Presumed RF Interference

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1

Greetings:

We have a client site that is driving us nuts...

...

I should also add some other points:
   -- We have observed failures when the building had zero power, except for the UPS .....
   -- The building only operates 0600 to 1800, so many failures are occurring after hours.
   -- There are no RF sources in the building.
   -- We are not near an airport.
   -- The building is steel framed and sided -- and a pretty good RF shield --....

Given what I have described, would you think this is an RF interference problem?

No...

Unless you have a Gigawatt radar parked next door, I'm highly dubious
that it's RF-instigated.

  3 DSL routers (cisco 8x7)
  1 edge router (cisco 28xx)
  1 FR router (cisco 36xx)
  1 patch panel
  1 telco smart jack (ATM/FR circuit)
  1 PBX T1 card
  1 patch panel (all jacks went open on the same pair)

  Make that Terawatt...

  6+ NICs

A) All these things say grounding issues. I have to wonder if
the building is fed from more than one power entrance. The blown
patch panel especially makes me think the router on one end of
the Cat5 was being fed from a different power source than the
one on the other. (Which pair was blown?) Given the UPS mention,
maybe there's a ground differential issue with it.

B) The other, less likely, path into equipment is telco. Those
mile-long pieces of copper from the CO are also called "antennas"
and they covet static. I have no idea where this location is --
are there thunderstorms around?

C) One more possibility; perhaps some piece of equipment in-house
is putting large spikes on the internal distribution. Twenty years
ago, I read of a building where large [50 HP HVAC] and small
[fridges] motors would regularly die. The high-tech gadgets of
that era, Texas Instruments calculators, would reset themselves
seemingly spontaneously. After MUCH work, they found the BIG
copier was putting nasty spikes back on the grid.

I vote A) 75% B) 20% C) 5%

You do need an EE, one prepared to look at the building wiring/grounding
grid.

2

David Lesher wrote:

Greetings:

We have a client site that is driving us nuts...

...

I should also add some other points:
  -- We have observed failures when the building had zero power, except for the UPS .....
  -- The building only operates 0600 to 1800, so many failures are occurring after hours.
  -- There are no RF sources in the building.
  -- We are not near an airport.
  -- The building is steel framed and sided -- and a pretty good RF shield --....

Given what I have described, would you think this is an RF interference problem?

No...

Unless you have a Gigawatt radar parked next door, I'm highly dubious
that it's RF-instigated.

3 DSL routers (cisco 8x7)
1 edge router (cisco 28xx)
1 FR router (cisco 36xx)
1 patch panel
1 telco smart jack (ATM/FR circuit)
1 PBX T1 card 1 patch panel (all jacks went open on the same pair)

  Make that Terawatt...

6+ NICs

A) All these things say grounding issues. I have to wonder if
the building is fed from more than one power entrance. The blown
patch panel especially makes me think the router on one end of
the Cat5 was being fed from a different power source than the
one on the other. (Which pair was blown?) Given the UPS mention,
maybe there's a ground differential issue with it.

B) The other, less likely, path into equipment is telco. Those
mile-long pieces of copper from the CO are also called "antennas"
and they covet static. I have no idea where this location is --
are there thunderstorms around?

C) One more possibility; perhaps some piece of equipment in-house
is putting large spikes on the internal distribution. Twenty years
ago, I read of a building where large [50 HP HVAC] and small
[fridges] motors would regularly die. The high-tech gadgets of
that era, Texas Instruments calculators, would reset themselves
seemingly spontaneously. After MUCH work, they found the BIG
copier was putting nasty spikes back on the grid.

I vote A) 75% B) 20% C) 5%

You do need an EE, one prepared to look at the building wiring/grounding
grid.

That is already half of a solution:

Go for fiber. That is imune to both ground and RF problems. Avoid
ground connections between the equipment.

Replace ethernet with fiber. Break serial lines with optical isolators.

Cut the ground wire in your power cords but ground the equipment directly
to a metal frame.

Avoid ground loops: Between two computers you have a ground connection
via the powerline ground. Connect them via RS-232 and you have a second
connection via the RS-232 ground. If your power ground is bad then you
might run amperes through the RS-232 ground that results in Volts, more
than your signal level, maybe.

regards
Peter and Karin Dambier

3

David Lesher wrote:

> Given what I have described, would you think this is an RF interference problem?

No...

Unless you have a Gigawatt radar parked next door, I'm highly dubious
that it's RF-instigated.

A) All these things say grounding issues. I have to wonder if
the building is fed from more than one power entrance. The blown
patch panel especially makes me think the router on one end of
the Cat5 was being fed from a different power source than the
one on the other. (Which pair was blown?) Given the UPS mention,
maybe there's a ground differential issue with it.

B) The other, less likely, path into equipment is telco. Those
mile-long pieces of copper from the CO are also called "antennas"
and they covet static. I have no idea where this location is --
are there thunderstorms around?

C) One more possibility; perhaps some piece of equipment in-house
is putting large spikes on the internal distribution. Twenty years
ago, I read of a building where large [50 HP HVAC] and small
[fridges] motors would regularly die. The high-tech gadgets of
that era, Texas Instruments calculators, would reset themselves
seemingly spontaneously. After MUCH work, they found the BIG
copier was putting nasty spikes back on the grid.

I vote A) 75% B) 20% C) 5%

Re: C, I think (hope) the power company has already eliminated internal power spikes. The have recording monitors on both the building feed and on the distribution panels for the office area. The only thing in the building that pulls more than 20A is a couple of 4 ton A/C units and the server room UPS.

Re: B, The "telco lines are antennas" concept is why we were thinking RF. The location is in the SE US, but no thunderstorms this time of the year.

Re: A, I don't remember which pair was blown. Since it was a new patch panel (less than a week old) we initially wrote it off as a manufacturing defect -- but now we are not so sure. Everything in the server room -- which includes PBX and all networking equipment -- is on a single UPS. The CAT6 in the building terminates at PCs. Each PC has its own separate UPS. A floating ground or ground current was among my first thoughts -- but a few things about it bugged me and made me look elsewhere:
   1) How could a bad ground cause DSL line noise that ia inaudible? Also, the noise is on the telco side, not the LAN side.
   2) Why would it be blowing DSL routers that are isolated from the LAN by a switch and another router? And, all of this equipment is in the same rack, on the same ground, and on the same UPS.

Well David, thanks for your thoughts. I guess the next step is to find an EE that want to tackle this challenge without asking for an open-ended purse!

Jon Kibler

4

This makes me think of a place where they used copper lines that ran alongside rail road tracks, and each time a train came by the leased line modems would go haywire. Electrical trains put a lot of current in the ground...

5

[ I am not a PE - IANAPE ]

I don't think that is good advice. You can't possibly have the
as-builts, existing condition, or line drawings in front of you.

Safety first. Call the consulting engineers.

-M<

6

Jon,

Peter Dambier wrote:

Cut the ground wire in your power cords but ground the equipment directly
to a metal frame.

As a time-served electrician... *****DO NOT DO THIS***** - it will kill someone.

However....

You could try separate earth bonding of each components (ie connecting all the chassis together via a provided grounding terminal using nice thick copper wire), however if there is a significant earth fault even that could be dangerous (think fire) - so get a qualified electrician to do it - if there is a ground fault it will use the chassis and the bonded earths as it's route to ground.

Earth faults are often easily detectable by using a digital volt meter (Note: analog volt meters do not work for this unless there is a serious fault). First check for induced and ungrounded 'floating' voltages (any AC or DC voltage above 0.05v should be investigated), then if the DVM is fused, check for any current (amps) between chassis.

If you have money to spend before investigation find out if the building has a grounding stake and if not add one... A couple of meters of copper stake which will be connected to either the armoring of the supply cable (TN-S) or to the incoming return cable and installation earth PME (TN-C-S) - likely based what someone else in this threat said. In either type of grounding scheme the structure metal frame could (and should) be grounded (esp if exposed) which is likely to cause the phone RF signal drop. A faulty bonding in the structure (esp as it is steal) can also provide for some interesting ground faults as it is not uncommon to provide localised grounding to building frames. (In the UK where I served my apprenticeship, we were required to provide earth bonding to the copper plumbing system, additional bonding at every exposed fitting - this caused a few issues when plumbers first starting using PVC pipes)... All this said with the faults appearing with no external power and with just UPS supply, ground faults really do not 'fit' the problem - however if a generator is used also, you are in an IT type installation (electrical term 'IT' not 'Information Technology' ;-)) and will have to have a grounding stake on site.

Please note, I am trained from the UK - laws and regulations change from country to country - get a local qualified/licensed sparky to do the work or assist you.

Regards,

Mat

7

Cut the ground wire in your power cords but ground the equipment
directly to a metal frame.

i strongly recommend that you do this, especially in your 240vac
environment. excellent solution to a lot of problems.

randy

8

Randy Bush wrote:

Cut the ground wire in your power cords but ground the equipment
directly to a metal frame.

i strongly recommend that you do this, especially in your 240vac
environment. excellent solution to a lot of problems.

randy

I agree, dont propose this to a wood logger :slight_smile:

But yes, I did.

I have seen an installation where "ground" was floating somewhere
at 110 Volts AC. There was no way to tame it. We had to cut it.
Ofcourse we did it not on the wire but in the sockets and we got
a reasonable ground before we did.

Dont read in the books - and dont tell a lawer :slight_smile:

The soil was extremly dry (not in europe) and the powerline was
extremly long...

Regards
Peter and Karin

9

The US National Electrical Code (which has no national force of law;
it's a model code voluntarily adopted by many jurisdictions) now bars
grounding to pipes except within (as I recall) six feet of where the
pipe enters the building, for precisely that reason.

10

The use in modern times of teflon tape at joints in copper
piping makes them unuseable for earth grounds even near the entry
point to the building. A long (e.g. 2-3 meters) copper stake must be
driven for a proper earth ground, or else a large copper mesh mat if
the ground is rocky -- unless you are certain that the copper piping
that you want to use extends a significant distance underground and
unbroken.

-w

11

Randy Bush wrote:

Cut the ground wire in your power cords but ground the equipment
directly to a metal frame.

i strongly recommend that you do this, especially in your 240vac
environment. excellent solution to a lot of problems.

Don't even joke about doing this, please. If there is potential on the grounding conductor, then that problem needs to be corrected as it is a safety of life issue. Even if you cut the conductor and safely ground the equipment in that one rack, you are ignoring the fact that you have very strong evidence of a serious wiring problem in the form of destroyed equipment.

Say you do what you suggest, ensure that your rack is well and solidly grounded. And, you're aware that the building grounding wiring is defective. And then someone comes in (maybe you) and plugs in a piece of portable test equipment next to your nice grounded rack. And then
puts one hand on the test equipment (plugged into one of the defective outlets) and the other on your well-grounded rack. Especially in the 240 volt environment.

There is a serious, potentially fatal, wiring fault in that building. Get it fixed properly.

12

The purpose here is not to use the piping *as* a ground, but to ensure that the piping *is* at ground potential. Otherwise, if an electrical failure causes the pipe to reach a dangerous potential then so does the water in it, then so do the hands you're washing in that water. Thus if there's an electrical discontinuity in the piping it is even more important to earth bond any conductive piping/taps etc. that are on the non-earth side of that discontinuity. The same applies too to gas piping except here the principal risk is static, sparks and the subsequent explosion.

13

Ian Mason wrote:

(In the
UK where I served my apprenticeship, we were required to provide earth
bonding to the copper plumbing system, additional bonding at every
exposed fitting - this caused a few issues when plumbers first starting
using PVC pipes)...

The US National Electrical Code (which has no national force of law;
it's a model code voluntarily adopted by many jurisdictions) now bars
grounding to pipes except within (as I recall) six feet of where the
pipe enters the building, for precisely that reason.

The use in modern times of teflon tape at joints in copper
piping makes them unuseable for earth grounds even near the entry
point to the building. A long (e.g. 2-3 meters) copper stake must be
driven for a proper earth ground, or else a large copper mesh mat if
the ground is rocky -- unless you are certain that the copper piping
that you want to use extends a significant distance underground and
unbroken.

The purpose here is not to use the piping *as* a ground, but to ensure that the piping *is* at ground potential. Otherwise, if an electrical failure causes the pipe to reach a dangerous potential then so does the water in it, then so do the hands you're washing in that water. Thus if there's an electrical discontinuity in the piping it is even more important to earth bond any conductive piping/taps etc. that are on the non-earth side of that discontinuity. The same applies too to gas piping except here the principal risk is static, sparks and the subsequent explosion.

I think it is also important to note that NEC 250.52(B) prohibits gas piping as a grounding electrode(1990 or so). The gas pipe ceased as a grounding electrode due to the dielectric fitting at the meter. The gas company did not want a bond around the meter because it defeated the isolation fitting.

The presence of gas is not relevant, IIRC.

In the old days, it was a big no no (at least according to the hourly wage fellows who actually do the work) to hook the gas line "as" ground other than any incidental grounding which ocurs in a gas furnace as an example.

Good place for resources is http://www.mikeholt.com in the forums. Decent community of knowledgeable folk there.

Good luck, and "no" do not use your body/fingers/arms/etc to connect various pieces of equipment to see if a voltage exists:-) That's best left to close friends who stand near electric fences.

I had problems in the mid 1990's in an older home where the galvanized water supply pipe was the primary ground. Over time, corrosion of the pipe reduced conductivity, and lightening storms toasted a few expensive items (e.g. ISDN gear, sun workstation, etc) before finally driving a few grounding bars into the soil in the basement.

Cheers,
andy