Trane RTAA217

[drivewizard]

I always like the look on the electrician when you show him an inside delta starter and how all the motor terminals are hot with the motor off.

I feel your pain, and they want to take our work! At least in your State.
A few years ago I had a Sparky tell me on a new chiller start up that the Wye-Delta starter would not work. That there was a direct short.
He proceeded to show me the K3 contactor, I just thanked him and told him I would take care of it.

[Chiller Guy]

Randy,

What do you mean about the motor terminals being "Hot" when the motor is "off"?

[Randy S.]

In an inside delta starter, the contact or the soft start SCR is in series with each delta connected winding. Each terminal will be hot, but the starter completes the circuit to run. There is also a shunt trip breaker on the soft started ones in case an SCR shorts. Even that relies on the soft start electronics to shunt trip the breaker.

Every one I've ran into was a soft start. The whole idea is to allow the use of a smaller soft start. A real bargain if you cook a very expensive chiller stator.

[jayguy]

I always like the look on the electrician when you show him an inside delta starter and how all the motor terminals are hot with the motor off.

not just electricians either!!

good luck.

[Chiller Guy]

Randy,

OK, I am with you now! I was still in the Star-Delta thinking mode and you threw me a curve with the " inside the delta". Here we just call it a solid state starter. The bleed through on the SCR's will truly keep some parts energized and spoil your day if not careful.
In fairness to the electricians, most are not trained for control or service work and never get into these units.

[Randy S.]

On an inside delta, it's not just bleed through. The starter is actually inside the delta, and only has to be rated for 67%.

Draw a 6 lead delta configuration with one SCR block of the soft start in series with each winding, and you'll see what I mean. Each phase goes to one end of a winding, and also to the line side of another SCR block in series with another winding.

McQuay did it for a while on centrifugals in the 90's and then gave up, going to a "conventional" soft start of the delta configuration at full amperage.

[jayguy]

here is a pic. you can see what randy was talking about with power being hot at all times.

good luck.

[Chiller Guy]

Randy & Jay,

I can see what you are saying now! I never had a solid state starter on a air cooled machine and not one exactly like your picture. My last one was a 500T CVHE.