Grounding the grid...

[elliott]

Some background:
This past year I've been working at a theater in NYC that was built inside an old warehouse. This is a temporary space while a new permanent space is being built over the next few years. The lx setup is 12- and 6-circuit mult running from ETC dimmers along a grid of schedule-40 that is overhung on an I-beam support structure that is not original to the space. Approx 1/3 of our inventory is Source 4 ellipsoidals, 1/3 Par-56 and Par-64, 1/6 Source 4 pars, and a variety of older instruments including some 500W Fresnels and Mini-Tens, which we use as house lights.

The symptoms:
Occasionally the following things happen, especially during a bright full-stage cue or house light cue: The wireless comm buzzes so loudly that it is painful to use and overpowers the other voices; Video projection signal is interrupted with a rolling white line, whether Cat5 or VGA; A stagehand or electrician going up in a genie to the grid gets a static shock when they touch the grid (mostly in winter).

The solution?
A couple of video designers and other production people this season have recommended grounding the grid, but I have been looking for months for information on how to do this with very little success. We're in a city, which means the water pipes may work as a grounding rod, but we don't have an outside space (or unpaved ground) to put a grounding rod. There's no dark corner of the theater because the entire warehouse is essentially the theater, and the space is used very differently by different productions/directors throughout the season. Has anyone had a successful experience grounding a grid? What's the best metal to use? What's the best way/place to attach it to the grid? What if the water pipe doesn't do the trick? Is it even safe to use the water pipe?

 

[Les]

I'm not an electrical expert, but I'll take a shot at this. First off, this work needs to be carried out by an electrician.

There is already a ground rod associated with your building, probably near the service entrance. You would need to run a single conductor to that location, or tie in at the box as long as it's legal in your area.

To answer a few questions, copper wire (through conduit) is really the only option, and they do make pipe clamps for grounding purposes - usually for earthing an antenna pole/lightning arrestor, grounding metal piping for water, gas, etc).. You'd need to buff all the paint off the area of the grid you're clamping to, and as far as location - as far out of the way as possible (and the shortest distance from the grounding path). Grounding to a water pipe sounds pointless as it would probably be the same amount of work to reach the actual grounding location. That and it probably won't be to code.

Now, is your grid suspended from wooden beams or something? I am surprised that it isn't grounded by design. Also, when you use a pipe clamp to attach a grounded fixture to the grid, that grid is then grounded through your electrical system.

 

[jonliles]

Have you considered changing the circuit you basestation is plugged into? Any luck?

 

[JLNorthGA]

Look for your water supply line coming into the building. There hopefully is an interior cut-off valve. At any rate, if you have a metal supply line (copper or galvanized), you may be able to ground to that. E.G, - have an electrician run conduit with a nice beefy ground wire to that location.

You also probably have ground lines near your electrical service (and a grounding rod) - which means you may have to run it back to the service location.

Another alternative (which I used in an older building) was to go to the HVAC chase which was adjacent to the electrical panels and sink grounding rods in the HVAC chase. That worked nicely.

 

[STEVETERRY]

Some background:
This past year I've been working at a theater in NYC that was built inside an old warehouse. This is a temporary space while a new permanent space is being built over the next few years. The lx setup is 12- and 6-circuit mult running from ETC dimmers along a grid of schedule-40 that is overhung on an I-beam support structure that is not original to the space. Approx 1/3 of our inventory is Source 4 ellipsoidals, 1/3 Par-56 and Par-64, 1/6 Source 4 pars, and a variety of older instruments including some 500W Fresnels and Mini-Tens, which we use as house lights.

The symptoms:
Occasionally the following things happen, especially during a bright full-stage cue or house light cue: The wireless comm buzzes so loudly that it is painful to use and overpowers the other voices; Video projection signal is interrupted with a rolling white line, whether Cat5 or VGA; A stagehand or electrician going up in a genie to the grid gets a static shock when they touch the grid (mostly in winter).

The solution?
A couple of video designers and other production people this season have recommended grounding the grid, but I have been looking for months for information on how to do this with very little success. We're in a city, which means the water pipes may work as a grounding rod, but we don't have an outside space (or unpaved ground) to put a grounding rod. There's no dark corner of the theater because the entire warehouse is essentially the theater, and the space is used very differently by different productions/directors throughout the season. Has anyone had a successful experience grounding a grid? What's the best metal to use? What's the best way/place to attach it to the grid? What if the water pipe doesn't do the trick? Is it even safe to use the water pipe?

I suggest that you first eliminate the possibility of one or more ground-to-neutral shorts in the rig--which can cause severe ground loop problems.I have found that the symptoms you describe can often be created by such shorts. The smoking gun is the fact that the audio and video problems appear connected to the dimmer settings.

1. Power down the dimmer racks and disconnect from feeders.

2. Using a multimeter, do a continuity check between ground and neutral on the rack inputs. If there is any continuity, it should be a high resistance, say 20K ohms or greater. If it is a low resistance connection, proceed to 3 below.

3. Unplug one multicable at a time from the rack. If the short goes away, you have found its location. Plug it back in, and unplug one circuit at a time from the breakout on that mult. If the short goes away, it's in that instrument or connector (a very likely location for the short is inside a pin connector).

4. You could have a G-N short in multiple places in the rig. Therefore, you'll have to monitor the G-N inputs to the rack as you plug each of the mults back in--repeating step 3 if the short returns.

It's tedious, but there is no other practical way to find it. If you have multiple racks, do this test on each rack.

Let us know how it goes!

ST

 

[FMEng]

Look for your water supply line coming into the building. There hopefully is an interior cut-off valve. At any rate, if you have a metal supply line (copper or galvanized), you may be able to ground to that. E.G, - have an electrician run conduit with a nice beefy ground wire to that location.

You also probably have ground lines near your electrical service (and a grounding rod) - which means you may have to run it back to the service location.

Another alternative (which I used in an older building) was to go to the HVAC chase which was adjacent to the electrical panels and sink grounding rods in the HVAC chase. That worked nicely.

It's a bad and possibly dangerous idea to connect to a different ground. All grounds in the building, including the rod for the service, water pipes, waste pipes, building steel, etc., all must be bonded together at the service entrance.

It wouldn't be a bad idea to ground the grid for added safety, not to solve the electrical noise issue. Bond the grid to the panel ground. If you run the wire through a conduit, the conduit must be bonded to the wire where the wire exits it. Otherwise, the conduit adds inductance which reduces the effectiveness of the wire.

Mr. Terry's advice is right on, as usual. You have current from the lighting system going someplace it shouldn't.

 

[MNicolai]

I would be venture a guess that the grid is already grounded one way or another, apparent or not.

Static buildup is not uncommon as lifts roll across the floor. Some lifts have grounding straps for this reason that ground the lift by dragging across the floor, except that painted stage floors, superior ground electrodes do not make. Thus, instead of the static discharge going through the strap into the floor, it goes through the operator into the nearest grounded apparatus (in this case, the grid or a batten).

If the only suspicion of the grid is the occasional static shock from someone in a lift, I'd keep looking somewhere else for the root cause(s).

 

[STEVETERRY]

Some background:
This past year I've been working at a theater in NYC that was built inside an old warehouse. This is a temporary space while a new permanent space is being built over the next few years. The lx setup is 12- and 6-circuit mult running from ETC dimmers along a grid of schedule-40 that is overhung on an I-beam support structure that is not original to the space. Approx 1/3 of our inventory is Source 4 ellipsoidals, 1/3 Par-56 and Par-64, 1/6 Source 4 pars, and a variety of older instruments including some 500W Fresnels and Mini-Tens, which we use as house lights.

The symptoms:
Occasionally the following things happen, especially during a bright full-stage cue or house light cue: The wireless comm buzzes so loudly that it is painful to use and overpowers the other voices; Video projection signal is interrupted with a rolling white line, whether Cat5 or VGA; A stagehand or electrician going up in a genie to the grid gets a static shock when they touch the grid (mostly in winter).

The solution?
A couple of video designers and other production people this season have recommended grounding the grid, but I have been looking for months for information on how to do this with very little success. We're in a city, which means the water pipes may work as a grounding rod, but we don't have an outside space (or unpaved ground) to put a grounding rod. There's no dark corner of the theater because the entire warehouse is essentially the theater, and the space is used very differently by different productions/directors throughout the season. Has anyone had a successful experience grounding a grid? What's the best metal to use? What's the best way/place to attach it to the grid? What if the water pipe doesn't do the trick? Is it even safe to use the water pipe?

This was a really interesting issue that went dead!

What did you discover after all the advice you received here? Did anything fix your problem?

ST