Is there a Rule of Thumb for estimating the ....

[ToughButterCup]

.... amount of electrical cable needed for a house of a given size?

 

I'm busy itemising my shopping list of electrical requirements : it's easy  (almost) to pick things  from a catalogue or online database.  And I know my house is roughly 10m by 10m; but at the rate at which I seem to be adding a this, that or the other thing, I'm thinking that my guess at cable needed will be way out.

[redtop]

sorry cant help other than say whenever i have tried to calculate it i have always underestimated by loads.  Its amazing how much goes into a re-wire / new installation.  On the other hand if you buy a bulk load you can sell me any spare cheap :-) 

[Jeremy Harris]

The general rule of thumb is that, as cable usually comes on 100m reels, the amount you will need is about 1m longer than a whole number of 100m reels...

 

On a more serious note, I've just checked and for our 130m², 6 habitable rooms, plus two bathrooms, a utility room and WC, it looks like I bought:

 

200m of 2.5mm² T&E

 

200m of 1.5mm² T&E,

 

100m of 1mm² T&E

 

50m of 1.5mm² 3 core and earth,

 

25m of 10mm² T&E

 

25m of 6mm² T&E

 

I know I had to buy another reel of 2.5mm² T&E when I came to wire up my workshop, though, but I have more than half that reel left over.

 

 

 

[SteamyTea]

8 minutes ago, JSHarris said:

need is about 1m longer than a whole number of 100m reels

 

8 minutes ago, JSHarris said:

but I have more than half that reel left over.

So enough to wire up 50 houses.

 

This is the old joke about asking my Chinese neighbour about how many rolls of wall paper he bought to decorate his front room.

He said he bought 9, so I bought 9.

Decorated the room and had 5 left over.

When I challenged him about it, he sad he had 5 left over too.

Edited August 26, 2019 by SteamyTea

[Ferdinand]

1 hour ago, AnonymousBosch said:

.... amount of electrical cable needed for a house of a given size?

 

I'm busy itemising my shopping list of electrical requirements : it's easy  (almost) to pick things  from a catalogue or online database.  And I know my house is roughly 10m by 10m; but at the rate at which I seem to be adding a this, that or the other thing, I'm thinking that my guess at cable needed will be way out.

 

The last one I did I drew all the bits on the walls, took the lecky round for 20 minutes, and he gave me a list of what to buy two days later!

 

This is amenable to a bottom up estimate imo, which should be quite quick to do.

 

More seriously, I would do this by reviewing my plan, perhaps with a highlighter, and break it down into sub elements that I can do by inspection or guestimate in my head, then add a bit extra, then either accepting that I would use more cable later (piggery?), or buying the extra reel from somewhere I knew I could take it back 2 weeks later - as you would with tiles.

 

It is nice that cable lasts for years and years.

 

Or deconstruct it in my head - eg for a 10m x 10m house with a 3 room x 2 room plan, I know that a ring main round them all will be 4 full runs one way and 6 the other way from counting walls basically regardless of room shape and qty of sockets except for eg wiggly walls, which is 100m per floor plus twiddles for back to the CU, 3m per time to go upstairs, 300mm per double for the loopout, 1m per double on the worktop in the kitchen, rooms with no power etc. I would write each sub element I can do in my head in a list, and then add them up and do a cross check of some sort.

 

Then repeat for each type of cable.

 

That is how I do skirtings - how many front to back inside walls + side to side for overall dimensions for an estimate, then match the mix against lengths of individual walls eg 3.6 4.2 4.4 to minimise small offcuts (add this list back up to check the numbers are about the same), add a couple of lengths to avoid an extra delivery cost which will usually cost more for skirtings due to minimum order for free delivery, and match list 2 against price lists to give me the lowest total.

 

Slight watch needed eg for outside corners which can require extra 100mm or so of skirting to be safe if there are several.

 

I would say any I miss out is because of things I have forgotten, rather than things I have miss-estimated as I know my room sizes and distances quite well.

 

The highlghter on the plan is one way to avoid missing things.

F

 

Edited August 26, 2019 by Ferdinand

[Mr Punter]

2 hours ago, JSHarris said:

100m of 1mm² T&E

 

 

What is this used for? A long time ago it was 2.5 for power and 1.0 for lights. Now it seems to be 1.5 for lights.

[Jeremy Harris]

13 minutes ago, Mr Punter said:

 

What is this used for? A long time ago it was 2.5 for power and 1.0 for lights. Now it seems to be 1.5 for lights.

 

Just some low power lighting stuff.  Could have run 1.5mm², really, but 1mm² was more than adequate. They are LED panels that are rated at between 3 W and 6 W each, so 1.5mm² seemed overkill, given the very small voltage drop.

[ProDave]

55 minutes ago, Mr Punter said:

 

What is this used for? A long time ago it was 2.5 for power and 1.0 for lights. Now it seems to be 1.5 for lights.

There has to be a very specific reason to make me use 1.5mm for lights (e.g a very long run of cable)  In 99% of cases you simply do not need 1.5mm for lighting, and with a lot of modern light fittings you will struggle terminating the cable, 1mm makes it so much easier.

[MikeSharp01]

I don't know how much cable you will need but I do know you need a cable drum frame. I made one that could hold 10 drums. Put it in the room where the wiring centre/ cònsumer unit is then pull the cables off the drums and out to their end points. I could run 2 or three runs of the same guage cable so, when I used it, I had a few drums of each. Although this did leave me with some ends of drums. It was much quicker than pulling one at a time. The only one I didn't do that with was the CAT6 for that it comes in boxes with a pull hole and you just pull it out of the box.

[ToughButterCup]

Top Tip. 

Cable drum frame - DIY . Piccy?

(For the Hard-Of-Thinking)

[andyscotland]

2 minutes ago, AnonymousBosch said:

Top Tip. 

Cable drum frame - DIY . Piccy?

(For the Hard-Of-Thinking)

 

In the past I've just made a couple of T-shaped legs from scrap timber, then a horizontal length between to keep it rigid and a broomstick / length of conduit across the top secured with the drums on it.

 

Sit something heavy on the legs or just screw them to the floor.

 

A real one looks like this but a T is easier than an A in wood IMO.



[andyscotland]

PS if you're pulling from the consumer unit end make sure you have help to ease the cable through holes / round corners otherwise it's very easy to damage the outer sheath (and, if you then keep pulling, the inner insulation).

[Dee J]

A lot depends on the style of the house and build, and how much thought was given to cable routes through the structure. Consumer unit placed in the far corner of an outer wing eats up cable, as do impenetrable steels forcing tortuous routes. A wired thermostat in every room adds up too, as do wired multi-way switched lighting circuits. 

[MikeSharp01]

56 minutes ago, AnonymousBosch said:

Top Tip. 

Cable drum frame - DIY . Piccy?

(For the Hard-Of-Thinking)

I will get a pic tomorrow but it's two bits of OSB for the sides two bits of broom handle for the rolls. I went for two rails as I could Make it narrower and the pull angle was less. The two rows of drums are one above the other.