Best practice to wire an instrument properly and safely

[yasmine01]

Good day every one,

I am puzzled/confused on what whould be the best practice when wiring an instrument and its shield.

Is wiring the shield at BOTH ends better? Or wiring at the JB is enough. What are the implications of each method considering the RF and the ground loop error?

Any comments will be very helpful.
Thanks all.

 

[leomiranda]

Hi!
Never connect the shield at both ends! Leave the shield in the instrument side isolated (not connected), and connect the other side of the shield in a ground bar, probably located in one panel.

More details here (in Portuguese, but you can use one web translator)

http://www.smar.com/brasil2/shownews.asp?Id=313

 

[IRstuff]

It really depends on what your overall shielding scheme is, and what the shield is subjected to electrically. For many military systems, the cable shielding is an integral part of the overall EMI shielding, and the shields are usually tied to the respective chassis grounds on both ends, since the entire chassis+shield is the EMI radiated protection.

In other cases, the shield at the end of an instrument probe doesn't always have a termination to go to. In others, there may be a possible termination point, but the grounding scheme might be messed up, and terminating the shield might actually make things worse, as unexpected currents wind up flowing through the shield.

TTFN

FAQ731-376

 

[djs]

For most industrial instrumentation systems, I like to ground the shield at the input to the control system, leaving the end at the instrument insulated. The reasoning behind this is that the shield supports the ground potential at the control system all the way to the instrument. This lowers the common mode voltage seen by the control system.
For outputs from the control system to actuators the exact opposite is true.