Ground loop damage to video accessories when mixing 24V and 12V power on Alexa cameras

2015General Discussion forum

DisputedParticipants disagreed and reached no conclusion. Read the findings as positions, not as an answer.

A ground loop can form when an Alexa camera is powered at 24V while a video accessory is powered at 12V through a D-tap or auxiliary battery port and connected via SDI cable, causing voltage to backfeed through the SDI ground and damage unprotected devices like the Paralinx Arrow X or Teradek Bolt.
The safest procedure is to connect all SDI cables first, then connect power cables, then batteries, and power the camera last; when shutting down, reverse the order by powering off the camera and sled before disconnecting SDI connections.
Some video devices like the BlackMagic Hyperdeck Shuttle have internal protection that trips the battery rather than damaging the device when exposed to this voltage condition.
Arri cameras do not supply D-tap functionality through standard Anton Bauer or V-mount adapters, and third-party wired D-tap systems may be wired to the 24V bus instead of the 12V bus, which will damage accessories rated for 7.5V to 17VDC operation.
Powering video accessories from the Alexa's 2-pin Fischer power receptacle rather than from auxiliary battery ports reduces the risk of ground loop formation.
Teradek devices have non-standard 2-pin Lemo polarity where pin 1 is negative instead of positive, which differs from most other manufacturers and can cause damage if standard polarity cables are used; always verify polarity with a voltmeter.

The exact mechanism of the ground loop was not definitively explained by an engineer and remains somewhat unclear in technical detail.
The damage pattern was recreated with a CineLive sled and Teradek devices but the original incident involved a non-CineLive setup, so the exact cause in the original case cannot be confirmed.
Some newer video devices may have built-in protection against this issue, but this was not verified with all manufacturers.
One participant successfully used a Teradek Bolt Pro powered from an Alexa 12V Lemo for three years without incident, suggesting the problem may depend on specific wiring configurations or third-party modifications.