Here on this DCUSA document. Paragraph #8 https://www.dcusa.co.uk/Documents/De-Energisation - FAQ Document v 1 0.pdf#search=de-energisationj It states A switch-fuse unit close to the meter and a sub- main compliant with BS7671 should be installed when the distance to the consumer unit requires more than 3m of cable. I think that's clear enough.
A bit of de ja vu - I posted these links in this thread the last time it came up. I think we just have to accept that @Coloumb is unconvinced and we should just agree to disagree.
Well it isn't is it? It says A switch-fuse, not the type of switch fuse should be of an appropriate rating against the cut out so as to comply with the requirements of BS7671, ie discrimination. @Bazza, if a switch fuse is installed of the same rating as the cut out, how does this make things more compliant, more safer, than just an isolator, if the Zs is correct for the type of fuse in the cut-out at then end of the run? Can you give me the regulations in bs7671 that specify that there must be a switch fuse if the run is greater than three meters?
@Comlec, if a switch fuse is installed of the same rating as the cut out, how does this make things more compliant, more safer, than just an isolator, if the Zs is correct for the type of fuse in the cut-out at then end of the run? Can you give me the regulations in bs7671 that specify that there must be a switch fuse if the run is greater than three meters?
You've missed a big thing here. We are not talking about BS7671, we are talking about the requirements of the supplier. They can say black is white, and refuse to connect you up unless you conform.
Right mate, the supplier. Not DCUSA. They are not the supplier. IF the supplier say's they won't do it then yes, there aint much you can do. I've done this twice, ie run a sub-main protected by the cut-out fuse and both times the supplier has said "everything beyond the meter is nothing to with us. We are not interested". And yes they have been there and seen me do it. Both times. Replaced the cut-out, fitted an isolator. They do not care. They are not interested. Tbh I don't think they even understand what I'm doing. So, if a switch fuse is installed of the same rating as the cut out, how does this make things more compliant, more safer, than just an isolator, if the Zs is correct for the type of fuse in the cut-out at then end of the run? Can you give me the regulations in bs7671 that specify that there must be a switch fuse if the run is greater than three meters?
Interesting. A DP isolator switch in enclosure is great for feed to DB1 etc. However on the Henly from said isolator switch, the feed for say a shed sub circuit would be via an appropriately rated switch fuse with appropriate discrimination..this does mean that the DP isolator negates all power if switched off and encompasses regs nicely.
Coloumb what you are forgetting is we are talking about complying with BS7671. BS7671 only covers the installation and the installation starts at the consumer connection point at the meter. So as far as BS7671 is concerned, there is nothing to discriminate with, because anything before the meter is nothing to do with BS7671. As for the people who make the connections, who knows?
Not an electrician. I thought I had enough problems being an accountant! But just on the logic of this the switch-fuse say 15 meters from the cut out could be 100 amp with the DNO' s fuse being 80 amp.
Mate, seriously, really seriously, do you honestly, in your heart of hearts, really, really think that this imaginary rule, one where you have two fuses in series with exactly the same rating, somehow manages to change the actually laws of physics so that somehow it's not applicable to British Stanard BS7671?
What has the laws of physics got to do with anything? It's all about your installation complying with BS7671, and not relying on something that is outside of your control.
And having two fuses of the same rating in series complies with BS7671 how? If you know the rating and fuse type of the cut out how is this outside your control?
This is so simple, I really don't understand why anyone cannot understand. BS7671 covers the installation. Whatever is outside of the installation does not matter. There could be 15 billion fuses outside of the installation, BS7671 does not care. It only covers the installation. So it requires that the tails be provided with overcurrent protection. To comply, you must provide it, simples. Don't go on about there being a fuse over there, it don't matter, it's outside of the installation, it's not covered by BS7671.
I am in complete agreement with Coloumb. The requirement for a fuse on tails more than 3m in length is a misunderstanding by the DNO and as such is a wrongly endorsed myth. They have misinterpreted the Regulation (as many still do) and have published what amounts to a daft requirement. Unfortunately electricians are very good at perpetuating misinformation and only a rare few ever bother to check out what they are told. The misinterpretation stems from this Reg: 433.2.2 (ii) What people fail to understand is that if the tails from the meter to the consumer unit are one continuous run then there is no device causing overload on the tails. Similarly if the tails are one continuous run there is NO CHANGE in the tails that would invoke the requirement to limit the length to 3m to the point of change. The Regulation 433.2 is entitled Position of devices for protection against overload. So, as stated, where is the overload coming from just by limiting the tails to 3m? Anser, there is none and it isn't necessary. The point made by coloumb is my point also, that a 60A or 80A fused switch in the tails is not doing anything extra in terms of overload protection than the cut-out already is.
I would add that Reg 434.2.1 is exactly the same principle as 433.2.2 and the same misinterpretation is being applied by the same DNO. By all means fit a switch if you WANT to, there is absolutely no need nor requirement to fuse it.
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