Electrical Cable Cross sectional Area or Diameter

[Dave100456]

Help Please!
I am selecting electrical flex to take to my boat to wire up my 30watt solar panel. I know that big diameter is best to avoid voltage drop but I'm struggling to identify the various types flex that I have available as they don't match up to common sizes. Am I confusing area with dia in specifying cables as both measurements are quoted?

Flex 1: orange twin (ex lawn mower) 32 strands of 0.13 dia I make this 0.425 sq mm
Flex 2 Blue 3 core artic 30 strands of 0.22 dia, I make this 1.14 sq mm. Shouldn't this be 1.5sq mm?
Flex 3 Twin 35 starnds 0.25 dia, I make this 1.78 sq mm.

Why don't these comply with usual cable sizes ie 0.75, 1, 1.5, etc?

 

[David2452]

Could be the dia is including the insulation? also the calculations are pretty close and those sizes are nominal, hence a small discrepency.

 

[TerryMac]

The size (gauge) of wires are measured in cross sectional area. In UK it is measured in mm2. That is just the conductor (not the insulation). Quite difficult to accurately measure I should imagine!

 

[biscuit]

It is very confusing: This may be helpful: googling "awg to sq mm" may also give actual wire diameter as well on some pages:

http://www.reuk.co.uk/AWG-to-Square-mm-Wire-Size-Converter.htm

 

[Dave100456]

Thanks.
All measurements of the conductor taken with micrometer and are mean values. The Artic cable was sold as 1.5mm and I thought this was a measurenment of area.

 

[theoldsalt]

Dave100456,

Domestic cable is not suitable for marine applications. Tinned cores are always recommended to iliminate corrosion of the copper in the salty environment. An exception may be inland waterways.

 

[Simondjuk]

Whilst it might be the ideal to use tinned wiring, there are plenty of boats out there with 30 or 40 year old un-tinned conductors which are still perfectly serviceable, so it's not something I'd spend a lot of extra money or bother over.

 

[nigel1]

As regards the cross area/diameter, of the conductor, this wiould depend on how tight or not the strands were twisted.
Mayhaps the manufacturers know the cross section of each strand, then multiply by the total number of strands.

Tinned wire: the original wiring my bene is not tinned.
When I was doing a job on the combined tricolour/anchor light, I noted that normal domestic flex had been used, with the earth wire used as the second switched live to the anchor light, they had not even bothered to fix red insulation tape as an identifier

 

[BERT T]

The first thing you need to consider is the length of your cable run. When that is established it is easy to calculate the voltage drop for the various sizes. The current on a 30 watt solar cell is only about 2.15 amps. The other tip is to solder your connections, don't use crimped or screw connectors.

 

[VicS]

Thanks.
All measurements of the conductor taken with micrometer and are mean values. The Artic cable was sold as 1.5mm and I thought this was a measurenment of area.

Yes it is a measurement of cross-sectional area ( and the units really ought to be mm²)
I am as confused as you are by your measurements but the sizes are I guess nominal and somewhere there ought to be specifications that should be complied with.
There may be some discrepancy due to the cables actually being AWG sizes.

There are a number of tables relating to cable sizes in the electrical section of "The Engineering Toolbox" which may be of interest to you
http://www.engineeringtoolbox.com/electrical-systems-t_33.html

In particular the table on cable sizing for 12 volt circuits.
http://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html

This table: http://www.engineeringtoolbox.com/wire-gauges-d_419.html gives the actual resistance of cables in ohms per 1000m which will enable you to calculate voltage drops directly.

Another table you might find useful http://www.powerstream.com/Wire_Size.htm

and a claculator specifically aimed at solar panel installations http://www.freesunpower.com/wire_calc.php
Note however this last one unusually uses the actual distance apart rather than a "there and back" figure

 

[ghostlymoron]

Dave100456,

Domestic cable is not suitable for marine applications. Tinned cores are always recommended to iliminate corrosion of the copper in the salty environment. An exception may be inland waterways.

I would always use tinned wire for external applications (eg up the mast) but inside the boat it's not really justified.

 

[Dave100456]

Thanks Vic for the info & links.
The mystery the cross sectional area is one I'll have to live with. I wonder (and think I have heard) that a stranded cable will offer less resistance than a solid cable of the same cross sectional area. - Witha plane to catch, probably one to discuss at another time.
I had planned on accepting a <2 % voltage drop and the panels are for winter/tempory use only to combat battery self discharge so not bothered about tinned cable (I always tin bare copper anyway at installation). I've gone for the bigger cable size but had to unpack items to get my suitcase below the max baggage kg with the large drum of flex in.
Cheers
Dave

 

[VicS]

Thanks Vic for the info & links.
The mystery the cross sectional area is one I'll have to live with. I wonder (and think I have heard) that a stranded cable will offer less resistance than a solid cable of the same cross sectional area. - Witha plane to catch, probably one to discuss at another time.
I had planned on accepting a <2 % voltage drop and the panels are for winter/tempory use only to combat battery self discharge so not bothered about tinned cable (I always tin bare copper anyway at installation). I've gone for the bigger cable size but had to unpack items to get my suitcase below the max baggage kg with the large drum of flex in.
Cheers
Dave

3% is the volts drop that is usually considered acceptable. If your requirement is only to combat self discharge volts drop wont be a problem anyway. It only becomes important if you are wanting to get the most out of the solar panel for recharging a discharged battery as quickly as possible.

30 watts is a big panel for just maintenance charging unless you have a very large capacity battery.

I hope you are fitting a regulator of some sort. For your use a simple inexpensive one that just disconnects when the battery is charged will do. No need to go for MPPT or even PWM types.

 

[mitiempo]

As one who removes old wiring from boats on a regular basis to rewire you may be surprised at the corrosion I see on un-tinned wire used originally, and the distance the corrosion travels under the insulation.
I always use tinned wire for any application on a boat and would highly recommend it, especially for a solar panel mounted outside.

 

[nigelmercier]

you may be surprised at the corrosion I see on un-tinned wire ...

You may also be surprised at the corrosion I have seen on tinned wire!

 

[Heckler]

Whilst it might be the ideal to use tinned wiring, there are plenty of boats out there with 30 or 40 year old un-tinned conductors which are still perfectly serviceable, so it's not something I'd spend a lot of extra money or bother over.

+1, indeed, I went to the marine leccy shop in Pwllheli and asked for tinned wire, she told me they didnt use it!
Stu