Typical EFLI

[JohnD]

This isn't something I usually do...

I am upgrading the Main and Supplementary Bonding at my mother's old house (old TNS), I picked up an old Robin Phase-Earth Loop Tester and thought it might be educational to measure the EFLI.

I tried it at my own house (modern TNC-S) and got 0.4 ohm on the Freezer circuit (which has no RCD).

I can't find my little book today but according to http://www.tlc-direct.co.uk/Book/5.3.4.htm the minimum for a B32 is 1.5 ohm, which seems fine. But what is typical?

Also, my meter (Model 4111 ) has no instructions and I can't find then on the Interwebby. It is not switchable. It has a socket on the top for a lead which connects to the same internal connection as the earth from a test plug, so I surmise it is intended for testing bonded pipework, but it could only do this if the earth at the test socket was disconnected. Is that right?

Any other things I should bear in mind or have misunderstood?

Ta

View media item 1689

 

[comms]

I can't find my little book today but according to http://www.tlc-direct.co.uk/Book/5.3.4.htm the minimum for a B32 is 1.5 ohm, which seems fine. But what is typical?

Thats the BS7671 max allowed, corrected its 1.20 ohms.
So yes if you have measure 0.4ohms as Zs & its the highest result obtained it does seem to be ok.

Cant help with the meter never used one of those, but glanford electronics do pdf's of instructions for all sorts of test meters.

 

[securespark]

EFLI readings can vary enormously. With my Alphatek, the No.10 setting (soft test) always gives a higher reading than the standard non-RCD No.7 test.

The lowest reading I've had was actually on TN-S, at 0.08, the highest (that wasn't off the scale) was 1936 Ohms, on TT supply.

But, from my 32 months experience using the Alphatek, the most common reading (taking into account all supply types) from my records is between 0.34 and 0.86.

 

[JohnD]

Ta!

It sounds from what you say that the TNS value will not be enormously different then? It's in suburban London, if that makes a difference. Clamped to lead sheath.

Any comments on my use of the meter?

 

[holmslaw]

..

 

[JohnD]

I thought that; but I had a squint inside and I can't see the probe socket switching.

But I will try it and see. (I have not got the original lead, but a substitute that seems to fit

Edited: You are absolutely right, that makes good sense.

The P-E confidence lamp also goes out when I plug in the probe lead. I'll go and prod some pipes

Edited again: I re-zeroed it, and got 0.3 ohms at the socket, and 0.32 at the cold water pipe under the sink (it is main-bonded in the garage but includes several compression joints). The P-E confidence lamp comes back on when the prodder is clipped to the pipe. Seems to be working as expected I don't know if the variance from 0.4 is my misreading the analogue scale, or a genuine change.

 

[securespark]

John, I'm a bit confused (easy for me!)

Are you testing the integrity of the MEB by using the pipe as a cpc?

If you want to check the continuity & effectiveness of MEB connections, do a resistance test end to end: you should have a maximum of 0.05 Ohms.

 

[JohnD]

I don't think so

I first wanted to test the EFLI out of interest, and then (with the pipe prodder) see if the water pipe was correctly main bonded.

In my house I know it is (and in my mind the good result off the pipe prodder confirmed it) , but in my mum's house I know it isn't and I want to see the difference after I've bonded it. Although the water pipe is bonded, the gas pipe isn't but will be picking up some sort of true earth as it's iron and comes in from underground.

Is it wrong to use this meter to verify bonding of the pipes against a handy socket? I also get 0.3 ohms against the boiler gas supply pipe (which is today not connected to the boiler, so not picking anything up from its electrical circuit CPC)

My high-street digital multimeter only resolves to 0.1 ohm

I have a better moving-coil one but I blew its non-standard internal fuse

p.s. I suppose, really, it's just inquisitive tinkering

 

[GaryMo]

Is it wrong to use this meter to verify bonding of the pipes?

You need to visually inspect the point of connection of main equipotential bonding conductors and unless you can see the whole run you would need to measure end to end resistance and ensure it's within 0.05ohms.
I've come across horror stories of MEB conductors being extended under floors etc with cable of much smaller CSA or even short pieces connected and pushed under the floor to give the appearance of being installed

 

[JohnD]

in the case of the Main Gas Bond I'm doing (not finished yet) I will have installed, and seen, the connections at each end, and the entire length of 10mm G&Y. I am particularly interested to see the difference between quality of bonding as it is now, and as it will be when I've finished. The total length will be between 15 and 20 metres (which might be why it was not done before) due to some solid floors and the awkward route.

I believe the meter I'm using puts two half-cycles of 20A through the P-E so would surely spot any badly-connected or high-resistance bits of bellwire?

 

[Spark123]

You don't use an efli tester to test the integrity of MEBs, testing as you describe will indicate the total sum of impedances for the supply phase conductor to the socket outlet, the MEB, the supply earth and the supply transformer. The proper way to test MEBs is using a wander lead back to the MET and a low resistance ohm meter, as Securespark says the max resistance should be 0.05 ohms.

 

[JohnD]

OK, thanks, will make up a 20m wander lead

I have some 2.5mm stranded single, will that do? I can crimp ends onto it.

 

[Spark123]

Don't see why not, remember to subtract the resistance of the wander lead from your result.

 

[333rocky333]

Untitled

• 333rocky333
• 19 Jun 2008
• 1

Untitled

• 333rocky333
• 19 Jun 2008
• 1

for future use do you want a probe?
If this robin lead fits, it is about 1.5 meters long , you can have it free.
It has a sort of 4mm prong inside the plug sleeve.
Let me know.

 

[JohnD]

thanks, that sounds ideal! I tried to message you but it looks like we have to set up the "friends" before I can do that. trying to puzzle out how to send you my address. I will pay P&P if you don't mind