How to know whether to wire as star or delta?

[whazza22]

Hi All,

When connecting a motor, how do you know whether it needs to be wired as star or delta?

Thanks

 

[Deleted member 26818]

It depends on what it is you want the motor to do.
If the output torque when wired in star is sufficient for the job you want the motor to do, then it can be wired in star.
If it is insufficient, then it will have to be wired in delta.
If the output torque required is so great, that the start up current will cause an overcurrent, then you will have to use a star/delta starter.
This allows the motor to be started in star, and when the motor is running at ideally 75-80% of the delta speed, contactors change the wiring configuration from star to delta.

 

[Knobhead]

Check the rating plate. It will give the voltage and connections, some will give two voltages.
400V Star
220V Delta

If it shows 400V Delta them it is suitable for star / delta starting.

It is inefficient to run a 400V delta motor in star

 

[whazza22]

Thanks, do you know the equation to work out the overload value of a motor?

 

[Knobhead]

Thermal or electronic set at 100%
Dash pot 115 to 125% but you have to know how to set the time lag.

 

[Engineer54]

Dash pot 115 to 125% but you have to know how to set the time lag.

Geezus, ....I haven't seen an oil dash-pot motor Overload unit for god knows how many years now!! Do they still make them Tony??

 

[Knobhead]

Yes, get in to the old heavy stuff and it’s still there. It’s like me and you, old but works when needed.

It’s one thing I’m dreading in starting the “Motor” sticky in this forum. I’ve got to get my brain back in gear

 

[silva.foxx]

As with everything within industrial electrics, wire as per manuf. instructions. In this instance the motor plate tells you almost everything you need to know. You need to know what supply characteristics you're applying to the motor you have. If you have a 3 phase 400Vac supply and a DOL starter then the plate tells you to connect it with respect to the ratings.

 

[Knobhead]

I've saved that photo, it will be usefull in time.

 

[silva.foxx]

Tony

I have numerous relevant photos that I've taken for the App. Program. Motor plates and connections.

If you want them PM me and I can forward them on.

 

[pmac10]

also come across 400/660V or maybe 415/690V or something similar a few times (the most recent 2 week ago), you wanna connect that as per Delta when using a 400V supply.

 

[pmac10]

Tony

I have numerous relevant photos that I've taken for the App. Program. Motor plates and connections.

If you want them PM me and I can forward them on.

fwd to me at the usual address Silva if ya don't mind,
cheers mate.

 

[silva.foxx]

Like this example

 

[silva.foxx]

12-18 months ago I carried out a maintenance check on a bottle inspection machine and declared a motor, in a wet area, needed monitoring due to low(ish) IR reading. This is the original's plate.

It caused a little confusion. The hierarchy decided to get in a 3000rpm 50hz model and have it fitted to allow the original to go for overhaul. The machine would not run correctly due to obvious speed differences!

 

[Knobhead]

Hmm, that’s a novel one to have thrown at you. Where the hell did it come from in the first place?