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2 cut-out fuses

Discussion in 'Electrics UK' started by b21playa, 15 Oct 2020.

  1. JohnW2

    JohnW2

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    I suppose I have to take your word for that, but I have to say that I don't recall having seen any terraced/semi houses with 'sheds adjacent to the front door' - and I'm not even sure what the Planners would have to say about sheds in front gardens! Do you really mean 'shed', rather than some sort of 'cabinet'.

    If there is joint access' to the 'shed', then I suppose that's not too bad. However, that's not really what we have been talking about (and is more akin to the multi-occupancy buildings you go on to mention). If the equipment is within one of two dwellings, then there are clearly some potential issues (in relation to both 'safety' and logistics/convenience) houses if the DNO fuse for one dwelling is within the other (and not necessarily always easily 'accessible').
    Sure, but that moves the goalposts well away of the situation we're discussing.
    I've already discussed that. What matters, electrically, is any part of the cabling which has to carry the combined loads of both installations. Consider the analogy of two 4kW loads in an installation, and two possible arrangements - (a) each fed by a separate 'dedicated' circuit from the CU and (b) both fed by a single 'radial' circuit from the CU. With the former arrangement, the cables from CU to load could theoretically be 1.5mm² (Method C) in both cases. With the second arrangement, the cable from CU to the first load would have to be 4mm² but (if the load were 'unlikely to create an overload', or if there were 'fusing down' after the first load) the cable from first to second load would again only need to be 1.5mm². Those two 'loads' are analogous to the two installations being fed with a 'looped' supply.

    You go on to mention diversity (and Christmas morning). Whilst, under most circumstances, and across many installations, it is reasonable to assume that multiple installations will not simultaneously have high demands, with just two dwellings on Christmas morning one cannot safely assume that they won't both have high demands.
    As I've said, the important (and really only) difference between your #3 and #4 is that in one case (#4) each of the two premises has the DNO fuse within it, whilst in the other case (#3) the DNO fuse for 'House 2' is in 'House 1' (and not necessarily always easily accessible to the occupants of 'House 2').

    In terms of loads on cables, in both #3 and #4 the entire load of both premises is carried by the DNO feed to the first house - which is why, in functional terms, I would not regard either as being different from a 'conventional' "looped supply" (your #2).

    Kind Regards, John
     
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  3. jelliottelectrical

    jelliottelectrical

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    From my own house.

    B31241D0-9E09-452D-8808-6851580E581E.jpeg
    ABAEFAB6-2981-432C-88C4-7EFA6F562BEF.jpeg
    I live in a terrace of 5 houses (ex council) and have a three phase cutout into the one meter box which serves my house and the neighbours either side. Only links are in the single phase cutouts in the ‘meter’ box. So if one of the neighbours were to blow a cutout fuse, WPD would need access to my porch to replace the fuse.

    I discussed it with an engineer I know from WPD and he said it was common at the time (mid 70s) and it is referred to by them as a looped supply
    We have the dreaded consac cables feeding this estate and I’m reliably informed that this method was used to reduce the number of joints on the cable
    For anyone that doesn’t know, Consac cable is notorious for failing, particularly at the joints, to the point where most DNOs that have it on their network have started running schemes to overlay it. More that one person has told me in the past that consac was only ever designed to go from A to B (think between transformer and switchgear) and not meant to have multiple services jointed onto it
     
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  4. JohnW2

    JohnW2

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    Interesting. If they call it a 'looped supply', I suppose that must be because, in a physical sense, there is literally just one 'cable' serving three installations.

    However, if you're saying that each of the three properties is fed by a separate phase (albeit fuses for all three are in your house) then, thinking 'electrically', I don't think that "even I" would call it 'looped', since no line conductor is carrying the current of more than one installation - i.e. it just 'happens' that the three line conductors (on different phases) spend some of their path inside a single outer sheath. If the three L's split into three separate 'cables' outside of the properties, I don't think anyone would consider the supplies to be 'looped' (regardless of where the fuses were), would they?

    As you imply, and as I previously mentioned, there is obviously a bit of an issue (convenience and safety) with having all three fuses in the same house - 'convenience', as you say, if the DNO need to replace the fuse for one of the other houses but, potentially, 'safety' if flames are coming out of the meter or CU (assuming no external isolator) in one of those other properties.
    I must confess that I've never heard of it (what exactly is it, I wonder?), but it would certainly afford an explanation as to why they fed the installations in that way. Mind you, I wonder why they used it (cheap?) - on the face of it, if they knew that it was so likely to fail that they had to adapt their practices to minimise joints, one might have expected them to decide not to use it at all!

    Kind Regards, John
     
  5. jelliottelectrical

    jelliottelectrical

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    Consac is Concentric Cable with Solid aluminium conductor.

    470E5184-1E5A-4725-8830-56D1C0571373.jpeg

    Seen here, it’s a three core paper cable with an aluminium N/E outer and a PVC oversheath. It was a cheaper cable that PILC which was typically lead with copper cores. There is a special depth saw to strip it live (as in the picture) to retain the neutral/earth continuity. I believe though that after a few incidents that some DNOs won’t work on it live anymore. Certainly on the larger sizes, the aluminium outer could be thicker on one side that the other so the saw would go through the paper cores as well resulting in a bit of a bang

    The other issue was third party damage. If the sheath was ‘nicked’ during laying or other roadworks, water Ingress would rot the aluminium, over a Period of time and then one day, you’d have part of an estate losing the neutral and earth supplies which as you probably know has interesting effects! I believe Alpex cable has similar issues (alpex is waveform cable with aluminium n/e strands in rubber bedding around the aluminium cores) which is why modern waveform cables are aluminium cores with copper neutral and earth strands

    I agree with you though on the looped supply designation, all that is different that three independent supplies, is that there is one joint and it all goes via my house. Interestingly though all three are fused at 60amp. Hypothetically If I were to enquire with WPD about installing a vehicle charge point I’d be interested to know if they would alter the setup. For information, vehicle chargers are not recommended on looped supplies and I believe all DNOs are obliged to alter supplies to remove the loop free of charge if you request it
     
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  6. JohnW2

    JohnW2

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    That sounds like a bit of a nightmare - and, from what you've said, the only 'advantage' of it is cost?
    That's presumably just a question of the CSA of the conductors and the capabilities of the local supply, isn't it? If the cores of the 3-phase cable have the same CSA as they would have used for a single-phase supply to a single installation, then I presume the 'possibilities' as regards fuse rating would be the same?
    I could understand that with a supply which was 'looped' in the way I think of it (i.e. with some conductors carrying current from more than one installation), but if they are three separate phases, sharing no conductors, I can't see why the suitability of the installation for an EV charger would be any different from the situation with just a single, single-phase, supply 'from the road', can you?

    Kind Regards, John
     
  7. jelliottelectrical

    jelliottelectrical

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    I agree with you, and the three phase and single phase cables are all 35mm now for services, so I see no issue with loading whether It is single or three phase

    My main point was, if WPD deem my supply to be ‘looped’ when technically it isn’ t by the traditional standards, whether they would do anything, whether actually necessary or not. More an issue of terminology really
     
  8. JohnW2

    JohnW2

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    True. If, for whatever reason, they have decided/chosen to call it 'looped', and if they say that they will remove looped supplies, on demand, free-of-charge, then it would seem that they've probably talked themselves into a bit of a corner :)

    Kind Regards, John
     
  9. jelliottelectrical

    jelliottelectrical

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    I think electric vehicles will cause the DNOs a headache for years to come!
     
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  11. JohnW2

    JohnW2

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    ... and the generators of electricity.

    It was pretty recent, but before everyone started talking about EVs and EV charging, that there were discussions all over the place (including here) about how the capacity of the UK electricity supply was probably going to fall behind demand within a small number of years. Add to that the almost unthinkable additional energy requirements of widely-implemented EVs and there would seem to be scope for some very serious headaches.

    That's one of the reasons why some fear that Big Brother will take over (and restrict) their use of electricity if/when the rollout of 'smart' (pretty dumb, IMO!) meters (and, perhaps more importantly, 'smart appliances' for them to control - a type of animal that I have personally not yet seen at all!) ever gets completed!

    Kind Regards, John
     
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  12. SUNRAY

    SUNRAY

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    As has also been said in following posts this is not what I'd call a looped supply, if that is the acceplable term for this installation then so be it and I'll try to get into the habit.
    However if the supply companies are removing looped supplies I'll bet a pound to a penny this installation will very quickly be reclassified to a different title as there doesn't seem to be technical reason for its alteration.
     
  13. JohnW2

    JohnW2

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    As I've said (and jelliottelectrical seems to agree), in that situation, with three different phases, each with totally separate conductors/fuses, I personally definitely would NOT regard it as being in any sense 'looped'. It only differs from a plumb-normal set of three installations in that (a) the three (different/separate) L conductors 'happen to be' within the same outer sheath for some of their path and (b) the fuses for all three (separate) single-phase installations 'happen to be' in one house.
    In this case (with three separate single-phase supplies, absolutely nothing 'common') I would certainly agree that there is no technical/electrical reason to change it (the only conceivable reason I can think of being that relating to 'access to fuses'). However, if it were (what I would regard as) a true "looped supply" (i.e. with one L conductor carrying the total current for two or more installations) then there could be good 'technical reasons' for alteration, particularly if an EV charging facility were being installed in one (or more!) of the houses.

    Kind Regards, John
     
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  14. SUNRAY

    SUNRAY

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    The word 'shed' is somewhat unintuitive. The irony is I have worked in 2 such properties recently but they are both in pedestrian walkway locations and not visible on Street View, hopefully this sketch will offer a better idea:
    upload_2020-10-18_1-0-34.png
    Typically there are a pair of walk in cupboards, my 2 recent are ~3x3ft and 5x3ft, which are often crammed to the gunwals with the sort of things usually found in the garden shed. It usually contains the meters and CU and commonly one has the I/C services. With a single head it's a perfect example of my 'Two Services'. May be 2ph but bearing in mind these date from >40years ago when power demand was nowhere near todays it's commonly 1ph with 2 fuses and sometimes even just the one fuse.

    If we're still referring to OPs situation either #3 or #4 could very easily be appropriate
     
  15. JohnW2

    JohnW2

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    Thanks for clarifying - so, as you say, essential an 'outdoor cupboard', closer to the 'cabinet' I suggested than a 'shed'!
    Indeed - but there's a big difference between 1-phase and 2-phase. The 1-phase case is what we've been discussing. However, if it's two separate phases then it's the same as what jelliottelectrical described - which , for reasons I recently explained, I would NOT dream of regarding as 'looped' - it would simply be two single-phase installations whose (separate) conductors happened to share an outer sheath in some places and with the fuses for both being in one house (or shed/cupboard!).
    If a cable from the currently unused fuse holder in the OPs installation once served 'somewhere else' (probably 'next door'), then if there were then a fuse in that holder then it surely would be #3, wouldn't it? It would only be #4 if you entertained the possibility that the holder may then have contained a solid link (rather than a fuse), with the fuse being in the 'somewhere else' location - but that would seem to make little sense, since the cable might as well have been put straight into the cutout rather than via a solid link in a fuseholder?

    Kind Regards, John
     
  16. jelliottelectrical

    jelliottelectrical

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    I think more information might help in this situation, I mean if the OP lives in a detached house with some distance between neighbours then it is unlikely that the second fuse ever served a neighbour

    My money is on it being an old Dc supply that has been converted and is now just two phases, given the age of the incoming cable and the cutout, and that the fuse holders have been changed

    That being said, the village where I grew up has no mains gas, and so a lot of people relied on storage heaters. A lot of people have now a second cutout fuse, that is redundant, having once served all the off peak heating. Most houses now use LPG or oil so they are no longer used. But the bigger houses around here were built like that, obviously too greater load for the one fuse, but not enough to warrant a three phase supply. Though on reflection the majority of these houses I have worked on are still overhead supplies, fed via singles to separate fuses, so I imagine it is easier to run three singles in this case. If it were underground I could see a three phase supply being installed and the third phase just not being used
     
  17. SUNRAY

    SUNRAY

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    Not an ideal example but here's one built into a garage [window beside it is downstairs toilet] This one is designed as a dustbin store with cupboard over. All the rest in this road have been bricked up to extend the garage space
    upload_2020-10-18_11-39-3.png upload_2020-10-18_11-46-47.png
     
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