Dad, What's a Circuit?

I can see the thinking ... BUT ... if we have two lamps in parallel supplied by the same double-pole switch (switching line and neutral), you could say the switch feeds two circuits using the same logic. It's still only one circuit in BS 7671 terms.

"I can see why ebee's friend considers two lighting circuits connected to just one M.C.B.to be two circuits connected together. Two individual circuits connected in parallel in fact."


Therein lies the problem.


One circuit by definition because they are on the same OPD.

If a designer elects to branch off in tees or trees for a radial circuit then it is still a radial circuit.

If branching occurs within or without the consumer unit is irrelevant .

You might consider it not as neat in some situations, you might consider it as not best practice but that does not render it as unsafe or unsatisfactory.

I might design an installation to have six lighting circuits for resilience.

Someone else might "double up" some circuits, for instance to free a spare way to create another circuit.

You might decide that this makes an installation less good than it was previously.

However we judge installations on BS7671 edition current at time of test.

If someone actually makes a situation "worse" than it was but it is still considered "satisfactory" then this does not detract from it.

Just as my old example of installations complying with previous standards but not the current one.

If this non compliance gives a C2 or aC3 then it is unsatisfactory today.

If it gives a C3 then it is satisfactory.

Past dates make no difference. Neither does the date it was actually installed.

We might, for instance, decide an installation installed prior the date for main bonding (or with 2.5 bonding) is unsatisfactory even though it was allowed in regs gone by.

By "doubling up" we might mean trebling, quadrupling or even 17 radial legs on a fuseway, that in itself makes no difference.

(17 is probably too many for any make of a consumer unit but the actual issue would be is the termination both electrically and mechanically sound and not whether those tee offs are inside or outside the consumer unit). 

To state that doubling up inside a consumer unit is, in itself, a defect yet doubling up outside the consumer complies with 7671 is absolutely ludicrous and bears no logic whatsoever.

Good practice or best practice might be a different issue but BS7671 is what matters when doing a periodic/EICR.


Two rings becoming "one ring final circuit" or even 3 rings with or without a spur, same result , termination at consumer unit applies and doubling/trebling is not an issue in itself.


Footnote - the On Site Guide is not the regs, it is merely one way of achieving compliance, alternatives are not precluded .


PS - that does not imply that I`d be happy to double up etc on my own works but I would not condemn it to BS 7671 either.

I am sticking to my guns and will not be moved.


What is the definition of the word circuit?

1 A roughly circular line, route, or movement that starts and finishes at the same place. ‘The circuit was almost finished, and I was second.’ ‘He finished a circuit around the main square.’

Circuit | Definition of Circuit by Oxford Dictionary on ...

www.lexico.com/definition/circuit


Z.

BS7671 uses its own definitions, listed in the first few pages. I know many people try to "interpret" these to meet their own ideas, but this is not the way to proceed. One must use the definitions from the front, and a good proportion of the duff EICRs I have are partly caused by the "I don't like the look of that" attitude that pervades the electrical industry. EICR comments MUST be exactly to the regulations, and their own definitions. Another example is a fuseboard in the centre of a property. There are 2 rings of sockets in 2 opposite directions but they both terminate in one CPD (32A, 4 wires). Would anyone like to comment on this?


We shall see what happens now!

13th Edition definition. Circuit: "An arrangement of conductors for the purpose of carrying current." (See Final sub-circuit).


14th Edition definition. Circuit: Not found. 

                                     Final sub-circuit: An outgoing circuit connected to a distribution board and intended to supply electrical energy to current using apparatus, either directly or through socket outlets or fused spur-boxes."


15th Edition definition. "An assembly of electrical equipment from the same origin and protected against overcurrent by the same protective device (s). 


So, it is the 15th edition that is to blame.


Z.

If you have two haystacks  in separate fields and we use the telehandler to move the bales so you merge them into a new pile  in another place, is it too great a mental leap to see that we still have one haystack, just a rather larger one ?

In that case  1+ 1 = 1 is not a problem, just the '1' symbols refer to different things, as this is not simple arithmetic..


Also something similar happens here.

If one electron leaves the MCB, another one will arrive at the neutral bar,  and some charge has completed  ' a circuit'.


Now that may be much like a runner going round a track in the simplest case, or perhaps more like a mini-bus load of  scouts going round  a motorway services, in both cases, in the end they all return to their point of arrival.. usually, some having expended more  than others,and some having longer routes ..


Much the same could be said at the substation -  for every amp (1.6E 19 electrons per second) that leaves down the red phase of the transformer the same number will return to the other end of the winding via one of many routes. 

This current too has completed ' a circuit' of the wiring but not all of it has taken the same route.

Mike.

Just watched the tight fit video reminds me I had a swimsuit like that happy holiday memories