Lighting with no CPC and installing new CU (Domestic)

[Silly Sausage]

So I just took two brand new pendant / ceiling rose prewired light fittings from my stock, one MK, one another brand, and tested resistance from the pins to the L and N terminals in the ceiling rose. In both cases, the pins are just connected, NO force is needed to make the connection.

morph is talking about lamp holders like these...
http://download.hager.com/Hager.ie/files_download/catalogue/Ashley_Wiring_Accessories.pdf

 

[SJD]

morph is talking about lamp holders like these...
http://download.hager.com/Hager.ie/files_download/catalogue/Ashley_Wiring_Accessories.pdf

Actually a quick search shows these quite reasonably priced, I'll consider using them in future instead of the the usual MK ones I've been buying, thanks.

 

[morph]

i love the hager range especially the switches with N terminals, wait a minute N's in switches ? is that allowed
LOL

 

[Geoffsd]

An RCD will make a (lighting) circuit without a cpc safer.

Obviously if all the fittings and accessories are plastic then the situation is not likely to occur, other than putting your fingers on the contacts.
Following this argument would mean that an RCD is of no use on an electric shower circuit as the shower is plastic.

However, should the homeowner fit a class one light fitting or switch on a circuit without a cpc and a fault occur causing it to become live then if touched the RCD will operate and disconnect the supply.
Therefore the circuit is safer because of the RCD.

RCDs do not rely on or use the cpc (other than N-cpc faults) to achieve their intended purpose and so the argument that they will not make a circuit without a cpc safer has no basis.
RCDs have the same result whether or not the circuit has a cpc (other than N-cpc faults).

 

[morph]

An RCD will make a (lighting) circuit without a cpc safer.

Obviously if all the fittings and accessories are plastic then the situation is not likely to occur, other than putting your fingers on the contacts.
Following this argument would mean that an RCD is of no use on an electric shower circuit as the shower is plastic.

However, should the homeowner fit a class one light fitting or switch on a circuit without a cpc and a fault occur causing it to become live then if touched the RCD will operate and disconnect the supply.
Therefore the circuit is safer because of the RCD.

RCDs do not rely on or use the cpc
are you for real ??
(other than N-cpc faults) to achieve their intended purpose and so the argument that they will not make a circuit without a cpc safer has no basis.
RCDs have the same result whether or not the circuit has a cpc (other than N-cpc faults).

rcd must have an earth to operate .......... L-E FAULT rcd trips
N-E FAULT rcd trips
L-N FAULT rcd does not trip since this is short circuit
so how does an rcd make it safer without an earth??????
you cant say what if the customer does this etc in the future , what if the customer opens the consumer unit and licks the buzz bar
should we lock the consumer unit away ???

 

[Geoffsd]

rcd must have an earth to operate

For shock protection - their purpose - yes, they need an earth path,i.e. a person, not a cpc.

What will happen if you touch a live exposed conductive part which has no cpc but is protected by an RCD?

 

[oldtimer]

Ok here is a scenario that I have encountered a customer got a shock because he was putting the kettle on whilst switching the kitchen lights on what was found was that there was no earth at the switch and the shock he got was induced AC as the fault was fixed by reconnecting the earth but what if the switch box was live now in the same scenario would you prefer an RCD or not I dont think there is or should be a debate here because I know what level of protection I would want

 

[Geoffsd]

L-E FAULT rcd trips

MCB would trip anyway but I thought we were talking about circuit without cpc.

N-E FAULT rcd trips

Agreed. I did say other than N-E but I thought we were talking about circuit without cpc.

L-N FAULT rcd does not trip since this is short circuit

MCB would trip anyway.

so how does an rcd make it safer without an earth??????

See above.

you cant say what if the customer does this etc in the future

If they have done it in the past it will be safer with an RCD.

what if the customer opens the consumer unit and licks the buzz bar

It will be safer (? less dangerous) with an RCD.

 

[somersetsparks]

rcd must have an earth to operate .......... L-E FAULT rcd trips
N-E FAULT rcd trips
L-N FAULT rcd does not trip since this is short circuit
so how does an rcd make it safer without an earth??????
you cant say what if the customer does this etc in the future , what if the customer opens the consumer unit and licks the buzz bar
should we lock the consumer unit away ???

Morph mate think about it, If you touch a live contact. I.e. lampholder pin, the current flows through you to earth, so regardless of having a CPC in the circuit and RCD will theoretically make it safer. RCD's act on imbalance of current between L and N, They don't care whether circuits have an earth,

If you touch a live contact stood on the bath on a NON-RCD protected circuit, 6A would need to flow through you to operate the MCB
If you touch a live contact stood on the bath on an RCD protected circuit, 30mA Would need to flow through you to earth (through the bath) to operate the RCD.

CPC in the circuit is irrelevent in this case. In fact I think the issue you are having is distinguishing between a circuits CPC and EARTHING.

 

[Pat Tester]

Is it not the case that if you were to touch the live terminal, conductor etc, you would unless standing on a rubber mat provide a path to earth for the current to flow (hence a shock) so this would unbalance one side of the rcd or rcbo and cause it to trip ? If so this would be the case with or without an cpc in circuit.

 

[somersetsparks]

Yes dead right! ^^^^

 

[nickblake]

rcd must have an earth to operate .......... L-E FAULT rcd trips
N-E FAULT rcd trips
L-N FAULT rcd does not trip since this is short circuit
so how does an rcd make it safer without an earth??????
you cant say what if the customer does this etc in the future , what if the customer opens the consumer unit and licks the buzz bar
should we lock the consumer unit away ???

No it doesnt nessesarilly it needs to have an inbalance if a neutral is disconnected whilst a circuit is in operation could cause an inbalance and operate the RCD yes an earth is an advantage . if you have a L to E fault then you will get a bang and trip the MCB as well as the RCD , and if the customer takes the cover off the consumer unit and licks the buss bar then appart from the benifits of an RCD they should seek Psychiatric help too

 

[morph]

yes theoretically if you quickly wip the neut out, it may pop out , but i would nt be certain

 

[morph]

For shock protection - their purpose - yes, they need an earth path,i.e. a person, not a cpc.

What will happen if you touch a live exposed conductive part which has no cpc but is protected by an RCD?

yes i fully agree but the initial claim was
all plastic circuit without cpc rcd makes safer in general use
but it wont be safer under normal useonly if some one takes something apart or does something silly
the rcd is additional protection which should operate before someone touchs a live part not because they do

 

[morph]

Morph mate think about it, If you touch a live contact. I.e. lampholder pin, the current flows through you to earth, so regardless of having a CPC in the circuit and RCD will theoretically make it safer. RCD's act on imbalance of current between L and N, They don't care whether circuits have an earth,

If you touch a live contact stood on the bath on a NON-RCD protected circuit, 6A would need to flow through you to operate the MCB
If you touch a live contact stood on the bath on an RCD protected circuit, 30mA Would need to flow through you to earth (through the bath) to operate the RCD.

CPC in the circuit is irrelevent in this case. In fact I think the issue you are having is distinguishing between a circuits CPC and EARTHING.

again fully agree mate
my post up there somewhere said i was playing devils advocate
my point was an rcd in a circuit without cpc would not be helpfull, untill an earth is provided , if a human or similar beast should provide that earth then it aint good, the average human / beast has a varying resistance and so disconnection times could be a tad longer than comfortable all though it would still be quicker than a 6 amp breaker