PeterW

Isolator Position - Submain

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Just looking at the meter box wiring for WPower and I've got a quick question that I'm prepared to put to the collective experience..!

 

House will be wired with a remote meter box at the boundary, followed by a sub-main providing gate power and lights, and a separate house sub main. 

 

Query is - if I put a 100A isolator into the box, which position does it go in..?? I can either put it before the Henley which splits the load into the gate sub-main and the house sub-main, or just on the feed to the house.

 

MB_1.JPG

 

 

 

MB_2.JPG

 

I guess the safest way is to isolate everything after the meter which means that both boards can be worked on fully isolated, but I've also been told that some companies don't allow this despite being advised that both methods meet 17th Edition.

 

Can one of our resident sparks @Onoff @ProDave make any sense of this...? I want it to be as neat as possible so its laid out prior to install of the meter and there are no issues.

 

 

 

 

 

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My set up is like your first picture. BUT you don't want just an isolator switch, you want a switch fuse. The reason being is the DNO's regs only alllow "their" fuse to protect up to 3 metres of cable. Your house supply will be a LOT longer than 3 metres so it needs it's own fuse.  I fitted an 80A fuse into mine in the hope that will blow before their 100A fuse in the event of a fault.


 

Some DNO's (e.g. SSE) fit meters with an inbuilt isolator switch so isolating to work on the consumer unit is not a problem.

 

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Thanks Dave

 

Will take that approach !

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@ProDave do these now need to be metal sub-main boards if they are in the meter box but is not in the house ..? I'm going to go with a standard 80a fused isolator which I assume can be plastic ..? 

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That's a good question. The metal CU thing is just for "domestic" you can still fit a plastic CU in say an office or a shop.  Mine are all plastic but fitted before the 3rd ammemdment came into force.
 

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It's applicable effective from Jan 16 where the cu is fitted in a DOMESTIC premises, garage or out building.

 

If ONLY it were that black & white! 

 

Personally in a separate meter box I'd happily see an insulated cu and use the OSG wording to back it up "where the cu is to be located in an external non-habitable building, e.g. garage or shed, which is not in close proximity to a dwelling, consideration could be given to installing a cu of non-ferrous construction". BUT you need to back it up with a risk assessment as to why and clip to the Electrical Installation Cert. Let's face it a painted or powder coated metal cu in an unheated, potentially damp meter box will start to rust around knockout holes etc. You can cite potential corrosion issues in the RA. The biggie though is it boils down to the fact metal cus we're brought in because of the perceived fire risk i.e.them being "combustible". Zero risk of the house going up if it's in a remote meter box!

 

Wylex has always been the switch fuse of choice but check out TLC. They have an alternative for about £30.

 

If you are looking at isolator switches, say before a cu then you won't go far wrong with a Wylex REC2. Funnily enough BG fit them round here when they put smart meters in and the REC2 is plastic!

 

How about in the meter box an REC2 before the gate cu and the switch fuse for the house feed. Once at the house you could fit an REC2. Thus both cus have local isolation and the +3m "tails" are protected.

 

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2 hours ago, PeterW said:

@ProDave do these now need to be metal sub-main boards if they are in the meter box but is not in the house ..? I'm going to go with a standard 80a fused isolator which I assume can be plastic ..? 

 

We did ours in metal. Three reasons:

 

1. On the better side of the regs (however you read them)

2. Simpler/neater termination of SWA.

3. More robust in an external meter box.

 

OK,third one isn't really a great issue and actually no.2 was probably the biggest factor.

 

20160404_175711038_iOS.jpg

 

 

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Lots to consider ..!! Sparky is suggesting that we use 16mm 2 core SWA with a 10mm Earth in the same duct - does that sound right ..?? 

 

Will terminate the SWA at the back of the board as it runs on the outside of the wall and run the two cores to the switch. 

Edited by PeterW
Cable Sizes corrected...

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Just looking at space and may fit two boxes side by side to give me a fighting chance of getting everything in ..!

 

The wall is plenty long enough to get the two in - also works out cheaper than a slightly larger one and having the DNO moan about stuff in their box ..!

 

Did anyone manage to get a free hockey stick free from their DNO ..??

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1 hour ago, PeterW said:

Just looking at space and may fit two boxes side by side to give me a fighting chance of getting everything in ..!

 

The wall is plenty long enough to get the two in - also works out cheaper than a slightly larger one and having the DNO moan about stuff in their box ..!

 

Did anyone manage to get a free hockey stick free from their DNO ..??

 

We have three :). That wall will eventually be stone faced and the boxes will have timber doors to hide them. They are way too fugly! 

 

I bought a hockey stick only to find that our three phase sized incomer doesn't fit in a stick so they just draped it down the wall! They didn't even put a single clip in!!

 

20160404_175531250_iOS.jpg

Edited by Barney12

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We are opting for a permanent masonry meter kiosk near front gate too and have been informed that we have to provide the earth. How is that best done?

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42 minutes ago, lakelandfolk said:

We are opting for a permanent masonry meter kiosk near front gate too and have been informed that we have to provide the earth. How is that best done?

 

As I understand it this is a regs thing. Temporary site supplies cannot connect to the DNO earth supply and you have to supply your own. I'll don't understand why.

 

if you look at the picture in my post above you can see the earth cable running to a black connection box on top of the earth rod. Your sparky will install and test for the correct resistance. 

Parts are cheap enough: https://www.tlc-direct.co.uk/Products/TLER58.html

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The local earth thing is because you will be using power tools etc and with a PME earth, the earth might no exactly be at local potential. So for the site socket and e.g a static caravan you bang in your own earth rod.  There is nothing stopping you connecting the DNO provided earth to the house when it is built.
 

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As an aside to the thread: Note how the earth rod in Barney12's link is 5/8" diameter and that it is THREADED. The 3/8" dia ones are not threaded so you can't couple them to make a longer rod which can be useful to get your earth electrode resistance (RA) down. Of course the 5/8" can be a bit harder to bang in but then they're less "bendy" when doing so.

 

The 5/8" one has obviously more surface area in contact with the ground anyway for starters!

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20 minutes ago, Onoff said:

As an aside to the thread: Note how the earth rod in Barney12's link is 5/8" diameter and that it is THREADED. The 3/8" dia ones are not threaded so you can't couple them to make a longer rod which can be useful to get your earth electrode resistance (RA) down. Of course the 5/8" can be a bit harder to bang in but then they're less "bendy" when doing so.

 

The 5/8" one has obviously more surface area in contact with the ground anyway for starters!

 

Indeed :) It took 5 attempts to find a spot where we could drive it in as our ground is very rough. But the bar withstood blows with a fencing mallet :) 

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Dragging this one back up...

 

We'll be on a pole transformer via an overhead, so definitely only TT.  NIE's favoured position for the meter box makes for tails well in excess of 3m. What's the neatest way of protecting those tails suitably? Switchfuse then 100mA -S RCD? Or does someone know where you can get an 80A/100mA type S RCBO?

And as it's in the box with the DNO's stuff, the housing can be plastic rather than AMD3?

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Don't assume an overhead supply won't come with an earth, our previous house down south had PME via an overhead line.

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this a 2-wire 240 uninsulated, and there's nothing at the base of the poles on our land.

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