jdc
Well-Known Member
The cardinal rule of wiring and circuit protection is that any wires down-stream of a fuse must withstand the full rating of that fuse (or, to put it another way, up-stream of any wiring there must be a fuse or breaker of a rating no more than the current carrying capability of the wire).
In the UK we have fused plugs. It's normal therefore to have a 5A fuse (for example) in a '13A plug' with =>5A flex between it and the appliance, the '13A plug' being plugged into a socket on a ring-main with as much as a 30A fuse or breaker. Should there be a short in the appliance between live and earth, it is the 5A fuse in the plug which which should blow. This will only happen if the current is flowing through the fuse, and since there is no fuse in the neutral side of the plug. wiring the polarity correctly is essential in the UK. - or used to be before we had RCCBs everywhere.
Why not in France? Several reasons, the most important of which is that since they don't have fused plugs they can't use ring-mains and they have to have a breaker or fuse per socket. Hence the breaker will blow if there's a short in the appliance irrespective of the polarity in the plug. Sound good, but of course their technique wastes copper, and is therefore frequently ingnored and appliance wiring is often a lower rating than the breaker. Unsurprisingly France therefore has (or used to have) a much higher incidence of house fires from electrical causes than does the UK. For that reason earth leakage trips became mandatory in France long before they were in the UK.
Back to the original poster's issue! The marina will have a normal electrical installation which connects Neutral and Earth together at the mains inlet to the marina (probably what's known as a 'PME'). So zero Voltage difference between Earth and Neutral at this point. Then very a long cable run, with associated resistance, R, to the end of the pontoon. All the load currents added up, I, flow in both the Neutral and Live wires, generating a potential difference at the pontoon end of V = I x R, between Earth and Neutral. It's probably only 10V or so rms, but may very well have lots of short spikes of much greater Voltage due to the inductance of the long cable run. 10V is not enough to illuminate, even faintly, the reverse polarity neon, but the spikes could do so. The reverse polarity light is simply a neon bulb between Neutral and earth; not very sophisticated.
So, while of course you should do all manner of checks with Voltmeter and polarity sensing plugs, probably all is well and what you see unsurprising.
j
In the UK we have fused plugs. It's normal therefore to have a 5A fuse (for example) in a '13A plug' with =>5A flex between it and the appliance, the '13A plug' being plugged into a socket on a ring-main with as much as a 30A fuse or breaker. Should there be a short in the appliance between live and earth, it is the 5A fuse in the plug which which should blow. This will only happen if the current is flowing through the fuse, and since there is no fuse in the neutral side of the plug. wiring the polarity correctly is essential in the UK. - or used to be before we had RCCBs everywhere.
Why not in France? Several reasons, the most important of which is that since they don't have fused plugs they can't use ring-mains and they have to have a breaker or fuse per socket. Hence the breaker will blow if there's a short in the appliance irrespective of the polarity in the plug. Sound good, but of course their technique wastes copper, and is therefore frequently ingnored and appliance wiring is often a lower rating than the breaker. Unsurprisingly France therefore has (or used to have) a much higher incidence of house fires from electrical causes than does the UK. For that reason earth leakage trips became mandatory in France long before they were in the UK.
Back to the original poster's issue! The marina will have a normal electrical installation which connects Neutral and Earth together at the mains inlet to the marina (probably what's known as a 'PME'). So zero Voltage difference between Earth and Neutral at this point. Then very a long cable run, with associated resistance, R, to the end of the pontoon. All the load currents added up, I, flow in both the Neutral and Live wires, generating a potential difference at the pontoon end of V = I x R, between Earth and Neutral. It's probably only 10V or so rms, but may very well have lots of short spikes of much greater Voltage due to the inductance of the long cable run. 10V is not enough to illuminate, even faintly, the reverse polarity neon, but the spikes could do so. The reverse polarity light is simply a neon bulb between Neutral and earth; not very sophisticated.
So, while of course you should do all manner of checks with Voltmeter and polarity sensing plugs, probably all is well and what you see unsurprising.
j
