I have an application where there will be 10-20 toroid transformers on a single branch circuit with a 20A breaker. Although each toroid is rated at only 200VA, just one of these toroids can produce a turn-on current spike of 95A peak for 1/2 an AC cycle (~8 ms). This is a unique characteristic of toroids. I'm not looking to discuss different types of transformers or their characteristics or trying to change the givens of this application. Also, assume the circuit will not be overloaded and the voltage is 120-277V (specific voltage is unimportant here). The current has been carefully characterized with a scope - so I'm quite familiar with the behavior. I'm also not looking to use a thermistor.
I have read about devices called Inrush Current Limiters or Transformer Surge Relays - these are basically a series resistor (about 10-20 ohms needed for my case) that gets switched out of the circuit by a relay after a short time delay on power-up. However, I fail to find any of these as a manufactured device (I may be using the wrong terminology). I only found a couple of devices but they are geared for the European market and don't have any US NRTL listings. Are there any companies that make such a device for the US market or so people build up such a device of recognized parts to meet the need?
I have read about devices called Inrush Current Limiters or Transformer Surge Relays - these are basically a series resistor (about 10-20 ohms needed for my case) that gets switched out of the circuit by a relay after a short time delay on power-up. However, I fail to find any of these as a manufactured device (I may be using the wrong terminology). I only found a couple of devices but they are geared for the European market and don't have any US NRTL listings. Are there any companies that make such a device for the US market or so people build up such a device of recognized parts to meet the need?
. You should be able to find others if you search for soft start circuits or relays.