Electrics in General - Stupid Question

[NotHimAgain]

Are all those components (sockets/lights) on the same ring dependent on one another

I have designed a number of 'domestic' installations' that have required 4.0mm² rings for voltage drop - my clients tend to occupy substantial abodes - they are the only types that can afford me .

BTW I am not a titan - I have been on a diet don't you know .

 

[martinxxxxxx]

Funny; I had heard that you weren't as big as a shed anymore

 

[GaryMo]

Funny; I had heard that you weren't as big as a shed anymore

I think BAS has an admirer!

 

[ban-all-sheds]

I have designed a number of 'domestic' installations' that have required 4.0mm² rings for voltage drop - my clients tend to occupy substantial abodes - they are the only types that can afford me .

Fair enough - and there's nothing non-compliant about a 30/32A ring final which uses 4mm² for reasons of volt-drop or installation method or because that's all you had to hand.

But if you had cable which because of size and/or installation method had a capacity of less than 20A, which regulations do you think would allow you to form it into a ring serving several points of use and protect it with a 20A device?

 

[NotHimAgain]

I am not quite sure what you have in mind there BAS - I have not proposed any particular design.

We must be careful here not to confuse the current carrying capacity of cables with the current carry capacity of circuits. Two cables could have a particular rating if used separately. However, a circuit formed by these two cables connected in parallel is likely to have a higher rating.

 

[ban-all-sheds]

I am not quite sure what you have in mind there BAS - I have not proposed any particular design.

You were proposing a ring final on a 20A device with cable rated at less than 20A.

We must be careful here not to confuse the current carrying capacity of cables with the current carry capacity of circuits. Two cables could have a particular rating if used separately. However, a circuit formed by these two cables connected in parallel is likely to have a higher rating.

Indeed.

Would your ring serving several points of use comply with the regulations for parallel conductors?

 

[NotHimAgain]

You were proposing a ring final on a 20A device with cable rated at less than 20A.

Was I - where have I said that then. I could make such a proposal, but only for money .

Would your ring serving several points of use comply with the regulations for parallel conductors?

Would it have to if I choose to define it as a ring final circuit.

 

[holmslaw]

..

 

[ban-all-sheds]

You were proposing a ring final on a 20A device with cable rated at less than 20A.

Was I - where have I said that then. I could make such a proposal, but only for money .

Hi guys, could someone gave me, or direct me to, a general overview of how a house is wired. Am I right in thinking that wire/cable goes from the mains all around the house, then back to the mains?

You are describing a ring circuit. If you break the circuit, then electricity can still reach all the other sockets either side of it as both sides go back to the consumer unit.
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It is becoming increasingly popular to run socket circuits as radials using a thicker cable, for safety reasons.

it is also becoming harder to install ring mains

Is it?

Yes, because the increasing amount of thermal insulation in houses is making it harder to achieve an Iz of 20A with 2.5mm².

The same would be true of any circuit, surely.

Yes, but with radials you have the added flexibility of changing the OPD rating as well as changing the cable size - with ring finals you're stuck with 32A.

no you're not, there's nothing to say you can't install a 6mm ring or a 20A ring.....

I don't think a 20A RFC is recognised by the regs?

It's not - 433.1.5.

Yes it is, as is any other properly designed circuit.

Would it have to if I choose to define it as a ring final circuit.

It would then have to comply with 433.1.5.

What do you do about 523.8 and 433.4.2?

Ignore them.

Do you do that with any regulation that inconveniently makes your designs non-compliant?

433.4.2, seems to be suggesting a way of rectifying a badly designed/installed parallel circuit.

If parallel cables are not carrying substantially the same load its because there is something wrong. And no gibberish regulation will rectify the problem.

Ring final circuits serving socket outlets do/can/frequently have parallel cables which are not carrying substantially the same load.

523.8, more gibberish,

Just because you don't understand it doesn't make it gibberish.

What is a "non-twisted single core cable"? I'm pretty sure there is no such thing, never has been and never will be.

So out of all the cables in all the world, which could be used in situations within the scope of BS 7671, there are no non-twisted single-core ones?

You being pretty sure doesn't mean that there are not.

And if you try to install "non sheathed cables in trefoil" your circuit will be inadequately mechanically protected and will not comply with the regs.

Will you please take a look at numbers 6/7, 10, 43, 45 & 50 in Table A2, and then explain the following:

1) Why those cables are inadequately mechanically protected.

2) In general terms why the arrangement of non-sheathed cables has any bearing on whether or not mechanical protection is required, and why any mechanical protection provided is less effective if the cables are in a trefoil arrangement.

The only necessary rules for parallel cables are same type, length and csa, run from point A to B with no other connection points or take offs, and connected between one protective device and one isolator - end of.

So your proposed 20A ring final circuit supplying socket outlets would not be a compliant circuit with parallel conductors.

I have no idea why ring final circuits have become associated with parallel circuits, they are chalk and cheese. And I doubt if anyone could give a sensible explanation.

Each point of use in a ring final circuit is served by two parallel conductors, but such circuits do not comply with any of the regulations for parallel conductors, hence the special exemption of 433.1.5 and the fact that in at least one parallel conductor regulation it is explicitly stated that the regulation does not preclude ring finals.

 

[NotHimAgain]

Well I haven't a clue what that lot is supposed to mean.

The only statement I have made concerning a 20A protective device current rating and cable size is this.

A design using a 20A protective device might be wired using 2.5mm² and, subject to installation conditions, this could comply with BS 7671 generally, including 433.4.2.

Now I was very careful to include the term 'subject to installation conditions'. I didn't even offer this as a proposal - you can tell that because I used the terms 'might be wired' and 'could comply', also there is no invoice attached .

 

[holmslaw]

..

 

[GaryMo]

So BAS "go boil yer hed" and have a Happy Christmas

That made me chuckle!

 

[Johnmelad502]

So BAS "go boil yer hed" and have a Happy Christmas

That made me chuckle!

 

[ban-all-sheds]

Well I haven't a clue what that lot is supposed to mean.

That'll teach me to try and multi-task...

Sorry about that.

But in my defence, given that the context of all of this is quite clearly a ring final circuit with a 20A OPD and cables rated at less than 20A, it was a bit pointless of you to make a post talking about parallel circuits with unequal current sharing where the conductors are not rated at less than the OPD...

 

[ban-all-sheds]

I do ignore some regulations as do many others,

I being the person responsible for the Design, Construction, Inspection & Testing of the electrical installation (as indicated by my
signature below), particulars of which are described above, having exercised reasonable skill and care when carrying out the Design,
Construction, Inspection & Testing, hereby CERTIFY that the said work for which I have been responsible is to the best of my
knowledge and belief in accordance with BS 7671:2008 amended to .......... (date) except for the regulations I have decided to ignore
because I don't like them or find them inconvenient.

Jolly good.

A ring final circuit is not a parallel circuit and vice versa therefore I ignore any regulation that implies they are the same or related.

In other words you don't understand that they are in many ways the same, so you ignore the regulations you don't understand.

If you want to read more gibberish about parallel circuits read appendix 10.

It's not gibberish.

If you don't understand it perhaps you should take up a different career.

I realise now why there's no chance of you explaining why you think that arranging cables in a trefoil would somehow lessen any mechanical protection provided - you don't understand what the word "trefoil" means.

So BAS "go boil yer hed"

So once again, when you're unable to argue your case with logic and reason, you stop behaving like a civil and intelligent adult.