Testing with 3 probe instrument help needed

[bleach]

Hi,

I am fairly new to all this so please bare with me. I have been up till now using a 2 probe megger. I have now purchased a 3 probe Kewtech KT62. Can anyone please inform me what test use 3 leads and when I join the 3 to become 2 etc. It does not say in the Kewtech manual! (specifically for PEFC?)

Help all all tests much appreciated,

 

[tuckermot]

Hi Bleach

the 3 leads are used on ze ( external earth) zs ( consumers earth ) pfc( prospective fault current) and psc ( prospective short circuit ) the 2 leads are used for ( continuity ) and IR ( insulation resistance ) I use a robin and i believe they work the same . When doing psc some meters you have to join the black and green leads together and conect to neutral of the ccu isolator supply side and red to line of the ccu isolator supply side .my leads are old colours so i assume yours is brown blue and green ??

Richard

 

[bleach]

Thanks Richard! am I right in understanding that all leads are seperate for those tests and connected to the corresponding conductors with the exception of doing PSC test because I join the green lead on to the blue and then test this on the neutral(supply side) and then the brown probe to line(supply side).

Thanks again!!

 

[amberleaf]

For PeFC connect the 3 leads to Line, Neutral and Earth. For PSSC connect the Red to line and the black and green to neutral.

Why don't the manufacturers instructions show this ? Email them am Sure they will Help You . CD ?? Book
Am only working of my Megger 1552. ◄

It’s a Start ? Amber . Good Luck . am Sure that someone will come Along to Help You .

 

[keniff]

Normally the 3 leads are if you are using a "no trip" test for zs or PFC on the output side of an rcd on a circuit, red to live, black to neutral and green to earth, otherwise its just red and green on normal setting, it's just so the rcd doesn't trip when doing a zs, I use megger 1553

 

[tuckermot]

HI
thats correct you only join the leads on psc when your at the board or on the circuit the other 3 lead tests are done as you said . I assume your testing at ccu clip to earth bar ,clip to neutral bar probe line supply side of isolator in ccu

 

[tuckermot]

Hi bleach

3 leads also used on testing rcd,s again clip to earth ,clip to neutral clip to line

 

[bleach]

Thanks for all replies!

Yes Tuckermot my leads are new colours and yes clipping to earth bar, neutral bar at the board etc. (when you say 'at the circuit', can this test be done elsewhere then?).

Just one last question: I have been taught to only measure zs at socket outlets and to calculateall others (lighting, cooker, showers etc) due to safety reasons. Is this best practce or do many of you test for zs other than in sockets?

 

[keniff]

When I do installs I test zs on ALL circuits, the electricity at work regs state not to work live unless reason to do so, live testing is a pretty good reason, it's easy to test lights etc if u have a neutral at the switch, on my Certs it states max MEASURED zs, hope this helps

 

[tuckermot]

working live grey( area ) if possible work dead using your rule zs = ze+ ( r1+r2 ) yes some times you have to do zs live when i am tested i do do live zs but it is acceptable to do zs via calculation not forgeting to multiply by 0.8 ( only on measured reading only ) my 2391 testing involved zs via plug in then zs via calculation for other circuits. why put yourself at risk when you dont have to

 

[bleach]

Oh ok I can see that measured values are beneficial. So with my 3 lead instrument at say a light switch: brown probe-L. blue probe-N, green clip-cpc. Getting fiddly eh with the 3!!

 

[bleach]

Think I will stick to calcs for now to play safe

 

[keniff]

Yeah but only if the switch is fed, otherwise u don't have a neutral. If ur more comfortable doing the calcs ur prob best stickin to it

 

[keniff]

Tucker mot, what are u multiplying by 0.8?

 

[tuckermot]

when you use you meter to mesure zs ( mesured reading ) you multiply the reading by 0.8 to allow for ambient tempratures of the cables hence the zs will be higher !!! you then check in your regs book against the zs reading ( max ) for that paticular protective device ( mcb/3036 bs88 ect ect

 

[keniff]

Oh right, I have never heard of that, I know that all the max zs figures in the reg book need to be multiplied by 0.8, for example if you have a max zs in the regs of 1.44 you multiply that by 0.8 (1.15) and what ever ur measured/calculated zs is should be below this, if ur working from on site guide they have already corrected the figures for you

 

[tuckermot]

only apply factor rule 0.8 to measured zs readings unless as you stated you use tables in osg as you say they have had the ambient temprature normaly 70 all ready added

 

[keniff]

Ah right, so if u measure ur zs do u multiply the given max from the book, and multiply the reading u have by 0.8? I never was taught that one, learn something new everyday!

 

[tuckermot]

multiply from the book only by using 0.8 it drops the maximum zs allowed !!! making it harder to achieve making the circuit safer hence a lower resistance a higher psc and a quicker disconnection time of the protective device

 

[pushrod]

when you use you meter to mesure zs ( mesured reading ) you multiply the reading by 0.8 to allow for ambient tempratures of the cables hence the zs will be higher !!! you then check in your regs book against the zs reading ( max ) for that paticular protective device ( mcb/3036 bs88 ect ect

Think you are getting this wrong (even though it is late at night lol) As keith said the usual way is to correct the BRB figure with the rule of thumb by multiplying by 0.8. If you want to do it the other way around, as you are suggesting, then you would want to increase the size of the measured value which would mean dividing by 0.8