New Build Housing Project

[trev]

New build housing project in the middle of a very hot summer (anyone remember both those things?) so everything is bone dry. One of your colleagues did the first and second fix so you have the job of testing IR is down just under 2 meg.
Discuss.

 

[Paul.M]

I'm guessing this is a global IR Trev?

 

[trev]

Oops well spotted mate. The IR on the lighting circuit is down to just under 2 meg. Sorry guys.

 

[Baker1988]

im honestly not sure about this one if its newly rewired why would it have only 2 meg, the only thing i could think is that they have cut abit of the isulation from pulling the cable in probily caught it on some thing, i would start by doing global ir then switching 1 circuit at a time off till i find the circuit that is the problem say its the sockets then i would guess about half way on the circuit undo the socket and disconnect both legs and do a ir on each leg that would tell me which side of the leg the fault is on then work my way back doing the same till i find between which socket it is and replace that bit of cable but as i say im not sure so a guess but isnt 2 meg ok according to regs any thing over 1 megohm is ok but any thing under 2 megohms should be investigated so in all fairness 2 meg is ok

 

[High Tower]

Ok forget the base value of 1Mohm we know this just scrapes it, problem is its a brand new install and should be >500

 

[Baker1988]

Ok forget the base value of 1Mohm we know this just scrapes it, problem is its a brand new install and should be >500

yeah it should be off the scale for ir that is what you would expect but as i said i dont know why this should happen except they have sliced the insulation while pulling in the cable

 

[Floody]

Ill go with what we already know to start.

its a hot summer, possible heat damage to insulation?

 

[Baker1988]

Ill to go what we already know to start.

its a hot summer, possible heat damage to insulation?

thats a good point i totally forgot about where it said hot summer it probily has melted a bit

 

[Floody]

The insulation must be able to withstand some heat as current flows through it. But on a boiling day in the back of a van where cable is left, it can become like an oven in there.

your collegue has done first and second fix, so you have no idea what the state of the cable was going in.

 

[Paul.M]

Ok forget the base value of 1Mohm we know this just scrapes it, problem is its a brand new install and should be >500

HT I dont understand your figure of >500 M Ohms for a new install. Rather I've forgotten something or I dont know something???


Ha, I now understand what you are saying HT. Yes it should be BUT that will never be in a C&G exam question.


Ok lads, 2 points on IR testing.

1. A global test on a new or existing installation should be higher than 2 M Ohms, lss than that requires further investigation.

2. An individual circuit IR test should be greater than 1 M Ohm.

But saying the above, if I got anywhere near these levels on a new install I would be testing everything that my work mate has installed to find out why. It should be over 500 M Ohms with new cable etc. Scratchy head time for the I&T lol.

 

[Baker1988]

The insulation must be able to withstand some heat as current flows through it. But on a boiling day in the back of a van where cable is left, it can become like an oven in there.

your collegue has done first and second fix, so you have no idea what the state of the cable was going in.

well normal thermoplastic cable (pvc) has a operating temperature of 70 degree c so it can withstand that before it starts melting and there is also thermo setting cable which can withstand 90 degrees c

 

[Paul.M]

Post #3, concentrate on the lighting circuit lads

 

[Baker1988]

the only other thing i could think of is that there is either a light bulb still in one of pendents or that there is a small neon light somewhere like on a fuse spur or something that would drop the ir by a lot so disconnect the bulbs and change the fuse spurs with neons and connect then with a chock block or something

 

[Paul.M]

the only other thing i could think of is that there is either a light bulb still in one of pendents or that there is a small neon light somewhere like on a fuse spur or something that would drop the ir by a lot so disconnect the bulbs and change the fuse spurs with neons and connect then with a chock block or something

I like your answer and the way your thinking but when would we put a neon fsu from a lighting circuit? Yes that is possible but I really like the idea of light bulbs/lamps

 

[Baker1988]

I like your answer and the way your thinking but when would we put a neon fsu from a lighting circuit? Yes that is possible but I really like the idea of light bulbs/lamps

true there wouldnt be any need to really as its only 6amp mcb and you wouldnt be down grading the cable size so no real reason too, there could be a celing fan/light

edit:
there could be an emergency light on the circuit they have a neon light and a battery pack