Ethernet STP Patch in STP installation
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Posted by on July 25, 2006, 9:38 am
Please log in for more thread options I'm looking at putting in an ethernet STP instalation for our factory but i know that the shield should not be connected at both ends to prevent ground loops (especially in our case: big motors, big power, long distances). I'm concerned standard UTP will be overwhelmed by electrical noise. I plan to setup a STP patch panel in the control room, with the cables sheild grounded there. Cables will run out from the panel to each machine's control cabinet and connect to the equipment inside. So i have a couple of questions: First, i'm worried if the computer inside the machines control box has a metal RJ45 jack, if i connect a sheilded patch cable i might end up with fireworks as this will be grounding both ends (the equipment i presume will be grounding the case of its RJ45 jack to its ground). Is this a correct presumption or do electrical equipment isolate their RJ45 jack from their ground? Second, if the first case is true, can i get RJ45 connectors which can crimp onto STP cable (im thinking of plastic isolated ones as in my first point), or would i be better off putting a socket/plate in the control box and running a patch lead from the plate to the equipment? Many thanks, Chris | |||||||||||||||||||
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Posted by Robert Redelmeier on July 25, 2006, 2:04 pm
Please log in for more thread options g18c@hotmail.com wrote in part: Your concern is common and not unreasonable. But perhaps excessive if those are constant load/speed motors. The EMI they generate is strong, but too low a frequency to trouble ethernet. OTOH, quickly variable loads or HF components like from arc welders or X-Ray are probably worse. Still, going ahead with STP is probably good insurance. > First, i'm worried if the computer inside the machines control
> box has a metal RJ45 jack, if i connect a sheilded patch cable > i might end up with fireworks as this will be grounding both > ends (the equipment i presume will be grounding the case of its > RJ45 jack to its ground). Is this a correct presumption or do > electrical equipment isolate their RJ45 jack from their ground? I would hope isolated, but only the mfr knows for sure. I've seen ethernet cards both ways. > Second, if the first case is true, can i get RJ45 connectors
> which can crimp onto STP cable (im thinking of plastic > isolated ones as in my first point), or would i be better > off putting a socket/plate in the control box and running > a patch lead from the plate to the equipment? You could probably squish an STP into a standard plug, but you should not want to do this. Your STP runs should be terminated near the equipment with a jack mounted on as solid and vibration-free permanent structure as you can find. Then run a patchcord to the equipment. It can take movement and vibration much better. Rather than leave the far end of the shield dangling, you could ground it through a resistor or capacitor. -- Robert | |||||||||||||||||||
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Posted by on July 26, 2006, 1:42 am
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Thanks for the reply Robert. > Rather than leave the far end of the shield dangling,
> you could ground it through a resistor or capacitor. Ok, i like the sound of a capacitor as it will block the current from any ground loop static voltage. What would be a sensible value that is typically used in such high noise environments? Would it be sensible to put a resistor in series with a cap for safety (incase the cap failed and shorted)? Thanks, Chris | |||||||||||||||||||
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Posted by Robert Redelmeier on July 27, 2006, 9:22 pm
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g18c@hotmail.com wrote in part: > Ok, i like the sound of a capacitor as it will block the
> current from any ground loop static voltage. What would be > a sensible value that is typically used in such high noise > environments? Would it be sensible to put a resistor in series > with a cap for safety (incase the cap failed and shorted)? I wouldn't bother. Caps usually fail open. Any fail closed is very short lived :) But if you must, something reasonable like 50-100ohms. For the cap, I'd use something with very low ESR like tantalums. Electrolytics are right out. -- Robert | |||||||||||||||||||
> factory but i know that the shield should not be connected
> at both ends to prevent ground loops (especially in our
> case: big motors, big power, long distances). I'm concerned
> standard UTP will be overwhelmed by electrical noise.