Physical separation between meter tail and other circuits.

[epsilonGreedy]

I have a situation near my consumer unit where the most convenient routing for both the inbound meter tail and the outbound RCD protected circuits for 80% of the house is from above the CU.

 

Before I can figure out the details of this routing what regulations might restrict how close the meter tail can be to the other protected circuits. The meter tail is a little over 3m and so is already switched in the cavity wall meter box. 

[ProDave]

None. They are all double insulated cables so can be in the same trunking if you want.

[PeterW]

Have you got switches at both ends or are you expecting to just put the meter tails into the  CU and use the main switch ..?

[TonyT]

No restriction in meter tail proximity to other circuits, unless I would say they are grouped together and you have thermal issues, as the tails will be carrying the full current of the house.

 

 

[Randomusername]

26 minutes ago, ProDave said:

None. They are all double insulated cables so can be in the same trunking if you want.

From exposure to electricians over the years, I’ve come to understand that meter tails are correctly described as “insulated and sheathed”. 
 

I've never been entirely certain exactly what that difference actually implies in reality though...

?

[TonyT]

Copper conductor with two layers of insulation

[TonyT]

Opposed to ‘singles’ which are generally used in conduit/trunking installations.

copper conductor with single layer of insulation

[Onoff]

https://electrical.theiet.org/wiring-matters/years/2019/75-may-2019/mythbusters-4-double-insulated-cables/

[epsilonGreedy]

This is the switched end of the trail in the cavity wall meterbox. The electrician added this before mounting a temporary 2 x RCD CU inside the house under a flap of dpc to keep the weather off before the roof is complete.

[epsilonGreedy]

1 hour ago, TonyT said:

No restriction in meter tail proximity to other circuits, unless I would say they are grouped together and you have thermal issues, as the tails will be carrying the full current of the house.

 

 

This is another concern which requires a second question. The meter tail will only cross the internal circuits if legit, however part of the solution will require a pinch point for the internal circuits through a masonry cavity wall.

[epsilonGreedy]

2 hours ago, PeterW said:

Have you got switches at both ends or are you expecting to just put the meter tails into the  CU and use the main switch ..?

 

 

The meter box end is switch as per the photo just uploaded.

 

When the proper CU goes in, it will have another master switch I assume.

 

The history to this wire routing complexity is that I got my brickie to create a 40mm recess for a flush mounted CU before I had time to think about the meter tail and routing of the internal. The CU is situated in the single story back door entrance lobby and it was only recently I realized the ceiling joists of the single story lobby roof trusses are a higher than the posi-joists the other side of a 300m cavity in the main two story section of the house. This ceiling height differential is going to require some creative wire routing. 

[TonyT]

The photo is fine.

THe DNO cut out fuse protects the first 2.5 m or up to 3m it varies on DNO.

Your switchgear protects the tails to the new consumer unit, so it’s all looking good.

 

the worst thing you can do is bring all the cables down together at the consumer unit and tape/tyrap them together in one group as the cables in the middle won’t be able to dissipate their heat to free air, but to other cables. So they are classed as touching. So better to have several groups of cables than 1 big one.

[Onoff]

If your cables are too dangly, i.e over a bit of a height you might look at strapping them to a bit of cable tray. Saves stain on connections.

[epsilonGreedy]

On 27/01/2021 at 15:18, Onoff said:

If your cables are too dangly, i.e over a bit of a height you might look at strapping them to a bit of cable tray. Saves stain on connections.

 

 

This sounds important so I better get a picture of this clear in my head...

 

The inbound meter tail emerges from the cavity about 3ft above the CU and this cable will I guess be looped below the CU to enter up into the lower half of the CU.

 

Looking at CU install videos on the net I get the impression the outbound circuit wires will emerge from the top of the CU. These will run 4ft up the block wall and then through some holes cored in the cavity to emerge horizontally at, I hope, a point between the top and bottom chords of the posi joist at ceiling height in the 2-storey section of the house.

 

I think I have a wire routing plan which results in the horizontal run of the inboud meter tail being about 1ft below the point where I core through the cavity wall to get the wires into the main house.

 

Given all that (can produce a diagram if needed) am I safe from the dangly wire problem?

[epsilonGreedy]

On 27/01/2021 at 14:38, TonyT said:

the worst thing you can do is bring all the cables down together at the consumer unit and tape/tyrap them together in one group as the cables in the middle won’t be able to dissipate their heat to free air, but to other cables. So they are classed as touching. So better to have several groups of cables than 1 big one.

 

 

Yes this bunching issue is now troubling me now that I understand the regs (or absence of ) about the meter trail crossing the domestic circuits. Think I have a plan that keeps them 1ft apart.

 

So on to thermal concerns. At the point where I core through the masonry cavity wall above the CU I need to think about feeding the the following high amp circuits through the cored holes:

• ASHP
• Cooker
• HW immersion
• Patio Heater

After that comes:

• High amp kitchen ring sockets?
• Upstairs ring
• Downstairs ring

Plus lights x 2, smoke detector

 

Oh and the MVHR but suspect that is a tiddler in terms of wattage.

 

The garage spur heads off in another direction. 

[TonyT]