STP vs UTP for industrial 100 Mbps ethernet 2

[cokeguy]

We recently installed a machine whose user console is a PC hooked to the control cabinet through a 50 meter long shielded twisted pair ethernet cable, cat 5. It simply didn´t work, we even tried changing cable trajectories a few times but with no success.

We then replaced the original vendor supplied shielded cable with a regular UTP cat 5 cable, and it worked perfectly, no problems, so we left it there.

We tested the original shielded cable in our office environment, worked OK. Is there any circumstance where UTP works better than STP for industrial applications?

 

[ScottyUK]

STP requires careful grounding. If the grounding is effective then noise immunity can be better than UTP, but if the grounding of the shield is poor it acts as an antenna and makes things worse by allowing RF to enter the equipment.

Slight aside: the cost of fibre-copper ethernet converters is relatively low and fibre 'patch leads' are available made-to-measure in fairly long lengths so if you are in an environment with high level electromagnetic noise (such as an HV substation) then fibre is a great way of making your comms problems go away.


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Sometimes I only open my mouth to swap feet...

 

[JBinCA]

ScottyUK is right.

You need to ground the shield at one end and one end only - otherwise, it's worse than not having a shield sometimes (as you unow well know).

Regards,

JB