Shorepower - does this Socket Tester give me enough protection?

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richardm47

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I've read and understand the warnings about the dangers if the pontoon shorepower is not correctly installed. Reversed polarity, no proper earth, French marinas etc. So I got this £6 socket tester from CPC Farnell to test for faults each time a new shorepower is connected: http://cpc.farnell.com/tenma/ten01024/socket-tester/dp/IN05267?in_merckFeatured Products. But .... I've just noticed that it doesn't detect all possible faults. Small print on the the tester says "This unit will not detect Earth Neutral reverse."

To detect Earth Neutral reverse, CPC says I'll need to upgrade to this better tester: http://cpc.farnell.com/martindale-electric/ez150/socket-tester-earth-loop/dp/IN04254. Much more expensive at £50.

So I thought I'd enquire here first. Is the failure to detect Earth Neutral reverse relevant to us boat owners? What does the team think?
 
I only have a minimal knowledge of electrickery, but if you were to take a fairly simple piece of machinery, say an old mains powered electric drill with a metal body and a three-core lead, reverse the Earth and Neutral wires in the plug and then plug it into the mains, I imagine you would be in for a nasty shock, especially in the context of a boat. In your place I would shell out for the higher spec tester. It could save your life.
 
richardm47 said:
I've read and understand the warnings about the dangers if the pontoon shorepower is not correctly installed. Reversed polarity, no proper earth, French marinas etc. So I got this £6 socket tester from CPC Farnell to test for faults each time a new shorepower is connected: http://cpc.farnell.com/tenma/ten01024/socket-tester/dp/IN05267?in_merckFeatured Products. But .... I've just noticed that it doesn't detect all possible faults. Small print on the the tester says "This unit will not detect Earth Neutral reverse."

To detect Earth Neutral reverse, CPC says I'll need to upgrade to this better tester: http://cpc.farnell.com/martindale-electric/ez150/socket-tester-earth-loop/dp/IN04254. Much more expensive at £50.

So I thought I'd enquire here first. Is the failure to detect Earth Neutral reverse relevant to us boat owners? What does the team think?
Click to expand...

If there is an RCD in the circuit somewhere and there should be if not on your boat but on the shore power point then an earth neutral fault will trip the RCD and cut off the supply. If not then everything will work normally except that all the metal work would be live. I've seen 13A sockets wired so that earth and neutral were swapped and no one was the wiser until they upgraded their consumer unit to one with RCD protection. On a lot of house wiring the neutral and earth wires are combined up to the meter and split off there.
 
I'm guessing here, but I imagine a N-E reverse is pretty difficult to detect with such a device; many earth feeds are connected to the neutral locally.

Note that the rather clever EZ150 is marginally cheaper on Amazon: http://amzn.to/1ws98f0, I've just ordered one; an earth loop test is a very good idea. Will probably have to bypass the GI to do it properly.
 
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richardm47 said:
........Small print on the the tester says "This unit will not detect Earth Neutral reverse."

To detect Earth Neutral reverse, CPC says I'll need to upgrade to this better tester: http://cpc.farnell.com/martindale-electric/ez150/socket-tester-earth-loop/dp/IN04254. Much more expensive at £50.

So I thought I'd enquire here first. Is the failure to detect Earth Neutral reverse relevant to us boat owners? What does the team think?
Click to expand...

The Farnell product recommended by them is referenced here:
http://www.pat-training.co.uk/socket_testers.htm
but it also states Like all other indicators this unit cannot detect common earth and neutral or earth neutral reversal
 
Spirit of Glenans said:
I only have a minimal knowledge of electrickery, but if you were to take a fairly simple piece of machinery, say an old mains powered electric drill with a metal body and a three-core lead, reverse the Earth and Neutral wires in the plug and then plug it into the mains, I imagine you would be in for a nasty shock, especially in the context of a boat. In your place I would shell out for the higher spec tester. It could save your life.
Click to expand...

No you will probably not notice ....... but if there is an RCD in the supply to the drill it will trip as soon as you press the trigger.

lumphammer said:
If there is an RCD in the circuit somewhere and there should be if not on your boat but on the shore power point then an earth neutral fault will trip the RCD and cut off the supply. If not then everything will work normally except that all the metal work would be live. I've seen 13A sockets wired so that earth and neutral were swapped and no one was the wiser until they upgraded their consumer unit to one with RCD protection. On a lot of house wiring the neutral and earth wires are combined up to the meter and split off there.
Click to expand...

The Op is talking about reversal of the neutral and earth in the supply, not about a neutral to earth fault.

ITYWF that a neutral to earth fault on board will almost certainly trip the RCD in the supply.

Also ITYWF that a reversal of the neutral and earth connections in the supply will trip the RCD upstream of the reversal as soon as any load is applied.


However I think this question should be answered by someone fully qualified to do so. Minimal knowledge can be a dangerous thing !


Come in David2452

.
 
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I'm confused about some of the replies so far. If the earth and neutral are swapped and the earth and neutral are connected together at the consumer unit (or equivalent), then I doubt you see any difference in the normal operation of the device. If a metal casing is connected to the earth and becomes connect to the neutral, because of the faulty wiring, then in normal operation the case should not be live, because the neutral is effectively earthed. However, the RCD should trip because the residual current will be non zero.

If No RCD is fitted and a fault occurs, then it's a different story.
 
lumphammer said:
If [there is no RCD] then everything will work normally except that all the metal work would be live. I've seen 13A sockets wired so that earth and neutral were swapped and no one was the wiser until they upgraded their consumer unit to one with RCD protection.
Click to expand...

These two sentences would appear to contradict each other, unless people somehow didn't notice that their metal appliances were live.

Pete
 
prv said:
These two sentences would appear to contradict each other, unless people somehow didn't notice that their metal appliances were live.

Pete
Click to expand...

I think it depends what people mean by "live". You (I think) are interpreting it to mean "at full mains voltage", others may mean "at some (perhaps small) voltage with respect to earth. The former would deliver a nasty shock, the latter a bit of a tingle.
 
Slight thread drift, but be aware that if the tester is using an LED albeit with a loading resistor it will provide a galvanic current bypass path around a GI. Having fitted a GI it wasn't reducing anode wear, then I noticed a faint glow at night from the Earth - Neutral LED I had installed at the inboard switch panel. I should have used a Neon indicator.

This made the GI completely useless. I have now removd the LED and use a plug in tester to check the presence of earth, live and neutral, and in particular that the live is correct. I don't leave it plugged in.
 
For a simple live neutral reverse the cheapo ones are fine but the Martindale one will give far better information, however to get the full benefit you must either throw the "ashore" switch or install the "ashore" link if you have an isolation transformer or if you have a galvanic isolator you should install a temporary bridge lead across the PE connections.
 
Interesting comments, thank you all.

One new piece of info. This morning I had a good look at the picture of the expensive £50 tester on its makers website (Martindale EZ150). And I found that the same disclaimer is there too, in small writing, on the front of the product. "Does not detect earth neutral reversal." Thus it seems that CPCs advice to me was wrong! And Steve Clayton was right.

So ... I think my conclusions are:
- an "earth neutral reversal" fault is not that important to us boaters
- the cheaper £6 tester will help protect me from important faults such as "live earth reversal"
- the £50 tester would additionally detect a weak earth connection fault

Anyone like to add to that?
 
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nigelmercier said:
Why would that be better?

You are meant to unplug these anyway.
Click to expand...

I'm not sure that I have completely understood superheat's post but presumably he is saying that there would not have been a high enough voltage present to turn a neon on so there would not have been a current flow at all.

There's an obvious temptation to provide an extra socket and leave one of these testers on all the time.

The snag then, or even with a couple of simple indicators be they leds or neons, is that the current flowing to earth through the "polarity correct" indicator will put the GI in to a conducting state rendering it completely useless for blocking the currents in the earth connection responsible for galvanic corrosion.
 
VicS said:
The snag then, or even with a couple of simple indicators be they leds or neons, is that the current flowing to earth through the "polarity correct" indicator will put the GI in to a conducting state rendering it completely useless for blocking the currents in the earth connection responsible for galvanic corrosion.
Click to expand...

Quite so, which is why I unplug mine after testing. I did however consider building one into my shore-power lead, where I already have a single neon (which is really handy). I also have one built into a 16A plug.
 
I think and that is always dangerous the situation is that in the way our normal supplies operate we use the potential between one phase and earth to get our 220 vac supply. Thus for practical purposes neutral and earth are the same. On the other hand if we are looking at a 415 volt installation the supply is derived between two of the phases so the 'neutral' is very definitely not connected to the earth. Of course not every one does it this way, some countries get their 220 or 110 supply across the phases so in these countries earth and neutral are not synonymous.

I am not certain that in all installations the rcd will trip with an earth/neutral reversal because the device simply compares live and return and trip on imbalance, and as the earth sompletes the return anyway other than a reversal in the rcd wiring
 
maxi77 said:
I am not certain that in all installations the rcd will trip with an earth/neutral reversal because the device simply compares live and return and trip on imbalance, and as the earth sompletes the return anyway other than a reversal in the rcd wiring
Click to expand...

It depends on where the reversal is in relation to the RCD. If the reversal is downstream of the RCD the RCD will trip when any load is applied as the return current will be flowing in the earth conductor at that point instead of the neutral .

So your onboard RCD ( or perhaps the pontoon RCD) will trip if there is a reversal in your onboard wiring or equipment.
The pontoon RCD should trip if the reversal is in the shorepower lead or the cabinet socket.
 
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