Splitting a Consumer Unit

[salawiner]

This might well be an odd question, or it could be really simple - so I'll start with an explanation...

Firstly, let me say: I am NOT an electrician, and have no plans to do this work myself - I am simply wanting to understand what is needed before proceeding.

Okay, the scenario is that I own a shop which used to be on three floors; shop, living area, bedrooms. A previous owner has separated the upper 2 floors from the shop by blocking off the stairs (not very well either!), and fitting a door to an external stairway to the side of the property. As a result, there are now three bedsit rooms with a shared bathroom & kitchen on the upper floors, with the shop on the ground floor. All the utilities are shared between both parts of the building, and given the cost involved I plan to leave it this way.

There is currently one (very old) consumer unit in the shop area, which has fuses which feed the shop and the flats. I would like to have a consumer unit in the hallway of the flats so that should a fuse trip the tenants can re-set it themselves. To do this I understand I would need to divert the cabling for the rings & lighting for the upper floors to the new consumer unit - this is not that big a job, as the new consumer unit would be above the current one, and the rings are separate from those for the shop.

Now for the questions:
1. How? I presume that you cannot feed one consumer unit from another (and if you did and the 'main' tripped, it would defeat the purpose), so assume that you would have to take the main feed into the building and split it to feed the two consumer units individually. If so, how is this done?
2. What type of cables would be used to take the mains to the 2nd unit (approx 4m away from the main feed)?
3. Does the 2nd consumer unit need to be mounted on a 'distribution panel' like chipboard panel?

...and probably more questions I haven't even thought of!

Please bear in mind that I am not an electrician, so might not understand the acronyms

 

[AdrianUK]

Do you want the electricity to the flats to be metered separately? How do you plan to charge (fairly) for the power that they use?

 

[salawiner]

Do you want the electricity to the flats to be metered separately? How do you plan to charge (fairly) for the power that they use?

Currently the flats are rented as including utilities, so there is no need for metering, plus they share the kitchen and all flats are on one ring. A later project may well be to install separate rings to each room, so some way of seeing if one has been greedy might be beneficial

I believe I saw something a while ago where there was a block inside a consumer unit which gave a digital readout of the usage for that ring, but may be mistaken. Is there something like this?

 

[AdrianUK]

Ok, obviously that is a commercial decision for you to make. When you are undergoing such a change its worth considering if that is the correct way forward - you are undoubtedly losing out financially on the energy bill since the tenants have no reason to switch off the electric heaters ... just open the windows!

There are digital meters which can be fitted to (newer) consumer units .... a photo posted here could answer a thousand questions.

The way forward really does depend on how you want to recover the energy costs. Adding private meters & individual consumer units per flat is possible and wouldn't cost the earth... much cheaper to do it now than in five years time!

 

[salawiner]

Ok, obviously that is a commercial decision for you to make. When you are undergoing such a change its worth considering if that is the correct way forward - you are undoubtedly losing out financially on the energy bill since the tenants have no reason to switch off the electric heaters ... just open the windows!

There are digital meters which can be fitted to (newer) consumer units .... a photo posted here could answer a thousand questions.

The way forward really does depend on how you want to recover the energy costs. Adding private meters & individual consumer units per flat is possible and wouldn't cost the earth... much cheaper to do it now than in five years time!

I understand what you are saying, and agree that it is better to plan ahead. Currently there is only one boiler though, so it feeds the water for the flats and the shop - fitting a 2nd boiler, re-routing all the pipes etc is a bigger headache than I was hoping for, so having the flats rented as including utilities is the easiest option for now.

I think you might well have provided the solution for the electricity metering though - as the consumer unit in the flats would be brand new, I could make sure it is capable of having the digital meters you speak of. As and when the flats are re-wired to individual rings I could have the digital meters fitted to allow the usage to be monitored.

The main issue at the moment is what is needed to install the consumer unit upstairs first.

 

[AndyPRK]

I'm not sure what you are trying to achieve in the short term.

Fuses don't blow for no reason and you wouldn't want a tenant changing them.


I guess it's really a question of is there an rcd at the moment ?

A picture would help.

 

[salawiner]

I'm not sure what you are trying to achieve in the short term.

Fuses don't blow for no reason and you wouldn't want a tenant changing them.


I guess it's really a question of is there an rcd at the moment ?

A picture would help.

I can't post a picture at the moment - I live away from the shop, but suffice to say that the current fusebox is an old metal one with fuses that still use fusewire!

My main plan is to replace the fusebox in the shop. The shop has been renovated in stages, and before I bought it had three separate rings for the three areas of the shop - but these all join together in a junction box and then feed into the fusebox via ONE 2.5mm cable. as a result there will be three rcd's for the three rings, another for the lights and another for a feed to the garage. The shop is a Fish & Chip shop, and there is a newer consumer unit that is used for the extractors, so they would probably be moved to the new consumer unit for simplicity. There is also the main feed to the range, it is obviously gas fed, but has electrical heaters in the top boxes. Currently the range is fed via Mineral Insulated Copper Cable to a big breaker switch which is fed directly from the mains. I do not know if this could be fed through the shop consumer unit, but if it could I would like it all in there.

With the overhauls of the shop's wiring and resulting consumer unit, there will not be space for the flats to be in the same consumer unit anyway, so AS the flats will need to be split into a separate consumer unit, I thought it would be sensible to locate it in the flats, so that if they manage to trip a fuse I don't have to travel to the shop to flick a switch. PLUS I then have the potential option in the future of billing for the usage.

So, back to the question: how would a 2nd consumer unit be connected given that it would be around 4m from the current feed into the building?

 

[salawiner]

sorry, duplicate post.

 

[AndyPRK]

Maybe add a switch fuse where the supply comes in.
Maybe some swa to the new CU and route the lights and socket cables to the new cu.

 

[viewer]

These are not flats but this is a house in multiple occupation so fireproofing of the entry points, under staircase areas etc needs to be taken into account in any plan.
That said, the simplest way to provide a separated supply to the upper units would be to take the incoming supply from the meter to a switched fuse. The cables from here would be a sub main. Take the cables (tails) from the switched fuse to a Henley connector block. From here two sets of cables (tails) would emerge; one going to the shop, the other to the upper floor CU. If you later wanted to split and meter the upper units separately this would be easily done.
The difficult part is going to be the wiring of fire alarms to ensure that these remain active on all floors at all times even if MCBs or RCDs trip in either CU.

 

[salawiner]

These are not flats but this is a house in multiple occupation so fireproofing of the entry points, under staircase areas etc needs to be taken into account in any plan.

Agreed - I'm afraid I have taken on something which has had a lot of oversights. The stairs from the shop to the first floor are still in place, with studwork and sheets of plasterboard at the top, which is both a waste of space and completely unsuitable, but this is an ongoing task. As it stands I may skim under the regulations as an HMO is officially "An entire house or flat which is let to 3 or more tenants who form 2 or more households". currently I only have 1 tenant, so although it is intended to be an HMO it is currently a 1 bedroom flat. Needless to say the sooner I get everything sorted the better.

That said, the simplest way to provide a separated supply to the upper units would be to take the incoming supply from the meter to a switched fuse. The cables from here would be a sub main. Take the cables (tails) from the switched fuse to a Henley connector block. From here two sets of cables (tails) would emerge; one going to the shop, the other to the upper floor CU.

That sounds like what I am hoping to achieve! I found a picture which shows what I believe you are describing

I believe the switched fuse is the white block on the lower left board, and the Henley connector block is to the side of the meter on that picture - is that correct? Can the tails be 3 to 4m long?

My meter is a newer digital one, does that make a difference?

Thanks for the advice.

 

[viewer]

The photograph is too dark on my screen for me to see clearly, but it does look like a Henley block at the side of the meter. The white switch is just that - an isolating switch - so you would need to take the tails from that switch to the new Henley Blocks. From here you'll have two sets of tails each of which goes into a switched fuse and thence to the two CUs. The tails to the CUs from the switch fuses can be 3 or 4 meters long because you now have protection for these tails (they are two sub mains).

 

[Aragorn84]

I doubt you'd need a switch fuse for the shop supply?

The switch fuse is only required to protect "tails" over 3M in length, so the existing setup can remain as is?

So you'd have something like:

[code:1]
Meter - Main Isolator Switch - Henley Block - Shop CU
- Switch Fuse - SWA to Flat CU[/code:1]

Hopefully that came out right!

 

[salawiner]

Thanks for the info & help, it has eased my mind on how to proceed. Now that I know what is needed I need to do some prep work on the excess crap that is in the shop's electrical box before getting an electrician to carry out this work. at least now I know what to plan for, so I can make sure I leave room for what is needed.

There are a load of defunct items in the electrical box which need to be moved/replaced (such as an electric shower that is not connected but was left with bare wires in the airing cupboard!). I can get on with this and do preparation for the big changeover and hopefully cut the costs on the main work!

One further question which will help my prep.: does the new consumer unit need to be mounted on a chipboard backing like the one in the current electrical box? it will probably be neater to do this anyway, but I'd like to know if that is the official requirement.

Thanks.

 

[AndyPRK]

no the new CU it doesn't need to be on chipboard