OT: 6 wires motor protection

I'm changing out a couple old contactors for a mixer with a 6-wires motor as seen in the diagram below. I've noticed that it doesn't have fuse or OL protection so I'm would like to add them but I'm not really sure if I should add them for the 2nd set of motor leads where the M2 and M3 are shown. Do you typically put fuses and OL on the 2nd set of leads?

Secondly, what is the purpose of the CT-3 current transformer in this case?

M1 M2 M3 are a star delta starter, any protection would have to be before M1. CT3 seems to be a current sense...maybe feeding an ammeter connected to 1IST. I would imagine that m1-3 are fed from this, and that this may provide some form of protection.

rgds

Dave

Wye Start Delta Run. The CT is to provide current reference for the powermeter i.e. power is a product of voltage times current.

The simplest method, if changing, is to use a soft-start or VFD.

I will leave the OL/fusing to others, having a mind-lock.

I Would fit them where you suggest the leads going into M-2 and M-3.

Ct-3 is measuring the current for the power meter, this system probably only has one ct. as it is a balanced load.

myles

The mind lock went away...kind of.

I think with wye (star)/delta start any overloads being used should be on the primary (M1 in this case) starter and rated for the motor.

When in wye (star) the voltage and current will be reduced so their would be no need for something in the lower ranges. The same applies to fusing, i.e. you just need to supply the ckt with what it needs.

Also have to consider some factors these days. Open transition is cheap and simple but not trustworthy per se i.e. can cause problems.

Closed transition may be more reliable but may be harder to deal with but these may cost as much if not more then using a solid state starter.

Since you need to make a change I would investigate all options and see what your local suppliers offer for this situation. The cost may appear to be more then you need but the ROI in the long run may be justified.

Thanks for the inputs. I believe the wye/delta is needed to reduce current rush so I was thinking of using one of these to save space. They are not that much more expensive.

http://www.ab.com/en/epub/catalogs/12768/229240/229262/3073021/1179229/index.html

Thats what I was trying to say, the newer starters offer better capabilities at the same or less cost.

Yes, thanks, RSDoran. You pointed me in the right direction. It's a big space saver. Just what I was looking for.

I have had 2 speed motors wired similar to the diagram above.
M2 and M3 were interlocked, but I cant remember much more.
It was called something like dallender, spelling is probably wrong it is quite a few years since I worked on these motors, from memory they were SEW motors.

Alan

It is Dahlander, this thread discusses it and shows a diagram.
http://www.patchn.com/SMF/index.php?topic=102.15

Put OL between M1 and 1M4 set to 58% FLA.