rcd tripping fixed

[chrisreid186]

here's one to be aware of

today i installed some lights, fan and mirror light in a brand new bathroom, all new cable etc, tested R1+ R2 and insulation resistance all good, the feed came from existing light circuit and went into my rcd, (power breaker unit)

so went to liven it all up and the rcd tripped straight away, so thought maybe i got a switch and feed mixed up after testing, belled all switch's out and they were fine, pulled all the lights down to make sure polarity was correct which it was

really couldn't work out why the rcd wouldn't work, then i decided to do a zs test from the supply side of the rcd which pointed out their was no earth, had a look at some of the existing lighting circuit joint box's and the cpc's had just been chopped off and left unconnected..

ended up running a fly lead back to a joint box which did have a decent earth and this corrected the fault. took a couple of hours to rectify this problem and from now on i will always check zs before extending a circuit rather then later ,

i think the problem was down to induced voltage (eddy current) on cpc's which were not correctly earthed causing the rcd to trip???

the earthing system was tns

 

[IQ Electrical]

How did you have an R1+R2 reading if there was no continuity of cpc?

 

[DurhamSparky]

money on he R1 R2 only his new install...!!

 

[Deleted member 9648]

money on he R1 R2 only his new install...!!

Mine too....Chrisreid...an R1 R2 reading is taken from the testing point right back to the CU,(to include existing)not just the bit of cable you have installed.

 

[Deleted member 26818]

From the information contained in your OP, it appears you have only RCD protected part of the circuit.
What are your reasons for the departure from BS7671?
How do you consider that the departure offers the same degree of safety as would be achieved by compliance with BS7671?

 

[IQ Electrical]

From the information contained in your OP, it appears you have only RCD protected part of the circuit.
What are your reasons for the departure from BS7671?
How do you consider that the departure offers the same degree of safety as would be achieved by compliance with BS7671?

How is it a departure to only RCD protect the extended part of the existing circuit?

 

[DurhamSparky]

what he did was correct...!! ensured his new works complied with 7671:2008..... sod the rest of the install...!

 

[chrisreid186]

yep only R1+R2'd my part of the circuit but will calculate for cert, spin are you saying that to comply with the regs i need to rewire the whole lighting circuit as some switch cables only have 2 cores, think about how much disruption and cost the would cause the customer, i would need to chase out all the light switch drops pull new cables in, re-plaster then on top of that re decorate, if your quote covered all that for only adding 4 spots and a fan then the customer would run a mile, probably in the direction of the nearest cowboy

 

[Hawk81]

From the information contained in your OP, it appears you have only RCD protected part of the circuit.
What are your reasons for the departure from BS7671?
How do you consider that the departure offers the same degree of safety as would be achieved by compliance with BS7671?

Please explain this further.

 

[High Tower]

Please explain this further.

#

I did wonder myself!

 

[Deleted member 26818]

How is it a departure to only RCD protect the extended part of the existing circuit?

Because BS7671 requires that the whole of the circuit of the location be RCD protected 701.411.3.3.
By only protecting part of the circuit, you are allowing any current caused by an earth fault on the unprotected part of the circuit to bypass the RCD into the location.

 

[Deleted member 9648]

I dont have access to my BRB but would question this.
The circuit,whether RCD protected or not must disconnect within 0.4s.....therefore regardless of the means of ADS the fault voltage will still be introduced into the locations conductive parts for the duration of the fault even if the whole of the circuit is protected....Your theory does not stack up.

 

[Deleted member 26818]

I dont have access to my BRB but would question this.
The circuit,whether RCD protected or not must disconnect within 0.4s.....therefore regardless of the means of ADS the fault voltage will still be introduced into the locations conductive parts for the duration of the fault even if the whole of the circuit is protected....Your theory does not stack up.

BS7671 requires the use of a device that disconnects 10 times quicker in this particular case, and at an amperage 200 times lower than that which would be allowed before ADS is achieved by using another device.
ADS wouldn't even be achieved if the current was 100 times that allowed for the operation of an RCD.

 

[Deleted member 9648]

It's not the amperage that is relevant to a fault outside of the location...it is the voltage that will be introduced onto conductive parts by a fault on a part of the circuit not within the location,and that voltage will be introduced regardless of whether the circuit is on an RCD at the origin of the circuit...or just covering the location.
I will have a look at the reg you have quoted on monday....not committing myself till then!

 

[DurhamSparky]

regulation 701.411.3.3 Additional Protection by RCD's

Additional protection shall be provided for all circuits of the location, by use of one or more Rcd's having the characteristics specified in regulation 415.1.1..........

where does it say the full circuit needs to be RCD...??? the OP has RCD'd the bathroom via a RCD FCU at origin of the power into the bathroom (in this case a feed from a lighting circuit) how has this not complied...!