NO vs NC Relay to reduce seizing

Currently have a relay thats rated for 15 amps for a 5amp AC PSU power source (high capacitive inrush current). I have it wired so that its in the NC state, and when the relay is powered it cuts power to the PSU (reason I want it like this is if the relay control logic fails on boot/power on, the AC circuit will still be closed and providing power).

The issue is that when the relay is opened and then closed again the high inrush current causes the relay to (i guess) arc and weld the contacts as it closes, so activating the relay again does nothing as its "stuck." A light tap or flick on the relay loosens it again, but so far seems like a 50/50 on whether the relay will get stuck again.

My main question is if I wire it in reverse (NO), will it reduce the likely hood of this happening? My logic is that in the NC wired state when its closed and "stuck" the relay coil is what is providing the force to move the arm and trying to open the relay...I am hoping in the NO wired state the force of the arm itself (when the coil powers down and the arm goes back to its natural position) is greater than the leverage force that can be supplied by the relay coil, and in most cases it wont get stuck. Of course in this case the relay has to be powered most of the time which has its drawbacks due to power consumption and failure of the relay controller. Thoughts?

Second question, I know most relay circuits you should have an RC/Varistor in parallel to the load...would this prevent this contact wielding regardless of how I have the relay wired? From what I've read it seems like this protects relay from motor/inductive type loads when the switch is open...so not sure if it would do much for the large inrush current of capacitive PSU loads when the switch is closed.

Hi,

There are two ways to kill a relay contact.
1) high inrush current when closing the contact
2) high voltage when opening the contact with an inductive load

The first makes the contact to weld each other. They do not open any more.
The later makes the contacts to burn, to oxidize. Then the contact resistance increases until it can not close it anymore. Often this causes heating and if this situation lasts for a longer time, then the contacts may weld each other or the plastics will burn.

High current, high power relays have big, hard contacts, like beryllium, with high melting temperature.
Low current signal relays have soft contacts like gold. They don't oxidize and have low contact resistance.

To avoid killing by high current...either use a high inrush current rated relay (mind, that a capacitive load may cause inrush current in the hundreds Amperes region.), or install a soft start, or an inrush current limiter, maybe an NTC.

To avoid killing by inductive loads, install a voltage limiter. A snubber, a varistor, a free wheeling diode or similar.

Klaus

NTC came to mind for me as well.

You have a real problem if your relay is welding which won't be fixed by changing from NC to NO.