Excessive current on Telco MGN connection?
Excessive current on Telco MGN connection?
(OP)
Let me start by saying I am not an engineer. I am a telecommunications technicain, I do have to work with the power company engineers and techs to resolve problems occasionally. I have attached a drawing of the premise where my problem exist. The setting is, this is an office building with 50 offices, all having computers, and all florescent lighting throughout the building, with 3 phase service. Problem being we have 3 to 7 amps of current flowing on the Telco ground, and it changes very rapidly up and down from second to second. We turned off all of their circuits one at a time, and no one ciruit seemed to be causing a problem, it was more cumulative. I suspected a bad connection in the neutral due to the rapid change on the Telco ground as well as their neutral in the panel that mostly has 110 circuits feeding out of it, the reading on the neutral in that panel is 11-22 amps also rapidly changing up and down. Their electricians came out and said that the load in that panel was not very well balanced, and this is why the return current is high. My question is shouldn't their neutral handle that current, and why is it jumping up and down so rapidly. The power company has tested and done some preventive maintenance on the neutral, and they say it is good up to the point of entrance. Problem for me is I am at the mercy of the power company and our customer's electricians. Any suggestions on how to resolve this issue would be much appreciated.






RE: Excessive current on Telco MGN connection?
RE: Excessive current on Telco MGN connection?
RE: Excessive current on Telco MGN connection?
Another possibility is that some of the neutral current is returning to the utility transformer via the ground. If possible, measure the voltage drop on the neutral and see if changes in the neutral voltage drop correlate with changes in the current over the ground conductor.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Excessive current on Telco MGN connection?
Important question, How is your facility grounded?
Your drawing has no sign of grounding.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Excessive current on Telco MGN connection?
RE: Excessive current on Telco MGN connection?
Don
RE: Excessive current on Telco MGN connection?
RE: Excessive current on Telco MGN connection?
Don
RE: Excessive current on Telco MGN connection?
Your cable is in parallel with the combination of utility distribution system ground (since you are connected at the pole) and building grounding system. It's not clear if the BT end is connected to a power system NEUTRAL or GROUND.
Waross has a good point:
This is a very common error of communications installers.
You said the BT end is connected to the MGN? By MGN, do you mean power system NEUTRAL? This would be a bad idea for several reasons:
1. It is most likely a violation of electrical code because,
2. It creates a safety hazard
3. As you are experiencing, the cable shield will share the neutral current which may disrupt the communications.
Power system neutrals are intended to carry current in normal operation. If you connect a cable in parallel, it will try to share the neutral current. The safety hazard is that it may become energized due to abnormal conditions such as short circuit on the power system and it may disrupt the power system protective functions.
If the cable is connected to a power system GROUND at the BT end, you have a similar set of possible problems:
The power system grounds will almost always have some amount of stray current which would be shared in your 200pr in this arrangement - not a good idea. If there is a short circuit on the power system, the short circuit current return on the power ground. If your cable is in parallel with the ground, some of the short circuit current will flow in your cable, possible destroying it and causing a fire.
I suggest you stop worrying about the power system neutral current and install a proper communications grounding riser (with a single point interconnection to the building power ground at the point of entrance). The cable shield should be connected to that grounding riser near where it enters the building.
RE: Excessive current on Telco MGN connection?
Computer power supples generate harmonics.
Triplen harmonics add on the neutral rather than canceling.
I am surprised that you have so little neutral current flowing.
It sounds like two problems.
1> A telco ground path in parallel with the neutral.
2> Either a fast cycling intermittent single phase load (Maybe a fact of life rather than a problem),
or
a poor connection in one of the parallel conductors.
Can you measure both the neutral current and the ground current simultaneously to see if there is a fluctuating single phase load (both currents track together) or a bad connection shifting the neutral current from the neutral to the ground conductor (neutral current goes up when the ground current goes down and vice versa).
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Excessive current on Telco MGN connection?
Thanks for your help as well resqcapt19, the only place I was able to access the neutral was in the 2 breaker panels shown in the drawing to the right of the disc panel. The panel on the left has very little current flowing on that neutral, but it is mostly 220 ciruits with a balanced load, the other panel has a very rapidly changing 11-22 amps constantly going up and down, just like the current on our ground. That is what lead me to believe they had a bad connection on their neutral somewhere. The power company says they are good up to the point of entrance. I'm not sure I am qualified to answer the question about adding impedance to our ground. Thanks again for your help, unfortunatley our telco noise mitgation gurus haven't been much help so far.
RE: Excessive current on Telco MGN connection?
RE: Excessive current on Telco MGN connection?