Shield and Drain Connections

DavidWalter84 · Mar 21, 2016

I am connecting a 4-20ma analog output from a power flex 70 ac drive to a 1769-IF4 card today.

I am using Belden 8761 for the connection which has a paper foil shield and a drain wire so should it be connected on both ends in the application or only at the source component which would be the drive in this case?

The paper foil is not connectable because it is so thin.

danatomega · Mar 21, 2016

The foil shield is not meant to be connected - it's in intimate contact with the drain wire and it's the drain wire that's meant for connecting.

I generally connect the shield at the signal source.
But, have had cases where I needed to follow the advice:
Connect it only at the source - OR -
If that's not so good, connect it only at the destination - OR -
If that's not so good, connect it at both ends - OR -
failing those 3 options, do not connect it at all.
One of those four should work.

Tom Jenkins · Mar 21, 2016

danatomega said:
The foil shield is not meant to be connected - it's in intimate contact with the drain wire and it's the drain wire that's meant for connecting.

I generally connect the shield at the signal source.
But, have had cases where I needed to follow the advice:
Connect it only at the source - OR -
If that's not so good, connect it only at the destination - OR -
If that's not so good, connect it at both ends - OR -
failing those 3 options, do not connect it at all.
One of those four should work.

This is expert advice, and shows obvious experience!

The "standard" is to connect the shields at one end only. I usually did it at my panel, since I usually had more confidence in the grounding there. However, I have had installations where each of the permutations Dan mentioned worked best.

kwade · Mar 21, 2016

The foil shield is not meant to be connected - it's in intimate contact with the drain wire and it's the drain wire that's meant for connecting.

I generally connect the shield at the signal source.
But, have had cases where I needed to follow the advice:
Connect it only at the source - OR -
If that's not so good, connect it only at the destination - OR -
If that's not so good, connect it at both ends - OR -
failing those 3 options, do not connect it at all.
One of those four should work.

Tom Jenkins said:
This is expert advice, and shows obvious experience!

The "standard" is to connect the shields at one end only. I usually did it at my panel, since I usually had more confidence in the grounding there. However, I have had installations where each of the permutations Dan mentioned worked best.

Tom, I appreciate your response. When I make statements like Dan's, people look at me funny - like dogs do with their heads ****ed sideways!

Shield and Drain Connections

DavidWalter84

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danatomega

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Tom Jenkins

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kwade

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