metal vs plastic PCB spacers

Hi guys I was hoping you could clear something up for me (sorry if the brewery isnt the right place for this, it just felt like more of a general question)

I finally got round to putting a couple of projects into proper cases, and I'm confused as to weather I should be using metal PCB spacers or the nylon ones.
I've noticed on the PCB's that the ground is connected to some or all of the PCB mounting holes.
Now I would assume that if the holes are part of the PCB ground schema then i SHOULD use a metal spacer to keep it in contact with the case.
But I have also linked pin 1 (shield) of my XLRs to the case, my concern is that this create a link between the sheilds and audio ground, something which I am to belive should be avoided.

If anyone could advise me either way if I should use metal PCB spacer to ground the PCB to the case or use the plastic ones and link it directly to the safety earth pin of my IEC socket?

Thanks

If there is a possibility of a physical link between the circuit ground and the chassis then I would use plastic stand-off and hardwire the ground  connection in the way I would plan to do.

However, if you plan your ground scheme to include connection through the stand-off then that is also an option.

#1 the chassis generally needs to be bonded to safety ground,
#2 XLR pin 1 should also be bonded to chassis.
#3 PS ground should have a relatively direct path to ground.

#4 In some products (like power amps) the chassis is used as a low impedance ground path.

In real production engineers work to eliminate redundant steps, so if a PCB spacer can also make an electrical connection that saves some labor. You generally don't need multiple connections between a circuit board to chassis.

For one off DIY, do what is easier for you, generally the labor impact of another wire is no big deal. Unless you are dealing with massive components (like transformers or big inductors), "and" planning to handle the finished product severely (like shipping it through the mail) plastic standoffs should be adequate.

JR