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Author Topic: Mobile trailer truck grounding  (Read 6381 times)

BobWitte

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Re: Mobile trailer truck grounding
« Reply #10 on: April 09, 2014, 10:14:42 pm »

No problem. I understand the floating generator problem but this seemed different with the way it was stated. Thanks.


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Stephen Swaffer

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Re: Mobile trailer truck grounding
« Reply #11 on: April 09, 2014, 11:28:44 pm »

I am reading this as a self-contained generator/pa/stage with everything on the truck and mobile while in use.  In his case there is really no option other than to "float" from earth ground-but as long as anything metal that can possibly become energized-staging/equipment and racks etc. is bonded to the truck frame which , in this case, serves as the "earth" ground and nothing separate from the truck is powered, all should be well shouldn't it?
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Mike Sokol

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Re: Mobile trailer truck grounding
« Reply #12 on: April 10, 2014, 05:04:09 am »

I am reading this as a self-contained generator/pa/stage with everything on the truck and mobile while in use.  In his case there is really no option other than to "float" from earth ground-but as long as anything metal that can possibly become energized-staging/equipment and racks etc. is bonded to the truck frame which , in this case, serves as the "earth" ground and nothing separate from the truck is powered, all should be well shouldn't it?

Yes, that does sound correct. But once you're powering a stage "on the ground" then there really needs to be an earth ground rod.
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BobWitte

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Re: Mobile trailer truck grounding
« Reply #13 on: April 10, 2014, 12:59:07 pm »

Yes, that does sound correct. But once you're powering a stage "on the ground" then there really needs to be an earth ground rod.

I think we are all on the same page now from this and Stephen's comments. The stage/truck, while grounded as far as the generator goes (safety ground and neutral bond), can still float compared to true earth. A piece of gear failure or pinched hot to the stage (hot to safety ground short path to neutral) should engage the circuit breaker.

Now, how does one earth ground the truck frame/stage/safety ground bond when parked on a large piece of concrete - which was probably the original question of this post.

Stephen Swaffer

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Re: Mobile trailer truck grounding
« Reply #14 on: April 10, 2014, 01:54:21 pm »

On my watch?  You park it where you can get a ground, or you don't power anything off  the truck, or use  GFCI protection.  Safety is not negotiable or a sideline consideration.
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TJ (Tom) Cornish

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Re: Mobile trailer truck grounding
« Reply #15 on: April 10, 2014, 05:32:46 pm »

Now, how does one earth ground the truck frame/stage/safety ground bond when parked on a large piece of concrete - which was probably the original question of this post.
I took the OP to mean that this was a rolling rig in a parade. Pretty hard to keep a ground rod attached, but also pretty to have a fault to outside the truck.
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Jonathan Johnson

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Re: Mobile trailer truck grounding
« Reply #16 on: April 10, 2014, 10:34:58 pm »

Now, how does one earth ground the truck frame/stage/safety ground bond when parked on a large piece of concrete - which was probably the original question of this post.

I think the proper thing to do is ensure there are no electrical interconnections (power or signal) between stuff on the truck and stuff off of the truck, especially if there are different power sources. If there must be an interconnect, there should also be a ground bond between the equipment to equalize potential. This might result in "ground loop hum" but it will also reduce the risk of electric shock, which is far more important than reducing hum.

Better yet, if there must be an audio interconnect, go optical with non-conductive fiber. How do you do it when feeding a signal to TV trucks?
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Chris Hindle

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Re: Mobile trailer truck grounding
« Reply #17 on: April 11, 2014, 07:58:30 am »

Better yet, if there must be an audio interconnect, go optical with non-conductive fiber. How do you do it when feeding a signal to TV trucks?
Many years ago, I supplied a feed to the CBC. Their tech hooked up to my board with a 2 conductor. He didn't take pin 1.
When I asked about this, he said it guaranteed no buzz in the broadcast, or my live PA.
He was right. (granted, we never tried WITH pin 1, but he had a bigass genny, and I had a dozen Yamaha/Honda's. The broadcast truck stayed in 1 place, and for each event over 4 days, the PA mixer was in 4 different locations, up to a mile and a half from the broadcast truck)
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Mike Sokol

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Re: Mobile trailer truck grounding
« Reply #18 on: April 11, 2014, 09:05:15 am »

Many years ago, I supplied a feed to the CBC. Their tech hooked up to my board with a 2 conductor. He didn't take pin 1.
When I asked about this, he said it guaranteed no buzz in the broadcast, or my live PA.
He was right. (granted, we never tried WITH pin 1, but he had a bigass genny, and I had a dozen Yamaha/Honda's. The broadcast truck stayed in 1 place, and for each event over 4 days, the PA mixer was in 4 different locations, up to a mile and a half from the broadcast truck)

I always put an audio isolation transformer on any console output feeding a line to the video truck. Sometimes they're on their own genny. Other times they're powered from an entirely different building. Either way, a direct copper/shield connection between your FOH console and the remote truck is an invitation for BIG HUM. I'll either use a WW ISO-2 to send line level signal, or an IMP2 to send a mic-level signal to the remote truck. Just use the ground-lift switch which essentially opens up the pin-1 line (as you note above) and the transformer feed gives you a nice balanced output that would even sustain quite large common-mode voltages between the trucks (up to 300 volts for a WW audio transformer). Yeah, you should never really have more than 1 or 2 volts difference between the two ends of your XLR feed, but you really don't want the shield in your XLR feed to become the grounding conductor for the remote truck. If that happens, then it's not only HUM, it can also be FIRE.  8)
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Mike Sokol
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Re: Mobile trailer truck grounding
« Reply #18 on: April 11, 2014, 09:05:15 am »


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