Question about non-automatic transfer switch

[sayedahmed]

hi,
i want to design non-automatic transfer switch by 2 contactors and push buttons.
my question is do i need mechanical between the 2 contactors? or it is enough to work with NO-NC for both contactors.
please help me

 

[ScottyUK]

Go buy a commercially built transfer switch.

Big multipole switches rated up to at least a couple of hundred amps are available from the likes of Craig & Derricott, Kraus & Naimer, and a few others.

If you use contactors then you need a mechanical interlock. Personally I'd also use electrical interlock backed up by a mechanical interlock: a plain mechanical interlock usually results in a cooked contactor coil if the interlock comes into play.


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If we learn from our mistakes I'm getting a great education!

 

[itsmoked]

Not sure what your application is sayedahmed but I've done the auxiliary contact method many times with good success. Often I've had applications needing three or four sources all hooked to the same load. You may end up with a mind numbing interlock circuit but it can work. In some situations just interlocking may not be adequate.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

If the result of a mistaken closure of both contactors will have a risk of life and limb, use both mechanical and electrical interlocks. Contacts weld, interlocks jam. Having both decreases the odds of a mistake dramatically.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[sayedahmed]

thanks all for reply.
I need this to work between generator and main , it is not manual with handle and also not ATS.
can i count on wiring the NO for the first contactor with NC for the second contactor and vice versa
so when the first is on the second is off and when the second is on the first is off.
i don't want the main power get into the generator

 

[nawao]

Why not use a change over switch?

 

[waross]

I have seen the damage that results when just electrical interlocks "Should have been enough." but weren't. Use a mechanical interlock, use the N/C contacts on the contactors, cross wired, and consider using cross connected N/C contacts on the push buttons. Also consider an off button that must be pushed before a transfer may be made.

Bill
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"Why not the best?"
Jimmy Carter

 

[sayedahmed]

Thanks all,
I think change over switch is more a Appropriate
also i will use mechanical interlock