Not thick.
You knew what you meant but we only knew what you wrote.
You knew what you meant but we only knew what you wrote.
25a Appliance on Unfused Spur off 2.5mm ring final with 32a RCBO
- Thread starter mike42
- Start date
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Anyway here is a thought EFLImpudence,
My Daughter and family live near Brisbane and I live in Lancashire.
What step up/down configuration of transformers and what design of pylons would be needed to send her 10Amps at mains voltage from here to there to run that extension using 2.5 sq mm conductors on the transmission lines ?
I`ll allow some approximation on the figures
Oh an approx what losses would you envisage
My Daughter and family live near Brisbane and I live in Lancashire.
What step up/down configuration of transformers and what design of pylons would be needed to send her 10Amps at mains voltage from here to there to run that extension using 2.5 sq mm conductors on the transmission lines ?
I`ll allow some approximation on the figures
Oh an approx what losses would you envisage
No idea.
Are you tunneling (approx. 12'250 km), or using the great circle (approx. 16'500 km), bearing in mind, you may need a diversion around Russia!?
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Well, yes.
Fuses are to protect the cable; not the appliance.
If appliances require fusing then the manufacturer will fit them inside.
If your appliance is 9A then you can fit a plug on its flex and plug it in to a socket circuit - ring or radial.
If it is 25A then you should not connect it to the socket circuit as it should be on a dedicated circuit.
Dedicated does not mean an individual circuit, although that might be the best option.
It means a circuit designed for your 25A appliance and any other appliances that may be used at the same time.
For instance you could connect it to a 32A cooker circuit if that was only being used for 7A worth of other items - or thereabouts if certain allowances are valid.
If it is 25A then you should not connect it to the socket circuit as it should be on a dedicated circuit.
Dedicated does not mean an individual circuit, although that might be the best option.
It means a circuit designed for your 25A appliance and any other appliances that may be used at the same time.
For instance you could connect it to a 32A cooker circuit if that was only being used for 7A worth of other items - or thereabouts if certain allowances are valid.
Thanks EFL and note what I'm about to say will not apply to my installation as (already mentioned) I will be putting it on a fused spur and monitor it. If it blows said fuse I'll put it on a dedicated circuit. The below is more theoretical than anything else.
The bit of the on site guide I pasted in here, says "unfused" i.e. no plug top and no 13A fuse. So presumably it would in fact be ok to connect anything rated less than 32A on that circuit (making diversity allowances for the sockets and ensuring the cable is sized correctly which above 27 it might need more than 2.5mm). So something that might once peak at 25a for a very short period then drop well below 9A could be directly connected as an un-fused spur using 2.5mm could it not ?
The bit of the on site guide I pasted in here, says "unfused" i.e. no plug top and no 13A fuse. So presumably it would in fact be ok to connect anything rated less than 32A on that circuit (making diversity allowances for the sockets and ensuring the cable is sized correctly which above 27 it might need more than 2.5mm). So something that might once peak at 25a for a very short period then drop well below 9A could be directly connected as an un-fused spur using 2.5mm could it not ?
Ok.
I do not have any faith in the OSG. It is a terrible publication.
Well, sort of but if you have a 2.5mm² unfused spur then you should not have anything connected to it which could cause an overload.
Absolute nonsense.
I don't know what to say about that given that there is no indication of limiting the rating of such permanently connected equipment.
I am not sure if I have ever seen an appliance connected to an unfused spur. Items on socket circuits are limited to 13A.
13A is the largest fuse that will fit in an FCU but on a 2.5mm² spur 25A could theoretically be fitted and with a double socket two 13A appliances may be used.
A novice reading this rubbish will presumably think they cannot have a large appliance through an FCU with its 13A fuse but it may be connected unfused to a socket - ideal for connecting one's cooker I suppose.
Throw away the OSG.
I see a few issues with what was proposed in the original post (disregarding for now that the appliance may not need 25A after all).
1. The dispensation that allows ring circuits with a cable smaller than the normal cable size for the breaker providing that overloading is merely "unlikely" (rather than not possible) is for circuits supplying accesories to BS1363. That means either sockets for fused plugs, or fused connection units.
2. While BS7671 doesn't require manufacturers instructions to be followed exactly, only to be "taken into consideration", if you ignore what the manufacturer says about fuse ratings and there is a problem then on your head be it.
3. You are using a large proportion of the circuits total capacity for a single load. Is that appropriate, remember overload protection is supposed to be overload protection not load limiting.
1. The dispensation that allows ring circuits with a cable smaller than the normal cable size for the breaker providing that overloading is merely "unlikely" (rather than not possible) is for circuits supplying accesories to BS1363. That means either sockets for fused plugs, or fused connection units.
2. While BS7671 doesn't require manufacturers instructions to be followed exactly, only to be "taken into consideration", if you ignore what the manufacturer says about fuse ratings and there is a problem then on your head be it.
3. You are using a large proportion of the circuits total capacity for a single load. Is that appropriate, remember overload protection is supposed to be overload protection not load limiting.
1/ I suppose the word unlikely is to take into account yes overloads are allowed, preferably of short duration are allowed otherwise we would have fuses popping all over the place. Small overloads can be tolerated for a long time, large overloads to trip in the "conventional time" often 2 hours but could 4 hours sometimes. Medium overloads of very long duration is something best avoided by design. If we consider most circuits can be able carry 13% overload indefinitely but 45% overloads must trip (eventually) then we consider that somewhere between 13+% and 45-% might/might not trip can become a sobering thought.
2/ Not that long ago the regs suggested than manufacturers instructions were paramount , given our history of decent diligent manufacturers that might seem OK but we opened up to not just European but worldwide manufacturers goods I suppose lead us to the taken into account phrasing.
3/ Indeed, load limiting is more of a design target, type of circuit and normal expected use/floor area served comes to mind.
One example that seems to have stood the test of time is the tradition of a cooker circuit first 10A then 30% of the remainder plus 5A if socket (normally assumed for occasional use of a kettle not a washing machine or tumble dryer) . I have never heard of a tradition of an Xmas day mass fuse pop or mass housefires or substation bonfires.
Who knows? - although it would be very useful at times, I unfortunately cannot read minds!
I suspect his 'point' (joke!) was that there would probably be quite an appreciable voltage drop in a cable running from the UK (ar any other country which used 'UK plugs') to Australia
Kind Regards, John
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