Sport Pilot Talk

For the record, I was not saying you can't size CBs to twice the rated load of devices, and I'm agnostic on how you size CBs.

What I'm saying is you can't appropriately size a CB unless you know the amp rating of the wires behind it. If you have your GDL-82 connected with 10 gauge wiring, a 50A breaker might be safe. If you use 26 gauge wire, 3A might be too much. The breaker has to be sized to the wire, not to the device requirement...

Seems to me you would size the wires and breaker to meet the requirements of the device.

TimTaylor wrote:Seems to me you would size the wires and breaker to meet the requirements of the device.

That is the best way...figure the device requirements, then size the wire & breaker to suit. But in this case we're discussing of adding a new device to an existing breaker, it takes a little more thought to make sure it's a good setup.

MrMorden wrote:

TimTaylor wrote:Seems to me you would size the wires and breaker to meet the requirements of the device.

That is the best way...figure the device requirements, then size the wire & breaker to suit. But in this case we're discussing of adding a new device to an existing breaker, it takes a little more thought to make sure it's a good setup.

Agreed. I would run separate wiring and breaker, unless it's such low draw it doesn't matter.

MrMorden wrote:

TimTaylor wrote:Seems to me you would size the wires and breaker to meet the requirements of the device.

That is the best way...figure the device requirements, then size the wire & breaker to suit. But in this case we're discussing of adding a new device to an existing breaker, it takes a little more thought to make sure it's a good setup.

Yup and dont forget to factor in the length of the wire as this will need to be in the equation also so the wire doesn't melt. The device only draws 0.5A max so it is a minimal load but still there's math to be done.

MrMorden wrote: The breaker has to be sized to the wire, not to the device requirement...

Actually, all three (wire size, breaker current, and device load) are all inexorably linked. AC 43-13 has tables for determining the wire size required for a given load. Once you've chosen the right wire, you can then select the appropriate circuit breaker. There's a bit of convoluted (iterative) math involved - which is why they pay us engineers the big bux!

My GTX 327 xponder is rated at an input of 15 Watts, typical, 22 watts max. (or well under 2 amps on a 14 V system). On the ground or in flight I've actually measured it (with alt encoder) at 1 to 1.5 amps.

So... it looks like adding the -82 to a 5 A breaker is possible, although as others have stated wire size, length, etc all are factors to be considered.

Pete