Talk:ElectroMagnetic Compatibility (EMC)

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Wiring an in-cabinet PC

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Relatively random (talkcontribs)

My company uses in-cabinet industrial PCs for our machine vision systems. While there's lots of useful information on this wiki, I'm not sure it answers all my questions for this use case.

The PC has a metal case, which is bolted straight to the back plate of the cabinet. The case also has an earth thread and there's an earth pin available on the 24V power connector. The PC needs lots of cables, usually DisplayPort and a few ethernets and USBs.

Most of those cables are shielded, but they break the rules laid out here in pages Cabinet cabling and Implementation of shielded cables. They are not bonded at cabinet entrance, but only after they connect to the PC. Should those pre-made cables be partially stripped and bonded at cabinet entrance, in addition to the bonding to the PC case? Would it help or hurt? All that's assuming that the PC's manufacturer even properly bonded the connectors to the case, of course.

LMischler (talkcontribs)

Hi @Relatively random

Find below the answer from the expert I have contacted:

"This answer is based on a basic principle which is to limit as much as possible the disturbances that may enter a volume.

Thus, even if we talk about a shielded cable, it is nevertheless a carrier of disturbances and it is therefore advisable to connect this shielding to the chassis of the cabinet (at the boundary between the outside and the inside of the cabinet) to provide a low impedance path to the ground and to limit the disturbances entering the cabinet.

Without this precaution, the length of cable inside the cabinet to the PC, which remains by nature an antenna, would be the path for the disturbances to radiate and to disturb the components inside the cabinet."

So yes, bonding the cables at cabinet entrance, as you suggest, is advisable and can help.

ps: sorry for the delay of the answer, it's my mistake as I have somehow missed your comment, my expert was very fast to answer back.

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