electric still trips even though i have isolated the curcuit

[pauldaq]

Hi, new to site and new to electrics. Im not an electrician by any means but i have basic understanding - or so i thought..

I am doing some wiring alterations to my new shop - putting some lights in and stuff. i have isolated the ring using the the consumer unit fuse/switch - tested the cable with a multimeter, a voltage detector pen and even a light screwdriver all show there is no live. Thing is..... when i cut the wire - that i have tested to be not live the hole building trips.

Am i going to blow myself up if i keep going?

I know i should get a sparky in to sort it but cannot afford it at the moment.

any info much appreciated

thanks Paul

 

[EFLImpudence]

Perfectly normal.

Your cutters would have connected Neutral and Earth and the RCD would have detected that as a fault even though the Live is switched off..

You would need to disconnect the Neutral at the CU to totally isolate the circuit.

 

[sparkwright]

It sounds like you have isolated the individual circuit breaker, but as you touch neutrak and earth together it's knocking out the RCCB or RCD.

Totally normal.

The miniature circuit breaker (MCB) or fuse only isolates the live.

Cutting a cable or touching wires together will still activate the RCD as an inbalance is detected.

 

[pauldaq]

thanks guys - so im not going to blow myself up.

 

[bhm1712]

Potentially yes you will die. If you are just cutting through cables and dont understand why the RCD still trips, then id say your a total novice and shouldnt be working on electrical equipment or wiring.

 

[pauldaq]

yes i am a total novice - i know where the wires are to go - unfortunately not sure what they all do. but if i make sure the circuit is off at the consumer unit and test the cable before i cut - i should be ok? right?

 

[bhm1712]

You should be ok, providing there are no anomalies in the wiring in your place. Sometimes, places which have been messed with in the past can have all sorts of electrical black magic going on, and even though a circuit may be isolated, turning something else on can indeed make something else live that shouldnt be. Just take it easy, dont rush and keep that multimeter (preferrably a voltage indicator, but thats another subject full of debate) at the ready.

Test between live and earth and live and neutral before cutting anything.

Edited for totally pants grammar and spelling

 

[RMS]

Test between live and earth and live and neutral before cutting anything.

Even that wont protect against the horrid borrowed neutral scenario.

Sometimes it's safer to isolate the whole installation if feasible.

 

[bhm1712]

Totally agree

 

[ban-all-sheds]

but if i make sure the circuit is off at the consumer unit and test the cable before i cut - i should be ok? right?

Test with what?

If the answer is "neon screwdriver" you should throw that away and buy a proper 2-pole tester.

This looks ideal for a household starter set - multimeter, voltage indicator and dedicated continuity tester, all in a handy case: http://www.amprobe.eu/de_DE/showproduct/115/Junior-Set/

PDF brochure: http://www.amprobe.eu/de_DE/downloadfile/115/beschreibung_1/

All in German, unfortunately, as is the blurb on each product:

Multimeter: http://www.amprobe.eu/de_DE/showproductdata/487/Hexagon_55/

Voltage indicator: http://www.amprobe.eu/de_DE/showproduct/116/2000_α_(alpha)/

Continuity tester: http://www.amprobe.eu/de_DE/showproduct/481/TESTFIX/

but it is sold in the UK - the company is now owned by Fluke, and I guess they haven't got all the websites sorted out yet - contact them (http://www.fluke.co.uk) for info on where to buy.

Right now the English specs are still lurking on the Internet Time Machine from when Beha was an independent company:

http://web.archive.org/web/20060920022629/http://www.beha.com/files_uk/multimeter/93549.pdf



There's an article here explaining what a borrowed neutral is, and how it can bite you: //www.diynot.com/wiki/electrics:sneutral


In general terms:

• http://www.google.co.uk/search?q=electrical+circuits+101
  
  
• http://kevinboone.net/electricity.html
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/domesticinstallations.html
  
  
• //www.diynot.com/wiki/electrics:books
  
  
• //www.diynot.com/wiki/electrics
  

 

[bhm1712]

http://www.test-meter.co.uk/product...-voltage-indicator-and-proving-unit-vipd-kit/

I use the 2 above items