Mains smoke and heat detectors

[stillp]

Of course compliance is possible.

No it is not, because there are no definitions which can be used to determine which category a circuit is in.

Can't you make a decision for yourself without the standard making it for you?

Of course compliance is possible.

No it is not, because there are no definitions which can be used to determine which category a circuit is in.

If you find the decision too difficult, just use 1.5 mm².

But what if I have good reasons for wanting to use 1.0mm² and I want to know if it is allowed, given the type of circuit I have?

What do you mean by "the type of circuit I have"?

Do you not see the problem?

No, I don't.

Then IMO you should not have any involvement in writing or QAing standards.[/QUOTE]
Thankfully, there are many people who would disagree with your opinion.

 

[JohnW2]

Can't you make a decision for yourself without the standard making it for you? ... What do you mean by "the type of circuit I have"?

I have to say that I'm with BAS on this one. If a Standard is going to impose different minimum cable CSAs for two different categories of circuit, it is surely incumbent on the authors to define those categories (unless 'obvious'). Whilst is often will be 'obvious' (e.g. a cooker or immersion circuit which serves no lights, or a circuit which supplies only lights), there will also often be 'grey areas', where nothing but a formal definition will allow one to know what is necessary in order to comply with the requirements of the Standard.

Kind Regards, John

 

[stillp]

A formal definition though would be likely to preclude some desirable and safe situations. Writing these things is a fine balance between writing enough to ensure safety, but not too much with the resulting limitation of choice, as suggested by BAS' comment "But what if I have good reasons for wanting to use 1.0mm²".

 

[JohnW2]

A formal definition though would be likely to preclude some desirable and safe situations. Writing these things is a fine balance between writing enough to ensure safety, but not too much with the resulting limitation of choice, as suggested by BAS' comment "But what if I have good reasons for wanting to use 1.0mm²".

I don't really see how they can have it both ways. If they want to leave scope for flexibility/discretion, they should say so - and just issue some sort of guideline. On the other hand if (as seems to be the case) they want to include a requirement that certain types of circuit must use cable of a specified minimum CSA, then I would say that they have to clearly define what those 'types of circuit' are.

As a matter of interest, would you say that it would be reasonable for a Standard to specify different requirements for, say 'small buildings' and 'large buildings' (or 'small cars' and 'large cars', or whatever) without defining what those terms meant?

Kind Regards, John

 

[stillp]

Depends on what the different requirements were.

 

[stillp]

I'm surprised nobody has asked yet for a definition of "Signalling and control circuits", and suggested that they could wire a ring final in 0.5 mm² if they used a couple of those powerline networking adaptors!

 

[ban-all-sheds]

Can't you make a decision for yourself without the standard making it for you?

Yes - I can decide that there is no such thing as a "power circuit".

What do you mean by "the type of circuit I have"?

I mean do I have a lighting circuit or do I have a "power circuit"?

Thankfully, there are many people who would disagree with your opinion.

Well, if you see no problem with a standard mandating that a {thing} must have a certain minimum characteristic and not defining {thing}, thus rendering {thing} a term devoid of any meaning precise enough for people to know what the standard mandates, then I guess we are stuck with standards which contain rubbish and nonsense which cannot be complied with.

 

[JohnW2]

Well, if you see no problem with a standard mandating that a {thing} must have a certain minimum characteristic and not defining {thing}, thus rendering {thing} a term devoid of any meaning precise enough for people to know what the standard mandates, then I guess we are stuck with standards which contain rubbish and nonsense which cannot be complied with.

I agree. For example, as per the question I just asked stillp, what if, instead of what is about to happen (itself undefined), Amd3 of BS7671 had included a requirement that only CUs manufactured from ferrous metal were allowed in 'large houses' - without 'large house' being defined?

Kind Regards, John

 

[ban-all-sheds]

I'm surprised nobody has asked yet for a definition of "Signalling and control circuits", and suggested that they could wire a ring final in 0.5 mm² if they used a couple of those powerline networking adaptors!

The only sort of person who would do that would be one who was so unfamiliar with BS 7671 that they were unaware of the explicit requirements for ring finals (for BS 1363 accessories).

But you do raise an interesting point, and in doing so show that you have thought of yet one more grey area that arises from the way that "power circuit" is used. If I've got a 0.5mm² cable supplying a bell, is that a signalling circuit, what with the bell being a signal that something has happened, or a power circuit, what with the bell getting its power through the cable?

What about Catn UTP being used in places for PoE - is it signalling, or is it power?

If I install a 0.5mm² cable from a 3A OPD to supply a few USB charger outlets and an indicator lamp to let me know it's on, is that a signalling circuit? A power circuit? A lighting circuit?


I wonder if there is any number of undefined situations which we could list here at which point you would admit that there is a real problem with the way 52.2 mandates something for a circuit type which has no definition?

 

[ban-all-sheds]

A formal definition though would be likely to preclude some desirable and safe situations.

Not if:

a) it's properly done

or​

b) if major problems in doing it properly arise that is taken as an indication that it cannot be done properly, and therefore must not be done at all.​

Writing these things is a fine balance between writing enough to ensure safety, but not too much with the resulting limitation of choice, as suggested by BAS' comment "But what if I have good reasons for wanting to use 1.0mm²".

I would love to know what safety concerns there could be with using 1.0mm² on the load side of an FCU to supply a socket outlet.

 

[stillp]

I would love to know what safety concerns there could be with using 1.0mm² on the load side of an FCU to supply a socket outlet.

Does it have adequate mechanical strength? Presumably IEC TC64 don't think so.

 

[ban-all-sheds]

I agree. For example, as per the question I just asked stillp, what if, instead of what is about to happen (itself undefined), Amd3 of BS7671 had included a requirement that only CUs manufactured from ferrous metal were allowed in 'large houses' - without 'large house' being defined?

That would not be a problem as the whole of 421.1.201 is in the "must be ignored" category because it is impossible to comply with, and will always be so until "non-flammable" is defined.

 

[ban-all-sheds]

Does it have adequate mechanical strength?

It does for lighting circuits.

Presumably IEC TC64 don't think so.

Why do they think it is strong enough for lighting circuits but not to supply a socket?

 

[stillp]

That's a good example of something which needs a clear and verifiable definition. (I thought it was "non-combustible BTW?)

 

[PBC_1966]

And fixed cables that are surface-mounted, and the devices connected to that fixed wiring, and even fixed wiring that is enclosed in conduit or trunking, or on cable tray. Remember these standards deal with installations, not just domestic.

What is the difference in lighting and power with cables installed in such ways?

None.

Then why the different rule for minimum cable size, assuming one can actually establish what a lighting circuit is and what a power circuit is anyway?

If there was some concern about the smaller cable being more susceptible to damage if surface run at lower heights, what would be the logical thing to do? Would you write a regulation which just says that the smaller cable should not be surface run below a height of whatever, or would you decide to come up with some convoluted way of reasoning that wiring to lights is more usually at higher levels so we'll allow it for lighting circuits but not other circuits?

Besides, if the concern really was about lower surface-run cables, how would this regulation prevent one from surface-running 1.0 sq. mm cable down a wall to, say, a low-level 5A or 2A socket intended for a lamp?

Sorry, but this idea just makes no sense.