0.4 disconnection time

[WACKY1965]

Hi
we all know about the 0.4 disconnection time, but why 0.4 has this something to do with body resistance, can anyone shed light on this.

 

[Jabbajaws]

I dont get that one personally. Everyones body resistance is different, dependant on size, moisture etc, so l dont get where 0.4 comes in.

Ive never heard this and would be interested in the explanation if you find one. I most certainly never came across it when l did my C&G 2230 (unless ive missed something somewhere along the line).

 

[Guest111]

I seem to remember it being based on an average figure and the amount of current that would flow through the body in 0.4s without being fatal,no doubt someone can explain it fully.I suffer from brain fade these days,now what was I saying? lol

 

[Farmelectrics]

Google it you might get a better explanation I no why but can't quite explain properly

 

[44ALLAN]

lol..............lol

edit
only did the double lol cos it said I had to add more words...........................

 

[Dizzy_Maskell]

Google it you might get a better explanation I no why but can't quite explain properly

Funny that's what I was gonna say

 

[Steve_P]

If I remember correctly, this conversation will get sorted and degenerate into the IP finger test.

 

[44ALLAN]

I'm guessing but surely 0.4 of a second is the time your brain needs to send a message to your body along the lines of...............why the XecX did you touch that ?
I hope your hands are dry?
I hope you have your wellies on?
I hope that ugly/fat/obnoxious person has done his sums right and not guessed at ADS !!
Why we allow plumbers to do these calcs is beyond me................on 6th beer

 

[sparks86]

Disconnection times come from the maximum touch voltage present on an exposed conductive part, that can be sustained indefinitely by a person during indirect contact. 92 volts according to IEC 61200-413 figure C2 can be sustained indefinitely for 0.4 seconds.

They obtained 92 volts from the equation c*Uo*m/(1+m).
Where-
c=The portion of the supply voltage available at the reference point during operation of the protective device.
Uo=The original supply voltage.
m=The ratio of the cross-sectional area of the protective earth and phase conductor in the circuit being considered.

So if we use a solidly earthed 400/230 system for example, assuming that the value m is 1 and 80% of the supply voltage is available at the reference point we get...
0.8*230*1/(1+m)=92volts.

Hope this helps.