Soft Starter with Star Delta Bypass Connection

OK, now that the acrimony is complete, lets get down to solutions.

Yes, there are ways to use SOME soft starters with Star-Delta wound MOTORS taking advantage of the 6 leads brought out from the motor. The only advantage this provides is that the Soft Starter can be sized at 58% of the motor FLC, rather than 100%, so the soft starter will be lower cost (significant on larger motors, not worth it on smaller ones). That is the reason some manufacturers offer that option. Most suppliers refer to this as using the soft starter "Inside the Delta" because that is what you are doing. Here is a schematic.

In that image, the diagram on the right (B) is the standard way of using a soft starter with 3 connections to the motor, on the left (A) is the "Inside the Delta" configuration using all 6 leads brought out from the motor.

BUT, it is loaded with significant dangers that potential users MUST be made aware of. First and most important is based on the FAILURE MODE of a soft starter, because the SCRs fail shorted, meaning they conduct full time and cannot be turned off any more. If ANYTHING happens to just one the SCRs (thyristors) inside of the soft starter connected to 3 leads of a motor (B), there is no inherent danger yet because with just ONE shorted SCR in a standard circuit, there is no complete path for power to flow when the other 5 SCRs are turned off.

Now look closely at the diagram on the left, and imagine replacing one of those SCRs with a conductor, then follow the path. You see that if just ONE of the SCRs short, there is a complete path through one winding of the motor with no way to interrupt it. You can't know there is a shorted SCR until after the starter turns off, so what happens is that 5 of the SCRs turn off and one stays on, which eventually burns out the motor winding. So in order to safely use this concept, it is IMPERITIVE that a "Line isolation Contactor" be added to the soft starter circuit that is then tied to the Shorted SCR Detection / Fault contact of the soft starter (often referred to as a "Fault Contactor"), so that when the starter detects that one unit failed to turn off, it opens the contactor and will not allow the motor to be restarted until the problem is fixed. The added risk of not using the Fault Contactor or the added cost of using one typically negates the savings attained by reducing the starter size. Yet, plenty of people take the risk in order to save up front cost, then end up regretting it later when they have to replace the motor.

Another significant risk is in the complexity of this concept. Most electricians and electrical engineers have never seen this done and/or and are unaware of the concept, as evidenced by the initial answers in this thread. So what happens is that even if YOU figure it out now and implement it, the NEXT person to come across it will be very confused. One mistake in wiring this up and the motor doesn't just spin backward for a second, you fry the SCRs and buy a new soft starter. Then it become TWICE as expensive!

The final risk is that not only do several soft starter manufacturers not allow this configuration at all so you have fewer to choose from, even some of those that do offer it have been designed so cheaply that they don't even HAVE the necessary Shorted SCR Detection circuit, because they KNOW that the chief market for these is OEMs who want to provide a cheap solution but have no long term risk involving motor replacement if it outlasts the warranty. This all but guarantees that you will eventually cook the motor, but the OEM is going to get the order for the replacement in many cases, so it actually benefits THEM, not the end user.

So bottom line, even though my company makes and sells a soft starter capable of being used this way, I do everything I can to discourage it's use. It is fraught with risk with almost no rewards and the only rewards it offers are based primarily on luck.

Luck is not a valid engineering strategy.