O/L Relay in Star-Delta Starer

One possibility is that the current taken by the motor differs when it is in star to when it is in delta. However, the forum has not seen the circuit diagram for this particular installation.

What about asking the designer, whose initials will be on the schematic drawing?

Sometimes the overload relay is only in the delta circuit, particularly when long, heavy current draw starting is necessary. There's no rule that says you can't put protection in both circuits (provided that you rate them correctly).

GA. A useful learning exercise. Thanks.

The O/L relay has to protect the motor during start up as well as normal running. Therefore it has to be in one side of the Y∆. The O/L's set at √3

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Wouldnt that O/L offer more protection if it was under the main contactor.If there was a stall condition on start up , there is no O/L protection on star .

Yes there is. Don't forget the motor winding configuration, which is not shown in that drawing. All current flow in that drawing involves passing 58% of it through the OL relay regardless of the internal path in the motor windings. The issue in the OPs question was whether the OL could be AHEAD of the main contactor (and ahead of the tap off point for the Star arrangement), and the answer was yes, but it would need to be sized for the FULL motor current, not just 58%.

It should be noted that when you use a Motor Protection Circuit Breaker (ie one with adjustable thermal trips used as the OL protection), that is exactly what it is doing, protecting the ENTIRE circuit at the motor FLA setting.

By the way here in the US, we are allowed to have no OL protection in the circuit during startup of a reduced Voltahe starter, as long as there is a timer that shuts down if there is no transition to full voltage (called an "incomplete sequence" timer).