Dad, What's a Circuit?

"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 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.