Very old henley fuse box

[JohnW2]

How does that equate to the oft-cited 3m limit? I would have thought that one could usually have a good few metres of 25mm² tails and still be able to meet that requirement.

You tell me! I've never been able to get to the bottom of how that particular length was decided, but it has been around for over 30 years. In modern terms it should equate to the Ze of the supply and have a maximum.

The arithmetic is obviously easy enough, but I see a potential problem. I don't have Tables/Graphs near to hand, so am guessing that it would take about 600A to operate one of your 100A fuses within 5 secs - is that roughly correct? If it were 600A, that would equate (at 230V) to a maximum loop impedance (from the location of the fault) of 0.38Ω - so if the Ze were any greater than 0.38Ω, your requirement could not be satisfied, even with tails of zero length! Maybe my guess of 600A is way out?

Kind Regards, John

 

[westie101]

Yes, but for a ph - e fault I suggest you would get rather larger currents that 600A (looking at the tables it's just over 500A)

Given the age of some of these figures in use I doubt it would be easy to get any information as to why, the detail will be lost in the mists of time.
They appear in industry documents, and no doubt the Ze figures were discussed prior to inclusion in BS 7671.

 

[JohnW2]

Yes, but for a ph - e fault I suggest you would get rather larger currents that 600A (looking at the tables it's just over 500A)

Well, even ESQCR can't change Mr Ohm's Law. Yes, you might get currents greater than 600A - but (at 230V) only if the Ze was less than 0.38Ω. If the Ze is above 0.38Ω, then the fault current would inevitably be less than 600A - because Mr Ohm says so!

Given the age of some of these figures in use I doubt it would be easy to get any information as to why, the detail will be lost in the mists of time.

As far as the 3m tails figure is concerned, it seems hard to belive that it's the result of a rational decision based on the sort of disconnection time requirement you quoted. After all, a pair of 25mm² conductors only add about 0.0018Ω per metre to the fault loop impedance, so only, say, about 0.018Ω for a 10m run - which would have a very trivial effect on disconnection time.

I'd be far more inclined to believe (and to some extent would sympathise with) that the 3m limit had resulted from an arbitrary common-sense decision - that once tails got longer than that (often implying travel from one room/cupboard to another, maybe concealed or semi-concealed) one was going to have a substantially increased risk of cable damage.

Kind Regards, John

 

[curlyzoo2002]

ok hear is the pics

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• curlyzoo2002
• 24 Jan 2013
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• curlyzoo2002
• 24 Jan 2013
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as you can see the flat is getting fed threw that.

hear is the pic of the meter and fuses box

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• curlyzoo2002
• 24 Jan 2013
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and no fuse at that end. so i dont know how the guy done it unless there is something behind that box in pic 2

there is no other place were the flat could get a feed

 

[ban-all-sheds]

H&S violation:

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• curlyzoo2002
• 24 Jan 2013
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I wonder where that installation gets its earth?

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• 24 Jan 2013
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[curlyzoo2002]

H&S violation:

could you explain what the violation is ? lol unless its all the stuff in the way of the only fire exit

 

[JohnW2]

I wonder where that installation gets its earth?

Indeed. I wonder what those (I think two) puny little wires entering the RH top of the CU are, and where they come from? One suspects that the best path from the CU's 'MET' to earth (albeit non-compliant) may well be via that new G/Y, which I guess is probably a bonding conductor, and the service supply pipes! I don't think we saw any evidence that the conduit was earthed at t'other end, but I suppose it's conceivable that those puny wires mentioned above (appearing from the ceiling) come from the flat end of the conduit.

The dramatic difference between the size of the 'in' and 'out' tails of the meter seems to indicate that I probably wasn't too wrong in my concerns about the size of the 'tails' between cutout and meter (and looks much the same at both ends).

Kind Regards, John

 

[JohnW2]

could you explain what the violation is ? lol unless its all the stuff in the way of the only fire exit

Yes, I would imagine that general obstruction of escape routes (and hazards to life and limb!) was probably what he had in mind!

Kind Regards, John

 

[ban-all-sheds]

It was, but I was thinking just generically - if it's obstructing a fire exit that's much worse.

If whoever left it there doesn't shift it tomorrow, call your local fire prevention officer.

 

[JohnW2]

It was, but I was thinking just generically - if it's obstructing a fire exit that's much worse.

Even if it weren't directly obstructing a fire exit, it's undoubtedly obstructing a fire escape route, so I doubt whether it could get a lot worse!

Kind Regards, John

 

[Scoby_Beasley]

That'll be all the stuff removed from the "might come in handy" cupboard to get the cu picture!!

 

[JohnW2]

That'll be all the stuff removed from the "might come in handy" cupboard to get the cu picture!!

Kind Regards, John

 

[curlyzoo2002]

That'll be all the stuff removed from the "might come in handy" cupboard to get the cu picture!!

lol no the cupboard the cu is in, is in a toilet so its hair gel and toilet roll andstuff

 

[rjm2k]

I don't think we saw any evidence that the conduit was earthed at t'other end, but I suppose it's conceivable that those puny wires mentioned above (appearing from the ceiling) come from the flat end of the conduit.

The dramatic difference between the size of the 'in' and 'out' tails of the meter seems to indicate that I probably wasn't too wrong in my concerns about the size of the 'tails' between cutout and meter (and looks much the same at both ends).

Kind Regards, John

Could be wrong, but that conduit looks a bit like plastic rather than metal, would they not have bonded to the gas pipe shown in the photo, the G/Y looks like it's heading down from that general direction.

Pretty scary install, I guess the equipment in question is definatly DNO property so will they come and tidy it up for free do you think? Interesting that the MOP put a new meter on those tails but nothing has been mentioned about the state of the installation.

 

[dhutch]

Presumably in side the '?' box is a junction which amungst other things splits out the netural.

I dont know how the six flats are arranged or where the other two non-highlighted feeds go, but without being qualified to say so, I would presume that there are other such boxes that split it again to the other flats. Looking back at the photos, ignoring the new light feed, there appears to be a live from each phase, plus one addtional one to nearest phase, and one the skirts completly and goes down with what appears to be the main incoming supply. The Earth?

Doesnt look too hard a job to replace it, its basicaly all surface mounted, and other than getting the last bit into the flat shouldnt cause much disturbance. But it sound a bit like nobody cares. At which point, its going to stay.

It also doesnt really give any answer to what the crack with the 'communal take off' , for the lights, or the intercom, the latter of which looks nackered, if im honest. Although the lights are clearly fairly new, or at lease, predate the last time it was painted! They even appear to be earthed.



For ref.

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• curlyzoo2002
• 23 Jan 2013
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• curlyzoo2002
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Do we know what the other grey box is, to the right of the main cutout, with the unpainted plastic conduit?


Daniel


Daniel