3 phase motor wiring

[Belle427]

I thought star delta was used where you want a reduced start up current and reduced torque, usually around a third of that of DOL delta.

That is correct, always check the nameplate on your motor. I connected up a 45kw motor in a quarry years ago and couldnt understand why it kept taking the trip out. Force of habit i had connected it in delta but when i checked the nameplate it specified a star connection at 415 volts.

 

[ricicle]

I thought star delta was used where you want a reduced start up current and reduced torque, usually around a third of that of DOL delta.

Correct. The torque is reduced proportionally to the current.

 

[fuzzytrifle]

Here's a pic of the original motor wiring, motor plate star and delta wiring diagrams stuck to the underside of the junction box cover.

View media item 55805
Both the original and replacement motors are identical, as are the motor plates, it's only the connections that are different.

I was probably being a bit over cautious and should have just copied the connections on the original motor, but I'd be kicking myself for not checking had there been another bang!

Thanks to everyone for your help, really appreciate it

 

[fuzzytrifle]

My brother has just purchased a large inverter to run a decent size lathe, we're struggling to identify L1, L2 & L3 at the moment and haven't attempted to connect it yet. I had no idea that he'd need to alter the motor's terminals to delta, is this usual practice?

You can set the voltage on the inverter usually, but it is quite common to see the phase-phase voltage of an inverter set to 230v, so a delta config would be required.ite.

I'll have to check the inverter, but if it can supply 415v do you leave the motor wired in star config and delta if not?

 

[Lectrician]

This is the important bit.

Delta 240v, star 415v.

For direct three phase connection (no inverter), you want star, so all links in a line along the top link W2 U2 V2.

 

[ricicle]

A 230v invertor will not be able to output 400v.

If you did connect 400v to that motor it will need to be star connected.

 

[ban-all-sheds]

I remember losing money betting there were not any 8 volt lead acid batteries in the stores seems there were made to improve lights on the donkey engine start side booms came with instructions on how to reset control box. This taught me a lesson and from then no bets.

'Tis a general rule of life that if someone willingly offers or takes a bet on something you think is bonkers it's because they know more than you about it, and they know that you are wrong.

 

[ericmark]

Yes anyway now we all know it should be star connected.

I found it interesting to see how many did not know what star and delta wiring was all about.

 

[SaladFingers]

sorry fuzzytrifle
Whenever the salad boy gets involved it goes to peices.

Twin and earth for lighting in the 50? They didn't have a cpc in the sheath in 50s lighting, good god, you're a wrong un

Make up your mind , In a post about twin and EARTH lighting circuits.

I've seen plenty of houses with 50s or 60s wiring

No, it's your ripping it to peices everytime, you just can't resist. Others love to rip things to peices if the way I say something is worded differently to how they would understand, now the tables are turned as someone DID post misleading information - not me, they still won't have any of it . Twin to lighting, twin and earth to sockets back in the old days. Everyone knows that but you. Even others pointed it out to you. Anyway, this is motor talk, enough about sheath and lighting

 

[SaladFingers]

You're quick to call everyone else but when you post misleading information that's ok?

It's typical isn't it. They like to stab at others, but when they post something misleading, they don't like it when someone else spots it!

 

[JohnW2]

I found it interesting to see how many did not know what star and delta wiring was all about.

Indeed - particularly since I'm all but certain that we learnt about such things in the name of A-Level Physics many many moons ago!

Kind Regards, John

 

[Scoby_Beasley]

Indeed - particularly since I'm all but certain that we learnt about such things in the name of A-Level Physics many many moons ago!

Kind Regards, John

That's easy for you to say John. Although I helped the leccy where I worked a few years ago where I worked, I have to admit star/delta, ???? I get lost. If you've any info (aimed at numptys) I would be grateful.

 

[JohnW2]

Indeed - particularly since I'm all but certain that we learnt about such things in the name of A-Level Physics many many moons ago!

That's easy for you to say John. Although I helped the leccy where I worked a few years ago where I worked, I have to admit star/delta, ???? I get lost. If you've any info (aimed at numptys) I would be grateful.

It's really pretty fundamental to understanding what 3-phase electricity (and, particularly, 3-phase motors) is all about. I'm sure that if you Google those topics, you'd find all sorts of useful stuff - varying from that designed for numpties right up to highly mathematical material (ISTR that Wikipedia's article on 'three phase' is mainly the latter!).

Kind Regards, John.

 

[Spark123]

I thought star delta was used where you want a reduced start up current and reduced torque, usually around a third of that of DOL delta.

I'm beginning to wonder now when I think about it...I have connected up several in pumping stations, and was always led to believe by the mechanical chaps, that it was to aid starting.

I think it's main objective is just to get the thing spinning using a reduced current hence the electrical side doesn't need to be as beefy, then once it has run up to it's max speed in star switches over to delta and then spins up to full speed. It is also helpful where the load doesn't want to be spun up too quickly with massive amounts of torque.

 

[matt1e]

can't be arsed to sift through the bickering but basically

Here's a pic of the original motor wiring, motor plate star and delta wiring diagrams stuck to the underside of the junction box cover.

View media item 55805
Both the original and replacement motors are identical, as are the motor plates, it's only the connections that are different.

If you are certain about the above and it s going to be connected to the exact same supply then you need to reconfigure the new motor terminals to match the old

you need to go by the rating plate as already pointed out earlier on the first page and here by Lectrician

This is the important bit.

Delta 240v, star 415v.
For direct three phase connection (no inverter), you want star, so all links in a line along the top link W2 U2 V2.

if it says delta 230 star 400 then reconfigure the links
if it says delta 400v star 680v which I doubt then leave it as it is

Matt