Installing two double sockets in loft..

[RF Lighting]

One tutor said not to cut into the ring in a JB so as to maintain the integrity of the wiring and not sleeve the earth.

A properley fitted joint box is no different to the two cables at the back of a socket. If you were not to cut the ring cable to maintain the integrity of the ring, then should we not be loopint the cable at a socket, and connecting the front to an uncut, unsleeved cable?

Anyway when you test the circuit afer working on it (like you must), this will show if you have lost the continuity on the ring circuit cables.

T'other one said cut the earth and sleeve it....

yup

Blokes at work said 'Uh! Why not cut the wires?'

yup

 

[RMS]

just to add,

when the earth is cut you can then sleeve it up wich is always the case with any joint box that is accessable.

RMS

 

[RMS]

RF,

dont understand what you mean about loosing continuity on the ring circuit cables, can you elaborate?

RMS

 

[Carloss]

Obviuosly the earth wire has to be cut but the live and neutral wires do not.

RMS

This is how i do it... one of the reasons for this is stated below. Was also what i were taught when i done testing and inspection 2391.

One tutor said not to cut into the ring in a JB so as to maintain the integrity of the wiring and not sleeve the earth.

'

There are many ways of doing it.
personal preference i guess.... i dont like breaking live conductors in an unaccessible place; reason for this is someone local had a loft fire because 'jim' filled the loft up with crap placing stuff on top of a jb obviously knocking it around a cable came out of the terminal and arched which caused a fire and caused ££££ worth of damage.

Its different for terminating into a back of a socket... its not as if the customer can pull the gogo gadget socket off the wall and move it around. as said before testing would pick up an open ring.

carlos

 

[RF Lighting]

There are many ways of doing it.
personal preference i guess.... i dont like breaking live conductors in an unaccessible place; reason for this is someone local had a loft fire because 'jim' filled the loft up with rubbish placing stuff on top of a jb obviously knocking it around a cable came out of the terminal and arched which caused a fire and caused ££££ worth of damage.

If the joint box has been properly made off, and screwed down then this will not happen.

The house fire would not be the fault of 'jim' and his rubbish, it would be the fault of the installer of the joint box.

There is just as much (if not more) chance that the cable feeding the spur will cause the arcing anyway, and short of soldering this is no worse or more dangerous than cutting and jointing the cable.

A splice with a spur is pointless.

 

[plugwash]

btw from a physical point of view just cutting the earth works very well (since the earth is in the center it needs to be slightly shorter than the others). But i'm not sure i like making the earth connection lower integrity than the others.

 

[RF Lighting]

RF,

dont understand what you mean about loosing continuity on the ring circuit cables, can you elaborate?

RMS

Right, I've done it in pictures as it is a bit difficult to explain.

This is how the circuit should be:

If the joint box is not properly made off the ring continuity could be lost.
I have shown a break on the live conductor. The circuit would continue to operate without a loss of power, but you now have what is effectivly two 20A radial circuits connected to a 32A MCB.

However carrying out an end - to - end continuity test of the ring will show that the live is open circuit.

Break in circuit:

I also added a spur of a spur (for the OP)
The cable between the joint box and the first spur could be overloaded, as you could draw 32A through the cable which can be rated as low as 18.5A

 

[RMS]

RF, what if you have to joint to a cable in a loft and there is no slack because the cable is neatly ran and clipped. Splicing it is the only option, i'm not siggessting that this the way to do all joints but ive had to do this on about 3 occassions in my six years in the trade.

Plugwash, think your clutching at straws with that statement

RMS

 

[RF Lighting]

RF, what if you have to joint to a cable in a loft and there is no slack because the cable is neatly ran and clipped. Splicing it is the only option, i'm not siggessting that this the way to do all joints but ive had to do this on about 3 occassions in my six years in the trade.

Plugwash, think your clutching at straws with that statement

RMS

I am not against splicing and I have on occasion had to do it my self due to lack of spare cable. I am just saying that it is not nescassary (and IMHO pointless) to splice every single joint box you make off.

 

[Pensdown]

Obviuosly the earth wire has to be cut but the live and neutral wires do not.

RMS

This is how i do it... one of the reasons for this is stated below. Was also what i were taught when i done testing and inspection 2391.

So from an electrical safety point of view, it's OK to cut and join the most important conductor but not the L&N?

 

[RMS]

RF, what if you have to joint to a cable in a loft and there is no slack because the cable is neatly ran and clipped. Splicing it is the only option, i'm not siggessting that this the way to do all joints but ive had to do this on about 3 occassions in my six years in the trade.

Plugwash, think your clutching at straws with that statement

RMS

I am not against splicing and I have on occasion had to do it my self due to lack of spare cable. I am just saying that it is not nescassary (and IMHO pointless) to splice every single joint box you make off.

RF, i agree with what you say here completely.

Pensdown, from an electrical safety point of veiw can you explain why the earth wire in a circuit is normally smaller and of higher resistance than the live conductors?

There is nothing wrong with cutting the earth wire as long as you maintain the mechanical connection and coninuity whch is proven on testing and inspection of the circuirt.

RMS

 

[RF Lighting]

from an electrical safety point of veiw can you explain why the earth wire in a circuit is normally smaller and of higher resistance than the live conductors?

Simple.
The live and neutral conductors are designed to theire rated load continually. So for example if you have a 2.5mm² T+E installed to reference method 3 it will happily carry 23A for 24 hours a day without getting hot and causing problems by being overloaded.
The earth conductor is smaller and has a slightly higher resistance because it is, to give it it's proper name, a Circuit Protective Conductor (CPC).
The only time this wire will be carrying any real current* is in the event of a fault such as a short circuit from live to earth, where both the live and earth will be carrying sometimes as much as 2000A but this high current will cause the Over Current Protective Device (fuse / MCB) to operate therefore removing the power. This is why your Zs must be low enough for the type of OCPD that is protecting the circuit, (see appendix 2 of the OSG) so that the current will be cut within a maximum of 5 seconds.

The lower the value of Zs, the more current will flow in the event of a fault, and the quicker the OCPD will operate.

So in summary the earth is smaller as it is designed to carry current for a very short amount of time (max 5 secs) in the event of a fault, whereas the live and neutral are designed for carrying current all the time.

*the earth will be carying a little current all the time, but it will only be earth leakage from appliances, and will be only a few mA.

There is nothing wrong with cutting the earth wire as long as you maintain the mechanical connection and coninuity whch is proven on testing and inspection of the circuirt.

RMS

There is nothing wrong with cutting the live or neutral either.

 

[RMS]

RF,

at what point did i say that it was impotant not to cut the live conductors?

RMS

 

[RF Lighting]

I never said that you did.

 

[Pensdown]

from an electrical safety point of veiw can you explain why the earth wire in a circuit is normally smaller and of higher resistance than the live conductors?

Simple.
The live and neutral conductors are designed to theire rated load continually. So for example if you have a 2.5mm² t+e installed to reference method 3 it will happily carry 23A for 24 hours a day without getting hot and causing problems by being overloaded.
The earth conductor is smaller and has a slightly higher resistance because it is, to give it it's proper name, a Circuit Protective Conductor (cpc).
The only time this wire will be carrying any real current* is in the event of a fault such as a short circuit from live to earth, where both the live and earth will be carrying sometimes as much as 2000A but this high current will cause the Over Current Protective Device (fuse / mcb) to operate therefore removing the power. This is why your zs must be low enough for the type of ocpd that is protecting the circuit, (see appendix 2 of the OSG) so that the current will be cut within a maximum of 5 seconds.

The lower the value of Zs, the more current will flow in the event of a fault, and the quicker the OCPD will operate.

So in summary the earth is smaller as it is designed to carry current for a very short amount of time (max 5 secs) in the event of a fault, whereas the live and neutral are designed for carrying current all the time.

*the earth will be carying a little current all the time, but it will only be earth leakage from appliances, and will be only a few mA.

There is nothing wrong with cutting the earth wire as long as you maintain the mechanical connection and coninuity whch is proven on testing and inspection of the circuirt.

RMS

There is nothing wrong with cutting the live or neutral either.

Thanks for that RF, you've saved me spending the rest of the day typing!

I think we are all saying the same thing. My comment was if you have enough slack, why go to the trouble of splicing a cable when you will have to cut at least one core and that core is as /more important.