Radial off a rings mcb

[ban-all-sheds]

Say the garage spur is loaded to 20 amps, the ring then is restricted in capacity as there is only 12A remainig until the mcb trips.

Actually, it won't trip that readily: //www.diynot.com/wiki/electrics:mcb2 but you shouldn't plan to overload it.

However, the situation you describe is no different from plugging those same items into any double socket on the ring and drawing 20A from it...

 

[ColinJacobson]

Say the garage spur is loaded to 20 amps, the ring then is restricted in capacity as there is only 12A remainig until the mcb trips.

Actually, it won't trip that readily: //www.diynot.com/wiki/electrics:mcb2 but you shouldn't plan to overload it.

However, the situation you describe is no different from plugging those same items into any double socket on the ring and drawing 20A from it...

You should read what was written. A ring can pass 32A, using a spur from the same 32A mcb that draws 20A means the ring can't reach its capacity of 32A. That means if high current appliances are used on the ring, say a kitchen ring, then the 32A mcb will trip.

Read the thread again. It is easier that way.

 

[Chri5]

You should read what was written. A ring can pass 32A, using a spur from the same 32A mcb that draws 20A means the ring can't reach its capacity of 32A. That means if high current appliances are used on the ring, say a kitchen ring, then the 32A mcb will trip.

Read the thread again. It is easier that way.

Most MCB's have head room, I think it's something like 1.45 x value for 1 hour.

We are splitting hairs here, a 32 amp circuit is designed for a load of 32 amps, what you choose to hang off spurs on the ring, spurs via the mcb or the ring doesn't matter. 32 amp should be seen as the deign max, end of.

So if you are silly enough to not consider overload then simply you are not working within the spirit of the regs or in an acceptable way for the end user of the system.
There is no value in designing something that is over tolerance and will fail frequently, or quickly fault due to excessive demand.

 

[ban-all-sheds]

I have read what was written.

Perhaps you'd like to explain

1. How spurring from a ring at the MCB is any different from spurring at any other point.
   
2. How taking 20A from any spur on the ring has a different effect on the capacity available for use by all the other sockets and spurs than does taking 20A from a socket on the ring.
   
3. Why, therefore, the situation you describe is different from plugging those same items into any double socket on the ring and drawing 20A from it.
   

Maybe you'd like to do some drawings, showing current flows at different points in the circuit - perhaps it would be easier that way.

 

[steveo44]

A normal 32A ring with both live wires into the 32A mcb. A 2.5mm T&E cable is screwed into the the 32A ring mcb's terminal. This goes to the garage

A 2.5mm cable taken from a rings MCB counts as a spur off the ring as far as regs are concerned. That means it should only feed one single or double socket or one fused connection unit (FCU).

I am trying to learn the right and wrong of adding an extra sockets/fcu. can somebody please explain why two single sockets should not be fitted, i.e daisy chained as two single 13amp sockets would = one 13amp double socket.

 

[ricicle]

I am trying to learn the right and wrong of adding an extra sockets/fcu. can somebody please explain why two single sockets should not be fitted, i.e daisy chained as two single 13amp sockets would = one 13amp double socket.

In theory you could fit two singles as opposed to one double. You could explain your engineering judgement and note the departure on any certification.

(Iirc the ring final circuit diagram is in the appendicies which are for guidance only anyway)

 

[ban-all-sheds]

2 x 13A sockets allow a load of 26A.

Officially a twin socket only allows a 20A load, which is what the minimum current carrying capacity of a cable used in a ring final has to be. If we assume that a spur cable will have the same installation method as the ring, it all dovetails.

 

[steveo44]

Ok thanks for the answers. The mist is now a little clearer.

Why are twin sockets not made at a rating of 26amps when there is the potential for 26amps through two 13amp plugs and the cable is rated at 27amps?

*edit. is it because a radial mcb is 20amp?

 

[securespark]

2 x 13A sockets allow a load of 26A.

Officially a twin socket only allows a 20A load,

Unless you refer to Ban's other postings, including a copy of MK's techsheet showing a 26A rating for their double socket...


My take on socket ratings is this: what value is shown on the rear of a BS1363 accessory?

 

[ban-all-sheds]

Is that a rhetorical, or a genuine Q?

I don't know what it says, and I don't have one to hand to look.

 

[ban-all-sheds]

You should read what was written. A ring can pass 32A, using a spur from the same 32A mcb that draws 20A means the ring can't reach its capacity of 32A. That means if high current appliances are used on the ring, say a kitchen ring, then the 32A mcb will trip.

Read the thread again. It is easier that way.

I have read what was written.

Perhaps you'd like to explain

1. How spurring from a ring at the MCB is any different from spurring at any other point.
   
2. How taking 20A from any spur on the ring has a different effect on the capacity available for use by all the other sockets and spurs than does taking 20A from a socket on the ring.
   
3. Why, therefore, the situation you describe is different from plugging those same items into any double socket on the ring and drawing 20A from it.
   

Maybe you'd like to do some drawings, showing current flows at different points in the circuit - perhaps it would be easier that way.

Or do you think that if you just ignore questions that you'd rather not answer that it will get forgotten and people won't realise that you're acting evasively?

If you do think that I think it only fair to warn you that others have tried that and it never works.

 

[ColinJacobson]

I have read what was written.

Poor comprehension.

It was quite clear what was written. HINT: Learn to count.

< snip irrelevant babble >

 

[ban-all-sheds]

I have read what you have written:

Say the garage spur is loaded to 20 amps, the ring then is restricted in capacity as there is only 12A remainig until the mcb trips.

That is perfectly true - if you load the spur to 20A then the ring is restricted in capacity as there's only 12A remaining.

But the same applies with any spur loaded to 20A, or indeed if any socket is loaded to 20A - there's still only 12A remaining for all the other sockets.

And when I pointed that out, you wrote:

You should read what was written. A ring can pass 32A, using a spur from the same 32A mcb that draws 20A means the ring can't reach its capacity of 32A. That means if high current appliances are used on the ring, say a kitchen ring, then the 32A mcb will trip.

Read the thread again. It is easier that way.

Which did seem to me to indicate disagreement, i.e. that you believed that a spur taken from the ring at the MCB somehow had a different effect on the capacity available to all the other sockets on the ring than a spur taken from a different place or, indeed, if that 20A was being drawn from one of the ring sockets.

If I'm wrong in that, i.e. you weren't disagreeing, and that you do accept that there are no special concerns, or differences, with a spur taken from the point where the ring passes through the MCB then fine.

But if you are disagreeing, and you do think that there are special concerns or differences then I think it reasonable to ask you to explain why, because I can't see what they might be.

Or if anybody else reading this can explain, that would be useful.

The questions are:

1. How spurring from a ring at the MCB is any different from spurring at any other point.
   
2. How taking 20A from any spur on the ring has a different effect on the capacity available for use by all the other sockets and spurs than does taking 20A from a socket on the ring.
   
3. Why, therefore, the situation described is different from plugging those same items into any double socket on the ring and drawing 20A from it.

 

[ban-all-sheds]

< snip incoherent babble from ban-all-sheds >

< snip irrelevant babble >

Do you think that any rational person would look at what I wrote and agree that it was incoherent or irrelevant babble?

Can you show, with relevant quotes from my text, that it was either of those?

Will you please start behaving reasonably, and answer what are civil, relevant and perfectly understandable questions with answers which are also civil, relevant and perfectly understandable.

Trying to avoid answering them with utterly groundless dismissals of them as being babble is unacceptable, and if you are not prepared to engage in proper debates here then you should just leave.

 

[ColinJacobson]

Can you

Please stop posting irrelevant babble! No one is interested. I don't even read your posts as they are not worth it..