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High earth leakage current on earth bar from mobile telecommunication's equipment

Ryan Anderson

I'm reviewing a mobile infrastructure power system where we have recorded (using a clamp meter) 16A on the MET earth and similar readings on the various bonds terminated onto a common 8 way copper bar earth bar. The site has a 300mA RCCB installed at the TN-C-S source which operates fine as expected however the high current running through the exposed copper earth bar in the meter cabinet is a concern. 

It's worth mentioning that the primary load is mobile network equipment which includes rectifiers and understandably will produce earth leakage from the DC systems. I suppose this would be considered 'planned' earth leakage, however the potential for electric shock from an exposed copper bar cannot be ignored.

I had assumed the IET Guide to Data Centre Power Systems would have some solution to DC earth leakage issues, however this has not yet been formally published. I have encountered high earth currents in a previous project (rail) which resulting the DNO repairing a cable joint in the street however this site is rural and the DC tech seems to be the prime suspect. Is there an IET guidance on how this should be dealt with?

**UPDATE**

The final outcome to this was a broken neutral conductor in the supply cable. When the DNO removed the LV earth link to separate the LV & HV earthing systems in line with G78 the supply was completely lost which identified the the system had been using the combined earth system as a return path. The supply was rewired back to the nearest joint and problem solved. 

Parents

  • Hi Ryan, I am having a similar problem but in an industrial plant with leakges going upto 13.5A when some motor loads are starting, I have been trying to get possible reasons for this and if there are any standards that we can base our earth leakage results on for an industrial plant. IEC 60479-1 has a graph that shows human response to electrical shock at varying currents and time. But that doesn't give a clear guidance on what would be deemed acceptable in an industrial setup

  • in reply to Amos Owaga

    13A may sound like a lot, but what is it as a percentage of the connected load ? - a percent or two is probably credible, though less would be nice. The other thing to bear in mind is what voltage would this rise to if the main CPC were ever interrupted  (please do not do this as a live test... ) - as that is the deadly fault condition. If the answer is more than about 50V then any interruption of the earthing is a single fault to danger, rather than the usual second or third fault to danger  so works that might interrupt this path, like plumbing or moving of metal supports for trunking, need more careful consideration, and earth wiring and termination methods need to be that much more robust.

    Mike.

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  • in reply to Amos Owaga

    13A may sound like a lot, but what is it as a percentage of the connected load ? - a percent or two is probably credible, though less would be nice. The other thing to bear in mind is what voltage would this rise to if the main CPC were ever interrupted  (please do not do this as a live test... ) - as that is the deadly fault condition. If the answer is more than about 50V then any interruption of the earthing is a single fault to danger, rather than the usual second or third fault to danger  so works that might interrupt this path, like plumbing or moving of metal supports for trunking, need more careful consideration, and earth wiring and termination methods need to be that much more robust.

    Mike.

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  • in reply to mapj1

    I have asked the client for PQA for now because the earth resistance seems to be very normal.

    Can the high leakage current be pinned to the nature of loads i.e inductive loads

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