Martindale EZ150 - worth buying?

[skotl]

I have one of the amazon/ebay £5 socket testers and I think I understand its capabilities and limitations.

Earlier this week, Eric mentioned this device; http://isswww.co.uk/martindale-ez15...dance-tester?gclid=CM301sDazsMCFRMatAodPxEAXQ

On the surface (no pun intended) I understand that this will do a much more complete measurement, especially around earth loop impedance.
I'd love to be able to afford / justify (I understand that these are different words!) a megger but I can't; As a DIYer, is it worth me spending £42 on the Martindale unit?

 

[deadshort]

Hi, the original price has been 'inflated' i bought mine for £40. If you want it for a quick check it's fine. I have had a non existent earth on a socket in a new build show up after tiler had been in ! so ideal for that speed check


Regards,

DS

 

[ericmark]

As an electrician when we make out our paperwork we are required to enter the loop impedance for the circuit. The plug in device first light is for earth loop impedance below 1.5Ω which for a TN system with a B32 MCB on a ring is above the range we are interested in. So as an electrician I have to have an earth loop impedance tester to get the readings required to fill in paperwork. So for the electrician the plug in tester is useless.

So we are not talking about following the regulations we are talking about by what degree we can brake the regulations and still keep the installation reasonably safe. At one 1/10 of the price of a proper loop impedance tester we can’t expect these units to replace the loop tester however they must be better than no test.

So what does a loop impedance test do? It in the case of the plug in tester uses 7mA (below what will trip a RCD) to test the earth which any bit of wet string is unlikely to transmit that amount of current. The neon in the cheap tester needs around 2mA to light. However the tester also measures the volt drop and 11.5 volt drop will reduce the current by just 0.35mA so the device measures this difference between load and no load and lights some lights to show the volt drop but these are labelled as 0-1.7, 1.7-5, 5-10, 10-100,100-200 and 200-500 ohm. In real terms only the first 4 are of interest. Most sockets on a TN system should show 0-1.7Ω on a B16 then could show 1.7-5Ω as we move to a TT system the 10-100 or 100-200Ω may be accepted clearly with RCD protection on the latter. But the main thing is where earth is not copper and one can get rust effecting the earth connection then these testers will likely highlight a fault but the simple tester will fail.

So are they worth buying? Well for a DIY guy with no proper loop tester and no RCD protection yes these testers will likely alert one of dangerous faults and could save some ones life. But with RCD protection then it becomes a little less important as likely faults will trip the RCD even when the earth is through a wet bit of string. So if your house is all RCD protected the very cheap without loop test is likely good enough. But without RCD’s then the loop test is really required. This of course assumes the RCD has been tested and does work.

For allied trades, plumbers for example he will not always know if the house is TN or TT or even if RCD is fitted or not so to test the socket before using it is a good heath and safety measure. He needs to show he took reasonable measures to ensure safety of himself and others and I would think these plug in testers show he was doing just that.

There has been some criticism on the use of plug in testers. The Electrical Safety Council best practice guide 8 it says how it can’t detect a reversal of line and PEN conductor with a TN-C-S system. Personally I can’t see how anything a DIY guy would do could cause such a reversal?

But as electricians we don’t use these plug in devices so we can only comment on what the label says. I have never used one and I suspect neither will any on the real electricians. So the only real report will be DIY’er to DIY’er and we then have no idea as to if used correctly.

I will watch for replies.

 

[ericmark]

Hi, the original price has been 'inflated' i bought mine for £40. If you want it for a quick check it's fine. I have had a non existent earth on a socket in a new build show up after tiler had been in ! so ideal for that speed check


Regards,

DS

Well that's me shot down in flames did not expect an electrician to use one. But question is would the very cheap plug in tester have also highlighted that fault? I will admit I did consider one but it's just as easy to plug in the earth loop impedance tester as the little LED/Neon device so could not see the point.

I was surprised when I came to look as earth loop impedance testers. The current used varies from 14mA to 24A on just a few examples I looked at. The High current testers will clearly find faults like rust on bolts but the low current models one has to question what faults they would highlight? Clearly the 14mA is so they will not trip a RCD. Some it seems now have selectable switches high and low current.

 

[OwainDIYer]

There has been some criticism on the use of plug in testers. The Electrical Safety Council best practice guide 8 it says how it can’t detect a reversal of line and PEN conductor with a TN-C-S system. Personally I can’t see how anything a DIY guy would do could cause such a reversal?

Some designs of sockets etc don't have the earth terminal open on the earth strap between the faceplate front holes, but recessed into the socket body like the L and N, so it's not impossible that the N and E could be transposed when wiring up the socket through mis-identifying the terminals.

Not terribly likely perhaps, but not impossible.

 

[ericmark]

There has been some criticism on the use of plug in testers. The Electrical Safety Council best practice guide 8 it says how it can’t detect a reversal of line and PEN conductor with a TN-C-S system. Personally I can’t see how anything a DIY guy would do could cause such a reversal?

Some designs of sockets etc don't have the earth terminal open on the earth strap between the faceplate front holes, but recessed into the socket body like the L and N, so it's not impossible that the N and E could be transposed when wiring up the socket through mis-identifying the terminals.

Not terribly likely perhaps, but not impossible.

But if you used an earth loop impedance tester would that find the fault? Clearly any RCD would trip. However it was reversal of line and PEN conductors it talks about and this is while it is still TN-C not after it becomes TN-C-S so beyond the remit of most domestic electricians never mind the DIY guy so why worry?

 

[skotl]

Thanks guys. Think I'll hold on to my cheapie tester, then, and spend my £42 on something else

 

[ericmark]

Since you have RCD protection yes likely what you have is good enough. But if you did not have the RCD it would be different answer.