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TN-S can be changed to PME or not ?

as its in a cupboard, maybe u can minimise work and "cost" by using a switched fused unit as the actual light switch ? just connect light to load side of FCU ... removes need for another switch, extra cable and joint boxes everything else sounds ok though

RCDs dont go over 500mA (0.5 amps) usually ? so the max current passing down the earth is in theory half an amp 2.5mm2 can take over 20 amp but..we use 10mm2 when we install earth rods because it helps keep the earth loop lower and looks better

OK so it used to happen to Voltage Monitoring 'RCDs' and its possible that it could happen to current RCDs if the RCD is close to tripping, it just tips it over the edge Is there no other web pages explaining this, that any one knows of ? or is it that uncommon its not experimented with

Im sure ive seen someone say something about it before here, but i couldnt find it when i looked I used TT because its one with most likely to have RCD on to trip, but any info for service bonds causing it to happen would also be great

Is it possible for overlapping earth fault paths to trip RCDs ? Two houses next door to each other, both TT systems One house has a fault which passes to earth, and it trips an RCD in the 'other' house ? Possible or not ? if yes, could you explain how it works? Thanks

oh yeah thats true :P

Cheaper (time wise) in the long run to use a Tester than calculate values evey time ?

if the MI dries out would the insulation improve again or is there some kind of reaction with the moisture and magnesium oxide? being MgO, i guess no reaction

Good, thanks alot for the help

Ok thanks for that, and the "Scenario" i gave, that is the sort of thing you would use the correction factor for ?

Is the following correct ? ... Tables in OSG are for 70c rated PVC cables The table figures are the Maximum EFLI values at 10c Amb. Temp. Scenario: 30 Amp BS3036, with 1.5mm CPC to disconnect in 0.4secs EFLI from Table in OSG = 0.91Ohms When I carry out the test the ambient...

I thought the correction factor would be so you can design circuits for a operating temperature, because resistance increases as cables get hotter or is the Correction Factor just for Testing purposes ? OSG gives values at 10c and so when you test it, you adjust the Table value with the...

Thanks very much :D didnt look in OSG which i suppose i should have looked there first thanks

If i have a Semi enclosed fuse of 30Amp for example, how do I calculate the maximum earth fault loop impedance that would allow the breaker to operate in the specified time 5 seconds or 0.4 of a second ? Looking at the Regs they give you tables and graphs, but they also say these values...

its all ok if u dont touch or operate it :P

The council employ people to do the testing Then a seperate compnay to do the remedial work This is because if the company that test did the remedial work, then they could make up false problems and say they fixed them, therefore getting money for no work The people that test get money...

what do u mean about remedials ? People test the school, and then other companies go in and fix the problems, we are fixing the problems its 2 core about 30 meters, 25mm2 i think i dont have Ze on me though 1 or 2 boards are further and on same fuse type, but EFLI ok

would taking R1+R2 be able to indicate a break in the earth ? they did not test that ... or did not write down a measurement for it if there is a break, the loop still works but not as well ? Rf the stuff u said makes sense yep we just ran the 10mm accross the floor before wasting...

well im not qualified but the people i work with are... i just thought id see if i could learn something from it, or even advise something they hadnt thought of replacing the cable i think would be last resort there are no breaks that are visable the boards in the school are old MEM...