Ohms Q

[Electroglow]

Hello all I have for got the equation on how to find out what resistance on a short will trip a rcd 30ma... Can any one help this may seem silly but I really have for got

 

[m4tty]

ohms law ?

 

[Sidewinder]

L-L, L-N, or L-E short?

 

[sparkytim]

ohms law is one of the fundemental equations required by Electricians nearly every day.

Google it if you have to but you really need not to just remember it but understand it.

ohms, Volts and Amps are the basics in this game.

 

[ProDave]

That's what he's asking. He has forgot (it's all one word) and doesn't know how to google "ohms law"

 

[Andy™]

That's what he's asking. He has forgot (it's all one word) and doesn't know how to google "ohms law"

well he could always click here

 

[Electroglow]

30000 \ 230

 

[sparkytim]

Thats Thirty Thousand / two hundred and thirty

 

[ProDave]

30000 \ 230

???????? :C

 

[Doc Hudson]

Hello all I have for got the equation on how to find out what resistance on a short will trip a rcd 30ma... Can any one help this may seem silly but I really have for got

The term 'short' is often used to describe a direct low resistance path between Line and Neutral, as such that would never trip an RCD as the current would still be balanced. It is only a Line - Earth or Neutral - Earth path that will trip an RCD.

Doc H.

 

[Electroglow]

Haha I typed it and it must have changed on my phone... I ment 0.03/230 lol

Now I had a fault on a cable between l and e and the continuity reading was 126 ohms now it should trip the rcd right?? But it didn't

It was 0mohm

 

[Andy™]

I ment 0.03/230 lol

almost...

but either way, L-E fault of 126 ohms should trip the RCD

 

[Electroglow]

But it didn't.

 

[steptoe]

were you measuring this with the cables still connected in the board?

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ANY cables?

 

[ProDave]

Strewth.

It's I = V/R or R = V/I or V = I * R

So to trip a 30mA RCD R = 230/0.03

Which equals 7666.66 ohms

P.S I like to use 240V in practice, because that's the voltage we really have.

 

[Electroglow]

No the cable that was test was a leg between sockets both dissxonnected

 

[steptoe]

are you sure there is NOT something else connected to this cable between the sockets?

---------- Post Auto-Merged at 21:43 ---------- Previous post was made at 21:42 ----------

BTW,

what is the earthing system?

---------- Post Auto-Merged at 21:43 ---------- Previous post was made at 21:43 ----------

and the Ze

 

[Andy™]

and the RCD test times

 

[Electroglow]

I'm not 100percent sure that nothing is connected they seem to spur of every were. Pme 0.09 Ze

 

[steptoe]

you need to measure the length of the cable using your meter, and if this is different to what you think it should physically be measured at then it probably doesnt just go between those two sockets.