Handling cable shielding through a relay for a Metro 4.1 ZL Loop

[ViperDoc]

I'm using a Metro 4.1 ZL effects loop in my present build. I'm using Hoffman DPDT relay boards to control channel switching between various elements including discreet clean and distortion channel tone stacks. The tone stack outputs head into the last relay whose common connection heads into the ZL loop board. Here's my question:

The ZL loop instructions show very clearly how to -- in a single-channel amp-- ground the shield on the preamp bus and leave the other end going into the loop un-grounded by heat shrink tubing.

See instructions here:

Rev 4.1 ZL loop Instructions.pdf

In this build, I need to manage two shielded cables coming from each channel's tone stack into the relay and then the common shielded cable into the board. I can ground the two shielded wires from the tone stacks and leave the relay ends un-grounded. Would I then keep both ends of the common shielded wire un-grounded, or would I ground one end of that cable also? I don't want to create a ground loop, but what would happen if I had an un-grounded shield on a common cable? Would you daisy-chain the shields together around the relay? Thanks!

[Phil_S]

Think of it this way. Grounding the shield to the chassis is more or less an extension of the chassis. There's no loop because you only ground one end. Just ground one end wherever it's convenient. If you can manage to use the same lug for both, that should be OK.

As I understand it, the purpose of the shield is to protect from interference. There is no electricity flowing on it.

This is different from a circuit ground, the function of which you might say is to create a "return" path for electrons in your circuit. Without the circuit ground, your circuit is incomplete.

[ViperDoc]

Thanks, Phil. My preamp-grounded cable shields will be fine heading into the relay. What I wondered was how to handle the shield on the cable leaving the relay. I could see how I could ground all the cables to the chassis ground they're closest to and, so long as they're not connected on both ends, we're good. I could just leave the relay ends of all three cables underneath shrink tubing.

[Phil_S]

I could just leave the relay ends of all three cables underneath shrink tubing.

Yes, that's the thing to do.
As I recall, that PDF you posted showed folding back the braid and covering with heat shrink. Maybe I remember wrong. Anyway, that seemed peculiar to me. Snip the braid/shield short as possible at the relay end and cover with heat shrink. I peel it back so the inner insulation is long enough to make sure the shield doesn't contact the circuit. Just make sure it doesn't poke through.