This is why we have rules and regulations

S

sparkyspike

I was called out early this morning by a customer complaining he had no power in the house. This is what I found...



I saw that the fault was an overload caused by a 2.5mm cable spurred into a 30A ring circuit. This cable supplied a workshop CU which was running a 3kW 3-phase convertor, a 3kW extractor fan, sockets and lights. :eek: It gets better...

From the workshop CU was a second CU for a washing machine, 50A water heater, 40A shower, sockets and lights. :eek: It gets better...

This 2nd CU then fed a third CU which supplied outside sockets and electric heating for 30 kennels. :eek:
So, I decided - yes, definitely an overload. I agreed to replace the burnt-out CU, but pointed out that a new supply was needed for the kennels and workshop. It gets better...

I noticed it was a TT overhead supply. The only earthing arrangement was a 6mm cable to the water main. The water main was fed in blue plastic pipe. :eek: There was no other earth cable. Somehow, the Ze came up as 110 Ohms.

They were so lucky their house hadn't burned down. The owner explained that he had wired up the new workshop and kennels himself, and that he thought he had done quite a good job. OMFG.
 
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Nice!!! Just shows that the bods who write the regs know nothing about the capabilities of cables and fuses :D :D :D
 
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When you click on either picture...
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Shouldn't you condemn the installation and refuse to power it back up until remedial action can be taken?
 
S

sparkyspike

When you click on either picture...
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Shouldn't you condemn the installation and refuse to power it back up until remedial action can be taken?


No. I fitted a new CU and earth spike. The spur to the kennels has been disconnected.
 
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Nice!!! Just shows that the bods who write the regs know nothing about the capabilities of cables and fuses :D :D :D

Au contraire, I think that bit of 2.5 has done extremely well to put up with that potential load without ending up like RF's piece of "welded" 1.5......

C'mon Rob, post a link, I can't find it!!
 
S

sparkyspike

By the way, the fuse wire was still intact. The only reason the power went off was because a 500mA RCD on the supply finally decided to give way.
 
P

PrinceofDarkness

It really isn't fair to go on about the 'bods who write the Regs' - not in this instance, anyway.

Yes, that Standard Wylex unit has clearly been overloaded, but an ordinary overload would be handled by the fuse element, by design. That damage has been caused by a combination of overloading and a loose connection - either on the actual terminal or due to an ill fitting fuse carrier/shroud.

Loose connections can cause havoc by generating localised hot-spots which by their very nature tend to get worse and worse with time.

This is where those 'bods' are correct in requiring a Periodic Inspection - simply to check for such signs of overheating/overloading.

This kind of problem can just as much occur with an up-to-date consumer unit as with an elderly fuse box.

No matter how careful a manufacturer might be - No matter how the Regs are written, it all comes down to the bloke on the end of the screwdriver.



Lucia.
 
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It really isn't fair to go on about the 'bods who write the Regs' - not in this instance, anyway.

Yes, that Standard Wylex unit has clearly been overloaded, but an ordinary overload would be handled by the fuse element, by design. That damage has been caused by a combination of overloading and a loose connection - either on the actual terminal or due to an ill fitting fuse carrier/shroud.

Loose connections can cause havoc by generating localised hot-spots which by their very nature tend to get worse and worse with time.

This is where those 'bods' are correct in requiring a Periodic Inspection - simply to check for such signs of overheating/overloading.

This kind of problem can just as much occur with an up-to-date consumer unit as with an elderly fuse box.

No matter how careful a manufacturer might be - No matter how the Regs are written, it all comes down to the bloke on the end of the screwdriver.



Lucia.
:D :D :D = taking the p*ss
 
P

PrinceofDarkness

Thank you Zambezi. I've never really cared for those primtive smiley cave-drawings, consequently I've failed to appreciate the subtle art.

However, sticking to the point, a BS fuse of any type will clear an overload without harm to its holder or terminals. So I maintain that such damage could not have been caused by a simple overload, but rather, the result of a high current combined with a loose connection.......



Lucia.
 
S

sparkyspike

The customer told me that they regularly had to change the fusewire on that circuit, but it had been like that for a few years and they had got used to it. They seemed to think that it was ok what they had done, as it was 'before Part P'! You would have thought that nearly having their house burned down was a very good clue. I think it will sink in later.

Anyway, I don't think it was a loose connection. I think that the current being drawn was less than the breaking current of the fuse but more than the CCC of the cable.
 
P

PrinceofDarkness

Well, Spikey, I can't agree with you, because if the current being drawn had been less than the fuse breaking capacity, then such awful damage wouldn't have occurred in such a localised position.

So, I repeat, that the likely cause was a loose connection. This doesn't necessarily mean the actual terminal connection for the circuit cable(s) - if you examine the reverse section of those fuseholders you'll find plenty of potential for loose connections - these only come to light once the whole unit has been removed due to replacement, being undetectable from the front view.

It's quite ludicrous to suggest that a simple overload, or an undersized cable would cause such local damage to a fuse board. Fuses are designed to handle over-current and S/C. But they cannot survive the heat generated by a poor connection.



Lucia.
 

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