So after the discussion that followed my recent thread about powering AIU's and what wire sizes to use, I got thinking about this some more. (Always dangerous! 
) I cobbled together an adaptation of an earlier wire size/voltage loss spreadsheet so as to analyze multiple daisy-chained AIU's end-fed by one TIU. This allows me to easily play with AIU loads, wire lengths and sizes to explore the effects. Some observations:
1. The first snip shows a kind of worst case scenario using 300 ma per each of 5 AIU's, with AIU 1 right at the TIU, and 10 ft of wire between each of the rest. The resulting voltages at each AIU are shown, with green being acceptable (min 9.5 volts) and red being too low. Note that AIU 5 in the 26 AWG case below is actually marginal at 9.31 volts, but this is likely still OK. Also note that the 28 AWG case becomes unacceptably low by the time we get to AIU 3.
2. This next snip shows a likely much more realistic load of 150 ma per each AIU. In this case even the 28 AWG wire case still looks acceptable. Note that 300 ma load would be only if all 10 ACC outputs were in latched mode. The load of 10 switch relays is not really significant, since it is only for a fraction of a second each time. The only time any more than one switch is actuated would be if you do a starting case switch setup operation.
3. The last snip is where you might have 3 AIU's, with one at the TIU, then a long run of 40 ft of wire to AIU 2, with AIU 3 nearby, using worst case 300 ma loads on each. Again it shows that 26 AWG should be fine, but 28 AWG might be marginal.
My conclusion is that if you have only 1, 2, or 3 AIU's and they are close together, 28 AWG should be fine. Any more AIU's, or longer wire runs, or combinations thereof, you should likely use no less than 26 AWG, just to be safe.
Of course a good alternative is to feed the last AIU in the chain with a separate regulated 12VDC power source, as suggested by Stan with the original idea coming from Marty Fitzhenry. Also using 24 AWG cat 5 cable would work well.
Does this look like it captures the essential elements?
Rod
