Testing with 3 probe instrument help needed

[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

 

[malcolmsanford]

If you measure a Zs their is a good chance that the cable will be of sufficinet temp and the ambient unless it's in a very cold enviroment will be also not be an issue so the 80% rule is not that relevant really, but I would not stop anyone doing it though as your erring on the side of caution, it would just mean if you have a close Zs value you may fail it. It's as always the testers judgement call.

Also you do multiply the max Zs by 0.8 out of the BRB and not the measured value. As it is a measured value your Zs will most likely be lower than calculated as you will have those lovely bonding and parallel paths to help your reading.

I would though like to comment that there is a big difference between live testing and live working. We have covered this in other threads and though the NICEIC advise that Zs should be done by calculation on circuits other than socket outlets, there is nothing stopping a competant electrician doing live tests. I'm sorry to say if someone feels unsure about doing live tests then perhaps they should think again about doing testing.

 

[tonys]

You couldn't make it up lol

 

[Lucas123]

what about when you use a fluke 1653 where you cant join the leads together to make a 2 probe tester bloody hard trying to get 3 probes on a cooker outlet or ceiling rose i tell thee !!!!

 

[keniff]

i always 3 lead on my megger, (when you need the no trip or rcd test) never had a problem with it? malcolm, i was told at college that dis assembling an accessory like light or cooker outlet to test was working live? ill check the threads thanks for pointing that out

 

[keniff]

with elecsa, the test sheets state MEASURED maximum earth fault loop so i have never calculated for my test sheets. never seen an nic sheet be quicker for me to calc though!

 

[malcolmsanford]

When you do proper isolation procedures you are not working live. If you wish to keep the circuit energised and then remove the front of a cooker CCU or dismantling the rose or light then you can be deemed working live. If on the other hand you isolate the supply and prove it is dead attach your leads, then energise the supply you are doing live testing, not live working.

The EAWR does not preclude you from working live, but in the case of testing you should not be doing live working as you should be carrying out safe isolation. Now in the real world of electrics it is up to the tester being the competant person to take a risk assement to see if you want to remove that CCU cover "live" and all that entails. Personally I would isolate the supply, remove the cover and when I wanted to test renergise it. Now wether all electricians do this is up to them, all I can say is that if you don't isolate sooner or later taking that cover off "live" is going to come back to bite you.

 

[pushrod]

what about when you use a fluke 1653 where you cant join the leads together to make a 2 probe tester bloody hard trying to get 3 probes on a cooker outlet or ceiling rose i tell thee !!!!

THESE make it much easier when doing lighting - still have to loosen the rose mind.


Re Zs readings on lighting and dismantling - the nic books that i have read actually say de-energise undo your ceiling rose, attach leads and then re- energise. I reckon you are at more risk from running up and down the the stairs and your step ladder than working live in this case

all I can say is that if you don't isolate sooner or later taking that cover off "live" is going to come back to bite you

.

And yes you are dead right - couple of months ago i took a metal light switch off and out popped the live straight onto the metal - very embarrassing when all the lights go off!

 

[ansteyelectrics]

When the isolator is in the off position you cannot pick up the neutral from the bus bar, both the earth and neutral probes dont fit into the live side of the isolator so how do you make contact?...do you need to turn on the main switch to get the test completed?...new here looking for the same kinda answers?

 

[pushrod]

When the isolator is in the off position you cannot pick up the neutral from the bus bar, both the earth and neutral probes dont fit into the live side of the isolator so how do you make contact?...do you need to turn on the main switch to get the test completed?...new here looking for the same kinda answers?

Hi Ansteyelectrics and welcome - see it's your first post. TBH if you are talking about an isolator fitted by a DNO then you can't usually get to the meter side as there is normally a seal. So you need whatever needs to be live for your test, to be live - and use crocs or probes to GS38

 

[ansteyelectrics]

Problem solved, just passed my NICEIC assessment........YIPEEEEEEEEEEEE...........LOL