Grounding Fault at Cell Sites

Is this a power-protective earth conductor or the earth condusctor for part of the transmission antenna's function, or both?

If the middle or latter, it would appear to be undersized.

If it is the first one, there is a sreious power supply problem that needs investigating and solving before someone gets hurt/killed.

is the protective earth conductor, E.

• Isolate the supply.
• Open a link in the earth conductor.
• Insert a voltmeter on a correct range in place of the link.
• With no-one touching the equipment as a precaution, energise the equipment. Measure the voltage. De-energise the equipment, remove the voltmeter and close the above link.

What did the voltmeter say?

Is the power supply supposed to be isolated? If you have an unintentional bond between the common power supply rail and station ground that may be causing this issue. A lot of manufacturers do this purposely to isolate any noise created by the SMPS.

If you are reading a voltage which is almost rail level between station ground and the negative side of the DC power supply, then the checks between the "dc part" should show a resistance value other than open or shorted. That should be spec'd for the installation.

The "ground to -ve" is 32VDC or -32VDC?

is 32Vdc.

You've got some sneaky ground issues there. I would check the specs for installation of that particular piece of equipment. I am assuming this issue appeared upon installation of the new equipment(?).

Are you using an unregulated external DC supply for the SDH? If so, I would check for compatibility i.e., grounding types.

Someone has put a short between the -ve power rail of the SDH to the cabinet somewhere. This bit of wire will be getting very hot.

Hi Randall

we were able to trace it and that was actually the cause.

many thanks to everyone!!

Crikey EnB!! You had a -48V to ground fault and a circuit breaker didn't trip or a fuse didn't, well, fuse. Protection is there to prevent conductors from "getting very hot". The protection obviously didn't work. The grounding system has not been correctly implemented (or designed) Under the condition you described and the fault that was discovered the "SDH" would not have turned "on" as you said. You are lucky that you did not start a fire. It is really sad that unqualified personnel are being used to perform installation tasks with equally ignorant supervision and a total lack of design. Keep up the bad work. It makes it easier for properly qualified folk to compete with cheap Charlies.

You have a -48Vdc supply and you're measuring 32Vdc between the hot side and deck? This is plainly not right. Let's review what you should have there. Telecomms DC power system should be +ve ground. The bonding conductor should be from the +ve busbar of the power supply to the station's main earth and be the same size as the largest conductor inside the power supply. Typically 35 to 70 sqmm. You didn't say where you were obtaining your ground reference for the measurement you made. If a conductor is heating up it is conducting current. Did you measure the current? Do you have a DC clamp meter? If not stop right now. You are not equipped to perform any analysis (not easily anyhow). Does your SDH transmission equipment actually function? Was there any smoke? I note some serious deficiencies in the way you are going about this. For one, why was the SDH (radio, mux, OFTE... you didn't say which) powered up before checking or commissioning the DC power system? My guess here with the limited information supplied is that the 0Vdc return conductor is open circuit or not properly connected at either end. The ground conductor is acting as the return via some internal 0v to ground bond inside the SDH equipment. Ground bonding practices at this site seem dubious too. Try not to set fire to the site.