Wiring Matters 93 - Nov 22 - High Protective Conductor Currents

Well Matt, there is nothing to say that. You use the data centre description but a single 60309 may well supply a lot more than one item of equipment, often a rack full which may have a lot of leakage. However in a data center the Earthing is not just the mains leads for signal integrity reasons, so surely this is all nonsense anyway? Gridded Earthing is the norm, Earth impedance is very low indeed, and there are a myriad of Earth paths. This article is written by a probable non-expert author, the Editor ought to know better.

The example of the ring circuit is also somewhat spurious, and addresses another very unlikely scenario. How likely is it that a fixed wiring Earth conductor feeding a number of sockets fails, and then because it is a ring another point suffers the same fate? A single item may loose an Earth from its flex or plug, but this is not a high risk situation is it as the leakage is less than 3.5mA (which may not even be felt). If leakage approaches 30 mA the RCD should disconnect the circuit as additional protection.

For some reason the issue of high leakage seems to be tied up with plugs and sockets, it is not obvious to me why this should be. A set of stage lighting dimmers (500 of them) each with fairly large RFI filter capacitors, may "leak" many amperes, does this matter and is it unsafe because the Earth conductor may fail? For many years now this has not been a problem. It seems to me that this article is written to worry simple electricians with situations they are very unlikely to encounter. This happens all the time, because the training is failing the industry. The concept of risk has changed to "what if", and the what if is now always the worst possible outcome, with undefined circumstances. Surely this is ridiculous?

Well Matt, there is nothing to say that. You use the data centre description but a single 60309 may well supply a lot more than one item of equipment, often a rack full which may have a lot of leakage. However in a data center the Earthing is not just the mains leads for signal integrity reasons, so surely this is all nonsense anyway? Gridded Earthing is the norm, Earth impedance is very low indeed, and there are a myriad of Earth paths. This article is written by a probable non-expert author, the Editor ought to know better.

The example of the ring circuit is also somewhat spurious, and addresses another very unlikely scenario. How likely is it that a fixed wiring Earth conductor feeding a number of sockets fails, and then because it is a ring another point suffers the same fate? A single item may loose an Earth from its flex or plug, but this is not a high risk situation is it as the leakage is less than 3.5mA (which may not even be felt). If leakage approaches 30 mA the RCD should disconnect the circuit as additional protection.

For some reason the issue of high leakage seems to be tied up with plugs and sockets, it is not obvious to me why this should be. A set of stage lighting dimmers (500 of them) each with fairly large RFI filter capacitors, may "leak" many amperes, does this matter and is it unsafe because the Earth conductor may fail? For many years now this has not been a problem. It seems to me that this article is written to worry simple electricians with situations they are very unlikely to encounter. This happens all the time, because the training is failing the industry. The concept of risk has changed to "what if", and the what if is now always the worst possible outcome, with undefined circumstances. Surely this is ridiculous?