MGL Avionics User Forum

Hi,

I am not sure what is recommended or best practice for canbus wire. The iBox manual warns for ground loops when using shielded cable and when it's connected to any other ground point in the aircraft.

The V16 manual states that preferably a shielded twisted pair cable is used for can bus.

What is recommended, using a shielded cable and connect the shielding only to the ground on the iBox and not on to any other ground or chassis of any other device ground/chassis ?

Or is unshielded safer to use ?

Any advice is welcome, thank you in advance.

Johan.

Usually the CAN bus does not need shielding as it uses differential signalling and twisted pair wires. This results in the field created in one wire being canceled by the field in the other wire.
However you can use shielded wires if you think it may be needed. In this case the shield connects on one side only. This really goes for any use of a shield - including your intercom audio wiring. If you connect on both sides you create a ground connection and yes - usually you end up with a ground loop as this connection will conduct any currents that would like to pass that way. This tends to form loop antennas (there is an area inbetween the loop and the dimensions of the loop will be tuned to some wavelength). This loops are very efficient receivers and transmitters of magnetic fields (not so much electrostatic as a normal antenna). Magnetic fields fall off in strength very rapidly with distance but in our confined spaces this is still very relevant - it can lead to radio interference or strange effects on other electronics when you press your PTT. It can also lead to severe equipment damage in case of a ground fault - a ground supply line to a high current user fails (say to a landing light as example) and the return current finds a path through a connected shield between two equipment pieces - you may now have a large current flowing through the equipment grounds and they are probably not designed for this and the inevitable results is that smoke escapes...

Thank you for the very detailed explanation!