RCD query.

[wade88]

Hi lads,

Just spent the morning re-wiring the office lighting at work, and have encoutered non-stop nuisence tripping from the RCD.

Its a standard 100A 30mA RCD, MEM, for a MEM shield 2 board. Now i am a newbie in the grand scheme of things, but i do understand how RCD's work, and im getting a little confused as to why im throwing it out.

The circuit im working on is obviously dead, therefore there is no current passing through the phase and neutral and therefore nothing can be passing by the toroid for the detector winding to pick up on? Could the tiny voltage that us humans dormantly posses be enough for the RCD to detect as im touching the cables and stripping them etc? I havnt done a ramp test on the RCD yet to determine where it is tripping at, as my megger is at home today.

Or have i just stood against the wall to be shot by totally over looking something very straight forward?

 

[telectrix]

are the neutrals still connected? if you are stripping etc. and short N to cpc. the RCD will trip.

 

[malcolmsanford]

Yes ............your touching the Earth and neutral and that is enough to trip the RCD.

But your a very naughty boy for not isolating the whole DB before you work on it, and how much data are you now responsible of losing because you didn't fully isolate.

 

[wade88]

Yes i know i should isolate the entire board, but the way this mornings gone its spent 80% of it in isolation anyway. Problem is the director is having a fuss because when the board goes down we lose comms so hes usually mid conversation with the president or something and he gets cut off....but he doesnt deem this particualr job important enough to shut down his whole office, so im now going to have to come back and do it in my own time on the weekend or in the dark after work, which im not paid to do, such is life however.

Right i see, obviously i dont know enough about RCD's as i need to. So even on a non live circuit the toroid will still pick up a disturbance down the E & N

 

[tony mc]

Yes
You need to remove the neutral from the neutral bar or it will still detect an imbalance if the neutral and earth touch out on the cct.

 

[telectrix]

think of how the RCD works. inbalance between current in line and neutral. there is zero current in the line, as you have isolated at the MCB. by shorting N/E you are allowing a current to flow in the neutral. hence inbalance> trip.

 

[diditrain]

Slap a copy of the newspaper showing the burnt body of the Electricians from that factory where they did not want to isolate, highlighting the fine recieved

 

[ezzzekiel]

trmming the cpc sepeately may help

 

[LlandrilloSpark]

Disconnect all the conductors for this circuit in the CU and then no current/voltage should flow providing their is no borrowed neutrals on it

 

[ian]

think of how the RCD works. inbalance between current in line and neutral. there is zero current in the line, as you have isolated at the MCB. by shorting N/E you are allowing a current to flow in the neutral. hence inbalance> trip.

[FONT=&quot]spot on, disconnect the N & CPC, the problem will disappear. [/FONT]

 

[wade88]

Yea thanks guys this is what i did at the end. was just having a bit of a moment...thanks for all the help chaps