Hi Richard,
Thank you for your reply.
Our current protection uses PTC's + TVS on the A and B lines however we have had some issues with the PTC's going high resistance possibly due to the environment they are in. We design and build ROV's and some of our boards are immersed in a hydraulic oil and used subsea to about 3000 meters and recently we have failures due to the PTC going high resistance. We are not completely sure if it is the oil type, the increased depth pressure or even heat from the enclosure, or a combination, as we have not had issues with other older ROV systems that use the same boards.
We are trying to find an alternative protection against both transients and faults.
Thanks
Carl