Soft Starters for Fans/Pumps

"Inside-the-delta" is a trick that takes advantage of a motor that is wound for Star-Delta starting so that the soft starter can be sized at 58% of the motor nameplate FLC instead of 100%. It ONLY works on that type of motor because what is done is that the soft starter is wired in series with the windings in Delta since the ends of all of the leads are brought out to the connection box. There are inherent dangers to it and in most cases there is no long term value if you are the end user of the equipment. It adds risk and gains nothing except a reduction in the device rating. There is no performance advantage or capability gain. The only people who benefit from this are the OEMs who can sell their equipment cheaper and still meet a requirement for providing a soft starter. The risks are:

1. If any ONE thyristor should short, you are at risk for losing the motor. In a normal "in-line" soft starter arrangement, it is necessary to short at least two thyristors in opposite phases in order for there to be a complete circuit through a motor winding. it is the same risk as welded contacts: you need TWO sets of welded contacts to lose the motor. When the inside-the-delta trick is used, one side of each winding is already connected to the next, separated by the anti-parallel thyristors. So if any single thyristor shorts, the path through the winding is completed and there is unrestricted power flow.
2. If, after some time, an electrician gets hold of this to remove and service the motor, the likelihood of them understanding the unique method of connecting it is low, which leaves a high risk of it being mis-connected and causing damage to the motor, soft starter or both. Suppliers play down that risk, but ask yourself, would you have understood? Do you even now? Is it unreasonable to believe then that someone else who was NEVER involved in the original decision and/or training will understand it later?
3. There is an argument made in some engineering circles that the PIV (Peak Inverse Voltage) rating of the thyristors must be higher in this configuration, because normally the PIV the devices would see would be to neutral, but when used inside-the-delta, there is no neutral path. So the voltage that the thyristors are subjected to and expected to block is technically higher. I don't happen to believe that, but it's worth noting. The subject came up in another industry forum when discussing an unexpectedly higher rate of SCR failures when inside-the-delta was used.

If you can't tell, I'm not a fan of it. I have seen plenty of electricians and technicians who are ignorant of soft starters all by themselves, let alone throwing an added complexity like that at them. My opinion is that the risks outweigh the gains.