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I have inherited some wiring that feels a bit odd, but I'm assured is fine, so am interested in opinions if it really is OK. I'm an Electrical Engineer so know the theory, but don't have any wiring qualifications so am vague on actual practice, but am always interested to learn (for interest, not to try and do things myself!).
The situation is this - an outbuilding has a CU fed with a large SWA cable from the house. A 32A MCB in the CU feeds a 4mm^2 armoured cable which runs outside around 10m to a small brick hut. At the hut the armoured cable goes into a rotary isolator switch for a swimming pool heat pump, and has a twin & earth spur coming off to 4 x 13A sockets, one of which is used for a water pump. There's no further protection in the hut.
Everything is running fine, but I'm surprised there's not a CU with RCD/MCB in the hut to provide local protection and I'm intrigued if there should be one.
Thanks for any information for my curiosity.
Alcomax no, no-one has assured me it's fine - as per my enquiry it's a system that I inherited with a house purchase and which is operating fine but raised my curiosity, hence wanting to understand the arrangement and whether it's correct. Based on the suggestions below I'll speak to an electrician to improve things.
AJJewsbury more investigation shows the origin at the house has a 60A fuse in a switch unit as shown in the picture below. The meter feeds the switch/fuse unit and the output SWA runs about 30m to the outbuilding. The photo just about shows the paired wires.
Sparkingchip will speak to an electrician to get it done.
I'm surprised there's not a CU with RCD/MCB in the hut and
At the hut the armoured cable goes into a rotary isolator switch for a swimming pool heat pump, and has a twin & earth spur coming off to 4 x 13A sockets, one of which is used for a water pump. There's no further protection in the hut.
Out of curiosity did someone assure you that all this was fine? Not trying to be funny, but was this advice given before 1983 and the IEE reg 471-12 ?
Sparkingchip has been trying his best to make the obvious point.
the 3m figure I took to be from cutout, thru meter to CU rather than from meter to CU. I might be wrong though (I often am!)
I can't read the size - it seems to be 4 core as there's red & yellow into the CU live inlet in the outbuilding, and blue & black neutral. Total O/D is around 3cm.That's pretty large - if it really is about 30mm diameter and 4-core that would put it somewhere around 35mm² or 50mm² - ether someone had the cable left over from another job or they were very worried about voltage drop - how long is this one?
so no protection in the house other than the main 100A inlet fuse.If you're saying that this SWA has been directly connected to the DNO's supply without any overcurrent protection at all, that's a bit worrying. Normally you'd expect at least a fuse within 3m of the meter and the cables before that fuse to be as short as reasonable practical, normally single core insulated & sheathed to minimise the risk of faults between conductors and placed to minimise the risk of damage (certainly not buried in the ground). In practice, if the SWA really is as big as it seems (and not too long), the actual dangers might not be that large in your particular case, but it's still way beyond what's normally acceptable.
I'm presuming you've got use of the DNO's earth terminal (TN) and don't rely on your own earth electrode (TT) - otherwise there'll be a stack of bigger problems too.
SWA needs to be properly terminated so the armoure wires are earthed at least at the origin end (at the load end the armour may be the way the earth is provided for the sockets or they may be "TT" earthed via an electrode and the armour stops )
As others have noted an RCBO or RCD at the origin would be good, and is mandatory on new work, especially with water and electrics in proximity.
I had assumed the feed came from the CU in the house, but I've just checked and it doesn't - the meter outlet is split to the house CU and to the outbuilding, so no protection in the house other than the main 100A inlet fuse. Outbuilding CU has a 100A main breaker and 32A MCB for this outlet.
I guess the obvious question is whether it's worth adding an RCD? The outbuilding itself also has a number of 13A sockets in it. Sounds like not legally needed, but certainly an area I'd rather adopt the best approach rather than the legal minimum!
There'd be little advantage in having another MCB between the 32A one and the sockets, except possibly to limit possible overloads from the sockets - for any faults MCBs most likely won't discriminate so you'll just as likely find the 32A opens as well as any downstream ones - cutting everything off anyway.
Sockets these days do require 30mA RCD protection though - so if there isn't one anywhere that might be an issue. Although it's not that long ago that the requirement was only for sockets likely to supply equipment outdoors, so if the installation is a few years old, it might have been acceptable at the time.