Capacitance! PAH!

[Steve_P]

Sorry but I'm getting the hump with capacitance in circuits.

First of all, I got a call out to a mystery tripping RCD. It tripped and the customer couldn't reset it then after a while they could then it tripped a minute or so later . . . . . . . turned out to be a small break in the insulation of the live conductor as it came through a metal back box with no grommet, the LAST one that I hadn't looked at that could have been firking looked at!

Now I have the same on a lighting circuit. 10 or so seconds and the RCD trips, wait a while, re-set it, 10 or so seconds and it trips. I'm back over there tomorrow to find the problem in the mean time, they're using table lights.

Both properties have had a load of DIY work (and by a load I mean most of the houses). I have a feeling that the lighting circuit will be something to do with one of the numerous JB's in the loft. Itchy coo park tomorrow then.

Grrrrrrr.

Oh, btw, after I left the one tonight, at about 9pm, drove home, got out of my truck to walk back from my garage, the heavens OPENED! Perfect end to a naff day or what?

Ok, nuff of that, night all.

 

[Richard Burns]

The joys of the total safety of RCDs!
Happens to us all at times, tomorrow is another day.

 

[Knobhead]

What's this got to do with capacitance?

 

[Steve_P]

It's what I've always known it as, I suppose it's because the rcd acts as though there's a capacitor on the circuit once it's tripped, dunno mate.

 

[Knobhead]

I give up...... Why do you blame a poor little capacitor for all your woe's?

 

[Steve_P]

Because I'm an evil scientist disguised as a spark, mwahahahahahahahahahaha.

 

[dpiers1980]

i don't understand doesn't a RCD trip when there is current coming back down through a earth path. So like a screw puncturing a lighting twin and earth and then coming back down through the earth.

 

[Richard Burns]

An RCD will only trip if the difference between the current flowing in the line conductor and the current flowing in the neutral conductor exceeds the tripping current of the RCD (I⌂n).
A(L) - A(N) ≤ ±I⌂n
Where the excess current is going is not relevant to the RCD tripping, though the logical route is to earth.
The actual current at which an RCD actually trips will always be less than the rated current.

 

[D Skelton]

What's this got to do with capacitance?

My thoughts exactly???

Sorry but I'm getting the hump with capacitance in circuits.

as it came through a metal back box with no grommet

I may be wrong but I think you could be confusing capacitance and induced voltage? Even then, induced voltage hasn't got anything to do with it. RCDs are really quite simple devices that do nothing but detect an inbalance between the current flowing in, and then back out of them.

In my experience, when there is a short time delay between setting an RCD and then it tripping again, water or the effects of damp have usually been involved. It's worth bearing in mind.

 

[dpiers1980]

like this ?

 

[Knobhead]

Nice drawing. Where did you get it?
DON'T tell me you drew it otherwise I'll sulk!