Do you have to do loop tests on all circuits

[ADS]

[quote name='Andy

 

[tom1]

They ask for Zs though - if they wanted Ze + R1 + R2, they'd ask for it

they do ask for zs but without getting books out i am sure i have read that it is accepterble to calculate zs, on the nic eic inspecting and testing dvd i am sure it says to calculate if you dont have non trip on your tester.

 

[ADS]

they do ask for zs but without getting books out i am sure i have read that it is accepterble to calculate zs, on the nic eic inspecting and testing dvd i am sure it says to calculate if you dont have non trip on your tester.

Precisely - if you have a good reason not to test.

It doesn't say just sit in the van and work them all out if you can't be bothered measuring.

I mean, why calculate any way?

It's primary school maths for a start, both Ze and R1 + R2 are recorded on the Certs - any monkey can look at your test certs and add the two figures together in about 5 seconds;\

 

[sparkytim]

I am sorry to repeat myself but YOU HAVE MEASURED IT.

Calculation means what is done at DESIGN stage i.e. taking Ze given and CALCULATING Zs by working out R1 + R2 for the circuit by length x r/mtr.

If you have MEASURED the Ze and MEASURED the r1+r2 then you have a MEASURED Zs.

 

[Megaohm7]

TBH the only people doing zs testing would be competent electricians who know how to handle a live open CU or switch and personally i always like to do zs tests rather than calculate it where practical.

When I done my 303 C&G 2330 We were told to measure the Zs at the lighting circuit by placing the probes on the terminals in the rose itself . I asked why a calculation was not sufficient for recording the result and my examiner said he wanted to see me measure the Zs has it was to do with my competence with safely working live . Fair point I suppose .

 

[NozSpark]

I didn't think you could get GS38 compliant probes into a rose????

 

[Megaohm7]

I didn't think you could get GS38 compliant probes into a rose????

We had to use GS38 compliant leads/probes and managed to get on to the terminal were the conductor enters .

 

[NozSpark]

I thought that'd be the only place you could get the probes in!

 

[ADS]

I am sorry to repeat myself but YOU HAVE MEASURED IT.Calculation means what is done at DESIGN stage i.e. taking Ze given and CALCULATING Zs by working out R1 + R2 for the circuit by length x r/mtr.

If you have MEASURED the Ze and MEASURED the r1+r2 then you have a MEASURED Zs.

You haven't measured Zs.

Zs is an AC impedance measurement on a live circuit.

You have measured Ze - external loop impedance,

you have measured R1 + R2 - conductor resistance,

and the two added together give you an estimated value of what Zs will be -

but you haven't measured Zs

.

.

.

Makes me wonder why Megger and co. bother making Earth Loop Impedance Testers when everyone just sits in their van and adds it up

 

[Megaohm7]

I thought that'd be the only place you could get the probes in!

It is easier to do a calculation in this case of course and probably safer if the rose is fairly high up as it is tricky although not impossible to get your probes securely on the terminals . Is a calculation the accepted way to record Zs on a lighting circuit due to the awkward nature of the terminals .

 

[NozSpark]

It's not a calculation....

It's a measurement... you measure Ze and you measure (R1+R2)

and it is an acceptable way to get your "max measured Zs"

 

[Zeespark]

Re this : why not use the kewtech adaptors? ok they cost money initially, but are so much better when working at heights.

Andy Guinness

 

[tom1]

It's not a calculation....It's a measurement... you measure Ze and you measure (R1+R2)

and it is an acceptable way to get your "max measured Zs"

i tend to do live test 9 out of 10 times, but i do think the above way is acceptable, can anyone give a good reason why measuring r1 r2 and ze is no good

 

[ADS]

It is easier to do a calculation in this case of course and probably safer if the rose is fairly high up as it is tricky although not impossible to get your probes securely on the terminals . Is a calculation the accepted way to record Zs on a lighting circuit due to the awkward nature of the terminals .

Yes, regulation 612.9 states:

'Where protective measures are used which require a knowledge of earth fault loop impedance, the relevant impedances shall be measured, or determined by an alternative method.'

So it's fine to calculate

 

[ADS]

i tend to do live test 9 out of 10 times, but i do think the above way is acceptable, can anyone give a good reason why measuring r1 r2 and ze is no good

All been mentioned in previous posts

 

[ianmacd]

i tend to do live test 9 out of 10 times, but i do think the above way is acceptable, can anyone give a good reason why measuring r1 r2 and ze is no good

Measure Zdb and add that and not Ze to R1+R2 to get Zs.

 

[Megaohm7]

It's not a calculation....It's a measurement... you measure Ze and you measure (R1+R2)

and it is an acceptable way to get your "max measured Zs"

You measure Ze and you measure (R1 + R2) and you add the two figures together to get your Zs for the circuit ( thats why I said calculation ) :Blushing

 

[Buildall]

It is easier to do a calculation in this case of course and probably safer if the rose is fairly high up as it is tricky although not impossible to get your probes securely on the terminals . Is a calculation the accepted way to record Zs on a lighting circuit due to the awkward nature of the terminals .

This was more where I was going by starting this thread. These days with H&S being the way it is. You are up a pair of steps trying to hold two probes in place on to live terminals with one hand and pushing the test button with the other. ray

 

[ianmacd]

Get a better meter/probe or accessories then . You should not need to hold any probes.

 

[m4tty]

This was more where I was going by starting this thread. These days with H&S being the way it is. You are up a pair of steps trying to hold two probes in place on to live terminals with one hand and pushing the test button with the other. ray

If you got a Megger MFT it automatically starts the test when the probes are placed on correct terminals so need need for a 3rd hand