Excuse me if this been answered million times but doing some testing at min and been advised by supervisor to join L and N and test these to earth for some lighting circuits and other circuits that have appliances connected. I know there is some logic in this but I don't fully see it. Even if these are joined am I right to still think that any live to neutral short will not be picked up. I thought point on joining these was to detect neutral shorts but when I join these and test to earth and create a short delibrately to see if it is picked up it isn't. So then what is the point of this test anyway? Thanks
Joining L & N on IR test
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phil d
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joining live and neutral is common when testing for a fault to earth or when fitting an rcd, linking live and neutral prevents sending 500v into any equipment that may be connected. it will show up a live or neutral to earth short, but obviously it won't pick up a live to neutral short.
as above, no chance of 500v L-N and blowing something up
phil d
Well-known member
Or chasing that fault that turns out to be a neon on a hidden fcu, lets be honest we've all done it.lol
Ok cheers fellas just thought I needed to hundred percent check that. It's new install flats in testing and seems like only option I have is to put LIM in live to neutral test on quite a few circuits. I have test lighting circuit with dimmer transformers and bulbs in. A fan circuit and ring with heater spur off it for instance. New installs as far as I know should not have many tests recorded as limited but supervisor seems happy enough to
Doc Hudson
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As a point on terminology, an IR test is not specifically looking for shorts. 0.00Meg Ohms is not a short circuit value. Remember 1MegOhm is 1000000 ohms. so 9,999ohms (nearly 10k) would show as 0.00MegOhms with an IR test., 9000+ ohms is far from being considered a short. IR tests are looking for breakdown of cable insulation between conductors that could be a relatively high resistance that would not normally trip an MCB. But with 230v flowing with a live circuit could become potentially hazardous.
I would have expected any short circuit to be identified while checking CPC continuity and polarity of conductors with your low resistance ohm meter, prior to doing your IR tests. Without verifying CPC continuity and polarity to each accessory point you would not know that the IR test is actually testing the full run of the circuit. Basically any actually short circuits would probably mess up your R1+R2 readings, but a higher resistance path due to damaged insulation would not necessarily be picked up until the IR tests. The catch 22 being you typically need to connect your accessories to the circuit to test the full continuity of the circuit. But with these accessories connected, they can then effect your readings or your testing could damage the accessories. There is an ever increasing number of items that can be a pain in the neck when it comes to getting your test readings done; USB sockets, Integrated LED light fittings, Fluorescent fittings, PIR sensors, Extractor fan timer circuits, Neon indicators etc
Doc H.
DaveS,
Welcome to the forum.
Just remeber, that LIM is not a valid entry on an EIC, only an EICR.
So if this is new work and initial verification, then you must have all of the details of the installation, thus you must know all of the vulnerabilities in the installation, and, thus know what can be tested.
There is a requirement under BS7671 to record the insulation resistance between live conductors.
Neutral is a live conductor.
Welcome to the forum.
Just remeber, that LIM is not a valid entry on an EIC, only an EICR.
So if this is new work and initial verification, then you must have all of the details of the installation, thus you must know all of the vulnerabilities in the installation, and, thus know what can be tested.
There is a requirement under BS7671 to record the insulation resistance between live conductors.
Neutral is a live conductor.
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612.3.3
Where the circuit includes electronic devices which are likely to influence the results or be damaged, only measurement between the live conductors connected together and the earthing arrangement shall be made.
Where the circuit includes electronic devices which are likely to influence the results or be damaged, only measurement between the live conductors connected together and the earthing arrangement shall be made.
and the note below that states it may be required to disconnect what may be damaged...
Do they not have maths in school anymore??
john..
john..
2+2 = 5, according to politicians, that hasn't changed :^O
phil d
Well-known member
Ah, that's down to elf and safety, you could get terrible eyestrain trying to read those figures in that little orange book, remember the one with the algebraic equations, tangents and cosines in, it was about 3 inches wide and 5 inches long? I hated Algebra, never understood it, they said you'd need it one day I never have, anyway it's so silly, If A=2 and B =3 then 2a x 3b+c = 40 what is the value of C ? Who cares, I certainly didn't!
Neither did I Phil ...and calculators were in the distant future . Even Dan Dare didn't have one .
You have now reminded me of the dread of the Maths lesson which began at primary school .
Aged about 8. Every day without fail , the teacher would ask in turns , (in pre-metric money remember) such things as how many tuppenny three farthing buns can I buy for £1 -17shillings & fourpence halfpenny ? You boy ,... come on !!! come on !!!! Right!!! stand out front to be ridiculed with the other useless idiots.
Or even better at age 11 , the cane for singing off key . " You boy !!! You're singing out of tune " "I know Miss, I can't sing" Obviously after one stroke of the cane ...there I was ..just like Pavarotti .
"If you think its tough here boy ..wait till you move up to the big school ....you've 'ad it easy 'ere you 'orrible little erks ....I wouldn't like to be in your shoes in the new term you won't know whats 'it you , you 'orrible lot !!!!
Nothing like some fatherly encouragement as you leave primary school is there. ?
You have now reminded me of the dread of the Maths lesson which began at primary school .
Aged about 8. Every day without fail , the teacher would ask in turns , (in pre-metric money remember) such things as how many tuppenny three farthing buns can I buy for £1 -17shillings & fourpence halfpenny ? You boy ,... come on !!! come on !!!! Right!!! stand out front to be ridiculed with the other useless idiots.
Or even better at age 11 , the cane for singing off key . " You boy !!! You're singing out of tune " "I know Miss, I can't sing" Obviously after one stroke of the cane ...there I was ..just like Pavarotti .
"If you think its tough here boy ..wait till you move up to the big school ....you've 'ad it easy 'ere you 'orrible little erks ....I wouldn't like to be in your shoes in the new term you won't know whats 'it you , you 'orrible lot !!!!
Nothing like some fatherly encouragement as you leave primary school is there. ?
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I gross, 1bakers dozen and half a dozen!
163 and a few crumbs
sorry, but it had to be done
phil d
Well-known member
Oh yes happy days, we didn't have much but the schools made up for it with the beatings, I shouldn't laugh because that's partly where my PTSD comes from, funny how hurling small children into brick walls and beating them with the edge of wooden rulers isn't considered acceptable these days isn't it.
Still I had to laugh when my mate told me about his new school, his family came from Holland and his father thought it important that his son received a decent education in his new country. He drove around the area but couldn't see anything that he liked until finally he spotted the perfect school, it had a number of separate buildings, so it was obviously not going to be overcrowded, lots of playing fields and a nice secure fence to keep trespassers out, and best of all it was approved by the government, the large sign at the entrance proudly displayed this fact in large letters, RED BANK APPROVED SCHOOL.
He was a bit put out when he was told his son didn't meet the requirements to attend this prestigious place of education, until the "headmaster" explained that an "approved" school was a posh name for a borstal. lol
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