Floating Ground?

 
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Old 10-30-2007, 08:45 PM   #1
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Floating Ground?


Today, the guy from the security systems company comes in and says he wants a clean ground to his system. We tell him that there are dedicated neutrals and grounds from the UPS panel. No good he says I don't want a floating ground. So we have to pipe from the ground box and provide a new ground. Now I've heard of floating neutrals, but anybody hear of floating grounds? The only thing I can figure is this guy got bit in the past on a bad grounding system. Any thoughts?
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Old 10-30-2007, 09:20 PM   #2
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Re: Floating Ground?


The guy sounds like a prima donna. Do what you normally do, and tell him you did it just like he wanted. He'll never know anyhow.

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Old 10-30-2007, 10:01 PM   #3
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Re: Floating Ground?


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Originally Posted by mdshunk View Post
The guy sounds like a prima donna. Do what you normally do, and tell him you did it just like he wanted. He'll never know anyhow.

Shame on you MD, now I am gonna have to drain all my panels so they won't float any more. LOL

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Old 10-31-2007, 12:46 AM   #4
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Re: Floating Ground?


Give him a 25kVA, 1:1 transformer on the ground and charge him out the wazoo.
Or ask him what exactly he wants, because the ground doesn't float.
And tell him he needs to speak in specific electrical terms because you are an electrician and not a charge out the wazoo designer/architect/engineer type person.
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Old 10-31-2007, 01:03 AM   #5
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Re: Floating Ground?


Tell him all the ground you could find sinks .......he'll need to find some pontoons or something.
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Old 10-31-2007, 04:06 PM   #6
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Re: Floating Ground?


I have some more specifics today. The monitors that display the sec. cameras have a bit of fuzz on the images. Hard to describe, but it is noticeable. Unfortunately, he does have a hook to hang his hat because the specs call for a ground to be run from building ground. OK, fine. However, everyone seems to think that the problem is being caused by the 24 AC power being run with the signal cable UNSHIELDED in the same conduit. Floating ground, my eye.
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Old 10-31-2007, 04:10 PM   #7
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Re: Floating Ground?


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Originally Posted by goose134 View Post
I have some more specifics today. The monitors that display the sec. cameras have a bit of fuzz on the images. Hard to describe, but it is noticeable. Unfortunately, he does have a hook to hang his hat because the specs call for a ground to be run from building ground. OK, fine. However, everyone seems to think that the problem is being caused by the 24 AC power being run with the signal cable UNSHIELDED in the same conduit. Floating ground, my eye.
This is a game the low voltage contractors play. You can offer to do a power quality survey for a price (or sub it out), and that'll shut them up. They always blame grounding, but it never is.

Last edited by mdshunk; 10-31-2007 at 04:13 PM.
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Old 10-31-2007, 05:41 PM   #8
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Re: Floating Ground?


Quote:
Originally Posted by goose134 View Post
I have some more specifics today. The monitors that display the sec. cameras have a bit of fuzz on the images. Hard to describe, but it is noticeable. Unfortunately, he does have a hook to hang his hat because the specs call for a ground to be run from building ground. OK, fine. However, everyone seems to think that the problem is being caused by the 24 AC power being run with the signal cable UNSHIELDED in the same conduit. Floating ground, my eye.

Hi Goose,

I am not siding on your "Security Guy" but if you could explain your last sentence. Is the "Signal Cable" you refer to COAX, CAT5, or something else???

Either way you answer the above and given your description there may be a different ground potential at the power supply than is at the camera. That may be caused by the camera mount/camera being ground to building and the signal cable being grounded at the head end. These two grounds may have different potential causing a ripple on the video.

The term "Floating Ground" is the wrong term. If he has a "good" building ground at the head end and he isolates the camera by changing his mounting so that it is not touching the building the problem may go away.

Depending on the severity of the issue an isolation transformer that is made for this problem will help as well.

I am not trying to fix his problem but trying to help you understand what might be going on so that you might suggest to him other possible solutions.

I hope that helps.

MD said: This is a game the low voltage contractors play. You can offer to do a power quality survey for a price (or sub it out), and that'll shut them up. They always blame grounding, but it never is.

I would not call it a game. When you are working with a video signal that is 1 volt peak to peak sometimes the smallest thing will reek havoc with the video. It depends on how good a picture the customer is expecting. If they are expecting video with the quality of their favorite soap then you are in a lot of trouble.

Les


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Old 10-31-2007, 08:45 PM   #9
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Re: Floating Ground?


Able,
The signal cable is cat 5, the power is 18/2 I believe. I'm not sure what you mean when you say grounded at the "head end". The cameras are mechanically grounded via the raceway, which is bonded to the ground. The corresponding power supplies are also mechanically grounded by the same means. In addition, there is an equipment grounding conductor to the power supply. Everything in the system is equal potential. There is no other grounding ( like I said, I'm not sure what you mean by Head end). Right now the working theory is EMI from the power source to the signal cable. I think if they were to switch to a DC power supply, it would be solved. Or a shielded power cable. We'll see tomorrow, when I finish running the "sinking ground".
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Old 10-31-2007, 09:28 PM   #10
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Re: Floating Ground?


Goose,

By Headend I mean where the equipment is located, the Power Supply, Monitor, and DVR. Not knowing the actual camera equipment some have a ground terminal some do not.

If he is using CAT5 cable then he is using either Passive or Active Transceivers on the twisted pair of the CAT5 cable depending on distance. The twisted pair cancels out any induction of the 60 Hz AC power source.

The following is from NVT one of the top mfg. of the Tranceivers. This is for the passive units.

The NVT Model NV-208A-M Video Transceiver is a passive (non-amplified) device that allows the transmission of real-time monochrome or color video over Unshielded Twisted-Pair (UTP) telephone wire. Baseband (composite) signals of any type are supported.

An improvement over NVT’s popular NV-213A video transceiver, the NV-208A-M features a Screwless UTP terminal block and Male BNC allowing connection directly to the camera or DVR. It is capable of delivering a fully equalized signal to the DVR when used with any Active NVT Receiver, yet is compatible with all of NVT’s passive products for applications under 750ft (225m). The NV-208A-M Video Transceiver also incorporates new improved transient protection that eliminates the need for a ground screw.

The unparalleled interference rejection and low emissions of the NV-208A-M allow video signals to co-exist in the same wire bundle as telephone, datacom, or low-voltage power circuits. This allows the use of a shared or existing cable plant. As with all NVT products, the NV-208A-M carries a limited lifetime warranty and is UL and cUL listed and CE compliant.



It would be my guess that the picture might improve if the camera was in a metal case and was removed from its mount and just hung from the cable for a quick test. If it is a plastic dome type camera then the transceiver BNC connector may be touching ground in some way. This is all guess work on my part at this time since I am not there to put my eyeball on the install.

Again I hope this help you and the installer tech.

Have a good tomorrow.
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Old 11-03-2007, 04:53 PM   #11
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Re: Floating Ground?


Soooooooo Just courious. What is the latest status on the "Floating Ground" thingie???
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Old 11-03-2007, 05:14 PM   #12
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Re: Floating Ground?


The security guy in question has not been back yet to assess the results. Every tele/data closet has a ground bus that has been bonded to the building ground. I simply piped over to the box, ran a #6 and tied it to each of the security boxes. I then took off the EGC from the UPS panel and closed it up. There is no measurable improvement in the picture quality. We'll see what he says...
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Old 11-03-2007, 05:26 PM   #13
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Re: Floating Ground?


Well keep us posted. We are all on pins and needles.
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Old 11-03-2007, 05:36 PM   #14
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Re: Floating Ground?


I was doing a TI in an office building.The computer guy said he needed a dedicated ground from his equipment to the building ground.So we did.$$$
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Old 06-16-2009, 04:21 PM   #15
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Re: Floating Ground?


I had a simular situation occur while I was out of town...returned home to find cable router offline, I verified that it was not internal to my house or was the router itself, so I called the cable crew in to check it at the street. came back to me and said that the coax at the street box was "melted" and that he received a good jolt when he disconnected it, and said that there is a floating ground in my house circuit. He repaired the line, and disconnected the earth ground at the house termination "until I get the floating ground repaired"

So how do I go about locating and repairing the source of the floating ground???
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Old 06-16-2009, 04:27 PM   #16
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Re: Floating Ground?


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He repaired the line, and disconnected the earth ground at the house termination "until I get the floating ground repaired"
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Old 06-16-2009, 04:37 PM   #17
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Re: Floating Ground?


I know, he said that it is grounded at the house's first termination, and at the box on the street. I am asuming he wanted to limit it to the single ground to prevent any more arcing at the box termination ( thats a guess)
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Old 06-16-2009, 04:48 PM   #18
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Re: Floating Ground?


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I know, he said that it is grounded at the house's first termination, and at the box on the street. I am asuming he wanted to limit it to the single ground to prevent any more arcing at the box termination ( thats a guess)
Could it be that the neutral wire on the outlet you had your router hooked to has bad connection? Grounding through the coax? I'm no sparky but it sounds like a bad neutral connection somewhere.
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Old 06-16-2009, 09:23 PM   #19
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Re: Floating Ground?


Let me guess...you Googled "floating ground" and came up with an ancient CT thread...then posted under Trade:Electrical.

Oh well. Seems like your cable carried current. Are you having any other electrical issues like flickering lights, bright lights or dim lights?
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Old 06-17-2009, 09:09 AM   #20
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Re: Floating Ground?


Yes the lights in the house do flicker when something like the dryer, or washing machine, or dishwasher or A/C comes on. The technician and I discussed all possibilities, and the lights flickering came to mind.
I do not have a history on the house, we moved in 2 months ago, but house inspection( for what it is worth--NOTHING) did not highlight anything--> and I did ask about the flickering lights..

thanks for any insight

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