Dodgy trade pictures for your amusement! - 1 Million Views!

[Wilko]

Hi - probably JD is using 100ms disconnect time from BS7671 ? IIRC using the manufacturer's detailed let through energy (reflecting shorter actual disconnect times) it worked out ok for 6kA. I haven't checked this recently so it might all be rose tinted glasses .

 

[davesparks]

t


true but only where the OPD is necessary: 433.3.1 (ii) allows the overload protective device to be omitted completely in this case (load not liekly to carry overcurrent)

For a socket outlet overload protection is required.
The ref you are referring to allows overload protection to be omitted where the load is not subject to overload faults, with a socket outlet the load is unknown as anything can be plugged in therefore must be assumed that it could be subject to overload.

 

[johnduffell]

Hi - probably JD is using 100ms disconnect time from BS7671 ? IIRC using the manufacturer's detailed let through energy (reflecting shorter actual disconnect times) it worked out ok for 6kA. I haven't checked this recently so it might all be rose tinted glasses .

Good theory, but that would need much bigger conductors, i used the class 3 energy let through for 32A 6ka which was quoted at 45000A²s if i remember right. That was described as necessary for pscc above 1kA

 

[johnduffell]

with a socket outlet the load is unknown as anything can be plugged in therefore must be assumed that it could be subject to overload.

Fair enough thanks, i did wonder if i could count a socket outlet as a "load".
In that case what allows an unfused spur on a ring final? Is that purely a special dispensation rather than due to the 20A Max for a double socket making an overload unlikely?

 

[Wilko]

Probably get razzed for putting this on the bad instal thread, but not to worry .
Just for fun - the Wylex data sheet seems to give 6kA let through for 32A MCB about 3.5x10^4 and plugging that into 434.5.2 with k=115 gave me about 1.4mm2 (hopefully not made a slip ... ). Although it's allowed, I don't use 1.5/1 in any socket circuit. Unfused spurs on 32A RFC should be 2.5/1.5 (App 15).

 

[johnduffell]

Got it, you're a genius @Wilko the thing I was missing was that the let through energy is also limited by the cutout fuse if the MCB can't operate quick enough. So we're actually limited to less than 20000A2s Makes perfect sense now!

 

[Wilko]

Good, now you'll need to splain it to me ...

 

[johnduffell]

Good, now you'll need to splain it to me ...

haha, well the way I understand it now, which hopefully is fairly accurate:
the let through is limited by any and all upstream OPDs
When a fault occurs, each OPD sees the same current flowing (PSCC or PEFC) and trips according to its time current curve given enough time.
The time-current curve of an MCB and a cutout fuse start off the way round you'd expect at low currents, but at very high currents (>kA) they cross over. This is due to the fact that the fuse melts quicker with a higher current, whereas the MCB has mechanical inertia so the time to unlatch is not sped up much regardless of the current. The arc time is presumably similar for both.
Therefore at these high currents, the cutout fuse will blow before the MCB trips, limiting the I2t to the fuse's I2c, therefore limiting the need for a larger CPC.

Make sense? I hope!

 

[Strima]

Mother in law has just had a summer house added to her garden a hot tub going in soon. SWA supply for the hot tub is ready to go but I'm not sure of the isolation carried out...

The SWA feeding the summer house isn't glanded to earth at any point either...

That's it running past the bottom of the meter...

I just have to wait for the certification to turn up before making any comments to the installer.

 

[MFS Electrical]

Dodgy Dave has been doing the rounds again. These are all in the same place. Where do I begin can fit your finger through every one of the holes on the top surface no protection for the cables entering the bottom or the side dodgy set up where that 2.5 t&e’s nuetral feeds something else in the CU god knows why old heating box tails enter two different holes unused holes in the old heating box that you can stick your finger in random unprotected joint down below CU.
Oh and the MCBs etc haven’t been fitted correctly so there is half a device’s width at both ends of the CU with no blanks aaaand a lovely pokey up bit of uncapped busbar just waiting to zap you if you try and reset your tripped lights in the dark and put your finger through the hole. What a mess...

 

[MFS Electrical]

Dodgy Dave has been doing the rounds again. These are all in the same place. Where do I begin can fit your finger through every one of the holes on the top surface no protection for the cables entering the bottom or the side dodgy set up where that 2.5 t&e’s nuetral feeds something else in the CU god knows why old heating box tails enter two different holes unused holes in the old heating box that you can stick your finger in random unprotected joint down below CU.
Oh and the MCBs etc haven’t been fitted correctly so there is half a device’s width at both ends of the CU with no blanks aaaand a lovely pokey up bit of uncapped busbar just waiting to zap you if you try and reset your tripped lights in the dark and put your finger through the hole. What a mess...

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Almost forgot that’s a joint taped up on the earth there just after the Henley block

 

[telectrix]

looks like:

 

[pirate]

but apart from that?

 

[123]

 

[telectrix]

View attachment 43627

that's terrible. the pins don't line up.

 

[Wilko]

Wonder if it's one of those exploding fuses too ? (Item on Fake Britain today about fuses without sand that go off with a proper pop).

 

[Toneyz]

Wonder if it's one of those exploding fuses too ? (Item on Fake Britain today about fuses without sand that go off with a proper pop).

Thats an old repeat saw this oiver a year ago.

 

[freddo]

During a rather cut down condition report I noted one of the emergency lights wasn't working. On investigating I didn't imagine this would be the reason. It looks like someone has replaced the battery in it recently too.

 

[Toneyz]

That's classed as safe compared to most things we see and hear on this forum.

 

[freddo]

Just a good job it is housed in a plastic enclosure...