit during startup. Any time i made up star delta starters this is where i put them as far as i can remember anyway. Most motors i connected in recent years used VSD`s.

M cebee

i notice on some manual starters they recommend a multiplier of 0.9

if the motor 'service factor' is 1

http://www.sprecherschuh.com/download/ssna9000/download/F/F98_KT4_v309.pdf

afaik if the service factor is above 1 it should be on the nameplate

some large motors also operate well below FLA and reducing the overload setting is possible without causing nuisance

Bruthal

Its all 1kw radio control model motors these days for me, with mini VSD`s or ESC`s as they call them.

.G.

robbie7730 wrote: »

The last picture shows it in the delta change over leg there by the look of it, so it should be set to 0.58 as he said, i would of thought.

No idea.I've never wired one in industry just in tech and We wired them that way and were told the overload should be set at FLC.

Maybe its down to the type of overload used as to what it should be set at.

Bruthal

superg wrote: »

No idea.I've never wired one in industry just in tech and We wired them that way and were told the overload should be set at FLC.

Maybe its down to the type of overload used as to what it should be set at.

If you look closely at the star/delta power circuit you will see that in star all the motor current flows through the main motor contactor, and when it changes to delta it now has 6 wires feeding the windings so the motor current splits in 2, half through the main motor contactor and half through the delta one, so if the overload is on one of these contactors it must be set at around half the full load current or just above.

If full load current to motor is 31.5 amps then it will be about 10 amps in star through main contactor, and in delta it will be about 16 amps through main contactor and 16 through the delta contactor, so the overload on one of these would be set at about 17 or 18 amps

If however its on the main supply to the first main contactor then its set at full load current at 31 amps.

M cebee

superg wrote: »

No idea.I've never wired one in industry just in tech and We wired them that way and were told the overload should be set at FLC.

Maybe its down to the type of overload used as to what it should be set at.

no .there may other variables such as service factor and the motor/overload characteristics but the multiplier of 0.58 will still apply


with a service factor of 1 the motor windings can handle 18 amps

brightspark

I think 2011 in his post has most things covered

http://www.boards.ie/vbulletin/showpost.php?p=65229125&postcount=4

As the circuit was running for 2yrs and is now tripping I wouldn't expect a problem with the original circuit design.

Overloads, fuses etc are there to trip and protect other parts of the circuit in the event of problems.

Yes overloads and fuses do deteriotate with age and may trip for no apparent reasons but other parts fail too.

In addition to 2011's points I would suggest checking the following.


Check the contacts/connections on the delta contactor. (and all other connections too)

Check bearings on the motor and on whatever is being driven by the motor. (you could try running the motor with the load disconnected)

Check that the star contactor is dropping out fully (though I would expect to blow fuses if it was sticking)

I expect that you have already checked that the supply voltage is ok and that you have full voltage when the motor is in star (in case there is a problem with the supply cable/switchgear)

If everything checks out OK then replace the overload

Bruthal

brightspark wrote: »

I think 2011 in his post has most things covered

http://www.boards.ie/vbulletin/showpost.php?p=65229125&postcount=4

As the circuit was running for 2yrs and is now tripping I wouldn't expect a problem with the original circuit design.

Overloads, fuses etc are there to trip and protect other parts of the circuit in the event of problems.

Yes overloads and fuses do deteriotate with age and may trip for no apparent reasons but other parts fail too.

In addition to 2011's points I would suggest checking the following.


Check the contacts/connections on the delta contactor. (and all other connections too)

Check bearings on the motor and on whatever is being driven by the motor. (you could try running the motor with the load disconnected)

Check that the star contactor is dropping out fully (though I would expect to blow fuses if it was sticking)

I expect that you have already checked that the supply voltage is ok and that you have full voltage when the motor is in star (in case there is a problem with the supply cable/switchgear)

If everything checks out OK then replace the overload

Would a simple grip meter current check and compare to overload settings not simplify all that i wonder. removing the load a motor is driving can sometimes be a bit of a job.

Bruthal

Just as a matter of interest for anyone looking at the star delta circuit m ceebee put up a link to, in star the main contactor is connecting a phase to one end of each winding and the star contactor is bridging out the other 3 ends instead of the copper strips that motors have in them for star connecting direct. And when the star contactor drops out and the delta one closes, the motor now has in effect 3 wires connecting across from one row of terminals to the other row instead of the 3 copper bars that would be used for delta direct connected. So brown will be across from brown, black across from black, and grey across from grey in the motor terminal box. I seen a few times when they were connected staggered which is not right, as the windings themselves are connected staggered to the terminals.

brightspark

robbie7730 wrote: »

Would a simple grip meter current check and compare to overload settings not simplify all that i wonder. removing the load a motor is driving can sometimes be a bit of a job.

An ampmeter reading would be useful to determine what's happening but the OP said that it's tripping as soon as it goes into Delta so you can't be sure he can get a reading.

As this worked for a couple of years and is now tripping either a fault has developed in the circuitry or the power required to turn the motor has increased due to wear on the motor or it's load.

Bruthal

brightspark wrote: »

An ampmeter reading would be useful to determine what's happening but the OP said that it's tripping as soon as it goes into Delta so you can't be sure he can get a reading.

As this worked for a couple of years and is now tripping either a fault has developed in the circuitry or the power required to turn the motor has increased due to wear on the motor or it's load.

A fault in the circuit of the starter should`t trip overload, only the overload itself being overloaded should, any other fault like a star contactor sticking would trip MCB. A grip ammeter with the high reading lock on it should tell the reading even if its quick trip out, although this reading may be higher just as it changes to delta because the motor under load might not be up to speed in star even though an unloaded motor will reach full speed in star, there may be a current spike on a loaded motor that changes to delta which then reduces as the delta now has full motor torque to bring load to running speed.

If the motor is running up to speed in star then it is safe to bypass the overload and do a current check in delta and compare to the actual full load rating or the overload setting depending on where is tested. The motor wont suffer any damage by being overloaded for short periods so the overload can be bypassed to test loadings and see all 3 phases are equal.

Another quick test to see all 3 phases are going to motor is to get all 3 supply phases and put grip ammeter around them, if it says 0 amps then all 3 phases are supplying the motor. If a phase is down somewhere in the circuit the ammeter wont read 0 amps

The reason overloads are used on motors are they can be very accurately set, a motor slightly overloaded for long periods will be damaged, but heavily overloaded for a test purpose it will be fine, once its running up to speed in star it will be ok. When delta comes in it could be a phase missing through that contactor, or machinery the motor is driving has now changed or is less free running, or motor itself less free, or if the insulation on windings themselves is gone bad, but if it was me testing i would bypass overload and do amp readings of the 3 phases right where the overload is. That quickly tells if its the overload. Just start it and when it runs in delta take reading, stop motor and set up next phase for reading.
We are assuming the motor is running up ok in star of course.

But its not me testing, probably just as well some would say.

Randyleprechaun

Thanks for the replies guys.

The original circuit that I designed and fitted two years ago had the overload in the delta line and I had it set at 18Amps.

I set the timer by allowing the motor to run up and watching the amp meter till it evened out and set to that time.

everything worked sweet till now. The motor is on a saw and it is quite easy to run without a load on(bar the blade itself that is). I did this and the overload trips everytime on changeover to delta.

I think the easiest thing to do first is replace the overload and see how that goes. If that doesn't work then I'll have to check out the motor itself, although there doesn't appear to be anything wrong with it.

M cebee

have you checked the delta contactor

swapping out the overload is a good idea otherwise

Bruthal

Randyleprechaun wrote: »

Thanks for the replies guys.

The original circuit that I designed and fitted two years ago had the overload in the delta line and I had it set at 18Amps.

I set the timer by allowing the motor to run up and watching the amp meter till it evened out and set to that time.

everything worked sweet till now. The motor is on a saw and it is quite easy to run without a load on(bar the blade itself that is). I did this and the overload trips everytime on changeover to delta.

I think the easiest thing to do first is replace the overload and see how that goes. If that doesn't work then I'll have to check out the motor itself, although there doesn't appear to be anything wrong with it.

If there is a phase missing through the delta contactor that would quickly cause a trip. An easy way to test that is to disconnect the 3 wires on the motor side of the main contactor and put into connectors (saves opening motor cover), press start button, the contactors should go through the timer sequence but without motor starting and when delta contactor closes test for 3 phases on the wires you put in connectors.

If motor winding insulation is deteriorated at the star connected end then it would`t show until it changes to delta, another possibility but probably not too likely.

With overload in delta line its not coming into the circuit until changeover to delta and if its running up ok in star its probably the overload. If you have another to replace it with thats the simplest test.

M cebee

well ya

but you're not testing under load conditions

a bad contact wont show with a voltage test- only an open contact

Bruthal

M cebee wrote: »

well ya

but you're not testing under load conditions

a bad contact wont show with a voltage test- only an open contact

Well yes, i have thought of that, thats why in earlier post i said bypass overload if dont have spare one, and run the 3 phases of supply through grip ammeter. Would that suffice as an on load test for missing phases??

I suppose now you`l say ye cant run motor with no overload on it.

M cebee

how do you test contactor exactly??

inspect contacts visually
energize contactor and check impedance of contacts
wire contacts in series and stick a load on the end-check for voltage drop

not so simple when the load is a motor and it's tripping the overload immediately

'main contactor' ,supply voltages should be checked too ,as well as the 'motor checks' 2011 mentioned

before swapping out overload is my best guess

Bruthal

M cebee wrote: »

how do you test contactor exactly??

inspect contacts visually
energize contactor and check impedance of contacts
wire contacts in series and stick a load on the end-check for voltage drop

'main contactor' should be inspected too ,as well as the 'motor checks' 2011 mentioned

before swapping out overload

Well it must be just my uneducated guessing at all this, but bypassing overload and one grip ammeter test of 3 phases in delta in one go to see a reading of zero to confirm 3 phases under load, if motor is running up in star then its not seized, so run into delta without overload and check 3 phase currents together, if zero reading then test 3 individually to compare to overload setting. Contactors are very reliable, if they are not obviously burnt then id just do the grip ammeter tests, thats what i always did, and would if i ever do electrical work again. But if ye have a new overload why not just put it in?
After that its motor bearings or winding insulation tests. Its not rocket science. Although its turning into it.

Randyleprechaun

Ok guys,

I'll disconnect the motor tomorrow and check that:

1. The control circuit functions properly(have already done this but I'LL CHECK AGAIN)
2. That I have 3 phases everywher they should be
3. All motor windings have same resistance.

If all checks out then I think swapping the o/l is the quickest thing to try next.

The o/l I had used was LRD 21 which has 18Amps at the top of its range. Is there any merit to using LRD22 which has the 18Amps toward its lower end.

M cebee

i'm not not so sure about bypassing overload -that's all

it's not rocket science but obviously heating ,lighing loads with no overload are simpler to check -in circuit

Bruthal

M cebee wrote: »

i'm not not so sure about bypassing overload -that's all

it's not rocket science but obviously heating ,lighing loads with no overload are simpler to check -in circuit

Thats fair enough, im just suggesting what i`ve done before, bypassing overload and leaving it running like that is one thing no one should do, but for a very quick test on a motor loading that is running ok in star i dont see much problem with it. It only involves connecting the two control wires in the overload contact together. And testing 3 phases together. If reads zero, then a current test of one phase coming from delta contactor is all thats needed and compared to overload setting which is in the delta contactor. An insulation test can be done first to rule that possibility out then the overload bypass and current readings because if the insulation is ok in motor what damage can bypassing the overload do.

Maybe someone changed the connections in the motor, who knows,
what would happen if the 6 wires are not right, i.e. brown across from brown, black-black, grey-grey(which is correct). It will start fine in star, but depending on how the phases are connected it can either stop from having the same phase on each end of winding or possibly trip on delta by having a winding reversed.
Maybe im having too much wine now:)

Everyone has their own ways though, not always the same and not always perfect.

Bruthal

Randyleprechaun wrote: »

Ok guys,

I'll disconnect the motor tomorrow and check that:

1. The control circuit functions properly(have already done this but I'LL CHECK AGAIN)
2. That I have 3 phases everywher they should be
3. All motor windings have same resistance.

If all checks out then I think swapping the o/l is the quickest thing to try next.

The o/l I had used was LRD 21 which has 18Amps at the top of its range. Is there any merit to using LRD22 which has the 18Amps toward its lower end.

18 amp upper limit one should be plenty on that. Its a saw with no load on it until actually cutting? If its running ok in star then the windings are likely to be ok, although winding insulation problem at the star end would`t show until changes to delta. Test the supply current with it running in star. The delta should be 3 times this value. As i said, i would link the two connections of the overload thats tripping together and so it will run in delta then, just to test the phase currents. But it might not be for everyone to do that, but it certainly is not a problen to do as the overload is mainly to protect an overloaded motor over time rather than something to protect a major fault in the motor. If you have new overload i`d just put it in and try it first, if it works then no more tests or anything needed.

Randyleprechaun

Does everyone agree(or anyone) that if the overload is on the delta line it should be set at 0.58 X full load amps

Bruthal

Randyleprechaun wrote: »

Does everyone agree(or anyone) that if the overload is on the delta line it should be set at 0.58 X full load amps

If its on the delta line or the main contactor it should be set at that value. Only if on the main 3 phases feeding the starter will it be set to full load.

Bruthal

Randyleprechaun wrote: »

Does everyone agree(or anyone) that if the overload is on the delta line it should be set at 0.58 X full load amps

If its turning something that is not a heavy load it would usually be put on the main contactor. They are put on the delta contactor to assist with starting up heavy loads to get up to speed because by being on the delta line it is not in circuit until it changes to delta, which means theres a motor running with no overload, so where is the harm in testing with overload bypassed for a few minutes even if it is in delta.

scubaH

If the timer on the star/delta is tampered or changed it will trip out,there should be at least 10 sec interval between the change from star in2 delta,overload should be set at FLC.

Bruthal

scubaH wrote: »

If the timer on the star/delta is tampered or changed it will trip out,there should be at least 10 sec interval between the change from star in2 delta,overload should be set at FLC.

If the motor now has 6 wires feeding it, one set through the main contactor and one set through the delta contactor, and the motor is taking 32 amps per phase, how much will flow down each contactor set, it would`t be FLC i would`t think. And the overloads are usually fitted on one contactor., usually the main one.

M cebee

robbie7730 wrote: »

If its turning something that is not a heavy load it would usually be put on the main contactor. They are put on the delta contactor to assist with starting up heavy loads to get up to speed because by being on the delta line it is not in circuit until it changes to delta, which means theres a motor running with no overload, so where is the harm in testing with overload bypassed for a few minutes even if it is in delta.

the 'motor line' overload at 0.58 FLA gives closest protection for 'star' if it doesn't trip on startup

http://www.patchn.com/index.php?option=com_content&task=view&id=42&Itemid=74


i imagine a saw should be well below FLA under no-load conditons

Bruthal

M cebee wrote: »

the 'motor line' overload at 0.58 FLA gives closest protection for 'star' if it doesn't trip on startup

http://www.patchn.com/index.php?option=com_content&task=view&id=42&Itemid=74


i imagine a saw should be well below FLA under no-load conditons

It does, but they are fitted in the delta leg on heavy slow to speed up setups, and is on the delta leg in this post i think, although i have`t fitted them there myself. The star current will be higher than the delta one ever reaches on any given load possibly. A motor starting takes a current of a seized stopped motor at the instant of starting and in star this is probably higher than it ever takes in the up to speed delta changed over motor.

And i`d agree, it must be a fair bit below FLA on a saw, so tripping so quick on changeover is interesting.

scubaH

Is the motor going in the right direction?Is it on a C rated MCB back at the board?there should be 1 overload on the outgoing.the current is split.

Bruthal

As for the overload itself, its not there to protect against short circuits, or insulation breakdown in windings, its there to very closely guard against even a small increase in motor current in motors that are running regular long term. So bypassing it is not a problem for a test purpose in my opinion. And a few grip ammeter tests would take no time and tell a lot about this or any motor setup. A motor thats not seized completely cant suffer any major problems from a bypassed overload as long as its not left bypassed as a fix.

Bruthal

scubaH wrote: »

Is the motor going in the right direction?Is it on a C rated MCB back at the board?there should be 1 overload on the outgoing.the current is split.

How would the MCB at the board have any effect. Maybe the wine is affecting me worse than i thought.

M cebee

robbie7730 wrote: »

As for the overload itself, its not there to protect against short circuits, or insulation breakdown in windings, its there to very closely guard against even a small increase in motor current in motors that are running regular long term. So bypassing it is not a problem for a test purpose in my opinion. And a few grip ammeter tests would take no time and tell a lot about this or any motor setup. A motor thats not seized completely cant suffer any major problems from a bypassed overload as long as its not left bypassed as a fix.

ah you might be right:D

Bruthal

M cebee wrote: »

ah you might be right:D

I know, but as you know yourself, i could be wrong as well, theres always something we might not think of.

Randyleprechaun

Thanks again for all the replies guys...case is now closed. I went today to check the control circuit and the motor etc etc. Control circuit was fine but on opening the cover of the motor terminal box I noticed a loose wire which actually broke when I touched it. Must be the vibration or something.

It was one of the wires leading from the delta contactor so in effect I suppose it was like a phase down.

Nyway, put it all backj together and it's fine now.

To clear up some of the confusion(which there seems to be alot of) there are a number of places that the thermal overload can be placed but it affects what the o/l should be set at.

1. It can go in the motor line but must be set to 0.58 X FLA.
2. It can go in the delta circuit but must be set to 0.58X FLA
3. It can go in the main supply(ie. line feeding from MCB or simillar) but must be set to FLA.

Well thanks again for all the help(even those who went of on their little tangents(argumnents ahem!!!!!))) Sure it's all aprt of the crack ha????

Randyleprechaun

Randyleprechaun wrote: »

Thanks again for all the replies guys...case is now closed. I went today to check the control circuit and the motor etc etc. Control circuit was fine but on opening the cover of the motor terminal box I noticed a loose wire which actually broke when I touched it. Must be the vibration or something.

It was one of the wires leading from the delta contactor so in effect I suppose it was like a phase down.

Nyway, put it all backj together and it's fine now.

To clear up some of the confusion(which there seems to be alot of) there are a number of places that the thermal overload can be placed but it affects what the o/l should be set at.

1. It can go in the motor line but must be set to 0.58 X FLA.
2. It can go in the delta circuit but must be set to 0.58X FLA
3. It can go in the main supply(ie. line feeding from MCB or simillar) but must be set to FLA.

Well thanks again for all the help(even those who went of on their little tangents(argumnents ahem!!!!!))) Sure it's all aprt of the crack ha????

Just to add to the above:

The 3 different positions for the overload also offer differing levels of protection to the motor

Bruthal

Randyleprechaun wrote: »

Thanks again for all the replies guys...case is now closed. I went today to check the control circuit and the motor etc etc. Control circuit was fine but on opening the cover of the motor terminal box I noticed a loose wire which actually broke when I touched it. Must be the vibration or something.

It was one of the wires leading from the delta contactor so in effect I suppose it was like a phase down.

Nyway, put it all backj together and it's fine now.

To clear up some of the confusion(which there seems to be alot of) there are a number of places that the thermal overload can be placed but it affects what the o/l should be set at.

1. It can go in the motor line but must be set to 0.58 X FLA.
2. It can go in the delta circuit but must be set to 0.58X FLA
3. It can go in the main supply(ie. line feeding from MCB or simillar) but must be set to FLA.

Well thanks again for all the help(even those who went of on their little tangents(argumnents ahem!!!!!))) Sure it's all aprt of the crack ha????

Thats good, its as good as a phase down alright. Its surprising it started in star at all, as even though the 3 phases are there from main contactor, one leg of star point is open, although 2 windings do have 2 phases so it might start. It must of been slow to start though. Although in this case you do have 2 windings still being fed in delta where as a direct on line setup missing a phase would only have one winding being fed properly in delta and the other 2 fed in series from that same 2 phases so all 3 windings would only have single phase,, haha another point for arguements and tangents.

Bruthal

Randyleprechaun wrote: »

Just to add to the above:

The 3 different positions for the overload also offer differing levels of protection to the motor

Yes it does, its simply this, Main feed position its set at FLA, but in main contactor it is set just over half FLA and gives closer protection to starting in star if startups dont have heavy load, and in the delta contactor its also set just over half but gives no protection in star to assist in long slow startup to speed. So putting in main feed at FLA gives protection in star also but gives more room for heavier slow starts than if put in the main contactor set at 0.58

I must have too much free time on my hands with all the posts

M cebee

grand job:D

shows the benefit of the closest 'startup' overload protection if possible(0.58 FLA motor line)

Bruthal

M cebee wrote: »

grand job:D

shows the benefit of the closest 'startup' overload protection if possible(0.58 FLA motor line)

This motor did`t have the closest `startup` benefit did it?
The overload was in the delta contactor. So it was`t in the circuit during startup. If one connection in the motor terminal box was gone, then it would not have been starting properly in star either and should of tripped overload during starting if it had been in main contactor set at .58. When it changed to delta it had the double problem of possibly not running up to speed in star as only 2 windings were connected in series to 2 phases, in effect only having single phase startup, and then when it changed to delta it had only 2 windings connected fully. In this scenario its not quite the same as a supply phase down in the delta stage, as 2 of the windings actually have the 3 phases connected, but one winding is open at the motor box connection thats gone bad.

The closer protection benefit of using the overload at .58 for starting only comes about when its fitted in the main contactor. I think it was in the delta one in this setup. But again i could be missing something.

M cebee

that was my point

it would have been better 'in-circuit' for startup if possible

Bruthal

M cebee wrote: »

that was my point

it would have been better 'in-circuit' for startup if possible

i know, i`l have to go to specsavers one of these days.