So could a missing earth on a radial circuit 
Ring Finals Vs Radials
- Thread starter PrenticeBoyofDerry
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Try to imagine an environment where a shortage of materials had not coincided with a rapidly increasing use of portable and non-fixed appliances, and radials were all that had been known.
Hand on heart, can you honestly say that if someone had put forward the idea of turning radials into rings so that the OPD rating could be doubled, and changing the design of plugs so that they could be fused, and devising special testing sequences, and creating the need to limit how branches would have to be done, it would have been seen as a good idea?
Hand on heart, can you honestly say that if someone had put forward the idea of turning radials into rings so that the OPD rating could be doubled, and changing the design of plugs so that they could be fused, and devising special testing sequences, and creating the need to limit how branches would have to be done, it would have been seen as a good idea?
I've been wondering for a while whether it would be possible, in theory, to use an RCD-like device with the lives from both ends of the ring in it and another with both neutrals in it. Break the ring, pop goes the RCD.
I'm thinking if you had a ring with a kettle plugged into the first socket the current on the shorter path would be higher than the current on the longer (less wire, less resistance) so you couldn't have the RCD-like device being too sensitive but then again, if you were only using them to protect against breaks in the ring you wouldn't need them to be very sensitive.
In theory an idea that could work or carpet chewing lunacy based on misunderstanding?
H
holmslaw
..
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DCC.. carpet chewing lunacy..
some interesting ideas there.
I guess both would take up too much room in the CU.
and with two MCB's you would need to make sure both were turned off if starting work.
An O/C neutral fault wouldn't be detected though.
I guess both would take up too much room in the CU.
and with two MCB's you would need to make sure both were turned off if starting work.
An O/C neutral fault wouldn't be detected though.
might be possible with a 3 phase + N rcd..
H
holmslaw
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I have seen the debate many times between ring and radial.
The radial does clearly have the advantage that the circuit can’t be broken without the user knowing and as a result overload likely hood is reduced.
However if you reduce the protective device size then you also increase the likelihood that a single circuit load will exceed the size of overload device. So once you reduce the size of the overload device then just 13A devices will cause an overload.
So I would say only by using 4mm² or 6mm² cable could one really move to radials, unless you go to old method of one socket to each fuse/mcb.
Using 4mm cable is still only 27A so either 90ºC cable or 6mm² is required, and the latter is right on the limit of what will fit in the holes so it will mean no spurs can be added.
Also there is the volt drop problem and although heaver cable is used it will still require extra circuits to keep cable length within volt drop limits.
Although the idea of twin mcb’s on rings may at first glance seem to cure some of the problems when one looks closer it would also need to monitor current in neutral cable as well so would need a quad mcb.
If new sockets were made available with twin terminals so 6mm² cable could be better accommodated then I agree the radial would be better option but although a radial per room will in most cases satisfy the needs in most houses in most rooms the kitchen it unlikely to be able to be served by a single 20A supply. To ensure that kettle and washing machine never end up on same supply would not be easy so likely kitchens will need 32A supplies.
So until manufactures alter their designs I think we as stuck with the ring main at least for kitchens.
The other problem is people expect ring mains and where 4mm² is used for a 32A radial it is very easy for electricians to make mistakes and extend them with 2.5mm² thinking it is a ring main. And even easier for DIY people to make the mistake.
I think to use Ali-tube 4mm² for radial circuits may work well and because the cable is not twin and earth people are likely to question what they have and less mistakes are likely to be made.
However using 4mm² twin and earth on a radial is asking for problems as even if 90ºC cable is used likely people working on it latter will make mistakes. 6mm² is too thick. So in the main I think the ring is here to stay.
The radial does clearly have the advantage that the circuit can’t be broken without the user knowing and as a result overload likely hood is reduced.
However if you reduce the protective device size then you also increase the likelihood that a single circuit load will exceed the size of overload device. So once you reduce the size of the overload device then just 13A devices will cause an overload.
So I would say only by using 4mm² or 6mm² cable could one really move to radials, unless you go to old method of one socket to each fuse/mcb.
Using 4mm cable is still only 27A so either 90ºC cable or 6mm² is required, and the latter is right on the limit of what will fit in the holes so it will mean no spurs can be added.
Also there is the volt drop problem and although heaver cable is used it will still require extra circuits to keep cable length within volt drop limits.
Although the idea of twin mcb’s on rings may at first glance seem to cure some of the problems when one looks closer it would also need to monitor current in neutral cable as well so would need a quad mcb.
If new sockets were made available with twin terminals so 6mm² cable could be better accommodated then I agree the radial would be better option but although a radial per room will in most cases satisfy the needs in most houses in most rooms the kitchen it unlikely to be able to be served by a single 20A supply. To ensure that kettle and washing machine never end up on same supply would not be easy so likely kitchens will need 32A supplies.
So until manufactures alter their designs I think we as stuck with the ring main at least for kitchens.
The other problem is people expect ring mains and where 4mm² is used for a 32A radial it is very easy for electricians to make mistakes and extend them with 2.5mm² thinking it is a ring main. And even easier for DIY people to make the mistake.
I think to use Ali-tube 4mm² for radial circuits may work well and because the cable is not twin and earth people are likely to question what they have and less mistakes are likely to be made.
However using 4mm² twin and earth on a radial is asking for problems as even if 90ºC cable is used likely people working on it latter will make mistakes. 6mm² is too thick. So in the main I think the ring is here to stay.
No it doesn't as the protection is in the line conductor only. 2 MCBs for one circuit is a rubbish idea imo.
Is this a problem commonly experienced in countries where 16A radials are the norm?
I can't imagine a situation where an electrician would be confused about what the circuit was, and what size cable to use.
And IMO a DIYer is more likely to simply copy the cable size that's already there.
I wonder how on earth the rest of the world manages...
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BAS said
Let's see now:
1) no problem turning radials into rings;
2) plug design was achieved without any great difficulty;
3) devising special test sequences - which ones are they then - I don't know of any 'special' requirements in BS 7671 other than checking continuity - a bell & battery will do nicely for that;
4) limiting branches - not sure what you mean by that, but all circuit designs have some limits. I understand that radial circuits in France are limited to eight outlets - mind you I have not checked that in the French national standard.
BAS said
Well they do 'manage' don't they, but do they have the high degree of flexibility we have? The supply in many continental countries has a lower capacity then ours (often just 40A), so maybe they have just learned to live with their inferior systems.
BTW, we will eventually lose the ring main and the BS 1363 socket and plug will soon follow. We will then have to install radial circuits similar to those used elsewhere in Europe. Forget radials with unlimited outlets - they require BS 1363 socket outlets.
We will ultimately loose the ring main because Group Schneider and some other large companies want us to. They want to sell structured wiring systems across the EU and the ring main does not fit in with their plans. They can, and do, swamp standards committees so they will eventually succeed.
Let's see now:
1) no problem turning radials into rings;
2) plug design was achieved without any great difficulty;
3) devising special test sequences - which ones are they then - I don't know of any 'special' requirements in BS 7671 other than checking continuity - a bell & battery will do nicely for that;
4) limiting branches - not sure what you mean by that, but all circuit designs have some limits. I understand that radial circuits in France are limited to eight outlets - mind you I have not checked that in the French national standard.
BAS said
Well they do 'manage' don't they, but do they have the high degree of flexibility we have? The supply in many continental countries has a lower capacity then ours (often just 40A), so maybe they have just learned to live with their inferior systems.
BTW, we will eventually lose the ring main and the BS 1363 socket and plug will soon follow. We will then have to install radial circuits similar to those used elsewhere in Europe. Forget radials with unlimited outlets - they require BS 1363 socket outlets.
We will ultimately loose the ring main because Group Schneider and some other large companies want us to. They want to sell structured wiring systems across the EU and the ring main does not fit in with their plans. They can, and do, swamp standards committees so they will eventually succeed.
H
holmslaw
..
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