Wire sizing (1 Viewer)

[Tonydom]

Hi folks can anybody help me with wire sizing, I'm quite competent with running circuits etc especially domestic 240v.

I can't get my head round all the 12v cable colours and having so many cable sizes. So what I'm proposing to do is wire all my 12v with AUTOMOTIVE 12V 24V STRANDED 2 CORE TWIN THIN WALL
Suitable for use at temperatures up to 105°C.
Cross Section: 2x 0.5mm
Current Rating(amps) - 11 Amps
Overall Dim’ns (mm) - 3.5 x 5.5mm
cable rated to 11amps.

As I have around 30 meters leftover from a previous project

I know this might be a bit heavy for some of my 12v stuff but I can't think of any items that will be near the 11amp. The biggest draw will be the fridge which by my calculations will draw around 6 amps and it will only be on 12v whilst moving.

Can anybody tell me what if any drawbacks to using this size of wire

Thanks

 

[funflair]

You say cross section so is that diameter or area? seems a bit skinny either way to me though, too much voltage drop.

 

[Lenny HB]

Can anybody tell me what if any drawbacks to using this size of wire

Totally unsuitable for your planned use.

For a start thin walled auto cable size includes the insulation so 0.5mm sq is not 0.5 mm sq it's a fair bit smaller.
Fridges normally draw 10 to 15 amps and when working out the cable size you need to take into account the length of the cable run. It's normally recommended to have a volt drop of less than 3 % I prefer to aim for 2 %.

So for a 4 metre run of cable carrying a current of 10 amps you would need a cable size of 6 mm sq.
For 7m you would need 10 mm sq.

Calculator here:

Cable Size Calculator - Cable sizing and selection | 12 Volt Planet

Cable Size Calculator - Read our guide to selecting cable of the correct type and size for your automotive, marine or leisure wiring application. Auto and Marine Electrical Components from 12 Volt Planet

www.12voltplanet.co.uk

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[Raul]

Fridge and pump manual, calls for 6mm2. The only place I would use 0,5mm is led lights and other small draw. And please don’t fuse 0,5mm2 with 10a fuse.

 

[Tonydom]

Think my head is going to explode with this I thought it all depended on the amp ratings for cables
This is what my 12v will be running

Electrolux 3 way fridge 12v only used while driving
I inderstand I will need to upgrade the cable for fridge as it's 12.5 amp

4 X 3 watt led lights = .25 amps each = 1amp
I led strip light 24watt = 2amps
1 mushroom extractor fan 7 watt = 1.2 amps
2 X dual USB sockets 36 watt = 3 amps
Cooker ignition
Water heater ignition
Toilet flush 3amp
Shurflo pump 4.5 amps
Roof fan 3 amps

Each item,/appliance will be run via a fuse box and corresponding blade fuse suited to the recomended amps for each item

This is the info on the cable roll

2 CORE FLAT TWIN THIN WALL CABLES
Thin Wall low voltage multicore wiring cables suitable for use in the automotive, marine and allied industries. Resistant to petrol, diesel, lubricating oils and diluted acids. This is proper automotive extension cable.

Suitable for use at temperatures up to 105°C.
Cross Section: 2x 0.5mm
Current Rating(amps) - 11 Amps
Overall Dim’ns (mm) - 3.5 x 5.5mm

Insulation Properties:
Calcium Zinc based insulation compound to ISO6722-2011 Class B
Tensile Strength 24.0 N/mm²
Elongation at break 300%
Shore “D” Hardness: 56 @ 15 secs
Specific Gravity 1.34g/cc
Thermal Stability 200 mins @ 200°C

Sheath Properties
Easy tear PVC sheathing to BS7655 Type 6
Tensile Strength 9.0 N/mm²
Elongation at break 260%
Shore “A” Hardness 79
Specific Gravity 1.60g/cc
BS Softness 36
Thermal Stability 70 mins @ 200°C
COPPER STRAND PROPERTIES
Plain Copper wires conforming to BS6360


If this is no good can someone please tell me or send me a link to cable that will be appropriate.

Sorry it's a bit long winded

Thank you

 

[Lenny HB]

You have not listened, when working at low voltage you have to take into account the voltage drop across the length of the cable or your appliances will not work properly.
For example, If you use your cable to wire the fridge you will have only 7 volts at fridge if the cable length is 4m.

I gave you a link eairler that will allow you to select the appropriate cable, if in doubt always go bigger.

Thin walled cable is not sized the same as normal cable as I said eairler.

The max current rating on a cable is the max current the cable can take before overheating.

Fuses in the distribution unit are to protect the cable not the appliance. So if you get a faulty appliance that draws too much current the fuse will blow before the cable is overloaded preventing a possible fire.

I would use standard auto cable more flexible easy to use and strip than thin walled cable. Also difficult to work out the size you need with thin walled.

Depending on the length of your cable runs probably OK to use:-
6mm for fridge.
6mm for pump.
2mm for lighting.
4mm for everything else.

<Broken link removed>

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[Tonydom]

Thank you so much Lenny you have been so helpfull I really do appreciate you taking the time to explain this to me

 

[Tonydom]

One more thing please Lenny
My battery will be situated middle of van passenger side directly across from it I will have to run cables for water heater/ pump and toilet flush would it be safe to run them between the van floor and the 12mm ply flooring housed in conduit channeled into the 30mm kingspan insulation to cut down on the cable run or would there be issues with heat or should I just run them under the van.

Cheers

 

[pappajohn]

There's a reason for using different colours..... Fault tracing.
If you have a fault and a bundle of black wires how do you know which wire is which at the other end of the loom.
If you have an orange wire it's easy to find the other end.... Its orange as well.

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[Lenny HB]

Should be fine with the cable sizes I suggested there will no heat given off.

 

[Lenny HB]

If you have an orange wire it's easy to find the other end.... Its orange as well.

 

[Raul]

There's a reason for using different colours..... Fault tracing.
If you have a fault and a bundle of black wires how do you know which wire is which at the other end of the loom.
If you have an orange wire it's easy to find the other end.... Its orange as well.

Or you clip a multimeter on it with dial at continuity on buzzer and a extension. That’s how I traced a ecu chaffed wire.

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[Tonydom]

Once again thank you Lenny

 

[pappajohn]

Or you clip a multimeter on it with dial at continuity on buzzer and a extension. That’s how I traced a ecu chaffed wire.

That is one way.... But monotonous.