Avionics switch normally closed?

[seriousflyer]

Anyone know why the avionics switch is normally closed on the ka200 ?

[nine sixteenths]

The relay is normally closed, powered open. The switch powers the relay in when it is in the off position. This gives you avionics power if your switch fails.

[seriousflyer]

"The switch powers the relay in when it is in the off position "

Do you mean the switch powers the relay OPEN ?

[nine sixteenths]

When you select the switch to ON, the relay relaxes. When the relay relaxes, the top contacts provide power to the avionics busses.

When you select the avionics master switch to OFF, the relay energizes, removing power from the avionics bus.

avionics relays.jpg (950.8 KiB) Viewed 1648 times

Sorry the image is so big, I cant figure out how to resize it. Hopefully this helps you out.

[CID]

The "normal" state is to have the power to the avionics bus(es). The master removes power from the avionics when you want them in stand-by during engine start to prevent damage to electronics from transients or to reduce the load on the battery.

If the master switch fails open (the most common failure) or the relay coil fails open (again the most common failure) then your avionics bus(es) will remain powered.

If it wasn't wired like that, a simple switch failure could cause all your radios to quit in flight.

[seriousflyer]

That makes sense.

Do you how the pilot would know if that switch failed in flight or post flight ? would it be as simple as when the master switch was selected off - power would still be delivered to the avionics ?

[nine sixteenths]

When the avionics master was turned off power would still be on the avionics buss. The battery master switch would still turn the whole works off

[seriousflyer]

O I see it now. Thanks for the assistance.