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how much will you really save doing inside delta and making it safe? the mfr of the starter will probably not highlight the additional costs.
That's exactly right. Yes, you can mitigate the dangers by adding an isolation contactor, but the amount you save by using inside the delta vs the cost of adding the isolation contactor makes it all an exercise in futility. So as I said, it's ONLY cheaper if you ignore the risks.
I was on my cell phone earlier and posting the risk issues was too tedious. Now I have a keyboard.
1) The SIGNIFICANT risk of hooking it up incorrectly. Yes, they provide instructions and when you first install it, if you follow the instructions CAREFULLY it works fine. But the NEXT guy to come along, who has to swap out the motor on a Saturday at 3:00AM and can't find those instructions, is going to make a mistake and blow out the SCRs on the soft starter, meaning it is down even longer.
2) With all soft starters, there is a slight risk of a severe line transient causing an SCR to short out, meaning it becomes a full time conductor. Soft starters usually have a method of detecting this and will disable any subsequent start so that the motor is not started with a sever imbalance. But when just ONE of the 6 SCRs shorts out on a standard (in-line) soft starter, there is no inherent added risk of damage to the motor, because there is no path for current to flow through the motor unless another SCR is turned on (or shorted), and having TWO SCRs short out is extremely unlikely. But in the inside the delta arrangement, each motor winding is permanently connected to the line source on one side, the SCRs are only on the other side of each winding. This arrangement is why the inside the delta version is cheaper, the SCRs are only going to see 58% of the line current, so they can be smaller. But because of this arrangement, if only ONE of the SCRs shorts in any phase, there is current flowing
unrestricted to one winding of the motor and no way to stop it automatically unless you use a Line Isolation Contactor ahead of the Soft Starter, tied to that Shorted SCR detection circuit.
So as mentioned, adding that isolation contact defeats the cost savings aspect of using the 58% rating of the soft starter. Most people who want to save that money are OEMs who are not concerned with the long range operating costs of a machine, they just want to save the initial $$ and pass the risk onto the end users, who usually don't know that there are risks. So the OEMs just provide the inside the delta version to save their $$ and don't use the line isolation contactor, exposing the end user to the risks.