DOL starter basics

[studentspark]

Would really appreciate some guidance on DOL starters

This is not for a job, just my own lack of knowledge!

Some (if not all the questions) may seem stupid, but I've struggled to find the answer to some basic points...

You can get a 240v coil and a 400 v Coil and no doubt other sizes as well.

Is the 240v coil suitable for 3 phase motor control, Just like a relay?

i.e the coil will take power from one phase and a neutral so you would get 230v to operate the coil, pull in and then connect the three phases on to the motor.

Neutrals never seem to be shown in lots of the diagrams I have looked at !!

Does a 230v coil have to have a neutral?

The attached wiring diagram is from a 230v coil DOL, but no mention is made of a neutral (To my eye)

Do 400v coils NOT need a neutral, because the different phases pull in the start contacts?

I have attached a drawing of a DOL started as it comes in the box.

Am I right in saying if no over load was attached the fly lead from A2 and from the stop button would just be connected together

An overload is not included as standard as you have to match the overload rating to the motor ?

What circumstances would an overload not be needed?


The phase to phase short circuit between A1 and A2 is prevented by the load (coil)?

Thanks

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[flyingsparks]

Yes your right. 230v coil uses one phase and neutral.
400v coil uses two phases.
Overloads would be omitted if for example the contactor was being used to control lighting or other loads.

 

[333rocky333]

The coil markings are nearly always A1 and A2 as its not clear when sold what voltage coil the user requires, and its guite easy to fit any voltage coil sometimes purchased seperately, how you wire them then depends on what voltage coil used.

400v coils generally used where the 3 phase plant dont need a neutral and possibly the supply dont have one.

240v coils generally better with 3 phase plant that has a 3ph and N supply, as it is slightly safer to have the lower voltage at the pushbuttons etc.
Some plant uses 24volt coils and control circuits for added safety