HELP 3 phase masonary saw wiring

[Pete999]

it's got to run in star full time, Pete. delta would burn it out. and if OP has to hold the start button in, the contactor needs looking at

Wht would a star delta starter burn the motor out?

 

[westward10]

This could be several things, a lost phase can prevent the contactor latching on hence they have to hold the button in.

 

[Strima]

Judging by the amount of masonry dust around a full strip, clean and service would probably help.

 

[telectrix]

Wht would a star delta starter burn the motor out?

because that motor is designed to run in star on 380V 3 phase or delta on 230V 3 phase (rare in the UK). either way it's got 230V across each winding. in delta on 380V you get 380V ( in our case 415V) across a 230V winding.

 

[Pete999]

because that motor is designed to run in star on 380V 3 phase or delta on 230V 3 phase (rare in the UK). either way it's got 230V across each winding. in delta on 380V you get 380V ( in our case 415V) across a 230V winding.

Are you on about the refrigeration motor Tel? Cus I cant see how a three phase squirrel cage induction motor, with 3 winding ends back at the terminal block would burn out if wired to a S/D starter, sorry if I'm missing something.

 

[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