electrics...whole house RCD?

moonrakerz

ffym wrote: »

In my opinion a RCD is one of the most important pieces of electrical protection (human) on any earthed electrical system.

Totally agree !

The point of having an RCD only on circuits feeding something outdoors, I find rather rather a half-hearted safety measure.
My house has all circuits protected by an RCD (why didn't they stick with ELCB ??), a few months after we moved in a fault was detected on a lighting circuit by this device. This fault was potentially very dangerous as a damaged cable had bare conductor exposed.

The RCD,
1. Detected this fault
2. Would have provided considerable human protection had someone touched this damaged cable.

j77wilko

yeah I love all this talk of earths and stuff thing is guys we put in these new upgaded earths 16mm main bond and 10mm on the water and gas and then when we look closely there is a very tiny bit of cable on the suppliers side that is no where near 16mm?? Also the suppliers are still fitting 16mm tails when we have to fit 25mm. Surely this in itself does not make much sense?? Just another bit of food for thought!!!!!

Andy_L

moonrakerz wrote: »

(why didn't they stick with ELCB ??)

Becasue RCD's use a different method of operation & are better

vivat

My landlord has just installed a new consumer unit, along with new earth cables in large ugly trunking (even from the bathroom light switch). The kitchen socket circuit, the electric cooker circuit and the circuit for all the other sockets in the flat are all guarded by the one hypersensitive RDC.

The problem with this is that if a kitchen appliance has a problem (with planned obsolesence we find this happens frequently), every single socket in the flat shuts down. Thus our computer has been crashed shut seven times already (mostly caused by steam in the kitchen). The computer hates this, I hate this. Usually we have two or three computers running at once, for various family member's work, homework etc. We cannot afford to buy an RDC for each individual socket.

Does anyone know if it is possible to have two RDCs on one consumer unit? And if so, how? I desperately need to have the kitchen sockets plus cooker circuit on one RDC, and something else or another RDC for the rest of the sockets. The landlord's contractors say this is not physically possible. Are they right?
We are half way up a block of flats, so not going to be powering anything outside from any sockets here.

HugoSP

ffym wrote: »

I am rather confused by these comments. Whilst I agree that certain supply configurations need RCDs to clear electrical faults efficiently are you suggesting that RCDs are unnecessary as a safety device (for human protection)? In my opinion a RCD is one of the most important pieces of electrical protection (human) on any earthed electrical system.

You need to consider the question and answer in hand.

Basically we are talking about an earthing system for the whole installation.

Earths supplied by distributors are of low impedence, that is to say that given earth fault conditions they will be able to carry the current safely away from harm's way. Consider a floodgate bursting open on an irragation waterway when the flow rate gets too high and the water starts bursting its banks. This floodgate is big enough to remove the water before it can do any harm elsewhere. Water flows in but is carried out through the floodgate quite happily until the root cause of the high flow rate is sorted out.

TT systems employ an earth rod in the ground, they are present because for whatever reason the distributor has not provided an earth. The impedence on these is measured in hundreds of ohms rather than ohms. Hence there is much more difficulty in removing any earth leakage current. As a result the RCD on the whole system is employed to respond to a trickle. Using the floodgate analogy, the TT system only has a small pressure relief valve to activate when the waterway is about to burst its banks. Hence there needs to be something in there to divert the water away from the waterway. The RCD is like shutting off the supply to that waterway when the pressure relief valve is activated.

You can always improve safety by adding extra RCDs to serve the whole circuit in a non TT installation, but whilst there is an effective low impedence earth route it is not as necessary. The Regs outline how the human body can cope with shocks resulting from earth faults from these types of installations and earthing systems, but not from TT systems. I won't go into detail here but trust me.

In addition the installation within a non TT system would be adequately protected via the earth wire (CPC) so that no damage would occur to the wiring.

A shock from an earth fault on a low impedence distributor earthed installation would give you a jolt but is unlikely to do anymore than that. This is unless you happen to be standing outside or in a puddle of water. Sockets that could reasonably be expected to supply equipment used outside must be powered via an RCD according to the regs, this is normally the ground floor sockets. Quite often installers put all sockets via the RCD. In addition showers and cookers are often wired via an RCD, although the regs don't require this at the moment.

For non TT systems lights and smoke alarms are not wired via an RCD for very good reason. Let us suppose there is a fire in the house and the RCD has tripped because the fire has damaged the wiring. The occupants would still very much appreciate the smoke alarms being activated, and the lights to work.