rcd protection

[soulman]

(please note i'm in my second year of training and doing bit of homework not trying to do a job, just trying to understand)
1.
a 3036 board, tt system. no rcd. earth rod and main bonding in place. which was in my friends house. am i correct in saying this is potentially lethal. (as no earth fault protection) to install an rcd could either be via a new board fitted with rcbo for tt system. or would it be acceptable to remove tails from board install an rcd then go into the board. so rcd before the board. also is there a test that can be performed on the wiring, prior to installation of rcd device, to ensure that it will take the rcd. without tripping. also i have read that rewirable fuses can be repaced with circuit breakers if this is so, are rcbo,s available that can replace fuses.

secondly what would the difference be if the supply was tn-cs or tn-s

and thirdly can electricians condemn electrical systems similar to gas fitters on a boiler.


thanx in advance for any replies

 

[bugsy]

oh dear oh dear oh dear, yes the installation is dangerous, may I respectfully suggest I f your not sure about what your doing don't touch it.

Get your reg's book out and look at the requirements for a TT system get a qualified spark in and by all means ask if you can go through the whole test and verification proceedure with him.

out of curiosity how long has it been like this

 

[soulman]

cheers bugsy i wouldn,t attempt any job. he has no intentions of getting any spark in. i,m just asking out of interest as i wish to learn. it has been like this for at last 8 years since he moved in. (i,m always looking at friends consumer units. sad i know but everyone starts somewhere)

 

[Spudnik]

A global IR test would confirm the installation was clear to take an RCD upfront, but only as a temporary measure.

However, earthing and bonding would be a priority in my book!

 

[bugsy]

I would strongly - very strogly recommend he gets this looked at .
Prehaps you could enlighten him to the possible dangers, and remind him that if anything did happen his home ins. poloicy might be void.
Funny how people put such a low value on them selves and their family-

 

[Spudnik]

Im not sure its that so much, more the point of being "unaware" of the potential dangers.

 

[soulman]

thank you i do appreciate the replies and if your not electrician most people wouldn,t call one in until a fault or require work if it broke attitude.
i will print off and give to him to make him aware.

but can you please answer my questions thanx.

 

[Spudnik]

Ok, TN systems generally have a supplied earth by the DNO and it is their responsibility to maintain it below the limits.

With TT, the electrician must provide earthing via a rod.

And no, we dont have the "power" to turn off a dangerous install, especially domestic.

 

[soulman]

thanx jason i understand the difference betwen earthing arrangements what i wanted to know is what would be the difference of how you added the rcd protection or was it any more dangerous etc
cheers

 

[oldtimer]

Soulman
First things first you need to understand the basics in other words dont run before you can walk now I am not having a pop as I am 50 and my approch is every day is a school day in other words I am open to learn as for being sad that you are checking out fuseboards I disagree I would rather you asked questions other than jump in. Me thinks there has been a major shift when it comes to training newbie sparks I was always encouraged by the majority of my tradesman where a minority were only to happy to keep the knowledge is power mantra. Anyhow tread carefully and stick in

 

[Guest123]

Ok, as a very basic description of the issue of no RCD protection on a TT system.

Basically every fuse or circuit breaker has a job of disconnecting the supply within a specified time before fault voltages reach a dangerous level to touch.

Every fuse/circuit breaker has a maximum earth fault loop impedance value (the rough maximum is 7.5 ohms for a lighting circuit breaker) to which it will achieve this disconnection time. In a TT system the earth fault loop impedance is too high (usually between 50 and 200ohms) for the fuse/circuit breaker to achieve this disconnection time so we must provide additional earth fault protection with an RCD.

Without the presence of this RCD a fault voltage has the potential to reach a level above the accepted safe limit and NOT cause the fuse/circuit breaker to operate in the required time, in some instances not at all therefore the fault voltage will "sit" on any metallic parts of the installation and any main service pipework with the potential of transferring to YOU should you come into contact with the metalwork.


In other words it's a bit iffy.


Hope this helps.

 

[soulman]

i have shown my friend your replies and he contacted his electrcity provider they said they will install an rcd device free of charge.

 

[Spudnik]

Ok, as a very basic description of the issue of no RCD protection on a TT system.

Basically every fuse or circuit breaker has a job of disconnecting the supply within a specified time before fault voltages reach a dangerous level to touch.

Every fuse/circuit breaker has a maximum earth fault loop impedance value (the rough maximum is 7.5 ohms for a lighting circuit breaker) to which it will achieve this disconnection time. In a TT system the earth fault loop impedance is too high (usually between 50 and 200ohms) for the fuse/circuit breaker to achieve this disconnection time so we must provide additional earth fault protection with an RCD.

Without the presence of this RCD a fault voltage has the potential to reach a level above the accepted safe limit and NOT cause the fuse/circuit breaker to operate in the required time, in some instances not at all therefore the fault voltage will "sit" on any metallic parts of the installation and any main service pipework with the potential of transferring to YOU should you come into contact with the metalwork.


In other words it's a bit iffy.

Quality

 

[bugsy]

Well there you go -

 

[Guest123]

i have shown my friend your replies and he contacted his electrcity provider they said they will install an rcd device free of charge.

If I read that correctly then the DNO are going to install 1 RCD to offer blanket protection of ALL circuits......does this not contravene BS7671 regs with regard to minimising disruption in the event of a fault?????

Or is it just me???