Temporary Hybrid/Lollipop Circuit

[tvrulesme]

I'm in the process of renovating a house. As I go through room by room I am removing old plaster and as the cables are exposed at this point I figured I may as well get the wiring updated as I go. The ring main (~6 sockets) is currently fed from 2.5mm T+ E. Eventually I would like to have the whole house in 4mm radial though I can't do this all in one go.

Is there anything wrong with the proposal below which would allow me to replace the ring with a radial when I get round to that room and add a socket in the process?


Basically the 4mm would be connected to the start and end of the circuit (i.e. lollypop/hybrid) within the back box of the socket until the electrician gets round to replacing all with 4mm radial.

I will of course be getting a spark to do notifiable work. Circuit is protected by 32A fuse and is clipped direct

 

[James]

I would get an electrician on board now ( before the work starts)
being on site and understanding what your plans are is really crucial to your project being completed without problems.

this is likely to be notifiable work so you need somdone who can write you up the correct certificates anyway, so why not involve them from the start?

 

[tvrulesme]

I would get an electrician on board now ( before the work starts)
being on site and understanding what your plans are is really crucial to your project being completed without problems.

this is likely to be notifiable work so you need somdone who can write you up the correct certificates anyway, so why not involve them from the start?

Yes, as mentioned I will be getting a spark to do the work but I always find you get a better experience with all trades people if you understand what they are talking about when discussing the job which is why I ask questions on forums like this.

 

[James]

Personally I would not do it, a temporary supply needs to meet the same requirements as a permanent one, we don’t get to cut corners just because it won’t be there for a long time.

you mention that the ring is currently supplied from a fuse, is There an rcd in the supply?

I would be installing a temporary “builders socket” with rcd protection near the fuse box. Disconnect the old ring and confirm that ALL SOCKETS ARE DEAD

run in your new cables and commission when ready.

edit:
I would also question the suitability of running a whole house on a 4mm radial circuit.
it may be ok but most of the time it is not the right way to go.

 

[tvrulesme]

Personally I would not do it, a temporary supply needs to meet the same requirements as a permanent one, we don’t get to cut corners just because it won’t be there for a long time.

you mention that the ring is currently supplied from a fuse, is There an rcd in the supply?

I would be installing a temporary “builders socket” with rcd protection near the fuse box. Disconnect the old ring and confirm that ALL SOCKETS ARE DEAD

run in your new cables and commission when ready.

Yes it's RCD protected.

Not possible to do what you are suggesting without ripping out all the cables from the plastered walls which I am not ready for and will not be for some time. I don't think this is cutting corners, I am just doing the 1st part of what will be the end state in advance.

What I am trying to establish here is am I suggesting something which would not meet regulations or be dangerous in some way? I know my end state is compliant (4mm radial throughout), but I would of course very much like to be compliant in the short term before I can get round to having this part rewired

 

[tvrulesme]

I would also question the suitability of running a whole house on a 4mm radial circuit.
it may be ok but most of the time it is not the right way to go.

Should have been clearer. It's not the whole house. Kitchen has its own circuits so this is just living room and bedroom sockets. 2 rooms in total, ~5-6 sockets

 

[UNG]

The way I see it you have a few options and for me yours is not one of them as apart from your initial part of the lollipop it is not clear how you intend to proceed from there unless you drop the MCB rating
You could wire the whole radial circuit and where you don't want to remove plaster at the moment put the cable(s) in minitrunking until such time you are ready to refurbish that room when you can remove the trunking and bury the cables
Or
For the cost involved I would suggest a radial for each room easy enough to remove the sockets in the room you are working on pull back the cables from each socket to a position where you can fit a JB's and then install the new radial wiring for that room

I'm assuming the 5 - 6 sockets you mention is what exists currently, replacing like for like sounds a bit light for 2 rooms with today's general requirements

 

[Dartlec]

In terms of overloading the cable there is nothing dangerous with your proposal. However, it is non-standard and as such any electrician doing it would need to do the calculations to be sure that it complies with all relevant regulations, not to mention be happy to put their name to it on a certificate.

If the circuit was in place, it would likely be considered safe, but recommended for upgrade.

The main issues I see are

1. Because it is non standard it will not be obvious to anyone new how it has been done so any new work may not take everything into account. Obviously you will know, but an electrician installing new has to consider the lifetime of the installation, what happens if you suddenly sell before completing the work, etc.

2. getting 2 x 2.5 and 1 x 4mm into a socket will be a challenge, so that may need to happen in a junction box, or in a much deeper back box than normal so that not all the terminations are at the socket.

If the 2 rooms involved don't contain any heavy loads (heaters for example), then an alternative solution may be to drop the protection on the circuit to 20A, making the whole circuit a radial. Then the 'lollipop' arrangement is no longer an issue.

In most rooms outside of a kitchen, 20A is more than sufficient unless there are high draw appliances, which these days usually only means heaters or similar (which are better on a separate circuit anyway).

As and when you get 4mm throughout, the protection could then be raised to 32A again if necessary (and calculations with cable installation methods allow).

That assumes your consumer unit is suitably protected for the new installation

 

[tvrulesme]

In terms of overloading the cable there is nothing dangerous with your proposal. However, it is non-standard and as such any electrician doing it would need to do the calculations to be sure that it complies with all relevant regulations, not to mention be happy to put their name to it on a certificate.

If the circuit was in place, it would likely be considered safe, but recommended for upgrade.

The main issues I see are

1. Because it is non standard it will not be obvious to anyone new how it has been done so any new work may not take everything into account. Obviously you will know, but an electrician installing new has to consider the lifetime of the installation, what happens if you suddenly sell before completing the work, etc.

2. getting 2 x 2.5 and 1 x 4mm into a socket will be a challenge, so that may need to happen in a junction box, or in a much deeper back box than normal so that not all the terminations are at the socket.

If the 2 rooms involved don't contain any heavy loads (heaters for example), then an alternative solution may be to drop the protection on the circuit to 20A, making the whole circuit a radial. Then the 'lollipop' arrangement is no longer an issue.

In most rooms outside of a kitchen, 20A is more than sufficient unless there are high draw appliances, which these days usually only means heaters or similar (which are better on a separate circuit anyway).

As and when you get 4mm throughout, the protection could then be raised to 32A again if necessary (and calculations with cable installation methods allow).

That assumes your consumer unit is suitably protected for the new installation

Brilliant answer. Thank you so much.

 

[tvrulesme]

The way I see it you have a few options and for me yours is not one of them as apart from your initial part of the lollipop it is not clear how you intend to proceed from there unless you drop the MCB rating

This I don't understand. Using Table 4D5 clipped direct 4mm has capacity for 37A, 2.5mm has 27A (so using a ring 54A). Both well within the breaker capacity of 32A. So why would my option not be viable?

sounds a bit light for 2 rooms with today's general requirements

Yes it's a listed building built in 1800 so this doesn't surprise me. One of the reasons I would like to rewire although current wiring has clearly been carried out a lot more recently than that

 

[UNG]

This I don't understand. Using Table 4D5 clipped direct 4mm has capacity for 37A, 2.5mm has 27A (so using a ring 54A). Both well within the breaker capacity of 32A. So why would my option not be viable?

Why are you using the clipped direct figures when the existing cables are buried in plaster and I assume your new cables will also be buried in plaster. For 4mm² T&E buried in plaster you are looking at 26 - 27A so your lolipop fails at the start as I doubt it is all clipped direct allowing you the 37A you quote. The reference methods are there for a reason and you can't just pick the figures that suit your needs

Unless you have followed the route of the existing cabling it is likely that the skts are not in order on the ring through each room also adding skts as you go would more than likely cause more issues than it solves

 

[tvrulesme]

Why are you using the clipped direct figures when the existing cables are buried in plaster

As I put in the original post this will be clipped direct. In reality this will be clipped direct up to the point of the 1st socket which is the only part I am doing now after which it goes to 2.5mm ring. So not picking figures that suit my needs, more what is intended to be followed

Now in future when it switches to a 4mm radial throughout the other rooms will indeed be burred in plaster at which point I would need to switch to a lower breaker

 

[tvrulesme]

For 4mm² T&E buried in plaster you are looking at 26 - 27A

Also are you sure about this? Reference method C I have seen referred to as "Clipped directly to the surface / buried below the surface on a plastered wall."

Method C

• Clipped to a wall or ceiling.
• Buried direct in plaster.
• SWA running down wall.

reference method explained - https://www.electriciansforums.net/threads/reference-method-explained.70017/

 

[UNG]

Also are you sure about this? Reference method C I have seen referred to as "Clipped directly to the surface / buried below the surface on a plastered wall."

Method C

• Clipped to a wall or ceiling.
• Buried direct in plaster.
• SWA running down wall.

reference method explained - https://www.electriciansforums.net/threads/reference-method-explained.70017/

Maybe I read the regs differently to you
Read the notes for Table 4D5 then refer to Table 4A2 as the notes suggest and Installation Method 20 does not look like a cable is buried in plaster

 

[tvrulesme]

Read the notes for Table 4D5 then refer to Table 4A2 as the notes suggest and Installation Method 20 does not look like a cable is buried in plaster

I read TABLE 4A2 Number 57



Which refers to note o


Which states Reference Method C