Lighting with no CPC and installing new CU (Domestic)

[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