Why? Inline fuse on switched line to master solenoid

[walkman]

While reviewing my new -8's electrical system and doing some planning I found an inline (barrel/bayonet style) fuse holder coming off the master solenoid and running to the master switch.

Clearly this is intended to protect the line that grounds the solenoid to energize it and power up the main buss. But why? I've never had this on any aircraft I've owned or panels I've built. I don't recall seeing it in Bob N's book either.

If the wire shorts to ground somehow (one of the normal failure modes a fuse is typically intended to protect against) then it powers up the buss as normal. The fuse won't blow in this case as its still handling the same amount of power as if the master switch was turned on. However if the fuse blows/fails for some reason I loose all power (currently no e-buss).

I intend to remove this single point of failure unless anyone can explain why it should stay.

Internally regulated alternator if it makes any difference (I can't see any).

 

[flyinga]

I agree with you. It looks like a possible failure point to me. I don't have on in my 8.

 

[Canadian_JOY]

Flame Out - it's worthwhile to keep in mind that many aircraft builders are not electrical wizards. With this point made, I'd hazard a guess and say the fuse was put in line when the builder saw a wire going to the contactor and thought, "gee, that wire is connected directly to the battery!".

The reality is that we normally wire the master contactor such that the +12V side of the coil is hardwired to the battery input, thus our master switch in the cockpit is used to apply a ground to the other side of the contactor coil. When this technique is used (which is just about all the time) the coil of the contactor is acting as the current limiting device. In normal operation with the master contactor closed, you will measure very near 0Vdc at the master switch. When considered in this context, no fuse is required in this wire from master switch to master contactor.

 

[walkman]

Flame Out - it's worthwhile to keep in mind that many aircraft builders are not electrical wizards. With this point made, I'd hazard a guess and say the fuse was put in line when the builder saw a wire going to the contactor and thought, "gee, that wire is connected directly to the battery!".

The reality is that we normally wire the master contactor such that the +12V side of the coil is hardwired to the battery input, thus our master switch in the cockpit is used to apply a ground to the other side of the contactor coil. When this technique is used (which is just about all the time) the coil of the contactor is acting as the current limiting device. In normal operation with the master contactor closed, you will measure very near 0Vdc at the master switch. When considered in this context, no fuse is required in this wire from master switch to master contactor.

Yep, exactly this situation I think.

I'm yanking that inline fuse.