Disconection times

[daiplayer]

ok this q come up in college. And we couldn get to a conclusion.

Max dis time : 0.4s......

TT system , not possible ( high Ze).

So must have rcd to obtain 0.4s...rcd testing , : must operate in 0.4 s @ x 5 current.

However bs7671 states disconection time for TT system as 0.2 secs ? ( portable equipment) .

Why isnt the rcd time for TT 0.2 secs @ 5 x current ?

 

[Silly Sausage]

Check your decimal places...
0.4s is 400ms...or 40ms is 0.04s

 

[daiplayer]

oh yeah of course :-/

 

[daiplayer]

ok so basically its this? :

times : 0.4 for TN : 0.2 for TT .

So TT : 40 ms for rcd @ 5 x current ( 0.04) < 0.2 (200) ?

 

[Silly Sausage]

ok so basically its this? :

times : 0.4 for TN : 0.2 for TT .

So TT : 40 ms for rcd @ 5 x current ( 0.04) < 0.2 (200) ? Yes, 40ms < 200ms; 415.1.1

For non RCD protected circuits, faults to earth are 0.4s (400ms) for TN, 0.2s (200ms) for TT; Table 41.1, so yes, your're right there.

With RCD, @ 1 x In, clear fault within 200ms, TN or TT (someone check that for me!)

(BRB refs)

 

[daiplayer]

For non RCD protected circuits, faults to earth are 0.4s (400ms) for TN, 0.2s (200ms) for TT; Table 41.1, so yes, your're right there.

With RCD, @ 1 x In, clear fault within 200ms, TN or TT (someone check that for me!)

(BRB refs)

Yeah : 1In 200ms : 5In 40ms ....i think . ...ok , cant believe nobody in college picked up on tha...lol

 

[IQ Electrical]

And the next question is "how does an RCD to BS 61008/61009 comply with a 0.2 second disconnection time?"

The answer is in the note at the foot of table 41.1 and then the additional time/current figures for RCD's in Appendix 3 of BS 7671