insulation resistance

[markthebuilder]

Testing my first house today4 bed 3 floors TT earthing Got a split board and I am using a megger 1552 I am getting a wapping <299 Mohm P-e P-N and N-e on 500vdc are these results realistic or am I obviously doing something wrong ie should I have a link in somewhere

to achieve the above I did have to identify and pull a dodgy lighting circuit which is sub .5 P-e and will fix next week
there is also a ring which is coming up at 6.8 (if I connect the ring then the whole system drops to 6.8)

iff general result of <299 is correct should I worry about the 6.8 as its well over the minimum

finely Ze is 256 dry should I wack in another spike and conect to existing

 

[plugwash]

it is not at all unusual for IR tests on brand new cable to be off the scale.

 

[martin43]

Wapping's a place in London isn'it, and you surely mean >299MR not<. Seriously nothing wrong with the readings at all, I assume your testing the cabling only? I did some tests recently with a 1552, exactly the same result.

regards
Martin[/u]

 

[markthebuilder]

thanks for quick response I was just eddditing my question I will relax a bit now Ive got test kit books and bits of wire all over the live rm floor trying to work out if I was doing somefhing wrong

what about the other couple of points

 

[securespark]

Rod should be sub 200 Ohm worst reading.

Is it good condition copper-clad steel 4 ft?

If you have TT, make sure board had TD incomer.

 

[markthebuilder]

I didn't think of that i've used an MK 12 way with standerd 100amp incomer with 80amp rcd guess thats a trip to cef then dont suppuse you have a part number

yes the rod is new but possibly going into filled rocky ground I remember the apprentice taking ages trying to get it in

 

[Gaz the Sparky]

I hope I have read your post wrong but if you have got a TT system then you require a RCD to protect ALL THE CIRCUITS so if you have got a split load board then you need a 100ma time delayed RCD for protecting the whole board instead of the 100 amp isolator them a 30ma RCD protecting the sockets shower ect

When testing insulation resistance >299 is a superb result the best you can get if you get a reading of 2Mohm or less then the regs state further investigation is required but the minimum value that is acceptable is 0.5Mohm

you need to test the earth rod the reading should be below 200 ohms

 

[markthebuilder]

unfortunatly u didnt read it wrong. a perfect case of a littel knowledge can be a dangerouse thing
This is first new instalation/rewire Job I have done start to finish without a sparks of long standing /fully qualified being around to help with design and final testing due to part p that relationship dosn't realy work anymore

so thats me with a lot more study, a 5 day wonder andhopefully a straightforward assesment day

But Will they cover it all on the five day wonder, will I remember, and will my assesment pick up on the fact that they didn't , or that I havent

 

[viewer]

Hi Mark,
Your questions have been answered, but if you don't mind me chipping in. I did the 5 day wonder (Rotherham) so that I could wire the house I'm rebuilding. It was just what was needed. They did spend time on testing and the reasons, meanings and problem solving. Including buying the test equipment it was a bit expensive, but great fun and I did learn a lot (I needed to!). With the insulation test I get >1000Mohms insulation on the new cable at 1000V and at first I too thought it was too good to be true. I've a TT system and with 2 linked metre rods I can get down to 197ohms in winter. The problem is we're on dry rock. I too have a split load board with the CU supplied RCCB protecting most circuits and RCBOs protecting the shower and main radial circuit. This gives protection without losing everything if an appliance is faulty. The discrimination does work.
V

 

[comms]

6400s is the MK part number for the time delayed 100A 100mA rcd to use as mains switch.

Viewer why are you testing IR at 1000v, domestic it's 500v unless elv then 250v.

 

[viewer]

Hi comms,
Just as a check to the readings at other voltages because the resistance was off scale (referring to same situation as OP). Always start at 250 in case there is a nail-type problem then move up.

 

[scousespark]

This post demonstrates the insanity of part-p. Part-P was supposed to improve the safety of domestic electrical installations, but how the hell can this be achieved by letting a 5-day wonder in to start rewiring houses.

Mark has queried the readings he has from his tests. He then tells us he has fitted a CU in a TT installation, without RCD protection and goes on to ask if he needs another rod when he gets a Ze of 267 ohms.

Mark, you'll probably learn enough in 5 days to qualify as a DI, but you can't really believe that 5 days will qualify you as a spark. As a time-served spark I think it's ridiculous that a law that was introduced to improve safety (based on dubious stats) has this way of fast-tracking people in to the industry. At the same time a 20 year spark who is a QC for an NICEIC registered firm cannot rewire his own house without notifying BC.

Before any of you jump on me bear in mind this is a DIY forum but this guy is installing for profit.

 

[Taylortwocities]

And Mark, hold your breath when you buy your MK 6400S. You'll be looking at £100

TTC

 

[securespark]

I remember the apprentice taking ages trying to get it in

Yes yes, but what about the earth spike? Fnarr, fnarr!

 

[securespark]

I did the 5 day wonder (Rotherham)

Lowes?