I just need a understanding of this issue. What causes it? How does grounding solve this problem? Our video conference room has problems with noise. My supervising electrician suggested we ground the racks better that the video equipment is on, and we check our grounds at the panel. Could someone help me understand this.
Noise
- Thread starter JdoubleU
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zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
What causes noise? To grossly simplify, electrical noise happens in anything over absolute zero temperature.
To better answer- what kind of noise do you have? Since you mention a VC room, is this noise in the audio, the video, or what? Just grounding the racks, which are probably already gounded through the equipment grounds, isn't likely to solve any problem. You'll probably have to look at the VC system design, including the signal returns and where they hit "ground" and the gain structure.
To better answer- what kind of noise do you have? Since you mention a VC room, is this noise in the audio, the video, or what? Just grounding the racks, which are probably already gounded through the equipment grounds, isn't likely to solve any problem. You'll probably have to look at the VC system design, including the signal returns and where they hit "ground" and the gain structure.
cadpoint
Senior Member
- Location
- Durham, NC
It sounds like you need to supply either another panel at this point of usuage, or supply a complete circuit or a few circuits to this point.
With new circuits or panel, I'd do away with the ground bar, and let the panel or circuits carry your ground, this is secondary point of usage (in thought) and should not be grounded to the water pipe and and also the conduit that was used to apply service. Besides, is the ground bar isolated from the equipment structure itself ?
A example of the perfect storm of a undesired application. IMO ...
With new circuits or panel, I'd do away with the ground bar, and let the panel or circuits carry your ground, this is secondary point of usage (in thought) and should not be grounded to the water pipe and and also the conduit that was used to apply service. Besides, is the ground bar isolated from the equipment structure itself ?
A example of the perfect storm of a undesired application. IMO ...
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
When there are potential for multiple ground paths, I like to install ground wires in a star configuration (dedicated ground wire back to a single common point in the room) instead of daisy-chain (where a single wire is run from device to device).
brian john
Senior Member
- Location
- Leesburg, VA
Are you having any operational issues at this time?
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
Does the 'noise' look like static or does it look like slowing moving horizonatal bars? The latter are called "hum bars" and are almost always due to ground loops in the video lines. Sometimes you can get rid of them with some stragically-located humstoppers. OTOH, they hardly ever show up if all the equipment is in one room.
If you have static, that's more likely to be bad connectors, flaky equipment, or a really bad signal level problem. In that case, no amount of grounding will fix it.
If you have static, that's more likely to be bad connectors, flaky equipment, or a really bad signal level problem. In that case, no amount of grounding will fix it.
brian john
Senior Member
- Location
- Leesburg, VA
A grounded neutral which results in circulating current which can result in hum bars does not care if it is in one room or 20 rooms.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
I assume you mean an improperly/multiply grounded neutral
. But, yes, that can cause hum bars. OTOH, I'll still call it less likely unless the overall system is a hack job, and from the sound of it, it might be. Either way, if there are multiply-grounded neutrals, they need to be corrected. If there are multiple sets of racks, be it in one room or more, they should to be star-grounded. if there actually are hum bars and depending on system architecture, you may need to add some signal isolators (Jensen Transformer makes them, or you can get the old Allen Avionics ones on ebay).
ohmhead
Senior Member
- Location
- ORLANDO FLA
Well we kinda worked once on a large arena which had a sound system and lots of audio /video equipment kinda comsat / data/ tv/ satellite stuff ya know for telebroadcasting magic basketball games , after our company installed isolation transformers in these rooms and 3 foot long copper ground bars to grounding rings everything attached to that bar in that room the conduit to sound/video racks cable trays all metal everything went to grounding bar , guess what happen after the electrical inspection the arena people took out every ground wire took out all grounding in these rooms said it would be a LINK COUPLING something about loading points they dont like grounds when it comes to sound /video?comments best to yas
cadpoint
Senior Member
- Location
- Durham, NC
It's audio, a self contained system, yes I agree, it's a hack Job!
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
Noise is generally electrical current traveling on the equipment ground path. The EGP is not supposed to carry current other than fault current.
Having multiple grounding connections increases the potential of current flow on the EGP substantially, such as the connection of the rack to the cold water...what is that all about?
Noise on the Equipment grounding conductors/raceways/path is generally a wiring mistake...again, such as the neutral to ground connection on the load side of the service disconnect or 1st means of disconnect of a separately derived system.
Noise
I was asked to take a sump pump off a circuit that is shared by a computer. They said it was because it would cause noise on the line. If it is grounded correctly would this not be an issue.
I was asked to take a sump pump off a circuit that is shared by a computer. They said it was because it would cause noise on the line. If it is grounded correctly would this not be an issue.
Speedskater
Senior Member
- Location
- Cleveland, Ohio
- Occupation
- retired broadcast, audio and industrial R&D engineering
I have been involved in broadcasting and recording A/V for about 45 years, never heard of "link coupling". I have a 280 page book by Steve Lampen (Of Belden Wire Co.) sitting on my desk called "Wire, Cable and Fiber Optics for Video & Audio Engineers" I don't think that "link coupling" is in the book.
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
Sierrasparky
Senior Member
- Location
- USA
- Occupation
- Electrician ,contractor
Try using a clamp on meter to measure current on the Ground wire.
Try to trace it back to it's source .
It could be a power supply leaking to ground.
Try to trace it back to it's source .
It could be a power supply leaking to ground.
76nemo
Senior Member
- Location
- Ogdensburg, NY
Any ol' current clamp on meter won't do you much of squat here
Something like Fluke's 360 would suffice much more.
http://us.fluke.com/usen/products/Fluke+360.htm
cadpoint
Senior Member
- Location
- Durham, NC
Each transformation of power at a transformer is concidered a seperator derived point of service, If I'm wrong, please not the code section that shows my though process as in-correct? Thanks in advance!
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Common mode noise is what it is called.
current on the grounding is what the cause is.
current takes all paths to the source this is where the problems arise when a neutral gets inadvertently connected to the grounding of a system, it can be a neutral wire somewhere in the system touching the outlet box or conduit, or a neutral bar in a sub panel with the neutral bar's main bonding jumper screw wrongly installed. as it shouldn't be. what happens is most audio and video systems are coupled together with a shielded coax type cable which is bonded at each end to the equipment grounding conductor supplying the equipment. this sets up a parallel path for this neutral current when it is present on the grounding system.
finding the place where this neutral/ground connection is can be frustrating, but it can be done. with audio systems it can be found by turning off breakers till the hum goes away, then looking at the affecting circuits, or any sub panels to make sure the neutral bars haven't been bonded to the case. but there are some cases where isolation transformers have to be installed on the low level signal feeds at the impedance of the cable being used. these are where it is imposable to not have the neutral bonded like having signal feeds running between equipment in different buildings or different services, where the neutrals have to be bonded at each service disconnect.
Grounding is there for safety, never disconnect the grounding to solve a noise problem. this is a sure way to get someone hurt and set your self up for law suits. always find the problem and repair it or find someone who understands how to.
current on the grounding is what the cause is.
current takes all paths to the source this is where the problems arise when a neutral gets inadvertently connected to the grounding of a system, it can be a neutral wire somewhere in the system touching the outlet box or conduit, or a neutral bar in a sub panel with the neutral bar's main bonding jumper screw wrongly installed. as it shouldn't be. what happens is most audio and video systems are coupled together with a shielded coax type cable which is bonded at each end to the equipment grounding conductor supplying the equipment. this sets up a parallel path for this neutral current when it is present on the grounding system.
finding the place where this neutral/ground connection is can be frustrating, but it can be done. with audio systems it can be found by turning off breakers till the hum goes away, then looking at the affecting circuits, or any sub panels to make sure the neutral bars haven't been bonded to the case. but there are some cases where isolation transformers have to be installed on the low level signal feeds at the impedance of the cable being used. these are where it is imposable to not have the neutral bonded like having signal feeds running between equipment in different buildings or different services, where the neutrals have to be bonded at each service disconnect.
Grounding is there for safety, never disconnect the grounding to solve a noise problem. this is a sure way to get someone hurt and set your self up for law suits. always find the problem and repair it or find someone who understands how to.
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