R1+R2 - two way lighting - 2.7 ohms, can i get your opinions please?

[SJD]

Having re-read your original post, if I understand correctly, the 2.7 Ohm R1+R2 is just for 1 light in the garage, with 2 way switching (switches at front and back of garage, I assume). I which case, it appears somewhat high. You know what cable size you have used, and can estimate the length to the nearest metre, including the additional 2-way switching length - you can use table F6 in the On Site Guide to estimate the R1+R2 (last column of table, Volts Drop, is in fact resistance in milliOhm/metre).

If this is for an assessment, I'd be surprised if the assessor did not query a Ze of 145 Ohm, I wouldn't be happy with a value that high. You could put in a decent earth rod (not a 1 metre long 3/8 twig, but something more substantial and longer). Or you could take note of some of the other posts suggesting you do this differently.

 

[TJ Anderson]

TJ, Even though this is a 2 way switch, so will measure the 3 core cable aswell.... ?

Test all to verify and record highest value which should be at the furthest point of the circuit. Regarding TT or extending PME, either is compliant, is it up to you. Do you have anything extraneous in your garage that would require bonding?

 

[telectrix]

failing which, plumbing might be an alternative career path.

 

[srl-8]

yes, measurement at garage

 

[Simonslimline]

Check the terminations in-case a screw has been tightened on to insulation possibly?

 

[telectrix]

maybe a silly question, but did you null your leads before measuring?

 

[TJ Anderson]

That's pretty much exactly what I'm saying mate, if the armour isn't connected then it's not that big a deal to put that right.

What does not comply with what he has done? Nothing wrong with TT. if he wants to. The only issue it seems is a high R1 +R2 on garage lighting circuit.

 

[Plonker 3]

For someone who is about tomstart doing work on peoples homes this is quite scary that the OP doesnt even know what to do or work out what is wrong here, even with all the advice given.

Still I suppose the scams wont mind ££££££££££££££££££

 

[srl-8]

SDJ - You have understood correctly, I will test the ze at the garage board using the swa as the earth tomorrow and see what result I get. I presume I will be looking for a sub- 0.35 ohms being a tnc-s system.

As for the high r1+r2.. ill have to go through It again tomorrow.

 

[srl-8]

maybe a silly question, but did you null your leads before measuring?

yes, nulls the leads

 

[Plonker 3]

SDJ - You have understood correctly, I will test the ze at the garage board using the swa as the earth tomorrow and see what result I get. I presume I will be looking for a sub- 0.35 ohms being a tnc-s system.

As for the high r1+r2.. ill have to go through It again tomorrow.

please go and have a read of GN3 that will explain testing and the procedures.

Youmdo know there is only one place to take a Ze reading dont you?

 

[Simonslimline]

SDJ - You have understood correctly, I will test the ze at the garage board using the swa as the earth tomorrow and see what result I get. I presume I will be looking for a sub- 0.35 ohms being a tnc-s system.

As for the high r1+r2.. ill have to go through It again tomorrow.

The swa should be earthed at the supply side even if you are not using it as the earth for the garage db. Why would the Zdb need to be below 0.35? It is not the Ze of the installation.

 

[srl-8]

TJ Anderson - This was what I thought, but somehow my 145 ohms reading on a TT (under 200 is considered stable) has got everyone suggesting not to use a rod..?

 

[TJ Anderson]

SDJ - You have understood correctly, I will test the ze at the garage board using the swa as the earth tomorrow and see what result I get. I presume I will be looking for a sub- 0.35 ohms being a tnc-s system.

As for the high r1+r2.. ill have to go through It again tomorrow.

No offence, but you are going to have to really brush up for your assessment, they wont hold your hand, they will expect you to know. Understand what Ze, Zdb & Zs mean. Also when you test,you need to have expected values, otherwise you are just guessing. Like Dillb said read GN3, and then read it again, it is all in there mate.

 

[srl-8]

The swa should be earthed at the supply side even if you are not using it as the earth for the garage db. Why would the Zdb need to be below 0.35? It is not the Ze of the installation.

Simonslimline - Sorry, this is my first garage (outbuilding), so ZE is at origin at main House supply. What is the equivalent at the garage end..