I am trying to solve noise problem at one telecom site in Florida.
The system noise appears on all telephone pairs in the office and traced down to the ground and potential ground loops.
The noise is coming through the ground conductor carried by entrance cable onto CEGB (Cable Entrance Ground Bar).
Here is the configuration:
Copper pairs cables come to the outside pedestal where it is spliced and carried further into a stand along telecom hut (remote terminal or RT). The shelds of both cables, incoming to the pedestal and outgoing to the hut, are bonded to the ground bar in the pedestal which then is bonded to the ground rod. The rod is connected to the RT ground field that is within 30 feet.
The cable that comes from a pedestal enters the hut and spliced into the tip cable right at the entrance. The shield of the entrance cable is connected to the CEGB. The CEGB is insulated from the bay frame. CEGB is then connected to the MGB (Master Ground Bar) in the P-portion of the bar. The shield of the tip cable is connected to the MDFGB (Main Distribution Frame Ground Bar) which then too connected to the MGB.
MGB, of course, is bonded, on one hand to the MGN and, on the other, to the ground field.
There is also a power transformer about 200 feet away from the aforementioned pedestal and HV power line not far away either.
I believe that noise is injected into the cable from that transformer and power line.
I think that grounding of the copper pair cable in the pedestal through the ground rod and its subsequent connection to the ground field (GF) is fine. However I am concerned that grounding the entrance cable in two places, one at the ground rod in pedestal and CEGB-MGB-GF, is a potential problem of creating a ground loop. It is possible though that grounding of the entrance cable in the pedestal is required by the code (though I cannot find a reference to that) because we do not want to bring any "garbage" from outside into the office.
Could anyone please help me to clarify this issue?
I also would appreciate information on methods of how to isolate ground loops and solve the noise problem.
By the way. Should we connect the transformer and a HV power tower to the Remote Terminal ground field as well? What is the minimum distance that requires this scheme?
Yours truly,
Boris Zaretsky
The system noise appears on all telephone pairs in the office and traced down to the ground and potential ground loops.
The noise is coming through the ground conductor carried by entrance cable onto CEGB (Cable Entrance Ground Bar).
Here is the configuration:
Copper pairs cables come to the outside pedestal where it is spliced and carried further into a stand along telecom hut (remote terminal or RT). The shelds of both cables, incoming to the pedestal and outgoing to the hut, are bonded to the ground bar in the pedestal which then is bonded to the ground rod. The rod is connected to the RT ground field that is within 30 feet.
The cable that comes from a pedestal enters the hut and spliced into the tip cable right at the entrance. The shield of the entrance cable is connected to the CEGB. The CEGB is insulated from the bay frame. CEGB is then connected to the MGB (Master Ground Bar) in the P-portion of the bar. The shield of the tip cable is connected to the MDFGB (Main Distribution Frame Ground Bar) which then too connected to the MGB.
MGB, of course, is bonded, on one hand to the MGN and, on the other, to the ground field.
There is also a power transformer about 200 feet away from the aforementioned pedestal and HV power line not far away either.
I believe that noise is injected into the cable from that transformer and power line.
I think that grounding of the copper pair cable in the pedestal through the ground rod and its subsequent connection to the ground field (GF) is fine. However I am concerned that grounding the entrance cable in two places, one at the ground rod in pedestal and CEGB-MGB-GF, is a potential problem of creating a ground loop. It is possible though that grounding of the entrance cable in the pedestal is required by the code (though I cannot find a reference to that) because we do not want to bring any "garbage" from outside into the office.
Could anyone please help me to clarify this issue?
I also would appreciate information on methods of how to isolate ground loops and solve the noise problem.
By the way. Should we connect the transformer and a HV power tower to the Remote Terminal ground field as well? What is the minimum distance that requires this scheme?
Yours truly,
Boris Zaretsky