How to Find earth Break in ring main

[dingbat]

No.

One circuit, one protective device, whether it's a ring, a radial, or multiple radial branches from a common origin.

If he had put both legs of the ring into one 20A MCB and then confirmed that the earth fault loop impedance was acceptable at each and every socket outlet, then that would have been just okay, although he should have diagnosed the fault properly and separated into two entirely separate radial circuits, but to allow any circuit conductors to be energised from two different MCBs is so, so wrong.

 

[bernardgreen]

Out of interest, why would a dual source of supply dangerous. Isn't the same as a ring main. Thats dual sourced (i.e. i.e Current will go clockwise or anticlockwise around in a ring to the socket.)

No it is single sourced onto two parallel routes to the sockets on the ring.

Because the two sources in parallel each take a nearly equal share of the load current. So two 20 amp breakers in parallel and 40 amps could flow before both get the 20 needed to break. If there is a spur of the ring and that spur has the fault then it is 30 amps on that 2.5 mm cable neither of the MCBs will trip ( they each have about 15 amps ) andthat cable is a hazard.

 

[richardhill84]

Out of interest, why would a dual source of supply dangerous. Isn't the same as a ring main. Thats dual sourced (i.e. i.e Current will go clockwise or anticlockwise around in a ring to the socket.)

No it is single sourced onto two parallel routes to the sockets on the ring.

Because the two sources in parallel each take a nearly equal share of the load current. So two 20 amp breakers in parallel and 40 amps could flow before both get the 20 needed to break. If there is a spur of the ring and that spur has the fault then it is 30 amps on that 2.5 mm cable neither of the MCBs will trip ( they each have about 15 amps ) and that cable is a hazard.

Thanks for the replies.

In response to a previous question, with the first MCB off and the second on, no sockets work in the house. So i can safely assume that it IS NOT 'dual source of supply'.

I'm just a tad confuded as to what he has done and why. Maybe i should give him a call to clarify. Just seems odd that iv'e gone from a 32AMP ring to a single 20AMP radial and a second 20AMP MCB that doesn't do anything.

 

[ELZ4742]

Yes, Turning off one MCB keeps all the sockets 'energised'.

and

i cant believe this guy has put the ends of each of the ring in 2 rcds. thats like soooo dodgy!

the best cource of action would be to identify 2 sockets that are obviously joined between each other and disconnct the cable that joins them.

this wont cure your earth continuity problem but at least you wont have 2 seperate mcbs on the same circuit.

 

[ELZ4742]

ok, just read your last comment, forget everything i just said....

except it really should be on a 16a breaker

 

[richardhill84]

Yes, Turning off one MCB keeps all the sockets 'energised'.

and

i cant believe this guy has put the ends of each of the ring in 2 rcds. thats like soooo dodgy!

the best cource of action would be to identify 2 sockets that are obviously joined between each other and disconnct the cable that joins them.

this wont cure your earth continuity problem but at least you wont have 2 seperate mcbs on the same circuit.

ELZ4742: Pls see previous post. The second MCB doesn't do seem to do anything.

 

[ELZ4742]

read my last post

 

[Steve]

except it really should be on a 16a breaker

 

[ELZ4742]

except it really should be on a 16a breaker

its called good practise..

 

[richardhill84]

why 16A?

 

[ELZ4742]

16 x 2 = 32a

kind of like putting a ring on 20 x 2 = 40a.

although its not actually wrong so-to-speak, just good practise.



4mm radial would go onto a 20a

 

[Steve]

But the capacity of 2.5mm² is 27 amps optimum. So this is why we can make radials rated at 20 amps with 2.5mm² cable.

4mm² radials are rated at 32A as a rule.

 

[ELZ4742]

But the capacity of 2.5mm² is 27 amps optimum. So this is why we can make radials rated at 20 amps with 2.5mm² cable.

4mm² radials are rated at 32A as a rule.

1.0mm cable is rated at 12a, would u put a lighting circuit on a 10a?

 

[dingbat]

16 x 2 + 32a

kind of like putting a ring on 20 x 2 = 40a.

4mm radial would go onto a 20a

Bolleaux. You are confused. Read BS 7671 Appendix 4... from the beginning. (We're not talking about BS 3036 fuses and 1 sq mm CPCs here.)

 

[Steve]

But the capacity of 2.5mm² is 27 amps optimum. So this is why we can make radials rated at 20 amps with 2.5mm² cable.

4mm² radials are rated at 32A as a rule.

1.0mm cable is rated at 12a, would u put a lighting circuit on a 10a?

For a short run, if all the tests checked out, maybe. But 1.5mm² is made for 10 amp lighting circuits.