2 fuse boxes one mains meter

[freyster]

Hi All

Wanted some advice being a newbie on this forum as well as a newish electricain.

Recently did a loft conversion and installed a 17th edition 10way consumer unit in the loft. Ran armoured cable from the fuse box in the loft to the main meter on the ground floor where the original fuse box is installed.

I’ve also upgraded the main ground floor fusebox to the 17th edition 15 way.

My question is, what’s the best process in connecting the loft fuse box to the mains:

Do I disconnect the main tail coming in to the ground floor fuse box, put this into a 100amp junction box and split the two fuse boxes this way.

Or do I connect the loft fuse box into the ground floor fuse box, only downside to this is when the fuse trips, will knock out ALL components in the loft.

Help/ Guidance is defiantly required.

Thanks

 

[oharaf]

How big is this place that it requires 25 ways???? What circuits are there/ being added and on which CU?

Have you done the numbers??

In the loft!! What is the reason?, would not think that is particularly 'accessible' in an emergency

 

[Taylortwocities]

Or do I connect the loft fuse box into the ground floor fuse box, only downside to this is when the fuse trips, will knock out ALL components in the loft.



Thanks

What size SWA have you/are you running to upstairs?
How many cores?

What sized earth conductor will you be running?

What makes you think the CPD downstairs will trip? it should only do that if there is a fault on the armoured cable.

The best way is to install the correct size switchfuse downstairs and split the feed using a henley block.


PS OHARAF. Read the OP. Its a LOFT CONVERSION!!

 

[securespark]

You need to connect the SWA to a metalclad switchfuse as a submain. Rate the fuse to the cable of course.

 

[Gees]

Untitled

• Gees
• 13 Apr 2010
• 1

 

[freyster]

Hi

Thanks for the feedback.

I do understand where you guys are coming from in terms of having a 25 way fuse box.

The reason why I had a seperate fuse box in the loft is, its a big loft 3 bedrooms and a bathroom, so if something trips rather then running down to the ground floor back and forth, i thought it would be easier to have it there.

For the loft I have:

RCD1:
Bedroom 1 (6amp)
Bedroom 2 (6amp)
Hallway (6amp)
Sky Lights (32amp)
Wall Sockets (32amp)

RCD2
Bedroom 3 (6amp)
Bathroom Lights (6amp)
Bathroom Fan, LED Lights (6amp)
Underfloor heating (32amp)

RCBO - Smoke Alarm for the whole house. (6 amp)

The Main fuse box will cover the Ground floor and 1st floor I was looking to do the following:

Shed Sockets
Side extension (boiler room) Lights
Side extension (boiler room) Wall Sockets
Bed 2 & 3 wall sockets
Master Bed 3 Wall Sockets
1st floor Lights
Ground floor hallway, reception lights
Kitchen, downstairs bathroom Lights
1st floor Bathroom Underfloor heating
Ground floor Bathroom Underfloor heating
1st Floor Bathroom Fan/ LED
Kitchen Sockets

I thought it was better to have it configured this way due to all the items I have.

So my initial thought is to go for the Henley block configuration, have the mains lead coming from the meter going into the henley block and from there have the 2 16mm tails running into each fuse box.

As mentioned I ran armoured cable to the loft which consists of 3 core 16mm each.

A couple of electricians have mentioned that the the fuse may trip downstairs if I decide to go down the route of having the cable installed in the mains fuse box, they also mentioned I may have to go for a large 80amp or so fuse.

I personally think the Henley block is the best solution, split the main cable then feed both fuse boxes independently.

Quick question to TAYLORTWOCITIES:

"The best way is to install the correct size switchfuse downstairs and split the feed using a henley block. "

What switchfuse would you recommend for the this sort of configuration

"What sized earth conductor will you be running?"
The only earthing Ive done so far is, Armoured cable has a 16mm earth, also ran 10mm earth to the central heating pipes, bathroom pipes and the loft fuse box will tie in back to the ground fuse box for earthing. Will I need to install some sort of earthing rod or anything else.

 

[freyster]

Untitled

• Gees
• 13 Apr 2010
• 1

Hhahah lol, or this

Damn thats a good idea ;o)

 

[freyster]

Hi All,

Another question. Ive been reading some posts most of them date back to pre 2008 and they mention anyone installing a 2nd CU must install a 100amp isolation before the Henley block.

So main tail goes into Isolation, then into Henley block were it is split between the 2 consumer units.

Is that something which pros recommend.

 

[ColJack]

as you've installed undersized SWA, you need to fuse down to 80A before you can feed it, so if you've got a 100A service fuse you need to connect it either through the existing CU or install a switch fuse..

it seems like nearly every light in your house has it's own breaker..
that's taking reg 314 a little too far maybe?

why 32A for a skylight?

 

[freyster]

No particular reason. I have 3 sky lights on that circuit, is that too much for what is required, i did think of the 6amp which will be sufficient. As it hasnt been powered up, is it worth while swapping this out?

ColJack

Slightly lost with you last comment.

"as you've installed undersized SWA, you need to fuse down to 80A before you can feed it, so if you've got a 100A service fuse you need to connect it either through the existing CU or install a switch fuse.."

I havent purchased the 100amp or 80amp isolater. In otherwords do I take the feed from the current CU from the Main Switch or do I go for the 80amp from the meter, then into the henley block then into the 2 consumer units. Whats the switch fuse for.....?

 

[ColJack]

you mentioned 100A junction box ( aka Henleys or service connector ), which is why I assumed you had a 100A main fuse in the cutout..
your 16mm cable is only rated for 89A clipped direct so you would have to use a fuse lower than that which is 80A..
in order to not lower your total capacity if you had a 100A main fuse, then you'd fit a switch fuse ( on/off switch with a fuse in it.. ) for the feed to the loft.

you split the tails using henleys, never wire from the main isolator, they're not usually designed to take 2 large cables..

 

[ban-all-sheds]

Wanted some advice being a newbie on this forum as well as a newish electricain.

Define "electrician"....

 

[Chri5]

Terminate both CU's on a henley.

The upstairs one since it's 16mm can't be rated by the main house supply fuse which is 100amp.

So fuse cu swa down to a metal box (for earthing the swa via gland) and then the LN cables term on a 60/ 65 or 80 amp switch fuse, the other side of the switch fuse has 25mm tails to the henley block.

Thus you are restricting the amp load available in the loft via the switch fuse to a level the cable can cope with.

Since we don't know the distance of the swa (about 12m at a guess), and because a switch fuse had some head end (say a 60 amp won't pop until 67-70 amp load) I'd tend to go for a 60 / 65 amp fuse.

If you minds eye everything 'on' at peak, the loft surely isn't going to hit a 70 amp load demand ever !

 

[Chri5]

Just read further bits of thread re: isolation.


mains supply 25mm tails out of meter >>>>>>> 100 amp isolator>>>>> 25mm tails to henley then 2 x tails

1st 25mm pair direct to grd cu
2nd 25mm pair to switch fuse rated "xyz" then on other side of switch fuse SWA 16mm up to loft.

Hope that makes sense

 

[freyster]

Been speaking to another sparky and they mentioned its probably worth while installing a Wylex 100amp REC2 DP switch from the meter and then have the 2 consumer units coming out that.

Seem to be confused even more........