- Reaction score
- 55
Hi all,
My colleague and I were having a discussion today about RCD protection, as you do, and the reasoning behind why it is stipulated that 30mA should be the rating of an RCD for additional protection. Now we all know the rules regarding the maximum trip times for the various tests, but I just wanted to understand it more and ask how the maths works? Is an earth fault of 30mA at the various maximum trip times a significant figure in terms of survivable electric shock? Im not sure I quite fully 'get' how the 40msx1 and the 200/300msx5 rule works mathematically? Does it bear any relation to the 0.4secs disconnection time that we are supposed to achieve for circuits <32A and or distribution circuits in TN systems? and the 0.2secs for TT...?
Hope that makes sense?
Thanks
My colleague and I were having a discussion today about RCD protection, as you do, and the reasoning behind why it is stipulated that 30mA should be the rating of an RCD for additional protection. Now we all know the rules regarding the maximum trip times for the various tests, but I just wanted to understand it more and ask how the maths works? Is an earth fault of 30mA at the various maximum trip times a significant figure in terms of survivable electric shock? Im not sure I quite fully 'get' how the 40msx1 and the 200/300msx5 rule works mathematically? Does it bear any relation to the 0.4secs disconnection time that we are supposed to achieve for circuits <32A and or distribution circuits in TN systems? and the 0.2secs for TT...?
Hope that makes sense?
Thanks