To ferrule or not ferrule and where to grommet

[MikeSharp01]

I am just about to wire the distribution box, see pic below and drawing below, This distributes the incoming power from the meter panel next to it out to the garden room 1x80A fused unit (upper), the main house - 1x80A fused unit and a local commando socket  (16A) and the garden lighting (1x small CU 16A / 6A breakers). I have three things I am not sure of so any ideas greatly appreciated;

 

1. Should I use ferrules on the ends of all the 10 / 16 and 25mm² tails across the cabinet (they are already on the internal wiring in the small CU). I would have though I would but installations I have seen don't always use them and the regs look agnostic (526.9.1 in 17th Ed)!
2. To get the cables in and out of the CU I propose to just use simple grommets around the holes, I don't think I need to seal them although I could.
3. Do I need to earth the earth connections, and run the earths through, on the Switch Fuse units as the earth common block will be used to terminate the earths from the cables these supply, it seems daft to introduce two additional points of failure by connecting the outgoing cable earths via the switch fuse units.

 

The cables will all be held down on the board by cable ties through table tie plugs in the board. All and any thoughts appreciated.

 

Edited October 9, 2017 by MikeSharp01
Wrong DWG

[ProDave]

No need for ferules on meter tails. the ones in the CU use them because they are fine stranded links.

 

No need to earth the switch fuses, take those earths direct.

 

The circuits fed from the CU should be earthed to the earth bar in the CU

 

The earthing is not as simple as you have drawn. I assume you have a PME earth? (most new supplies will be) connect that to your earth terminal. But your site socket power should be TT earth. you could just connect the rod to that socket..

[MikeSharp01]

Thanks @ProDave for that. The Commando is not designed as a site socket - just a socket I can use in the garden / drive, I can make it TT though. Is the image below what you expect to see for the TT scheme via the Commando Socket? I think we will have a PME supply although its the old supply just moved to the cabinet next door and the earth rod at the bottom of the power pole is less than 1m from the cabinets, so will have to drive in the earth rod a good distance away to meet the depth / distance rule. I have included the gland / sheathing earths for the main outputs as well.

 

 

[Onoff]

Grommets will let the creepy crawlies in. Glands won't.

[MikeSharp01]

Just now, Onoff said:

Grommets will let the creepy crawlies in. Glands won't.

All the ins and outs of the main cabinet will be glands only the internal wiring into the the little CU at the top of the cabinet will have grommets, so lets hope we can keep the creepy crawlies out of the main cabinet and then they will struggle to materialise in the internal CU.

[Jeremy Harris]

I'd also very strongly recommend binning the banjos on any SWA glands and using Piranhas.  They are massively easier to use and give a far better long-term earth connection, IMHO.  You will need a crimp tool to crimp eyelets on to the earth leads on the Pirana M4 screw connections, though, but they are a doddle to install and make working with SWA almost pleasurable.  Also, remember that any external SWA gland needs to be a waterproof one, with a boot.

 

Piranhas and external glands are here: https://www.tlc-direct.co.uk/Main_Index/Cable_Accessories_Index/Glands_SWA/

[MikeSharp01]

1 minute ago, JSHarris said:

Piranhas and external glands are here: https://www.tlc-direct.co.uk/Main_Index/Cable_Accessories_Index/Glands_SWA/

Thanks @JSHarrisThose are the very ones I have - I will get the piranhas and have a play.

[Dee J]

Hmmm. Don't know if I've got the wrong end of the stick, but all those live wires (L&N), are they all going to be  insulated and sheathed? If the box was a closed structure (like a consumer unit) that wouldn't matter, but given that access is needed for switching and isolation the the wires shouldn't be single insulated conductors.

[Jeremy Harris]

1 hour ago, Dee J said:

Hmmm. Don't know if I've got the wrong end of the stick, but all those live wires (L&N), are they all going to be  insulated and sheathed? If the box was a closed structure (like a consumer unit) that wouldn't matter, but given that access is needed for switching and isolation the the wires shouldn't be single insulated conductors.

 

Indeed, all the line and neutrals need to be double insulated right into the case of the switch/henly/meter etc.  Tails are usually all double insulated as standard, so as long as they are installed correctly they should be OK.   For the SWA, leave the inner core liner intact until it enters the switch or whatever if you can.  If you can't, then fit heat shrink sleeving over the inner cores and a heat shrink boot over the point where the cores come out of the SWA liner.  I had to do this where the 25mm² SWA cores came out and went to the fused isolator switch.  The switch case didn't have room inside otherwise, plus the earth lead needed to come out to the earth block anyway.

 

As long as all L & N cables that can be touched with the cabinet door open are double insulated you're OK.