What BS number is this?
- Thread starter Podooser
- Start date
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Its old school, so 4293
Thanks Lectrician. Is it bad practice to use an RCD as the main switch on the CU. (Ground floor flat, the only circuits that don't require RCD protection in this case are 2 lighting circuits so I figured a split board would be a waste)
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Yes it is bad practice.
Lights should not have RCD protection*
Imagine you are using a dangerous powertoool and you accidentaly sever the flex supplying it. The RCD trips and plunges you into darkness with the still moving powertool in your hands.
If the lights were not RCD protected they would remain on.
*Except in certain circumstances
Lights should not have RCD protection*
Imagine you are using a dangerous powertoool and you accidentaly sever the flex supplying it. The RCD trips and plunges you into darkness with the still moving powertool in your hands.
If the lights were not RCD protected they would remain on.
*Except in certain circumstances
outside lights, and lights in bathrooms..
ColJack said:
Na - no need. Thats purely a personal preference, and not a requirement.
Please note though that as the above RCD is a 100mA device is does not provide supplementary protection against direct contact as is required for socket outlets reasonably expected to supply portable equipment outdoors, a 30mA max is required for this purpose.
Depending on supply type a split load as you suggest should be OK, cooker might be better off on the non-RCD side without a socket outlet on the CCU. Socket circuits and shower etc on the RCD side. I take it you meant 30mA? How many circuits require RCD protection? Just wondering if a normal board and RCBOs wouldn't be much more expensive?
In a TT system (earth electrode) the path for the external loop impedance is via mother earth. This usually has a much higher resistance than a TN system (TN-S max is 0.8 ohms.)
The increased resistance means that the earth fault loop impedance is not low enough for the MCB/fuse to provide fault current protection, i.e. not enough current will flow through the system to trip an MCB or pop a fuse quickly enough, if at all, for the method of protection against indirect contace i.e. EEBADS - earthed equipotential bonding and automatic disconnection of supply.
An RCD works somewhat differently than a fuse/MCB as it looks for an imballance in phase/neutral and disconnects the supply if the imballance is above a preset value.
The regs require the external loop impedance multiplied by the RCD trip current to be less than 50v (or 25v for some special locns) although in reality an external loop impedance greater than 200ohms should not be considered for reliability(possibly lowered to 100ohms in the 17th edition).
The increased resistance means that the earth fault loop impedance is not low enough for the MCB/fuse to provide fault current protection, i.e. not enough current will flow through the system to trip an MCB or pop a fuse quickly enough, if at all, for the method of protection against indirect contace i.e. EEBADS - earthed equipotential bonding and automatic disconnection of supply.
An RCD works somewhat differently than a fuse/MCB as it looks for an imballance in phase/neutral and disconnects the supply if the imballance is above a preset value.
The regs require the external loop impedance multiplied by the RCD trip current to be less than 50v (or 25v for some special locns) although in reality an external loop impedance greater than 200ohms should not be considered for reliability(possibly lowered to 100ohms in the 17th edition).
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