RCDs, little info on them?

[MrS]

Just a little info on RCDs needed. I know these are to protect circuits, but can you please help on the ratings of them.

I know they are usually 30mA on TNS and TNCS systems but there is another figure like 30A, 60A….. Is this the rating for the supply or have I got things wrong?

How do you pick an RCD? Do you just always use a 30mA one in your consumer unit if it’s a split board?

 

[Justin_chan]

How to choose a RCD for you ? details :http://www.jr-china.com.

Protection against the effects of earth leakage overload and short circuit currents.
2P switching of ph&N,Phase only protected against overloads and short circuits.
In commercial,industrial and domestic electrical distribution systems.
Note:must mot be used as the sole means of providing protection against direct contact.
The RCBO incorporates a residual current operated electromagnetic release which operates without any auxiliary source of suppl to open a circuit automatically in the case of an earth leakage fault between phase and earth greater than or equal to In.The RCBO combined MCB&RCCB provides:
Protection against indirect contact
Complementary protection against direct contact
Protection for the installation against in sulation faults
Standard
GB16917
IEC61009
Main technical parameters

Type JVL5-40
Number of poles 1P+N
Rated Current(In) 1/2/3/4/6/10/16/20/25/32/40A
Rated operating current( In) 30/100/300/500mA
Rated Voltage(Un) AC 230(240) V
Residual operating current scope 0.5In~In
Residual current off-time 0.3s
Type AC
Ultimate short-circuit breaking capacity(Icn) 6000A
Endurance 4000
Terminal protection IP20

 

[Softus]

Why are you up all night asking so many hypothetical questions?

 

[JohnD]

As you say, an RCD has two ratings - the 10mA, 30mA, 100mA is the amount of earth leakage current that will trip it (measured in milliamps so is very small. 30mA is usual for equipment to be used out of doors; 10mA is very sensitive and used e.g. in hospitals where patients have wires and tubes poked into them. 100mA is not very sensitive so can detect certain faults including those can can start fires, but may not stop you getting a shock, though it is not usually fatal. The problem with having a very sensitive RCD is that it might trip from non-dangerous events and be a nuisance.

There is also a rating for the amount of time the fault current will persist before the circuit is broken. this is usually 30 or 40 milliseconds but can be deiberately delayed to give discrimination or reduce nuisance tripping. The makers of RCDs can give you a chart showing time/current graphs and the effect they can be expected to have on a person receiving a shock.

The other rating, 32A, 60A, 100A is the current-carrying capacity. So to protect a 32 amp ring main or garden sockets you would use a 30mA/32A RCD; but to protect an entire house you might use a 100mA/100A RCD (though this is not always considered a good idea).

If you tried to protect a 100A house installation with a 32A RCD it would be running above its capacity, overheating, contacts being too small and might arc or stick under excessive load.