Arc Suppression Switching between Mains/Off-grid (Interlocked Contactors)

[UV-PWRD]

I can currently switch power source instantly in my shed from mains power to a 48v system using interlocked contactors, however when switching from mains to off-grid specifically, I'm getting some arc flash on the contacts in the mains contactor. I presume because as the contactors switch, the load side is already energised by the off-grid supply, but I see this is common for contactors regardless.


Consider the following image, ignoring the arc suppressor for now and the lack of wiring showing the interlocking, rest assured they are interlocked.



I was considering using a passive arc suppressor (capacitor and resistor) or 2 (one for active one for neutral) on the mains contactor , but my concern is current flow across it to the mains supply side when I'm running on the off-grid supply. Or am I misunderstanding how the Arc suppressor works and no current will flow because it's a high resistance path once the contactors are fully switched?

Thanks

 

[UV-PWRD]

Quick update, chatted with my elec engineering mate, he believes it's a control circuit issue due to timing of the coils movement.
I'm collecting an interposing relay this afternoon and will drive the coils from that and we'll see how we go.

 

[UV-PWRD]

Update for anyone that was interested, in short interposing relay fixed it.

Long version.

Previous control logic, electronically interlocked contactors as you'd expect had one contactors coil being driven off the aux contactor on the other coil, so one cannot be opened while the other is closed - I'm using LS Metasol 65a units.

However, it seems the timing of this was an issue, because the aux contactor does not appear to operate until the contactor that it's attached to has fully completed its travel, meaning, in one direction there appeared to be a few ms of overlap between them when a few cheeky electrons could flow - bit of an issue when you have 2 unique AC sources not in sync etc.

I knew I needed to briefly delay the switching or build in some cleaner make/break logic and this interposing relay has done that. They are switching very nicely now and still very fast (clocks stay on etc) and of course no visible arcs. I have a replacement contactor on the way also to swap out the one I witnessed arcing.

So, this relay (AC coil so I can drive it from a smart plug via Home Assistant etc)

Finder 55 Series Miniature General Purpose Relay 7A 4CO 240V AC Coil with PB plus LED plus Mech Ind

Finder 55 Series Miniature General Purpose Relay 7A 4 Changeover 240V AC Coil with Push Button plus LED plus Mechanical Indicator

www.nhp.com.au

Plus this base to make it din mountable and just nicer to use.

Finder 90 Series Base for 5534 Relay 9902 LED

Finder 90 Series Base for 5534 Relay 9902 LED

www.nhp.com.au

Thanks all.