13 Amp socket tolerances

On 04/09/2011 02:17, geoff wrote:

Has dennis got a banana in his pocket?
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John.

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Can't think what else it might be
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geoff

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On 04/09/2011 14:18, geoff wrote:

Perhaps he is pleased to see you? ;-)
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John.

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On 04/09/2011 00:12, dennis@home wrote:

Damn dennis, you should go into comedy!
How is a modern radial "significantly different" from an older one?
Prior to the introduction of the ring circuit, what circuit topology do you suppose was in common use - the pretzel?

Without seeing the installation that is impossible to say for sure. However its very likely to be untrue for ordinary socket circuits.
20A radials are a PITA in kitchens or anywhere with concentrated high load appliances (unless you like one circuit per socket - sometimes applicable for commercial kitches), so I assume you would want a 32A radial and 4mm^2 cable[1]. Unless the layout is particularly unusual, the 4mm^2 cable is highly unlikely to be cheaper than the small extra amount of 2.5mm^2 required to join the end of the ring back to the CU. Its also significantly more difficult to work with, and hence more expensive to install.
[1] oh, and some 2.5mm^2 for the spurs from it! ;-)

I note you keep dodging the question about long term overloads on 20A radials (or any other for that matter). Exactly the same logic with which you attempt to sully the good reputation of other circuits, applies to these as well.

Wow!
What was that circuit that pre-dates the introduction of rings again?
Perhaps you are thinking of broadcast power as suggested by Tesla?

So its just you then...

Wrong...
From table 8A OSG (pg 158)
For a 30 or 32A protected ring, max floor area serviced is 100m^2 For a 30 or 32A protected radial, 75m^2 For a 20A protected radial 50m^2

Have you considered writing children's stories?

A tree is a radial... radials can branch anywhere any number of times.
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John.

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Old ones did not have lots of mobile phone cherges that needed plugging in.

Heck. One of the reasons the ring was developed was to save copper and money.

And purchace. 4mm is about 1.75 times the cost of 2.5mm. Very few circuits would be cheaper installed in 4mm radials than 2.5mm rings.

Can I have a guess? Is it a radial?

What else would you expect from dennise?

Or fiction stories.
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Adam



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That's called engineering, that is

or just emigrating to Afghanistan
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geoff

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On 04/09/2011 01:58, John Rumm wrote:

In the pre-war regs (11th ed, prior to its amendment) the number of sockets per circuit was strictly limited - e.g. to a maximum of three 15 A sockets per circuit. See section 3.1.2 in David Latimer's article on the history of the 13 A plug and the ring circuit.
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Andy

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On 04/09/2011 13:08, Andy Wade wrote:

Yes good point, I do have a vague recollection of the rule... (long before my time though!). Not sure I would count the same topology but a bit shorter, as significantly different though.
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wrote:

You can assume what you like, however you are wrong again.

So what, that's why i wouldn't do it.

Are you thick or something? You weren't allowed to put multiple 13A sockets on radials that predated rings.

What just me that doesn't penny pinch and do stuff to the *minimum* standard? I don't have to worry about how much extra beer i can buy by doing it as cheaply as possible. I leave that to the professionals who obviously need to maximise profits.

Why are you repeating what I said?
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On 04/09/2011 19:57, dennis@home wrote:

So how many 20/16A radials would you put into the kitchen/utility room?

Wouldn't do what?

You forgot to answer this yet again...

Well if we ignore the obvious point that 12A sockets did not actually exist at that point, we could look at the quote from the 11th edition:
From Regulations 202 C, D and E together with Schedule 23:
"up to three 15A sockets may fed via a 7.036 (4.52 mm^2) cable two 15A sockets via a 7.029 (2.93mm^2) cable and up to six 5A sockets via a 7.029 (2.93mm^2) cable"

Well firstly, many including myself would maintain that your suggested design will make for a less flexible installation. Probably at a higher cost. You have also not presented any convincing arguments that it would be in any way safer - especially as you keep failing to address why you believe the potential problems of long term overload are more severe on ring circuits than on radials.

Most first fix electrical work is done by professionals. They generally don't do it your way as far as I am aware.

I am not repeating what you said, I am highlighting the error in your sub classing. You said "it doesn't have to be a radial it can be a tree or anything else" - thus implying that a tree or "anything else" would not be a radial.
Had you have said that a radial does not have to be a linear chain of sockets, then I would have agreed with you.
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John.

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Why don't you answer it.. look in your book of tables as to what the maximum sustained current you can get through a 20A breaker and post it here.
Then you can tell us how much it exceeds the capacity of 2.5 mm2 cable.
One thing I can tell you is that its a lot less than it is with a 32A breaker.

You keep on arguing the same thing even though it is obvious that any circuit using 2.5mm2 cable and a 32A breaker is not as safe as the same 2.5mm2 cable and a 20A breaker. Its not as though you can even state that its a doubled up 2.5mm2 cable as it doesn't have to be when its installed and it can have undetectable faults that make it a single 2.5mm2 cable with a 32A breaker.
If you can't actually see that as a problem then there is no point talking to you about it.

thats what i said, they need to maximise profits.

There was no error in what i said.

No where did i say what the topology of a radial is. I just thought you didn't know it could be a tree as you think its harder to install than a ring.
Anyway I am bored with your repeating of the same wrong arguments so consider this thread closed.
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It's called not ripping off customers.
If a customer specified a certain sized cable then the customer would get that cable and they would pay extra for it and for any extra work involved in installing it. The profit would remain the same.
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On 05/09/2011 10:29, ARWadsworth wrote:

In commercial and industrial installations where there can be circuits with a high load factor it's common for oversized cables to be specified. The saving on energy that would be wasted in a smaller cable soon pays for the larger one.
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Andy

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On 05/09/2011 10:07, dennis@home wrote:

I can do it from memory...
A B20 MCB will carry a sustained overload of around 29A

In the case of 2.5mm^2 T&E using installation method A, it exceeds it by 9A or just under 50%

A circuit with a 32A breaker will in general have 5mm^2 of copper connecting each socket to the MCB, the 20A one will have half that.

Huh?
You do realise that the risks from sustained overload are fairly trivial compared to those from fault currents?

Make your mind up, now you are saying a tree is not a radial again?

A 32A radial is harder to install due to the use of heavier cable. A 20A radial is more work to provide adequate socket coverage in some locations due to needing so many of things to achieve the same job. Two 20A radials are far less use in a kitchen than a single 32A circuit (ring or otherwise).

Good plan, you are in a hole, so stop digging.
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Cheers,

John.

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And on 2.5 mm2 cable the 32A breaker exceeds it by?

You mean a ring without a fault or any spurs will have 5 mm2. A ring with a fault or a spur will have 2.5 mm2 cable to some of it.

The fault currents are not an issue, the breaker will trip. Or are you saying the 32A one won't on 2.5 mm2 cable?
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On 05/09/2011 23:46, dennis@home wrote:

More, less, or no overload at all depending on the circumstance. Hence why, as we keep having to explain, as a designer you follow the required guidance and make sensible design decisions about the best type of circuit.
That means that if you are running cables using installation method 100, and you are doing so in a potentially high load environment like a kitchen, it would be a sensible design decision to use a B32 protected ring, and not use any spurs. However it would be very unwise to install a B20 protected radials if using 2.5mm T&E.
If running a power circuit for the bedrooms of a three bed house, using method C, then you could use either, and spurs on a ring would be perfectly acceptable.
If running a non RCD protected feed to sockets dedicated to freezers and a boiler supply using method 100, then a B20 or B16 protected radial would be fine.
If running a circuit to a room full of PCs in an office, under a suspended floor, and into floor box socket enclosures, then follow high integrity protective conductor procedures, and use a ring or a radial depending on factors like overall cable length, floor area covered etc. Long term overload is a non issue since you are designing for a high load factor with little diversity.
This is not a difficult concept for most of us, I am not sure why it causes you so much difficulty... you look at the circumstances, and work out what the typical loads are likely to be. You look at the practicalities of the cable installation - what de-ratings will apply etc. You look at the physical distances and layout and work out how you will get cables to and from the CU etc. You look at the class of user, and typical usage patterns. Once you have assessed all that you can make a sensible decision.
You don't start the process mumbling "radial good, ring bad" (or any other ill thought through pre-conceived notion) like a drooling imbecile, potentially ruling out what may turn out to be the best design option before you even start.
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Cheers,

John.

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Still trying to avoid answering I see.
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On 02/09/2011 23:45, John Rumm wrote:

"Modern energy efficient" lights for instance. Now they really are a hazard, to the elderly at least.
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Old Codger
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On Sep 2, 2:48am, John Rumm wrote:

Or be growing cannabis.
Owain
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On 02/09/2011 16:01, Owain wrote:

BS 7671:2008 section 799: Hydroponic installations...
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Andy

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