Avionics specs needed

[Bruce Fenstermacher]

I'm installing a Collins 251 Com and 351 Nav radio in my 170 and need to know the load of each radio.

Anybody have this info or have these radios installed in their plane.

If you have them installed, do you have 1 fuse for both radios or 2 fuses one for each and what are the fuse values. I realize this info won't give me the exact load but it will tell me what has worked for other installs.

Thanks

[GAHorn]

I'm installing a Collins 251 Com and 351 Nav radio in my 170 and need to know the load of each radio.

Anybody have this info or have these radios installed in their plane.

If you have them installed, do you have 1 fuse for both radios or 2 fuses one for each and what are the fuse values. I realize this info won't give me the exact load but it will tell me what has worked for other installs.

Thanks

The size of fuses and/or Circuit Breakers is determined not by the current draw of the appliance,...but the current capacity of the wire guage used. In other words, the fuse/CB doesn't protect the radio, it protects the wire supplying the radio so that a short or appliance failure doesn't draw more current than the wiring will support without a fire.
The correct method of determining the guage wire to be used (and therefore the fuse/CB rating) is to determine the maximum current requirement of the appliance/radio, then use a minimum 20% greater capacity wire and circuit protection (fuse/CB). The current requirements of the radio should be found in the installation manual of the radio and/or on the data plate. A minimum wire size/guage would be 22 AWG with a 5 Amp fuse/CB. A better installation would be a 16 AWG wire with a 4 or 5 Amp fuse/CB for each radio. (Neither radio will likely require more than 3 or 4 Amps each.)
If you decide to wire them up to the same wire-buss (not my personal choice) then I'd suggest a 16 AWG wire with a 7.5 or 10 Amp fuse/CB. Either way, the wire carrying capacity would be greater than the fuse/CB, yet sufficient for the radio/s.

[Bruce Fenstermacher]

George I already knew the breaker protects the wires but in the interest of a shorter message didn't say that. I don't have an install manual and the radio is not marked as to it's current draw.

The curcuit including the breaker would have to be large enough to supply the required current to the radio or the breaker would blow. I'm just trying to find out what has worked for other people for these particular radios. I realize I could probably go with 18 gauge and a 10 amp breaker and have it covered but I'm hoping to find out if others have their Colins 251 (com) on a 5 or 7 1/2 breaker. If so I'll go with 20 gauge and a 5 or 7 1/2 amp breaker for mine.