RS-485 Surge protection?

Question

Remote camera surge protection:

I have a couple of remote control cameras. Each one is located about 150' from the house. The cameras have a coax (video), cat 5 (rs485 control), and of course 120v power. I have installed a typical power strip surge protector at the camera and run these cables through the surge protector. I also have installed an 8' copper ground rod and #6 cu wire. I occasionally still experience lightning damage.

I suspect telephone connection on the power strip may be my problem. I believe the voltage cut-off for a phone line is too great for the rs-485. I believe a telephone circuit is designed to operate around 40-80volts. The RS-485 operates less than 5 volts.

One the other end, I have whole house protectors, and in addition I run all the cables through another surge protector power strip.

Answer 1

A few years ago I worked with a DCS system which used RS485 lines that were several thousand feet in lenght. The systems was constantly getting zapped.  

TVSS was installed and did help but that was only part of the improvment. (Using fiber optic was the real solution)   In order for TVSS to be effective there has to be a low resistance path to ground.   Long story short, ground rod resistance measurements were made and found to be several hundred ohms on average.  25 ohms would be the target for electrical protection and 5 ohms for electronic protection.

Without a good ground the transient can't drain away fast enough and the protection fails.  

To improve the ground resistance we installed 30 foot electrolytic ground rods in order to get grounding resistance within spec.

The TVSS devices were connected to the grounding system with braided wire as close to the ground and in as short and straight a lenght as possible.

The TVSS devices used were from a company called Innovative Technlogy. The model number for the RS-485 protector is D4S15-2ML.   (www.itvss.com)   The company seems to have been bought by Eaton.  

Innovative Technology

15470 Flight Path Drive

Brooksville FL 34604

Phone: [phone]

Answer 2

You are correct, telephone lines are higher that logic signals. A couple things to try: put 6-7 volt zeners on the 485 lines (with fuses in series - with the lines, not the zeners). Use shielded cable, preferably double shielded. Put the wires in a metal couduit. Bury the cables.