Rcd tripping

[Kev2632]

Should the rcd trip everytime if somebody had softly touched the live core of a cable? Or does it depend on wha current is flowing?

 

[telectrix]

it should trip before the current passing through your body reaches 30mA. not the way i would test an RCD though.

 

[Kev2632]

No no it wasn't getting tested by this way, just somebody had softly touched the live core. Shouldnt the RCD trip though after 30mA?

 

[Kev2632]

Or does the rcd not trip until nearer 30mA??

 

[Paul.M]

Rcd monitors imbalances line to neutral and if a live conductor is touched and 30mA (or less in most cases) flows away from the return path (neutral) it will detect the imbalance and trip. It's what its designed to do.

 

[Kev2632]

Yea I understand, so it will trip either below 30mA and above 30mA, soo when the RCD test is done at half it's rating why doesn't it trip isn't that 15mA then?? As that would be an imbalance is at correct?

 

[telectrix]

the bx 1/2 test is to check that the RCD does not trip on too low a leakage current. most 30mA RCDs will trip at around 22 - 25 mA.

 

[tony mc]

As Paul M has said the coil in the RCD moniotors the flow of the Line and Neutral conductors.

If either conductor flows to earth it will put the coil out of balance and trip the unit.

The amount of imbalance differs on each RCD but up to 15mA it should not trip but anything after that its down to each RCD.

That is why a series of tests are performed to make sure that the unit will trip out in the specified time.

That is for a BSEN RCD 300m seconds and a BS RCD 200 m Seconds.

Only a Ramp test will tell you at what stage the unit trips and it will record the mA it trips at!

If you softly (whatever that is ) touch a uninsulated live conductor and you are earthed the RCD is doing its job but the cable should have least insulation on it !

I hope this helps!!

 

[Kev2632]

So basically anything pretty much below 22-25mA an RCD wont trip yea??

 

[telectrix]

basically,m yes. the trip threshold is set at 30mA as that is considered to be a level of current passing through your body that won't kill you.

 

[Kev2632]

Yea that a lot better thanks. Well the person was standing on a concrete floor while they touched it and they said it didn't trip. Would the concrete floor have anything to do with it?

 

[tony mc]

No have another read of my post

 

[Kev2632]

So the person wasn't down to the earth so that's why it didn't trip is at correct???

 

[tony mc]

Have a read of this it may help!

Residual-current device - Wikipedia, the free encyclopedia

 

[Kev2632]

So I'm basically wrong in what I'm saying yea? Just wondered as to why the rcd didn't trip when they touched the live cable, as they were standing on a concrete floor