How much Electricity do i need.

[peterduckett]

Very stupid question I know but its for a double garage that already has a supply.

The reason I'm having a new consumer unit fitted and was hoping to re-use the current SWA in place though I don't know the size

Any one know the outside diameters of 4 core SWA or the outside diameter of a single core within the SWA?

Anyway I'm being lazy I would like to buy a RCBO that is capable of meeting my needs while not overloading the cable now? any advice?

currently it is protected by a 20 amp fuse which would give around 5kw
though i estimate (overly)

Outside lighting (1kw)
Inside (0.6kw)
Heater (3kw)
Pond Electrics (0.1kw)

Though I'm guessing i could apply diversity i would say allot of those things are running when i'm their

could i put a 40amp RCBO on 4mm cable over 50 meters with the idea of upgrading it to 10mm in future

 

[ricicle]

Who will actually be carrying out the work ? They will need to assess the current set-up for suitability.

 

[peterduckett]

Please don't bring up the Part P tax

All I'm trying to do is measure the size of the SWA and match it with a sutible though probably limit RCBO

 

[ban-all-sheds]

The reason I'm having a new consumer unit fitted and was hoping to re-use the current SWA in place though I don't know the size

No EIC from when the circuit was installed?

Any one know the outside diameters of 4 core SWA or the outside diameter of a single core within the SWA?

4-core?

If the csa isn't embossed onto the sheath, is there a maker's name? If so, ask them.

Alternatively remove one conductor and measure the diameter of the conductor with a caliper gauge - since cables come in stock sizes that will be accurate enough to work out what size it must be.

Though I'm guessing i could apply diversity i would say allot of those things are running when i'm their

Then you can't apply diversity.

could i put a 40amp RCBO on 4mm cable over 50 meters with the idea of upgrading it to 10mm in future

NO!

http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

(Select 2-core PVC or it will give you invalid answers)

 

[ban-all-sheds]

Please don't bring up the Part P tax

It is not a tax, it is the law of the land.

All I'm trying to do is measure the size of the SWA and match it with a sutible though probably limit RCBO

Changing the size of the protective device is notifiable.

But since you are "having a new consumer unit fitted" then why on earth don't you leave it all to the person who is doing that?

 

[Hibbo]

You really need to ascertain the size of the SWA cable before you decide upon anything.

It should say on the PVC sheath covering the SWA, if not measure the diameter of one of the conductors, half it to get the radius, then do radius multiplied by radius multiplied by 3.14 (pi r squared!)

However a 40A OPD on 4mm^2 cable is not acceptable under any conditions, and with a 50m run you'd need some pretty hefty cable for 40A.

Do you really need 40A? Do you actually have 1000w outdoor lighting? Even if you do, 20A is sufficient for what you list.

Why not just use a 20A RCBO? 20A gives 4.6kW which should be plenty for what you need, and the volts drop will be within limits for a 50m run of 4mm^2 cable.


Part-P is the law, but it's you that's doing stuff, not me, so if you choose to ignore it it's none of my business...

 

[ban-all-sheds]

ignore

 

[peterduckett]

4-core?

Yeah 2 have been used to turn on lighting at the other end though its a strange set up as it been fused twice though two different consumer units

I had looked at TLC voltage calculator which suggest the max cable load at 50 meters would 32.9 to be fair im just being a tight ass wanting not to upgrade a RCBO later in life which i might have to do based on the fact of the cable size

40A will only require 10mm which i think most people advise to be installed for future proofing

 

[Hibbo]

What exactly are you trying to do/achieve here?

If you are installing new SWA and a new RCBO, then size both accordingly.

If you are trying to use the current SWA and install a new RCBO suitable for it, then 20A is your limit (assuming 4mm^2 cable).

You absolutely cannot install a higher rated RCBO to be 'ready' for fitting a larger cable.

You can however fit a 20A RCBO now, and upgrade your cable to as big as you want it in the future, still on the 20A RCBO, then upgrade the RCBO in the future future if you want to install an electric shower in your garage or something...

 

[peterduckett]

Thats the other question how much power is realistic if you wanted to use the odd power tool or compressor

 

[ban-all-sheds]

I had looked at TLC voltage calculator which suggest the max cable load at 50 meters would 32.9

Try looking again, only this time pick 2-core PVC. The real answer is 12.5A.

to be fair im just being a tight ass

A truly awful and unacceptable basis for circuit design.

wanting not to upgrade a RCBO later in life which i might have to do based on the fact of the cable size

If by "upgrading" you mean "changing to a higher rating" there is no point - you're already way over what the cable can carry.

40A will only require 10mm

No it won't - do your calculations again.

 

[peterduckett]

I had looked at TLC voltage calculator which suggest the max cable load at 50 meters would 32.9

Try looking again, only this time pick 2-core PVC. The real answer is 12.5A.

at what load i was using 4.6kw

 

[ban-all-sheds]

20A gives 4.6kW which should be plenty for what you need, and the volts drop will be within limits for a 50m run of 4mm^2 cable.

No it won't.

20A is your limit (assuming 4mm^2 cable).

No it isn't.

 

[ban-all-sheds]

at what load i was using 4.6kw

Try again, only this time pick 2-core PVC...

 

[peterduckett]

SWA 2 CORE
UNDERGROUND
Non lighting
30
1 circuit
10KW
230V
50M

Returns me

Required Cable Size 10 mm
Voltage Drop 9.57 Volts.
Percentage Drop 4.2%
Current Load 43.0 Amps
Max Cable Load* 53.4 Amps