Low Voltage conduit question

[MacG]

Greetings All,

I have a detail that I use for specifying isolated grounding in audio systems that requires no metal conduit/raceways touch the equipment rack. The rack is grounded via a conductor to the technical power panel. The low voltage audiovisual signal conduits are also insulated via PVC coupler at the rack and go to their respective destinations in various rooms where they terminate typically in a J-box to mount an an interface device (VGA connector RCA's etc). Typically our interface plates are anodized aluminum or stainless steel.

Is there a requirement for the low voltage metallic conduit to be bonded to building ground?

Thanks,

MAcG

 

[infinity]

Does the rack have any line voltage power in it?

 

[MacG]

Does the rack have any line voltage power in it?

Yes. However it is grounded via a separate insulated grounding conductor to the tech power panel.

MacG

 

[roger]

Greetings All,

I have a detail that I use for specifying isolated grounding
MAcG

Why are you specifying isolated grounding?

Roger

 

[MacG]

Why are you specifying isolated grounding?

Roger

Is this a test? To give you more work

I design audiovisual systems for performing arts venues, city council cambers, broadcast studios etc. We specify IG to minimize hums and buzzes in audio systems and video roll /distortions in, well, video systems.

Catch ya tomorrow!

MacG

 

[chris kennedy]

Why are you specifying isolated grounding?

Roger

To create a higher impedance fault current path to slow the operation of OCPD's. I mean, whats a couple extra cycles of fault current mean to a system that supplies a bunch of very pricey equipment?

 

[wireguru]

in your scenario, how do you keep the A/V conduits from contacting building steel and creating a ground loop? And what about when someone uses a piece of equipment which is plugged into a regular receptacle and into an input or output plate? Big ground loop between the isolated ground and normal. Seems like the setup is creating more problems than it is eliminating.

 

[roger]

Is this a test?

Kind of.

To give you more work

And I appreciate it too.

We specify IG to minimize hums and buzzes in audio systems and video roll /distortions in, well, video systems.

Why are the manufacturers of these systems not isolating their power supplies to remedy the problems they know they are creating. Why are the power supplies referencing the EGC as part of the circuit?

Catch ya tomorrow!

MacG

Have a good evening.

Roger

 

[MacG]

in your scenario, how do you keep the A/V conduits from contacting building steel and creating a ground loop?

That the AV conduits contact the building steel is mitigated by the PVC coupler at the equipment rack so the ground loop has no effect. Now you might ask about the interface plates where we connect our cables to he AV system. Those RCA connectors, Svideo connectors etc are isolated so the signal paths are not in contact with the box and conduit.

And what about when someone uses a piece of equipment which is plugged into a regular receptacle and into an input or output plate? Big ground loop between the isolated ground and normal. Seems like the setup is creating more problems than it is eliminating.

Definitely a problem which is why I specify an IG at each I/O plate to minimize this possibility.

MacG