Fuse the primary battery cable?

I have a Skytec starter with the solenoid mounted on the starter (O360 RV4).The high current power cable runs from the master solenoid through the fire wall to the starter solenoid. This cable is ?hot? as long as the master is on. Are builders installing a 300 amp fuse on this cable at the master solenoid? Or mount a 300 amp fuse on the positive post at the battery before the master solenoid? Or no fuse in the either line? I have not been able to find any posts that address this. I?m a little uncomfortable not having any protection on either cable. I would like to know what others are doing. Thanks!!

Those are not traditionally fused. Insulation tends to be quite thick and accidental grounding is not common. Just be sure to protect the cable well in the f/w pass through. Rubber boots are often used at the terminal ends of the cable.

Larry

The master contactor is your "fuse" for that fat wire. If that wire shorts, which is exceedingly unlikely with proper care in construction, you open the master and complete the flight on the alternator or your standby battery alone. Best to have an understanding of how your electrical architecture will behave in flight with the master contactor open.

Questions like this are good - they remind me of why I need to re-read the relevant chapters in the Aero Electric Connection as I design my last-ever aircraft electrical system this winter. It's good to halfway know what you're doing - and why.

Skytec starters come with the solenoid mounted on the starter . For that reason, a second starter solenoid is installed right next to the master solenoid to control the current to the starter.

Even with a 300 amp fuse protecting the cable through the firewall, a dead short to the stainless firewall would end with the stainless firewall burning past contact with the cable and never blowing the fuse. The fuse is useless. Just install the cable in a manner where it will never be in SOLID CONTACT with any metal of substance.