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When I wired my airplane I made up a circuit list and measured the current
on each device. Here are some of them. These amperage  numbers are for a 28
volt system. Double them for a 14 volt system:

Attitude Gyro 0.45
DG 0.57
Autopilot 0.92
VM1000 0.25
Dukes fuel pump 0.82 (low) 1.63 high
KN 90A GPS 0.83
Transponder 1.35
KX155 NAV COM 0.46
Instrument Lights 0.50

Based on these numbers an essential buss can be run on a current budget of
around 6 amps. A 6 amp hour (10 hour or J10 rating), 28 volt battery will
run the system for about 45 minutes, enough time to get on the ground.
Remember that the rated current draw of an installed device is usually the
maximum draw and not the typical draw. The only way to get the actual
current draw is to measure it. I used an 8 amp B&C standby alternator and a
2 amp hour battery to power N170BRs essential buss.

Regarding the 60 amp  wire size, it depends on what it is used for. For
intermittent operation, like the hydraulic power pack, 8 gage would be fine.
For the B lead from the alternator I would use 6 gage. BTW, if you twist the
power and ground leads for the hydraulic power pack together (about 1-2
twists per inch, use a power drill) and connect to the battery end of the
buss, you will greatly reduce the radiated EMI from this system.

Regards
Brent Regan

LML website:   http://www.olsusa.com/Users/Mkaye/maillist.html
LML Builders' Bookstore:   http://www.buildersbooks.com/lancair

Please send your photos and drawings to marvkaye@olsusa.com.