Fixed RCD in consumer unti - rating correct

[deanmacken]

hello all, been in my new house for 5 months, finding some nightmares! just noticed that the RCD on the consumer unit protects all circuits and the top rating shown on it is 80amps, i'm adding things up and the total load could be much higher, there are 2 x 50amp circuits (shower and oven) 2 ring mains - 64amp total, two lighting circuits, both on 15amp mcbs and a 32 amp breaker for the garage, although this wont have much happening, my question is does the RCD need uprating? or is it based on 'real' usage.

One other thing, i've found a few loose joints on my travels around the house so i've been to every switch, socket and connection i can find to make sure they are tight to prevent any heat, most of the leccys being replaced as we work through but in the mean time are RCD's\MCBs any good at stopping things like fires caused by heating of connections etc?

Thanks to all of you in advance

 

[JohnD]

in most cases, an MCB or main fuse wil not trip even if a cable or joint is very hot and causes a fire.

An RCD will eventually trip when a cable is sufficiently burnt or charred. that may be too late.

 

[davy_owen_88]

Why are your lighting circuits fused at 15A and what size cable is used?
Are you on a TT supply (earth electrode)?
What mA rating is the RCD (30 or 100mA)?

 

[deanmacken]

Apologies, the lights are on 6amp mcbs - being stupid.

the rcd says on it ln = 80amp, un = 240v.

Dont know what you mean by TT supply, can you point me how to check?

It says l(triangle)n = .03a, does that mean its a 30mA? sorry if thats a really stupid answer.

 

[davy_owen_88]

Apologies, the lights are on 6amp mcbs - being stupid.

That's more like it.

Dont know what you mean by TT supply, can you point me how to check?

On a TT supply, the main earthing conductor from your consumer unit should run to a rod that is driven into the ground somewhere outside. If an earth cable runs to the sheath of the supply cable, or to the incomer, then you don't have a TT supply.

It says l(triangle)n = .03a, does that mean its a 30mA? sorry if thats a really stupid answer.

Yes, .03A = 30mA. Are you sure this RCD protects the entire house? Press the test button and check to see what circuits get disconnected.

 

[deanmacken]

absolutely certain, i've had the face off the consumer unit and the bus bar is common for each mcb, i have also just tested by turning it off, it turns the lot off.

Ahh, so if the earths use plumbing for earth would that be a TT supply?

 

[davy_owen_88]

Ahh, so if the earths use plumbing for earth would that be a TT supply?

No, a green & yellow cable running to the water and gas pipes shouldn't be providing the earth for a property. Those conductors are used for main equipotential bonding. For a TT supply, a dedicated rod should be installed. That should be connected to the main earth terminal, along with all the circuit protective conductors and the main bonding conductors.

Could you post a picture showing your consumer unit, meter and incomer? That should enable us to determine your earthing arrangement.

Regarding the 30mA RCD - it shouldn't really be protecting the entire installation. It is common on a TT supply to have a 30mA RCD protecting certain circuits such as showers and socket outlets while the rest are protected by a 100mA time delayed RCD - this reduces the chance of nuisance tripping, and also means that if the RCD trips your lights do not go out as well. ON other earthing arrangements, there is no need for the 100mA TD RCD and 30mA protection is again only required for sockets/showers etc.

 

[deanmacken]

I can post a pic, bear with me.

i think i get what your asking now, the incoming supply has just 2 cables L+N, can see any earth going back to the supply.

So the RCD is safe, just likely to get nuisance trips etc?