Key points of lightning protection and grounding for tunnel information board and vehicle detector 485 bus

Key points for lightning protection isolation and grounding of tunnel information board and vehicle detector 485 bus

Published: 2026-03-07 EB-LINK Views: 1362 Lightning protection, photoelectric isolation, grounding, 485 bus, information board

The 485 bus in the tunnel is long and scattered, and the open area at the entrance is prone to induction lightning strikes. Common phenomena include occasional garbled code on the information board, data packet loss on the vehicle detector, and in severe cases, direct burning of the controller port. The root cause is often due to insufficient lightning protection and grounding.

If you can polish it, shorten the copper bus first.

Every meter of RS485 extension is an opportunity to introduce overvoltage. Switch long-distance sections to optical carriers, and only keep short copper wires near the equipment on site.8-channel video + 1-channel reverse 485 data video optical transceiveror independent2-way bidirectional RS485 data optical terminalCutting the bus at the entrance of the hole so that lightning cannot enter the center along the optical fiber is the most practical solution.

Isolation and Surge Classification Do

Select the data/reverse 485 channel with electrical isolation to block the peak and ground potential difference that comes in when the fan contactor operates.
Install signal lightning arresters on the 485 line at the entrance and exposed section outside the hole, and select the current and residual voltage parameters according to the line operating voltage.
The power supply side and the signal side are protected separately. Don't expect one surge protector to take care of both things at the same time.

The grounding should be single-ended and not in a loop.

It is recommended that the shielding layer and the chassis are grounded in a single-ended manner, using the nearest equipotential terminal. Grounding both ends will form a ground loop, which will instead introduce noise. The grounding of information boards, vehicle detectors, and optical transceivers should be handled separately from the grounding of the metal reinforcement core of the optical cable. Do not allow voice, data, and power to share a grounding point. Wolflight provides a list of methods for the tunnel's electromechanical lightning protection renovation by section inside and outside the tunnel. If you need to check the protection of your own tunnel entrance, please call 0755-83179002. If the copper wire is shortened, isolated in place, and grounded single-ended, the 485 bus will be much more stable.