Switch fuse for tails

ringer · Nov 21, 2018

New position of replacement Consumer Unit for my customer is now going to be 7m away from the supply head. DNO fuse is 100A BS1361 and this is a large house so I still need a (potential) 100A supply. I believe that I am supposed to fit a switch fuse if tails are over 3m long. Firstly, am unclear if this is a regulation or just an undocumented 'DNO requirement'. Secondly, can anyone recommend a make and model of switchfuse suitable for use in a domestic environment? Am concerned about aesthetics (it might have to be on show) and cost - I see some commercial/industrial ones cost £100s. Presumably the enclosure would have to be of metal construction, though that is not clear either. Which ones have you fitted and what is your opinion of them? One other point - if I fit a 100A switchfuse, how will that discriminate (select?) before the DNO supply head fuse?

MDJ · Nov 21, 2018

ringer said:
New position of replacement Consumer Unit for my customer is now going to be 7m away from the supply head. DNO fuse is 100A BS1361 and this is a large house so I still need a (potential) 100A supply. I believe that I am supposed to fit a switch fuse if tails are over 3m long. Firstly, am unclear if this is a regulation or just an undocumented 'DNO requirement'. Secondly, can anyone recommend a make and model of switchfuse suitable for use in a domestic environment? Am concerned about aesthetics (it might have to be on show) and cost - I see some commercial/industrial ones cost £100s. Presumably the enclosure would have to be of metal construction, though that is not clear either. Which ones have you fitted and what is your opinion of them? One other point - if I fit a 100A switchfuse, how will that discriminate (select?) before the DNO supply head fuse?

I agree a switch fuse is a good idea, I like Schnieder but you will have plenty of choice, speak to your wholesaler mate.

Wilko · Nov 21, 2018

Hi - could try this Wylex one
Wylex 100 Amp SP&N Switchfuses - https://www.tlc-direct.co.uk/Manufacturers/Wylex/Switchfuse_SP_and_N/index.html

[ElectriciansForums.net] Switch fuse for tails

ringer · Nov 21, 2018

To MDJ - Oh dear - is this now going to turn into a slanging match? I hope not. A genuine contractor here asking a genuine question about a real-life on-the-job scenario. As a sole-trader it is at times difficult to know exactly what to do for the best in some circumstances, hence my question. If you do not have a sensible answer then please refrain from muddying the waters further with your unhelpful response.

MDJ · Nov 21, 2018

ringer said:
To MDJ - Oh dear - is this now going to turn into a slanging match? I hope not. A genuine contractor here asking a genuine question about a real-life on-the-job scenario. As a sole-trader it is at times difficult to know exactly what to do for the best in some circumstances, hence my question. If you do not have a sensible answer then please refrain from muddying the waters further with your unhelpful response.

Not at all it was a bit of fun, and I gave you a answer afterwards, I thought your question was a good one, you have now had 2 answers, regarding the 2nd one, the wylex unit is also decent, there are dozens of types, I prefer the type where there is room around the busbar, in general these switch fuses are tight and seem to get smaller, not sure about BG which is the cheaper option, at 7 mtrs of tails a switch fuse is a requirement.

ringer · Nov 21, 2018

Thank you for a now helpful response. Someone else suggested Schneider but no model name given. Yes, I can ask my wholesaler but they are only likely to suggest whatever they have in stock. I am looking for recommendations of what others have successfully used. A model number would be useful so I can google it and see what they look like.

MDJ · Nov 21, 2018

ringer said:
Thank you for a now helpful response. Someone else suggested Schneider but no model name given. Yes, I can ask my wholesaler but they are only likely to suggest whatever they have in stock. I am looking for recommendations of what others have successfully used. A model number would be useful so I can google it and see what they look like.

How much room have you got in the area where the switch fuse will be fitted?

SparkyChick · Nov 21, 2018

ringer said:
New position of replacement Consumer Unit for my customer is now going to be 7m away from the supply head. DNO fuse is 100A BS1361 and this is a large house so I still need a (potential) 100A supply. I believe that I am supposed to fit a switch fuse if tails are over 3m long. Firstly, am unclear if this is a regulation or just an undocumented 'DNO requirement'. Secondly, can anyone recommend a make and model of switchfuse suitable for use in a domestic environment? Am concerned about aesthetics (it might have to be on show) and cost - I see some commercial/industrial ones cost £100s. Presumably the enclosure would have to be of metal construction, though that is not clear either. Which ones have you fitted and what is your opinion of them? One other point - if I fit a 100A switchfuse, how will that discriminate (select?) before the DNO supply head fuse?

I've just used a couple of Hamilton HLMFS. Significantly cheaper than the Wylex, seem to be good build quality, 100A maximum, comes with 63A, 80A and 100A fuses. Earth bar easily accommodates 16mm.

Nice units.

I wouldn't worry about discrimination. The switch fuse is there because the DNO won't guarantee their fuse will blow in time in the event of a fault on the tails if they are longer than 3m.

Gavin John Hyde · Nov 21, 2018

I have used the Lewden ones a bit in the past. not too pricey and most wholesalers can get them in, if you want to save money have a look at
Wylex Single Phase Switchfuses - Discount Electrical - http://www.discount-electrical.co.uk/section.php/108706/1/wylex-single-phase-switchfuses
you can get a wylex one for £60 inc of VAT. with free delivery.

ringer · Nov 21, 2018

MDJ said:
How much room have you got in the area where the switch fuse will be fitted?

Potentially as much as I want - the room where it will sit is going to be remodelled - currently a kitchen it will end up as a bedroom.

ringer · Nov 21, 2018

Am assuming here it is would be unwise to try and fit it in the meter cupboard outside.

MDJ · Nov 21, 2018

well the more room the better, I have a single phase 100 amp MEM switch fuse if you want it, not sure what the P&P would cost but it is immaculate and never used, probably 7-8 years old and industrial but it is yours if the postage is not a problem. In fact I may be wrong it may be an isolator I will have a look.