HELP 3 phase masonary saw wiring

[telectrix]

going by the rating plate on the OP's post. it says 230/380. had similar on a farm. installer wired it in delta on 415V. it lasted 20 minutes.

 

[Pete999]

going by the rating plate on the OP's post. it says 230/380. had similar on a farm. installer wired it in delta on 415V. it lasted 20 minutes.

Perhaps it would have bee a good idea to use a S/D starter in the first place, staring something in Delta is in my book asking for a burn out, after all that's why some motors aren't started DOL or in Delta,
https://www.quora.com/Why-is-star-delta-starter-preferred-with-an-induction-motor

 

[westward10]

It doesn't need star/delta it is only a toy motor with no initial load on it. As Tel states the motor in question needs 230v three phase to function in delta, if that motor was connected in delta on 415v three phase it will last minutes.

 

[Pete999]

I must be missing something obvious here

 

[westward10]

I must be missing something obvious here

A bit of motor theory

 

[Pete999]

Ah ha see what you are getting at now

 

[telectrix]

basically, that motor wants 230V per winding. which it gets on 230V 3phase in delta. put it on 415V in delta and it gets 415V across each winding.

 

[Shoei]

The motor may be fine in star on 415V but it depends on design margins. It's IP55 rated so not a lot of internal airflow, there may not be much headroom on power.

10% overvoltage means 20% more heat. I'd measure the temperature rise after running a while before relying on it, even with proper wiring and a stable supply. It's possible the erratic running and rapid heating are because a winding is already toast.

 

[Jim Cartledge]

Symptoms you describe suggest a missing phase - possibly a blown fuse.

 

[stevels4]

Motor theory.. was that Flemming’s left or right hand rule?
I would go along with a missing phase given the motor’s reluctance to turn unless helped to and the buzzing indicating it is phase locked.
Has anyone checked the PR?

 

[chris50450]

The wiring diagram shows a neutral to the common connection at the bottom. It is missing from the photo. That would then also supply the required 230v to the pump.

 

[John Arnold]

Same as westward10 and Pete999 , the electrics being in the spray from the masonry saw is cause for alarm bells, I hope the motor is protected from this slurry?

 

[timbobelfast]

hello got a problem with my 3phase masonary saw somebody has wired it up I don't think it's correct because the blade sometimes spins backwards and often doesn't start when turned on without a spin first makes a buzzing sound and does nothing it's also getting really hot. I will attach pics of the wiring diagram and the actual wiring on the saw

View attachment 46526

View attachment 46527

Have you got a locked rotor?
Try un- coupling the load and get the motor running before 're coupling. Assuming this is belt loaded.
Also sounds like you have lost the retaining contacts from the contactor hence why you need to hold start in.

This is apprentice type fault finding!

 

[bomjac]

Late to the party a little - but here goes.

If it "sometimes doesn't start without a spin" and "sometimes spins backwards" then it sounds as if you are missing not 1 phase but 2. If it were single phasing, then the motor would only run in 1 direction - the correct direction. The lost phases could be either at the supply end or the starter.

The only possible way that the motor could run in either direction would be if it were running as a single phase machine. The start direction would be dependant on which direction you spin it before starting it.

Overheating also supports this theory, as does the contactor not holding in. However, there could be another reason.

The "Azul" wire (blue) on the schematic right side looks to me to be a derived neutral from the star point that should connect to the neutral of the start contactor. In 400v mode, there is a derived neutral (230v across the winding), in 230v mode the motor would be delta so it gets 230v direct from the winding connection. Hence the reason the coolant pump (230v) is connected there also. If your buddy has connected the cooling pump at the starter across 2 phases then probably that has been fried by the 400v - although it is conceivable that it picks up the blue in the starter coil.

Recommendations - Get a qualified Electrician who actually knows what they are doing first of all. Based on the first picture, absolutely not the person who connected it. It is a deathtrap as it sits.
Lack of earthing, non-glanded cables, terminal box cover unable to be properly fastened due to hard wired cable.

Nice that they used crimps, but the crimps do not look to be propetly crimped either. Does it even have overload protection? It should, as it's 6.25 amps in star. Have they used the blue core as earth? Even if you do get it working, unless the cable is properly glanded and sealed, then pretty quickly your going to have a short in the motor due to water and damp stone dust.

My guess is that cable from the starter to the motor got damaged and replaced? If there was a short circuit it could have damaged the starter contactor.

Then get them to try below:

• Isolate and take a winding balance across the windings to verify all are good. Reading should be low ohms, all within 10%.
• Insulation test the motor - disconnect the star point if you need to test each winding individually.
• Verify that the contactor contacts make correctly when the contactor is pressed in. Should be almost zero ohms across each line.
• Verify that you have 3 phase 400v at the starter.
• If all the previous suggestions are good, connect the blue core to the star point, restore power and test run it.

Finally - whoever wired this thing up, made a shocking job of it. It is worthy of the hall of shame, and I really would not use them again for anything even remotely electrical. As it stands now, it is not safe to run.

 

[ex 2 Base]

You have a phase down/missing, could be blown fuse or dirty contact in the starter. Disconnect the supply and test for continuity of all three phases through out. You will have to carefully press the contactor down to carry this out. Wiring within the terminal box looks OK

 

[Pete999]

Wht would a star delta starter burn the motor out?

A star delta starter will in effect put 380/root3 volts across each winding, on start up, wouldn't it? into delta after a predetermined time the starter would change over and slap 380/400 across each winding.
The only way delta would burn out the motor would be because the mechanical load is to much, thus causing the winding's to overheat and burn out, purely a mechanical problem, that's why 3 phase squirrel cage motors are sometime started via a S/D starter, Star low voltage high torque Delta higher voltage lower torque due to the increased speed on star start up.
I agree Starting and running in Delta would probably burn the winding's out, but this will be due to overheating at a higher torque, nothing to do with the winding getting 230 v or 380 v, perhaps Westward's comment of more Motor knowledge is required is a bit wrong don't you think?

 

[telectrix]

could comment but it'sbrd time and after beer so i wiattill timmirrow.

 

[telectrix]

A star delta starter will in effect put 380/root3 volts across each winding, on start up, wouldn't it? into delta after a predetermined time the starter would change over and slap 380/400 across each winding.
The only way delta would burn out the motor would be because the mechanical load is to much, thus causing the winding's to overheat and burn out, purely a mechanical problem, that's why 3 phase squirrel cage motors are sometime started via a S/D starter, Star low voltage high torque Delta higher voltage lower torque due to the increased speed on star start up.
I agree Starting and running in Delta would probably burn the winding's out, but this will be due to overheating at a higher torque, nothing to do with the winding getting 230 v or 380 v, perhaps Westward's comment of more Motor knowledge is required is a bit wrong don't you think?

pete.you're missing the point.the motor is designed for 230V across each winding.on a 415 3 phase supply that's only in star. delta would put 415 on each winding. can only be delta on a 230V p-p supply.

 

[Pete999]

pete.you're missing the point.the motor is designed for 230V across each winding.on a 415 3 phase supply that's only in star. delta would put 415 on each winding. can only be delta on a 230V p-p supply.

A special Motor then?

 

[Chris1234]

I use 230v 3 phase motors when I’m using a single phase to three phase VFD.

 

[Chris1234]

Some motor glands just slot into the side of the terminal box, rather than go through a hole.