3P 115A Contactor Coil Power Consumption

GA Redfred.... for making me laugh....... many times in here (CR4) I have been helped by your thoughtful and precise answers. Thanks, Ray

If you check the website of the manufacturer of your contactor, you should find a downloadable catalogue that will give you the information that you seek.

It depends on the manufacturer. To pick one example, An Allen-Bradley Size 4 starter with a 120v coil requires 69va to hold the coil in, with 1224va inrush. If your starter is comparable, the 150va transformer should be able to handle it plus a couple pilot lights or so.

You actually have two issues (assuming only 1 contactor and no other loads):

1. The Inrush VA of the contactor coil. This can be obtained from the contactor manufacturer and only the specific data for the product you use will be valid. Coil designs vary widely among manufacturers so if you look at the data for one it may not match what another brand will take. For example a Siemens 120V coil for a 120A contactor is 270VA inrush, 22VA sealed. For a similar contactor from ABB, the Inrush is 880VA, the sealed is 44VA. There is too much variation there to make assumptions.
2. The Inrush capacity of the control power transformer. Regardless of the VA rating of the transformer, some designs offer better inrush capabilities than others. You can make some generalization but only in a very conservative manner. For example a Sola SBE Series 150VA transformer is capable of 969VA of inrush at 40% PF, an Acme 150VA transformer is only capable of 800VA inrush.

So either 150VA transformer would work for the Siemens contactor in my example, but if you had an ABB contactor, only the Sold transformer would work, or you would have to have a larger Acme transformer. The point is, you cannot make generalizations, you must do the research.