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.

 

[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

 

[123]

It's an HMO, not a block of flats. Unless that is different in Kent to here, it's a shared kitchen.

From your other post, no electric showers, hob is also gas. Could probably stick the entire lot on a 20A fuse and never have a single issue.

 

[Michaelwgroves]

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.

Sorry if I was not clear, it's for a secondary board, not final circuits.

 

[Michaelwgroves]

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.

It will be by the book 100%, no cutting corners, just looking for best solution.

Been running 60A main fuse for last 40 years no problem, and that was before new GCH. I think 100A will be fine, but if I gotta pull a new cable, might as well be a big one that could handle new supply if needed.

 

[ipf]

It will be by the book 100%, no cutting corners, just looking for best solution.

Been running 60A main fuse for last 40 years no problem, and that was before new GCH. I think 100A will be fine, but if I gotta pull a new cable, might as well be a big one that could handle new supply if needed.

Fair enough. Not knowing the full installation, too much may be being made of the situation. It's just the 25mm, seemingly way over the top.

 

[Michaelwgroves]

Fair enough. Not knowing the full installation, too much may be being made of the situation. It's just the 25mm, seemingly way over the top.

Agree, 25mm for current soliution is way over the top, also using 25mm for sub board does not make sense. But when you know it’s just incase I need to run a new supply hopefully it makes sense.

 

[westward10]

Sorry if I was not clear, it's for a secondary board, not final circuits.

I miss understood nothing.

 

[cprfenom]

Agree, 25mm for current soliution is way over the top, also using 25mm for sub board does not make sense. But when you know it’s just incase I need to run a new supply hopefully it makes sense.

You are totally over thinking this. With diversity and the main incoming supply 25mm2 for a Sub board is madness

 

[Michaelwgroves]

You are totally over thinking this. With diversity and the main incoming supply 25mm2 for a Sub board is madness

But if this sub board is converted to second new supply in the future, 25mm is the norm?

 

[cprfenom]

If, then you address it. HMOs do not really take a massive load outside of the kitchen. Your entire installation is limited by the incoming supply and the primary DB will be the local one to that.

 

[davesparks]

But if this sub board is converted to second new supply in the future, 25mm is the norm?

I doubt you’ll get a second new supply from a DNO, especially for such a small supply, they’ll normally only bring one supply in to a property. If what you have needs upgrading then they’ll normally bring a whole new supply in.