noise on the EGC

[electricalperson]

a place we work at requires us to run a #6 awg conductor to a ground rod for a "isolated" ground. i believe they are wrong by thinking that works but thats besides the point. i asked them why they do this and they say theres noise on the EGC's. there are a lot of subpanels in this place and almost all of them dont have an egc bar. egc's are terminated to the neutral bar all over the place. sometimes neutrals are terminated with egc under the same screw.

a way of eliminating the noise could be to seperate the neutrals and egc inside the panel? the feeders are ran in emt so it wont require a seperate conductor in each panel just a bunch of ground bars for the panels plus time. does everyone agree or am i wrong?

the place uses a lot of sensitive test equipment

 

[ceb58]

a place we work at requires us to run a #6 awg conductor to a ground rod for a "isolated" ground. i believe they are wrong by thinking that works but thats besides the point. i asked them why they do this and they say theres noise on the EGC's. there are a lot of subpanels in this place and almost all of them dont have an egc bar. egc's are terminated to the neutral bar all over the place. sometimes neutrals are terminated with egc under the same screw.

a way of eliminating the noise could be to separate the neutrals and egc inside the panel? the feeders are ran in emt so it wont require a separate conductor in each panel just a bunch of ground bars for the panels plus time. does everyone agree or am i wrong?

the place uses a lot of sensitive test equipment

If I understand what you are saying and the sub panels do not have the neutral and grounds separated you have a big violation on your hands. The nutral and grounds must be separated after you leave the MDP. You are not doing anything but wasting wire running back to the ground rod. Even if you have emt and you want to eliminate the noise I would pull an EGC back to the main distribution panel and tie it to the ground bars in each sub.

 

[dreamsville]

I think you need to run an isolated insulated EGC that doesn't bond to the conduit or metal boxes all the way back to the panels. :smile:

Gar probably has an opinion on this...

 

[brian john]

Rather that playing HOO DOO VOO DOO black magic electric work, why not tell them to SOLVE the issue IF it really exist.

This type of issue solving if it does anything at all complicates problems or at worst may be dangerous.

There are several ways to locate this problem.

1. Perform zero sequence readings on each branch circuit (if possible) use a True RMS amp clamp and measure the phase/phase and grounded/neutral conductors at the same time the circuits with any amperage are the culprits.

2. Measure grounded/neutral conductor voltage at the panel (should be close to ?0? millivolts) circuits with any loads should have an increase in measured voltage (between the grounded/neutral conductor and the Equipment grounding conductor (copper conductor or conduit makes no difference). If the voltage is low, similar to the reading in the PDU, that is a suspect circuit.

3. During a schedule outage turn off all the branch circuit breakers, unplug loads if possible and remove the grounded/neutral conductors from the neutral termination bar. Utilizing a low voltage megger 50VDC 0r 100 VDC (I use a low voltage megger to avoid damaging equipment with 500 or 1000 VDC meggers we normally use. The neutrals that megger bad, ?0? megohms, need to be traced out and the ?SHORTED? grounded/neutral conductor will need to be replaced, repaired, lifted depending on the exact nature of the problem.

 

[e57]

What is it they do - that requires no "noise" on the EGC's - the cleanest ground for most equipment IMO is going to be an insulated 500MCM back to thier puny main bonding jumper from each 4X16X.5" isolated ground bar mounted near each piece of equipment. Anything short of that is just plain cheezy....
Otherwise - just a simple insulated EGC in a single point arrangment. i.e. an isulated EGC with HR's to a single panel for all the "Noise" sensitive equipment - it need not be a main. Re-wire the entire building if need be!

And FWIW loose the multiple bonding jumpers would be a start. You are too right on that one - whoever these dopes are complaining about "Noise" need one of them slaps about the forehead - and taken to the cleaners for the corrections. Call it a tax for knowing too much.

 

[khixxx]

a place we work at requires us

If you are required to do something then do it?

Most instrumentation has separate grounds. Not sure of your application.

 

[ohm]

a place we work at requires us to run a #6 awg conductor to a ground rod for a "isolated" ground. i believe they are wrong by thinking that works but thats besides the point. i asked them why they do this and they say theres noise on the EGC's. there are a lot of subpanels in this place and almost all of them dont have an egc bar. egc's are terminated to the neutral bar all over the place. sometimes neutrals are terminated with egc under the same screw.

a way of eliminating the noise could be to seperate the neutrals and egc inside the panel? the feeders are ran in emt so it wont require a seperate conductor in each panel just a bunch of ground bars for the panels plus time. does everyone agree or am i wrong?

the place uses a lot of sensitive test equipment

Please tell me this is not a Critical Care Facility.

 

[Pierre C Belarge]

a place we work at requires us to run a #6 awg conductor to a ground rod for a "isolated" ground. i believe they are wrong by thinking that works but thats besides the point. i asked them why they do this and they say theres noise on the EGC's. there are a lot of subpanels in this place and almost all of them dont have an egc bar. egc's are terminated to the neutral bar all over the place. sometimes neutrals are terminated with egc under the same screw.

a way of eliminating the noise could be to seperate the neutrals and egc inside the panel? the feeders are ran in emt so it wont require a seperate conductor in each panel just a bunch of ground bars for the panels plus time. does everyone agree or am i wrong?

the place uses a lot of sensitive test equipment

250.54 Supplementary Grounding Electrodes.
Permits this type of installation. The supplementary grounding electrode is required to be bonded to the equipment grounding conductor within the enclosure to which it is installed in.

So, add as many ground rods as they like.


Read Bryan's post and make sure to remove the grounding issues..you will be their hero.

 

[Karl H]

This company will be moving to a new building soon,stating that the last
building had too many "Power Quality" issues.

I terminate my IG's to XO at the transformer that supplies the panel(s).

By bonding the EGC's to the Neutral bar in the panels is actually
silently destroying their "Sensitive" Equipment. I guess Human Safety
isn't a concern.

 

[electricalperson]

i know that running a seperate ground rod out is pointless and does not do anything for fault current. there just attaching to a piece of wire that isnt really doing anything. i was just thinking of what was causing the noise and i was thinking about all those panels. every one i open has neutral to ground connections. a lot of there equipment produces harmonics too

 

[Karl H]

i know that running a seperate ground rod out is pointless and does not do anything for fault current. there just attaching to a piece of wire that isnt really doing anything. i was just thinking of what was causing the noise and i was thinking about all those panels. every one i open has neutral to ground connections. a lot of there equipment produces harmonics too

Suggest they lower the temp of the testing room to zero degrees,that should eliminate the ground noise.

 

[Pierre C Belarge]

i know that running a seperate ground rod out is pointless and does not do anything for fault current. there just attaching to a piece of wire that isnt really doing anything. i was just thinking of what was causing the noise and i was thinking about all those panels. every one i open has neutral to ground connections. a lot of there equipment produces harmonics too

B-4....BINGO!!!!


I think you have answered your own question.

 

[LarryFine]

a way of eliminating the noise could be to seperate the neutrals and egc inside the panel? the feeders are ran in emt so it wont require a seperate conductor in each panel just a bunch of ground bars for the panels plus time. does everyone agree or am i wrong?

I agree with you. The neutrals should be on bars isolated from the enclosures, and the grounds whould be on the enclosures and conduits.

 

[LarryFine]

Even if you have emt and you want to eliminate the noise I would pull an EGC back to the main distribution panel and tie it to the ground bars in each sub.

That would only help if the EGC bars were isolated like the neutral bars should be.

 

[quogueelectric]

More than one ground neutral connection creates more ground loops which will create more problems that they are trying to eliminate.

 

[brian john]

i know that running a seperate ground rod out is pointless and does not do anything for fault current. there just attaching to a piece of wire that isnt really doing anything. i was just thinking of what was causing the noise and i was thinking about all those panels. every one i open has neutral to ground connections. a lot of there equipment produces harmonics too

Read my post and follow instructions and you can resolve these issues.

 

[gar]

090310-0810 EST

electricalperson:

The way the building is currently wired is a code violation, and does not solve noise problems, and probably makes noise problems worse. Supplementary ground rods may not attenuate noise very much.

Isolation of the equipment chassis from the EGC and using a local ground rod for the chassis connection is a major NO NO and a very serious safety problem. There are apparently some equipment manufacturers that tell their customers to do this.

Even if you have a code compliant EGC this does not mean you won't have a noise problem.

A normal code correct EGC system does not provide a very low impedance path and may need to be a much lower impedance or use isolation techniques between different areas of the building.

The nature of the instrumentation and/or other sensitive equipment will determine what needs to be done to solve the noise problem.

If radio frequency or electric field noise is a problem, then a Faraday shield (screen room) and filters on incoming electrical lines may be needed. If high data rate communication lines need to pass into the screen room, then isolators will be need at the screen room wall entry point.

For certain types of measurements a full screen room may not be necessary. Just a wire mesh ground plane in the floor may be sufficient.

Magnetic field interference may be a bigger problem to solve. An electrostatic screen room (copper screen wire) will not solve this problem.

If the noise problems are related to communication between different areas, then isolation in the communication lines is the best solution.

With my Fluke 27 and the standard test leads I did a couple quick voltage measurements. The experiment used the AC V range with the leads spread out in a straight line and I was holding the leads or lead depending upon orientation. vertically I let one dangle down and I held the other up.

Vertical orientation. In the eating area with no lights on the reading was about 5 MV, in the kitchen with the 8' Slimlines on and below a light fixture about 60 MV. Midway between the two fixtures about 20 MV. With the kitchen lights off about 6 MV. In a hallway under a 100 W incandescent about 30 MV. Dimming this did not seem to make much difference. Note these are not controlled experiments, but just quick rough tests.

Horizontally about 4 ft below the kitchen light about 25 MV. A foot from the face of my 20" monitor about 130 MV.

Shorting the leads and making an approximately circular loop read about 1 MV at the side of the monitor and zero in front of the tube face. This is reading the magnetic field.

Input resistance of the Fluke 27 is 10 megohm.

Note: from my recollection of a test some ago the Fluke 27 and 87 got flaky in AC between 30 and 100 kHz. On the Fluke meters I do not detect local radio stations, but on a oscilloscope I do.

.

 

[e57]

IMO there is a lot that can - as mentioned - get rid of the "noise" FIRST is to isolate the grounding from the grounded (neutral) conductors.

But....

The next is to make them 'feel like a man' so-to-speak when they do ground something. And there is nothing like huge lugs and several tens of thousand dollars in copper to make one feel like they're not lacking. Something that makes them stand taller when they speak of it. It will also be guarnteed to make you feel better when you hand them the bill - just try not to snicker.

Something like this:

Or even some buswork:

This of course would go to 10' rods, 4 on each side exothermically welded in a ring around the building all interconnected with 250MCM, and a single #6 to the MBJ in the main panel.

i was just thinking of what was causing the noise and i was thinking about all those panels.

The 'noise' is current flowing on the EGC's energized by the neutrals. Say you have equipment with a chassis ground in one part of the building with a coaxial cable connected to it. That coaxial is also grounded at the entrance of the building. The result is current flowing on the coaxial due to the difference in potential caused by the neutral in the sub-panels.

How to get rid of that? Single point grounding for all AV senitive equipment. Isolating interconnections between AV equipment with specialized connection. Usually in the form of transformers made to transfer audio or video.

 

[electricalperson]

we install that copper bus for there ESD.

 

[brian john]

IMO there is a lot that can - as mentioned - get rid of the "noise" FIRST is to isolate the grounding from the grounded (neutral) conductors.

But....

The next is to make them 'feel like a man' so-to-speak when they do ground something. And there is nothing like huge lugs and several tens of thousand dollars in copper to make one feel like they're not lacking. Something that makes them stand taller when they speak of it. It will also be guarnteed to make you feel better when you hand them the bill - just try not to snicker.

Something like this:

Or even some buswork:

This of course would go to 10' rods, 4 on each side exothermically welded in a ring around the building all interconnected with 250MCM, and a single #6 to the MBJ in the main panel.

The 'noise' is current flowing on the EGC's energized by the neutrals. Say you have equipment with a chassis ground in one part of the building with a coaxial cable connected to it. That coaxial is also grounded at the entrance of the building. The result is current flowing on the coaxial due to the difference in potential caused by the neutral in the sub-panels.

How to get rid of that? Single point grounding for all AV senitive equipment. Isolating interconnections between AV equipment with specialized connection. Usually in the form of transformers made to transfer audio or video.

Spare the rod spoil the circuit?