Lighting Fault, Earth to Neutral Tripping RCD

[silentboarder69]

Hi,
I was called to a customers house as their RCD keeps tripping. I isolated the faulty circuit and began testing.
The fault unfortunately is on the feed from the CU to the 1st floor lighting circuit, and between the neutral and CPC.
I know from installing CUs, that if a lighting circuit has no CPC, you can still install a new CU as long as the resistance between R1/Rn and the earth terminal is > 1MOhm, you can install the new CU (ESC Best Practice Guide 6).
The customer has just had their house refitted, and it wouldn't be ideal to replace the faulty cable.

Would it be safe to reconnect the circuit without connecting the CPC? It is RCD protected. Assuming it meets the tests outlined in ESC Best Practice Guide?
If it is OK, would there be any point in connecting the CPC to the CPC on the 32A circuit?

I'm just exploring these options...

 

[somersetsparks]

Not really IMO. What has caused the fault?

 

[Deleted member 9648]

No....not acceptable IMO. The cable is clearly damaged,and if you remove the cpc you cant justify by the fact that there's an RCD protecting because without an earth fault path the RCD is redundant as a means of disconnection if the fault 'develops'......a way to rewire the affected cable or otherwise clear the fault has to be found.

 

[silentboarder69]

Not really IMO. What has caused the fault?

No idea. The installation is approx six months old. The CU is in the cellar, and the first point is on the first floor. There is nothing obvious, so anything I say would be a pure guess. There doesn't seem to be any defects in the walls, or new work that has been carried out since the installation. I could only guess at rodent damage?

 

[ExArmy]

would it be easy to connect the the first point of the lighting circuit to the nearest other CPC on the first floor? i have no idea if this is acceptable or not, just a thought

 

[Strima]

No idea. The installation is approx six months old. The CU is in the cellar, and the first point is on the first floor. There is nothing obvious, so anything I say would be a pure guess. There doesn't seem to be any defects in the walls, or new work that has been carried out since the installation. I could only guess at rodent damage?

Carpets, plumbing, things screwed into the ceilings etc etc etc???

If all the points are in good order then it's break the circuit into legs and test until you find the culprit. If it's a damaged cable then it needs replacing.

 

[somersetsparks]

It is fairly uncommon but I have known the neutral to be moulded into the earth in T+E direct from the factory, only showed up under load. Whatever your problem is though, disconnecting the earth is not an option, all circuits have required a cpc since (quite a long time, well before my time) and think if you were to remove the earth and leave it in the cables (i.e. cut off the ends) any further faults e.g. screws through cable, would not be detected but could lead to a nasty belt from the un-earthed cpc.

Find the fault and repair it is the only option!
Good luck!

 

[telectrix]

as above posts.bite the bullet and replace the damaged section. maybe you can find a route up in cupboards.

 

[Knobhead]

I can’t believe you even considered disconnecting the earth, never mind coming on here asking if it’s OK.

First and foremost it would be downright dangerous as others have explained.

 

[Edd]

Not sure how many lights your talking about, and if theres other lighting circuits.(would be best if there is) But what about disconecting the damaged leg completley and Refeeding any of the affected lights via a fused spur off a socket.
not ideal and rewireing the faulty leg would be best but sometimes needs must...

 

[Darkwood]

The fault is what it is if it needs replacing thus effecting the deco then that be the case.... yes take your customers wishes into account but dont let the cart lead the horse here, communication is just as much a skill as been competent so break the lighting circuit down into sections, find the offending section and further break it down until you have located the fault to one leg or joint in the cable then tell the customer what is required and the options be careful they dont dictate to you but be aware of their concerns.
NO! its not acceptable to piggy back the earth onto another circuit, final circuit earthing must be seperate in your particular case, just for reference it is permitted to use 1 earth for multiple circuits if say your using a trunking or conduit as the earthing with more than one circuit contained within, in you idea all it would take is for someone to disconnect the earth of another circuit to effectively leave the lighting without earthing whether this be for testing purposes or alterations by a future electrician.

Check also that outside lighting isnt the issue here with water ingress, ask if any recent works have been done be it pro' or DIY of any type, get as much info as possible, the number of times in my early days ive located a fault and the customer has then said Oh yes we just had someone in working on or fitting that.... now i know exactly what to ask to minimise my time and effort and keep the customer smiling....in most cases!

 

[silentboarder69]

The Electrical Safety Council say it's fine to wire up a lighting circuit with no CPC, why don't you send your poorly thought out email to them as that's where I got my info, and I would suggest they know more than you.

This is supposed to be a professional forum, not a childs forum for slagging people off. I suggest you find an alternative forum if this is what you wish to do.

 

[silentboarder69]

I can’t believe you even considered disconnecting the earth, never mind coming on here asking if it’s OK.

First and foremost it would be downright dangerous as others have explained.

The Electrical Safety Council say it's fine to wire up a lighting circuit with no CPC, why don't you send your poorly thought out email to them as that's where I got my info, and I would suggest they know more than you.

This is supposed to be a professional forum, not a childs forum for slagging people off. I suggest you find an alternative forum if this is what you wish to do.

 

[silentboarder69]

The fault is what it is if it needs replacing thus effecting the deco then that be the case.... yes take your customers wishes into account but dont let the cart lead the horse here, communication is just as much a skill as been competent so break the lighting circuit down into sections, find the offending section and further break it down until you have located the fault to one leg or joint in the cable then tell the customer what is required and the options be careful they dont dictate to you but be aware of their concerns.
NO! its not acceptable to piggy back the earth onto another circuit, final circuit earthing must be seperate in your particular case, just for reference it is permitted to use 1 earth for multiple circuits if say your using a trunking or conduit as the earthing with more than one circuit contained within, in you idea all it would take is for someone to disconnect the earth of another circuit to effectively leave the lighting without earthing whether this be for testing purposes or alterations by a future electrician.

Check also that outside lighting isnt the issue here with water ingress, ask if any recent works have been done be it pro' or DIY of any type, get as much info as possible, the number of times in my early days ive located a fault and the customer has then said Oh yes we just had someone in working on or fitting that.... now i know exactly what to ask to minimise my time and effort and keep the customer smiling....in most cases!

Thanks mate, that makes perfect sense re the CPC connecting to another circuit.

Re the fault, I have located it, but it's the worst kind, a fault in a cable burried in the wall. My first line of advice was to replace the faulty cable, but just want to be double sure I'm not creating work when there may be a better option. A fused spur off the 32A may be a good alternative that I hadn't thought of.

All the best.

 

[Darkwood]

The Electrical Safety Council say it's fine to wire up a lighting circuit with no CPC, why don't you send your poorly thought out email to them as that's where I got my info, and I would suggest they know more than you.

This is supposed to be a professional forum, not a childs forum for slagging people off. I suggest you find an alternative forum if this is what you wish to do.

Who are you directing this at? My post IMHO is both helpful and informative, having no earth in a lighting circuit can be acceptable but usually steps have to be taken, clearly identified at the board all fixtures and fittings are class 2 etc etc ... you case is you are going into an existing circuit which has an earth, therefore you cannot leave it without an earth to satisfy clearing a fault as you would be leaving it less safe than you originally found it.

Edit..... soz was typing before you posted last so ignore the first bit of this.