Discuss Protection for cables suppling Consumer Unit, due to distance greater than 3 Metres. in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

R

Rik

Hi Folks,
I'm currently doing a full re-wire to the Mother-in-Law's bungalow which she has just bought. The bungalow was built around 1960's so needs a complete over-haul with both electrics and other building works.

The earthing system is TT.

Currently, the supply meter is indoors in the same cupboard with the Old Consumer Unit. The supply meter is being re-located to a flush mounted external meter box.

Due to the meter being re-located outdoors the distance between the Meter and the new Consumer Unit is now aroung 7 Metres. My question is - what will be the best practice to protect the the cables supplying the consumer unit? Should I install a Switched Fused as in in link below to protect the cables from overload or is both a Time Delay 100mA RCD (as per second link) and Switch Fuse required?

100A Mains Switched Fused c/w 80A & 100A fuses

100 Amp 100mA Time Delayed RCD 2 Pole - Wylex

Much Appreciated for your help Guy's.
 
Re: Protection for cables suppling Consumer Unit, due to distance greater than 3 Metr

is there a regulation dealing with distance from meter to c/u?
 
Re: Protection for cables suppling Consumer Unit, due to distance greater than 3 Metr

You have a TT system,that being one thing that will govern the choice of protection for your supply cable
What cable will you use?
What method of installation will be used ?

You need to provide this information initially
 
Re: Protection for cables suppling Consumer Unit, due to distance greater than 3 Metr

The consumer unit will be approx 7 metres from the main cut-out.

The installation method will be, up through the wall cavity using 25mm SWA. The SWA will be glanded into Galvanished Adaptable boxes at both ends, one dappy box in the meter unit enclosure with tails onto the new switchgear. One dappy box in the loft, with tails onto the new consumer. Dappy boxes will earthed.
 
Re: Protection for cables suppling Consumer Unit, due to distance greater than 3 Metr

The 100 m/amp time delayed is a must have (unless of course you can squeeze a PME out of them when they do the alterations)
The Switch fuse is only necessary if the supplier impose distance restrictions,most will state from 3 to 4 meters, personally to save any possible refusal to connect, or having to get this info from them somehow,I would go with both your suggestions

The other thing to consider is using the meter box for this equipment,many have had problems because they may not permit
I have never had a problem using the cabinet
 
Re: Protection for cables suppling Consumer Unit, due to distance greater than 3 Metr

Thanks Des.

I've tried asking for the DNO to supply an earth but got refused, don't know why this would be such a big deal as there are 5 cables running along posts on the front road. Obviously, these being the 3 phases, neutral earth. I have spoken to the the DNO installer who says just and isolator needs fitted for them to terminate into but think this needs more protection that just an isolator.

Given that, do you think I should just install the 100mA time delay RCD, or still run with both?
 
Re: Protection for cables suppling Consumer Unit, due to distance greater than 3 Metr

Can you consider using a 1-way cons unit with the s type rcd as the main isolator and mcb for overcurrent
 
Re: Protection for cables suppling Consumer Unit, due to distance greater than 3 Metr

If your doing this via the BC you might get there hackles up a little with a cable going down the cavity, technically I would be arguing they are tails but you never know ......................

Also it as it sounds it's an external cavity wall remember there maybe now or in the future insulation in there, which will seriously affect your CCC

And let's not forget 522.8.4
 
Re: Protection for cables suppling Consumer Unit, due to distance greater than 3 Metr

I've tried asking for the DNO to supply an earth but got refused, don't know why this would be such a big deal as there are 5 cables running along posts on the front road. Obviously, these being the 3 phases, neutral earth.

The road I first bought a house on had five O/H lines. The three phases, neutral and street lighting. Things mat not be as they appear.
 
Re: Protection for cables suppling Consumer Unit, due to distance greater than 3 Metr

Hi Des 56,
I like your solution, however, I'm unable to find a 1 Way Metal Clad D/B that has a 100A RCD 100mA Time Delayed as the incomer, with an outgoing 100A MCB.

Is there a manufacturer doing such a board? Or, even if it can be ordered as individual items?

Cheers.
 
Re: Protection for cables suppling Consumer Unit, due to distance greater than 3 Metr

Thanks for your help Des. A good solution.
 
Re: Protection for cables suppling Consumer Unit, due to distance greater than 3 Metr

The road I first bought a house on had five O/H lines. The three phases, neutral and street lighting. Things mat not be as they appear.

Your dead right tony, In our area the Fifth line, which is usually smaller is a swithed lighting feed for the street lights running back to a call point, in the old days this was where the lighting man switched on the street/area, these days there is usually a photocell on top of them. However this system is being phased out in most areas in favour of indiviually switched lamps as it gives them a longer time to repair a faulty one!
 
Re: Protection for cables suppling Consumer Unit, due to distance greater than 3 Metr

One way to find out if PME is available is to look at the posts.

Every third post should have a cable running down to the ground, and this is where the earth point is.

ANother way is to look at the OH lines coming to the house.

A single cable is normally concentric and sometimes proves an earth is available.

If there are two cables coming in then its a no.

However, all this needs to be approved by the DNO.
 
Re: Protection for cables suppling Consumer Unit, due to distance greater than 3 Metr

I've just had a similar situation. Asked both DNO and NICEIC about the need for additional protection of tails. The answers I got were definitely isolation (so fit a type S (time delayed) RCD) however, unless you're reducing the CCC of the tails, you can rely on the service head fuse for overcurrent protection. If I were you I would consider using standard tails inside of flexible conduit for the run in the cavity. Tails are th only cables allowed to run in the cavity but you should protect them from possible future cavity insulation. Also fixing the conduit could help to stop bridging of the cavity.
 

Reply to Protection for cables suppling Consumer Unit, due to distance greater than 3 Metres. in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock