Use of RCD's

[nightlight14]

Importance is now placed on the use of RCD's. both permanently fitted in consumer units or portable plug in types. Many of the appliances used in a domestic situation are type II, double insulated. Does the RCD provide and further protection than the double insulation affords, if so in what situation?

 

[DPG]

Have you just posted an exam question without even a hello or please or anything? I predict you ain't gonna get a good response here. Daz

 

[Octopus]

You don't need an earth connected to the appliance to enable the RCD to work.... any path to earth will do.

Is this a college question?

 

[LeeH]

Yes, you can still get an earth fault and the RCD will still detect the imbalance.

I can see your train of thought thinking that as it has no metal case you won't get a fault to that. But you still have a cord and potentially somebody wet stood on wet grass touching a damaged flex.

 

[nightlight14]

No not a college question, I'm just trying to understand in what circumstances an RCD would provide extra protection. I'm 70years old!!

 

[DPG]

No not a college question, I'm just trying to understand in what circumstances an RCD would provide extra protection. I'm 70years old!!

Whoops, apologies for that. You should write exam questions - you would be very good at it! Daz

 

[telectrix]

basically, a short circuit will take out a fuse/MCB. a RCD is there to detect a current leaking to earth ( through your body ) of the order of 30mA. then it will trip, hopefully before your heart stops.

 

[nightlight14]

Thanks for your replies Gents, as I thought it's mainly the fuse / mcb which will provide the protection except in the case of a damaged cable allowing a fault current to ground and causing the RCD to trip.
Alan.

 

[iamelectric]

Brilliant !!!!! thats the best thing i have seen on here " is this an exam question "................." I am 70 years old "

 

[telectrix]

but it shows that you're never too old to learn. i'm about to apply for a law degree. nobody moans about £30/hour with them sharks. all are happy to pay £180/hour for a solicitor, but gripe at paying a spark a pittance.

 

[Marvo]

Thanks for your replies Gents, as I thought it's mainly the fuse / mcb which will provide the protection except in the case of a damaged cable allowing a fault current to ground and causing the RCD to trip.
Alan.

There's two types of protection in a CU. The normal circuit breakers (MCB's) protect the cabling against overload and fault currents which could damage the wiring or cause a fire. The RCD protects the user of the installation by detecting even a very small current that flows to earth when they touch something that's live.

ClassII insulation also protects the user by ensuring the chassis of an appliance can't become live but there's still always a chance you can get a shock from a classII appliance if there's water damage or physical damage, so, yes an RCD would afford some extra protection although the regulations may not explicitly require it.

 

[GLENNSPARK]

Yes, you can still get an earth fault and the RCD will still detect the imbalance.

I can see your train of thought thinking that as it has no metal case you won't get a fault to that. But you still have a cord and potentially somebody wet stood on wet grass touching a damaged flex.

dont forget that voltages can `track` across wet surfaces...

 

[GLENNSPARK]

There's two types of protection in a CU. The normal circuit breakers (MCB's) protect the cabling against overload and fault currents which could damage the wiring or cause a fire. The RCD protects the user of the installation by detecting even a very small current that flows to earth when they touch something that's live.

ClassII insulation also protects the user by ensuring the chassis of an appliance can't become live but there's still always a chance you can get a shock from a classII appliance if there's water damage or physical damage, so, yes an RCD would afford some extra protection although the regulations may not explicitly require it.

also that an RCD is fault protection for TT earthing arrangements...

 

[Marvo]

also that an RCD is fault protection for TT earthing arrangements...

Yep although some may say an upfront RCD is a required addition to a TT arrangement that's not fully functional.... but that's an argument for another thread

 

[nightlight14]

Thank you Marvo, I hadn't considered the damp or damaged situations.

Alan

 

[Engineer54]

but it shows that you're never too old to learn. i'm about to apply for a law degree. nobody moans about £30/hour with them sharks. all are happy to pay £180/hour for a solicitor, but gripe at paying a spark a pittance.

Same can be said for any and all parasitic professions!! lol!!