Square peg round hole.......

[Michaelwgroves]

I'm looking at running 25mm SWA to supply secondary CU to future proof HMO design. See my previous threads for details House of Multiple Occupancy Design - https://www.electriciansforums.co.uk/threads/house-of-multiple-occupancy-design.124817/

My issue is a 100A CU and SP Distribution boards seem to only have 16mm neutral terminals from what I can find. So I'm stuck, can you buy bigger terminals, if not what about placing Henley block in CU/SP Distribution board to run main neutrals. At the risk of being scalded, dare I say drill out to accommodate 25mm ?
Otherwise only solution would be to buy 3Phase which seems like massive overkill for what I'm looking to do.

 

[Pete999]

I'm looking at running 25mm SWA to supply secondary CU to future proof HMO design. See my previous threads for details House of Multiple Occupancy Design - https://www.electriciansforums.co.uk/threads/house-of-multiple-occupancy-design.124817/

My issue is a 100A CU and SP Distribution boards seem to only have 16mm neutral terminals from what I can find. So I'm stuck, can you buy bigger terminals, if not what about placing Henley block in CU/SP Distribution board to run main neutrals. At the risk of being scalded, dare I say drill out to accommodate 25mm ?
Otherwise only solution would be to buy 3Phase which seems like massive overkill for what I'm looking to do.

May seem daft, but why 25mm2SWA? without being rude or condescending have any cable calculations been done? What is the distance of the cable run? what method of install? you say 100A but that is the rating of the CU.

 

[Michaelwgroves]

Pete, take a look at my HMO post, it'll them make sense. I didn't want other post to get distracted.

 

[Pete999]

Pete, take a look at my HMO post, it'll them make sense. I didn't want other post to get distracted.

Just seen it

 

[Pete999]

Pete, take a look at my HMO post, it'll them make sense. I didn't want other post to get distracted.

Still can't get my head around it Micheal, you must have calculated the Max Demand, it can be a lot lower than you may think, as already said in your previous post

 

[Leesparkykent]

Taking a distribution circuit from the CU is poor design as it will not achieve discrimination. If you insist on doing it then you could use a 25mm to 16mm reducing pin.

Un-insulated Reducing Pin - SWA - http://www.swaonline.co.uk/cable-terminations/copper-pin-terminals/uninsulated-reducing-pin

 

[123]

No Electric Showers, Hob is gas...why do you need 25mm?
Why take the SWA to a consumer unit, it's not a good setup to have a sub board fed from an MCB imo.

 

[Michaelwgroves]

All fair comments, which I tend to agree, but better suited to HMO thread.

Can I use a reducing pin, does that not reduce down to 16mm capacity,although at the point I need 25mm I can simply cut it off. But that only works in CU, if I use SP Distributionim from outset I’m still restricted to 16mm?

 

[Leesparkykent]

All fair comments, which I tend to agree, but better suited to HMO thread.

Can I use a reducing pin, does that not reduce down to 16mm capacity,although at the point I need 25mm I can simply cut it off. But that only works in CU, if I use SP Distributionim from outset I’m still restricted to 16mm?

The max size OCPD device is going to be 63A if your using 60898's...The CCC of 16mm SWA is above that anyway...I assumed you selected 25mm for voltdrop.

 

[westward10]

I would never consider running 16.0 swa final circuits from a consumer unit let alone 25.0, forgetting discrimination it is a bad idea. You need a more substantial board if you go down this route with BS88 fuses or 947-2 devices.

 

[Leesparkykent]

I would never consider running 16.0 swa final circuits from a consumer unit let alone 25.0, forgetting discrimination it is a bad idea. You need a more substantial board if you go down this route with BS88 fuses or 947-2 devices.

Exactly my thoughts.

 

[westward10]

You would have to be a pretty slick cable dresser to form 16.0 or 25.0 conductors which are xlpe insulated so they were not placing undue stress on terminations and the devices, impossible I would say. That is assuming the devices fit once you have made off all the cables to the enclosure.

 

[ipf]

You would have to be a pretty slick cable dresser to form 16.0 or 25.0 conductors which are xlpe insulated so they were not placing undue stress on terminations and the devices, impossible I would say. That is assuming the devices fit once you have made off all the cables to the enclosure.

Yes. It would be a case of individual switched fuses, or equivalent, local to supply position for me. If cost is the main factor, there could be problems doing things by the book...but, that's how it should be, imo.
Is a 100amp single phase suitable? A 3 phase supply would solve a lot of problems.

 

[Strima]

Yes. It would be a case of individual switched fuses, or equivalent, local to supply position for me. If cost is the main factor, there could be problems doing things by the book...but, that's how it should be, imo.
Is a 100amp single phase suitable? A 3 phase supply would solve a lot of problems.

There's a lot of single phase circuits that are a bugger to balance which suppliers don't like and tend to charge the customer more money for.

 

[123]

With no Electric Showers, Heating, or Hob...not sure why 3 Phase would be needed?

 

[Lucien Nunes]

Looking at the other thread, it's an HMO with 12 rooms that might be separately let. If the communal GCH packs in. 12 x 2kW fanheaters will go on. There are also some electric hobs.

Returning to the subject of terminating 16 & 25mm² in DB's, we sometimes have to do this where the cable has been selected for VD or running through very high ambient temp. A terminal pin is OK, it won't automatically reduce the CCC, but then typically you won't hit the CCC with the kind of outgoing way you will have in a regular 60898 DB. Beware the effect of poor quality terminals though, sometimes they don't hold well on a solid lump of copper. Tthe same is true of solid MI cores which can be a problem to terminate in marginal single-screw terminals.

An alternative is to use an inline uninsulated butt crimp sized for the SWA core, with a tail of smaller cable with the correct number of strands carefully doubled over inwards, so that all strands contact the crimp. A suitable length tail will allow flexibility to minimise stress on the terminal.

I have been known, when pressed, to put three strands in one hole and four in the next, but I don't recommend it. I would be more likely to do this on an outsize EC, where it also gives the advantage of redundancy.

FWIW here's a pic of a 60898 board with 3x 3-phase 50A outgoing circuits in 16mm², admittedly conduit cable. I didn't wire the straggly stuff in the background, only the 16mm.

 

[westward10]

Not quite the same as a single pole board.

 

[Michaelwgroves]

Still can't get my head around it Micheal, you must have calculated the Max Demand, it can be a lot lower than you may think, as already said in your previous post

It's currently tiny, but as I've not been given final demand it's impossible to say. If I was a betting man I think 100A single supply will be just enough. I need to pull a cable to first floor anyway, so thought if I pull 25mm I am well covered for almost any eventuality.

 

[Michaelwgroves]

No Electric Showers, Hob is gas...why do you need 25mm?
Why take the SWA to a consumer unit, it's not a good setup to have a sub board fed from an MCB imo.

You'll need to read HMO thread to fully appreciate, but simply I'm pulling a bigger cable than I need to future proof expansion.

Surly most garages & shed's are run as a sub?

 

[Michaelwgroves]

Taking a distribution circuit from the CU is poor design as it will not achieve discrimination. If you insist on doing it then you could use a 25mm to 16mm reducing pin.

Un-insulated Reducing Pin - SWA - http://www.swaonline.co.uk/cable-terminations/copper-pin-terminals/uninsulated-reducing-pin

This looks like the answer for me, thanks