EMI & Cat5
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Posted by Smowk on March 5, 2005, 10:25 am
Please log in for more thread options anybody have any experience with cat6 and 440 volt power lines. we've run parallel to them for a while and everything works perfectly. i thought you werent supposed to do this? smowk | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by James Knott on March 5, 2005, 5:06 pm
Please log in for more thread options Smowk wrote: It's a bad idea, because you can induce enough voltage in the wires, to cause a hazard. It generally won't bother the NICs though, as the frequencies used to carry the data are well above those used for power and they're also supposed to be able to withstand several hundred volts, without creating a safety hazard. Now if you were to touch the cat6 conductors, while also touching some grounded metal, you might see why you're not supposed to do that. | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by Al Dykes on March 5, 2005, 5:17 pm
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>Smowk wrote:
> >> anybody have any experience with cat6 and 440 volt power lines. we've run
>> parallel to them for a while and everything works perfectly. i thought >> you werent supposed to do this? >> >
>It's a bad idea, because you can induce enough voltage in the wires, to >cause a hazard. It generally won't bother the NICs though, as the >frequencies used to carry the data are well above those used for power and >they're also supposed to be able to withstand several hundred volts, >without creating a safety hazard. Now if you were to touch the cat6 >conductors, while also touching some grounded metal, you might see why >you're not supposed to do that. > How does anything get induced into the CAT5/5e/6 wire? The pairs are twisted and carefully balanced to meet CATx specs and certification. When CAT3 was new there was lots of discussion about EMI and if any was found it was only in the most extreme situations. One way CAT5e wire differs from CAT3 is carefull symetric twists, which cancel out induced currents from external magnetic fields. For that matter, for the OP, 440 volts is a "don't care" or even a plus since it halves the amperage and it's amps, not volts that create a magnetic field. IMO Follow construction codes and be happy. -- a d y k e s @ p a n i x . c o m Don't blame me. I voted for Gore. | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by James Knott on March 5, 2005, 7:26 pm
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Al Dykes wrote: > How does anything get induced into the CAT5/5e/6 wire? The pairs are
> twisted and carefully balanced to meet CATx specs and certification. > When CAT3 was new there was lots of discussion about EMI and if any > was found it was only in the most extreme situations. One way CAT5e > wire differs from CAT3 is carefull symetric twists, which cancel out > induced currents from external magnetic fields. > > For that matter, for the OP, 440 volts is a "don't care" or even a > plus since it halves the amperage and it's amps, not volts that create > a magnetic field. There's both common mode and differential mode coupling. Twisted pairs reduce only the differntial mode coupling. As for coupling, there's both inductive and capacitive coupling between the power and lan cables. There will be some of both. | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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Posted by Al Dykes on March 5, 2005, 8:18 pm
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>Al Dykes wrote:
> >> How does anything get induced into the CAT5/5e/6 wire? The pairs are
>> twisted and carefully balanced to meet CATx specs and certification. >> When CAT3 was new there was lots of discussion about EMI and if any >> was found it was only in the most extreme situations. One way CAT5e >> wire differs from CAT3 is carefull symetric twists, which cancel out >> induced currents from external magnetic fields. >> >> For that matter, for the OP, 440 volts is a "don't care" or even a >> plus since it halves the amperage and it's amps, not volts that create >> a magnetic field. >
>There's both common mode and differential mode coupling. Twisted pairs >reduce only the differntial mode coupling. As for coupling, there's both >inductive and capacitive coupling between the power and lan cables. There >will be some of both. > Small amounts of common mode currents/volatges are blocked by the transformers used to couple the cable to the circuity. This document is interesting. (The text I've quoted is about 3/4 down) My reading of the document says that in the normal home/office/light manufacturing environment EMI is a non-issue with an ethernet plant built to proper CAT5/5e spec and proper grounding of the hubs, switches and computers. The Allen-Bradley paper also addresses heavy industry applications where I imagine the ground currents could make common mode issues interesting. Shielded cable comes off worse than UTP. http://www.ab.com/networks/enetpaper.html "Testing was performed on a system where the communications conductors (four-pair Ethernet cables) were placed in wire ladder-ways. These cables were placed along side conductors carrying 480 V drive-control voltages connecting the controller and a high-horsepower motor. The differential voltage coupled into the Ethernet cables varied, depending on the type of cable tested. The picture in Figure 12 shows the cable routing with respect to the drive conductors. Table 3 shows the differential voltages measured on the communications cables. The additional CMRR is referenced to the shielded cable. The shielded cable is used as a reference because this cable provides adequate performance in environmental testing for Ethernet modules. It is worth noting that there were no physical layer communications errors during this sequence of testing" [....] "The four-pair Ethernet cables were tightly strapped to the high-current secondary of the welding conductors and routed in close proximity to the weld tip. This setup provided both magnetic and radiated noises during the welding event. Figure 13 shows the routing of the cables on the robot arm. A telecommunications analyzer was used to generate 100Mbit NRZ data that was sent to a pair of Fast Ethernet transceivers for encoding and decoding into MLT3 type data. The telecommunications analyzer provided bit-level error detection. The performance statistics were recorded for each of the five cables tested. Surprisingly, zero data errors were recorded for each of the five cables tested during the welding events." -- a d y k e s @ p a n i x . c o m Don't blame me. I voted for Gore. | ||||||||||||||||||||||||||||||||||||||||||||||||||||
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> parallel to them for a while and everything works perfectly. i thought
> you werent supposed to do this?
>