Surge protector and grounding`
Surge protector and grounding`
(OP)
I'm not familiar with instrument grounding and I am experiencing some issues with our RS485 surge protector and trying to get ideas on what could be causing it. When it storms, the 485 channel on our device is burned up. I want to say that the ground resistance on our SP is high enough where the surge just goes through the 485 channel rather than through the ground wire. I'm looking at the resistance of that leg that is connected to the SP that goes back to our ground bus. The total system resistance is low, but is it possible that the leg of that ground wire for the SP is too high? I'm trying to look at this as a equivalent circuit and that leg is parrallel with other devices ground wire and that is tied all back together.
Also, one soluation is to use an optical isolator. Any thoughts on those?
Thanks,
Also, one soluation is to use an optical isolator. Any thoughts on those?
Thanks,





RE: Surge protector and grounding`
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RE: Surge protector and grounding`
Do a wire-by-wire check of EVERY connection.
RE: Surge protector and grounding`
1. Ground for the surge suppressor and the device being protected must be the same. Many RS-485 devices provide a RS-485 port that is isolated from the rest of the device. So device ground is not necessarily the same as the RS-485 ground. And yes RS-485 does have a ground with must be interconnected between the various communications ports.
2. Surge suppressors have a protected side and an un-protected side. Make sure that yours have the protected side toward the local communications port.
3. Make sure that you surge suppressors are three stage deices and have both line to line and line to ground protection paths.
4. Use LARGE grounding wires (the bigger the better) and make sure that it is solidly grounded to the electrical ground, not the local lighting ground.
RE: Surge protector and grounding`
RE: Surge protector and grounding`
RE: Surge protector and grounding`
What abouve comments on the thought above concerning the length run and resistance? Is this plausable or in the right line of thinking?
Thanks,
RE: Surge protector and grounding`
RE: Surge protector and grounding`
The 485 device in the field is the part which is failing? Is this field device grounded to the same ground bus bar as the SP? It could be possible the surge is hitting the device where it's mounted and not coming through the RS-485 wires from the control cabinet meaning the SP is useless where it's applied.
RE: Surge protector and grounding`
The SP must be the shortest point of contact to earth ground. This is the path from the ground lug on the SP to earth ground. Where does earth ground begin? If I have a ground rod 10' in the ground with a 20' 2 AWG wire, earth ground to me would be anywhere on that wire, therefore I need to run that into the bus bar in the cabinet and then have a 10 AWG wire less than 3' to that bus bar based on manufactures installations. Any surge will disipate that power into that ground. I'm looking at this first as some of the SP have 12AWG tied ot the bus bar with 10AWG that is 5-10' in lenght that is then tied into the ground wire. I been told that doesn't matter, but to me, I think it does.
RE: Surge protector and grounding`