I am putting in SWA cable to the garage, total length max 30 metres,
load just a few sockets for low powered tools, and lights, connected to 32A RCBO in the house CU. Should I use 4mm or 6mm SWA ?

Cheers,
Simon.

On 14/02/2019 14:43, sm_jamieson wrote:
I am putting in SWA cable to the garage, total length max 30 metres,
load just a few sockets for low powered tools, and lights, connected to 32A RCBO in the house CU. Should I use 4mm or 6mm SWA ?


It's a garage.

One day you may want to charge an electric car...

Andy

On 14/02/2019 14:43, sm_jamieson wrote:

I am putting in SWA cable to the garage, total length max 30 metres,
load just a few sockets for low powered tools, and lights, connected to 32A RCBO in the house CU. Should I use 4mm or 6mm SWA ?

So are we assuming the design load is 32A?

Current capacity for either are fine (the current carrying capacity
"clipped direct" for PVC clad [1] SWA would be 38A/49A (4mm^2/6mm^2))

So we can check voltage drop. Since you have lighting, that ought to be
a 3% or 6.9V. At 11mV/A/m 32A load would give ~ 10.5V, so 4mm^2 cable
will not meet the spec.

Going to 6mm^2, that would be 7.3mV/A/m or ~7V

So you could easily argue that 6mm^2 will get you close enough -
especially as it does not sound like the circuit will likely have
anything near that load on it normally. (you could also argue that the
effects of small voltage drops with modern low energy lighting are
overstated anyway).

You have not said what the earthing system is at the head end, but we
can make a crude disconnection time check: If you are using 2 core 6mm^2
SWA, the core resistance will be about 3 mOhms/m, and the armour
7mOhms/m for a total of about 10 mOhms/m round trip. That gives us 0.3
Ohms. If it were a TN-S head end you could add on 0.8 for Ze, so 1.1 Ohm
total. Low enough to meet then 1.37 Ohms min for a B32 MCB [3].

Prospective fault current = 230/1.1 = 253A, enough to be in the magnetic
part of the trip response.

Adiabatic check, sqrt( 253^2 x 0.1 ) / 115 [4] = 0.7mm^2 minimum CSA
wire required. The copper equivalent 7mm^2 of armour being 3mm^2 if we
use the 2.255 conversion factor. So plenty good enough.



[1] Much SWA will be the 90 deg C XLPE style sheathed stuff anyway,
which has higher limits)

[2]
http://wiki.diyfaq.org.uk/index.php/...our_as_a_C PC

[3]
http://wiki.diyfaq.org.uk/index.php/...g_Voltage_Drop

[4] Appropriate k factor for a PVC cable - but low for a XLPE one - see
[1] above.




--
Cheers,

John.

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On 14/02/2019 21:39, John Rumm wrote:

Going to 6mm^2, that would be 7.3mV/A/m or ~7V

So you could easily argue that 6mm^2 will get you close enough -
especially as it does not sound like the circuit will likely have
anything near that load on it normally. (you could also argue that the
effects of small voltage drops with modern low energy lighting are
overstated anyway).


This is where the tightening up of lighting circuits to a 3% voltage
drop in the regs may need to change.

The 3% voltage drop for lighting became a reg before the use of LED
lighting became mainstream.

The use of a deviation from the regs is a useful tool. If the OP fits
LED lighting that works from 80 to 250V (most of it does) then you can
ignore the 3% voltage drop and calculate for a 5% drop.

There are other reasons not to design the circuit to the absolute
minimum allowed.

The three most obvious ones are

1. Most of the cost is actually the labour to fit the supply cable. You
only have to do the job once.

2. If running at near max allowed current for long periods you get
wasted power in the cable.


3. Future expansion of the system (if 2 does not apply)

--


Adam

Point 3 is very important for garages used to park daily cars in.

Eventually

Point 3 is important particularly for detached garages used for storing daily use vehicles overnight.

Eventually we will all be driving electric vehicles which will need charging overnight....

I have been informed that my 80a cutout is only sufficient for charging 1 vehicle. If I want to charge two vehicles overnight, I have to have the cutout upgraded to 100a and possibly the service Cable to the cutout.....

So a detached garage having a 3 core 25mm2 SWA cable does not now seem excessive to put in while the trench is still open instead of that 6mm2 or 10mm2 SWA cable.....

On 17/02/2019 11:44, wrote:
Point 3 is important particularly for detached garages used for storing daily use vehicles overnight.

Eventually we will all be driving electric vehicles which will need charging overnight....

I have been informed that my 80a cutout is only sufficient for charging 1 vehicle. If I want to charge two vehicles overnight, I have to have the cutout upgraded to 100a and possibly the service Cable to the cutout.....

So a detached garage having a 3 core 25mm2 SWA cable does not now seem excessive to put in while the trench is still open instead of that 6mm2 or 10mm2 SWA cable.....


Believe it or not the most logical thing to put in the trench is a duct
with a draw cord next to your SWA.

As for upgrading your cut out to 100A. If you have to do this then so
would most the people on your street. The infra stucture of the grid
cannot not cope with this.

Electric only vehicles may be fine many people but not ATM for me, no
matter how fast they charge or far they can travel.

They are probably suitable for my gf with her fixed mileage to work (9
miles round trip) and a couple of shopping trips a week. A 13A supply
could keep her car topped up. I seldom do less than 100 miles a day.





--
Adam

On 17/02/2019 14:59, ARW wrote:

As for upgrading your cut out to 100A. If you have to do this then so
would most the people on your street. The infra stucture of the grid
cannot not cope with this.

I have 63A out here (the SWA cable predates the building!) but even if I
wanted I couldn't go all the way to 100A. That's the house main fuse limit.

Andy

Regarding your point about the infrastructure being unable to cope....

I reckon that electric car owners will sign up to economy 7 electric which means their cars will be charged between midnight and seven am where the majority of people will be in bed.

The infrastructure is clearly able to cope with peak load during the morning get up, shower and have beakfast run and again for when people get home, shower cook and watch tav, surf internet and then go to bed.

So instead of two peak time periods every day we could see three peak periods every day.

When you consider all the kettles, electric showers, toasters, electric cookers etc during day time Vs battery Chargers during the night....

Having said that, houses with night storage heating systema may struggle to charge cars without having a 250 amp cutout supply!

wrote

Point 3 is important particularly for detached garages used for storing
daily use vehicles overnight.

Eventually we will all be driving electric vehicles which will need
charging overnight....

Dont believe that, particularly with most in here, they'll be dead first.

I have been informed that my 80a cutout is only sufficient for charging
1 vehicle. If I want to charge two vehicles overnight, I have to have the
cutout upgraded to 100a and possibly the service Cable to the cutout.....

So a detached garage having a 3 core 25mm2 SWA cable
does not now seem excessive to put in while the trench is
still open instead of that 6mm2 or 10mm2 SWA cable.....

On 17/02/2019 16:54, Rod Speed wrote:


wrote

Point 3 is important particularly for detached garages used for
storing daily use vehicles overnight.

Eventually we will all be driving electric vehicles which will need
charging overnight....

Dont believe that, particularly with most in here, they'll be dead first.

Care to lead by example and show us how it is done?

--
Adam

On Mon, 18 Feb 2019 03:54:53 +1100, cantankerous trolling senile geezer Rot
Speed blabbered, again:


Eventually we will all be driving electric vehicles which will need
charging overnight....

Don¢t believe that, particularly with most in here, they'll be dead first.

Not with most, but with you certainly, you 85-year-old senile Ozzie cretin!

--
Sqwertz to Rot Speed:
"This is just a hunch, but I'm betting you're kinda an argumentative
asshole.
MID:

On Sunday, 17 February 2019 16:55:02 UTC, Rod Speed wrote:
wrote

Point 3 is important particularly for detached garages used for storing
daily use vehicles overnight.

Eventually we will all be driving electric vehicles which will need
charging overnight....

Dont believe that, particularly with most in here, they'll be dead first.



I have had an electric car for seven years.
The charge leads supplied with electric cars range from 10 to 13 amps.
They go into a domestic socket.

On Sunday, 17 February 2019 11:44:34 UTC, wrote:
Point 3 is important particularly for detached garages used for storing daily use vehicles overnight.

Eventually we will all be driving electric vehicles which will need charging overnight....

I have been informed that my 80a cutout is only sufficient for charging 1 vehicle. If I want to charge two vehicles overnight, I have to have the cutout upgraded to 100a and possibly the service Cable to the cutout.....

So a detached garage having a 3 core 25mm2 SWA cable does not now seem excessive to put in while the trench is still open instead of that 6mm2 or 10mm2 SWA cable.....

Overnight EV charging is very low current.
My EV charger is only 10 Amps.

On 07/03/2019 19:04, harry wrote:
On Sunday, 17 February 2019 11:44:34 UTC, wrote:
Point 3 is important particularly for detached garages used for storing daily use vehicles overnight.

Eventually we will all be driving electric vehicles which will need charging overnight....

I have been informed that my 80a cutout is only sufficient for charging 1 vehicle. If I want to charge two vehicles overnight, I have to have the cutout upgraded to 100a and possibly the service Cable to the cutout.....

So a detached garage having a 3 core 25mm2 SWA cable does not now seem excessive to put in while the trench is still open instead of that 6mm2 or 10mm2 SWA cable.....

Overnight EV charging is very low current.
My EV charger is only 10 Amps.

That's because you have car with the battery capacity comparable to a
bulk pack of AAs from Poundland.

Most dedicated chargers (i.e. hard wired rather than plug in) will draw 6kW.

A Tesla with its more practical 130kWh battery would take more than two
and a half full days to charge at the charge rate delivered with your
charger.


--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

sm_jamieson wrote:
I am putting in SWA cable to the garage, total length max 30 metres,
load just a few sockets for low powered tools, and lights, connected to 32A RCBO in the house CU. Should I use 4mm or 6mm SWA ?

Cheers,
Simon.


6 or 10 for me

On Friday, February 15, 2019 at 3:40:34 AM UTC, FMurtz wrote:
sm_jamieson wrote:
I am putting in SWA cable to the garage, total length max 30 metres,
load just a few sockets for low powered tools, and lights, connected to 32A RCBO in the house CU. Should I use 4mm or 6mm SWA ?

Cheers,
Simon.


6 or 10 for me

I suspected 4mm would be iffy. Load will be lowish (def. no electric cars !)
Thanks for John's calcs.
I will use 6mm.
Most of my neighbours have a string of 2.5mm nailed to the fence.

Simon.

On 15/02/2019 11:58, sm_jamieson wrote:
On Friday, February 15, 2019 at 3:40:34 AM UTC, FMurtz wrote:
sm_jamieson wrote:
I am putting in SWA cable to the garage, total length max 30 metres,
load just a few sockets for low powered tools, and lights, connected to 32A RCBO in the house CU. Should I use 4mm or 6mm SWA ?

Cheers,
Simon.


6 or 10 for me

I suspected 4mm would be iffy. Load will be lowish (def. no electric cars !)
Thanks for John's calcs.
I will use 6mm.
Most of my neighbours have a string of 2.5mm nailed to the fence.

6mm minimum.

No electric cars ATM:-) What would be the extra cost to put 10mm cable in?


--
Adam

Well last July I bought 20 m of 10mm2 three phase SWA cable for 70 quid from denmans so I would expect 30 m of 10mm2 to be around 105 quid....

My SWA cable is awaiting connection at both ends with suitable coloured sleeving to mark it has single phase, neutral and earth.

one is at the garage end and the other is for the wood shed and greenhouse

On 15/02/2019 22:13, wrote:
Well last July I bought 20 m of 10mm2 three phase SWA cable for 70 quid from denmans so I would expect 30 m of 10mm2 to be around 105 quid....

My SWA cable is awaiting connection at both ends with suitable coloured sleeving to mark it has single phase, neutral and earth.

one is at the garage end and the other is for the wood shed and greenhouse


First hit for 10mm 3 core on line finds 30m at £104 inc delivery.

--
Adam

On Friday, 15 February 2019 11:58:13 UTC, sm_jamieson wrote:
Most of my neighbours have a string of 2.5mm nailed to the fence.

That's probably okay in winter.

Owain

On 15/02/2019 19:06, wrote:
On Friday, 15 February 2019 11:58:13 UTC, sm_jamieson wrote:
Most of my neighbours have a string of 2.5mm nailed to the fence.

That's probably okay in winter.

Owain

Realistically, while not correct, how often do most people use enough
power in a shed or garage to actually trouble it unless they use
electric heating there?

SteveW

On 16/02/2019 23:16, Steve Walker wrote:
On 15/02/2019 19:06, wrote:
On Friday, 15 February 2019 11:58:13 UTC, sm_jamiesonÂ* wrote:
Most of my neighbours have a string of 2.5mm nailed to the fence.

That's probably okay in winter.

Owain

Realistically, while not correct, how often do most people use enough
power in a shed or garage to actually trouble it unless they use
electric heating there?

Depends what you do in there.. but if its used for anything of any
duration in winter, then some form of heating seems likely.


--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Thursday, February 14, 2019 at 2:43:17 PM UTC, sm_jamieson wrote:
I am putting in SWA cable to the garage, total length max 30 metres,
load just a few sockets for low powered tools, and lights, connected to 32A RCBO in the house CU. Should I use 4mm or 6mm SWA ?

Cheers,
Simon.

OK thanks all.
I've ordered 30m of 10mm 3-core SWA even though its way over for current usage.
If I ever needed to make use of its capacity I'd have to upgrade some internal wiring, but hey ho as they say.
And it will certainly sort out the earthing requirements.

Simon.

On 07/03/2019 14:00, sm_jamieson wrote:
On Thursday, February 14, 2019 at 2:43:17 PM UTC, sm_jamieson wrote:
I am putting in SWA cable to the garage, total length max 30 metres,
load just a few sockets for low powered tools, and lights, connected to 32A RCBO in the house CU. Should I use 4mm or 6mm SWA ?

Cheers,
Simon.

OK thanks all.
I've ordered 30m of 10mm 3-core SWA even though its way over for current usage.
If I ever needed to make use of its capacity I'd have to upgrade some internal wiring, but hey ho as they say.
And it will certainly sort out the earthing requirements.

You will not regret it. Just another small point in oversizing the cable
means a smaller voltage drop and so less losses in the cable. So even a
13A sustained load (future small EV charging point) will make savings
over time.

--
Adam