Lighting with no CPC and installing new CU (Domestic) | Page 4 | on ElectriciansForums

Discuss Lighting with no CPC and installing new CU (Domestic) in the Domestic Electrician Forum area at ElectriciansForums.net

SJD

-
Mentor
Arms
Joined
Feb 10, 2012
Messages
2,287
Reaction score
2,976
Location
Braccan heal
I have the ESC’s guide to replacing a CU where the lighting circuits have no CPC, and this says the initial approach should be to persuade the customer to upgrade the circuit to provide CPCs. If that fails, the guide then includes a risk assessment table (at the back), where it is allowed to proceed with the CU replacement if certain conditions are met (like no class 1 fittings, for example).

My question is, in practice, for those out there meeting this situation on a regular basis, what is the typical outcome (assuming the circuit meets insulation test requirements)?

Do you generally persuade the customer to upgrade the circuit (or decline to do the job)?
And if you do upgrade the circuit, do you typically rewire with new T&E, or instead fit a separate CPC and use the existing wiring?
Or are you happy to remove any class 1 fittings, place a warning notice, and proceed with the CU replacement with the existing wiring as is?

I'm thinking of an inhabited property, where costs and disruption are a concern, and all the customer originally wanted was a new CU to replace an old fuse box.
 
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
 
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.
 
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.
 
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.
 
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
 
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 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
 

Reply to Lighting with no CPC and installing new CU (Domestic) in the Domestic Electrician Forum area at ElectriciansForums.net

News and Offers from Sponsors

  • Article
Join us at electronica 2024 in Munich! Since 1964, electronica has been the premier event for technology enthusiasts and industry professionals...
    • Like
Replies
0
Views
710
  • Sticky
  • Article
Good to know thanks, one can never have enough places to source parts from!
Replies
4
Views
1K
  • Article
OFFICIAL SPONSORS These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then...
Replies
0
Views
3K

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

YOUR Unread Posts

This website was designed, optimised and is hosted by untold.media Operating under the name Untold Media since 2001.
Back
Top