So I'm replacing my house's switchboard (which is 40+ years old) and I'm required to install several residual current devices (aka ground fault circuit interrupters - GFCIs - in the US). My googling has given me a pretty good idea of how they work, but I'm confused about the circumstances in which they actually do anything, in terms of real life scenarios.
This is how I understand it: if an appliance plugged into the mains is live, and someone somehow comes into contact with the live circuit, the RCD will detect the current leakage, flick off, and turn the power off also, saving that person's life.
That much I get. But a mate of mine who has some electrical training pointed out that the RCD wouldn't trigger if the person was wearing rubber-soled shoes, since the person wouldn't be grounded. The end result would be the rubber-soled-shoe-wearing person would be electrocuted, since the power wouldn't turn off. So since 90% of shoes you wear are rubber-soled, doesn't that render the device a bit useless?
And this got me thinking more. Let's look at another scenario: a bunch of water on a bathroom or kitchen floor, that somehow has mains current running through it (say, the plug end of a live extension cord is sitting in it). This death trap would sit there until someone walked into it, in which case the RCD would flip, cutting off the current. Right? But not if that person was wearing rubber shoes (though I guess if that were the case, they'd be protected from the current anyway)? Or would the RCD flip as soon as the power came into contact with a grounded load that was sufficient enough to cause a significant current leakage?
As you can see I'm highly confused. Can someone explain in what circumstances an RCD will trip in practical terms? In particular, the two scenarios outlined in this post?
This is how I understand it: if an appliance plugged into the mains is live, and someone somehow comes into contact with the live circuit, the RCD will detect the current leakage, flick off, and turn the power off also, saving that person's life.
That much I get. But a mate of mine who has some electrical training pointed out that the RCD wouldn't trigger if the person was wearing rubber-soled shoes, since the person wouldn't be grounded. The end result would be the rubber-soled-shoe-wearing person would be electrocuted, since the power wouldn't turn off. So since 90% of shoes you wear are rubber-soled, doesn't that render the device a bit useless?
And this got me thinking more. Let's look at another scenario: a bunch of water on a bathroom or kitchen floor, that somehow has mains current running through it (say, the plug end of a live extension cord is sitting in it). This death trap would sit there until someone walked into it, in which case the RCD would flip, cutting off the current. Right? But not if that person was wearing rubber shoes (though I guess if that were the case, they'd be protected from the current anyway)? Or would the RCD flip as soon as the power came into contact with a grounded load that was sufficient enough to cause a significant current leakage?
As you can see I'm highly confused. Can someone explain in what circumstances an RCD will trip in practical terms? In particular, the two scenarios outlined in this post?
