6mm wtin sheath cable

[oldboot]

Just to summarise a few things.

when we design wiring for electrical loads we have to consider the following in order.

The voltage of the system we are working on, because if system is very low voltage like our 12 or 24 volt boats and cars we can not afford to have much at all go missing, in some things 1 volt of voltage drop in a 12 volt system is a real problem

The current drawn by the piece of equipment, remember the item particularly a motor may draw very much more than its rated or more than the fuse or breaker for a short time or under certain situations...... fuses & breakers will hold twice their rated for a specified time often 60 seconds.

The circuit distance, remember this must go all the way back to the source of supply and in our boats the distance from the positive to the item and back again to the negative......usually twice the cable run distance

Current carying capacity of the wire, we calculate only on the crosss-sectional area of the conductors. The current carrying capacity of the wire as listed will be at 20 or 25 deg celcius, and in open air so if the wire is going somewhere hot like an engine bay or tied up in a bundle we have to consider that and go heavier

The voltage drop of the whole circuit, bassed on the wire size, the circuit distance and the current drawn. Once we get into heavier drawing items this will over ride our current carrying capacity selection.

Select circuit protection, this can be a bit more complicated, we want a fuse or breaker that will allow the item to operate, but will trip quickly under overload.
Certainly we want a breaker that will not allow the wiring to melt or burn.


Quite often our wire selections are restriced to one of a few choices that are available.

Remember we need to be talking in terms of cross sectional area (10mm2), in auto and marine electrical it is common to talk in terms of the nomonal outside diameter of the insulation which is most misleading.
6mm automotive wire is infact approximately 4.6mm2...and it gets worse in smaller sizes.
While we suposedly live in a metricated country, all the sizes and strandings of automotive & marine cable are derived from the US system and often sold in US guage.
OH hell I wish they would just call a spade a spade and tell us the cross sectional area in mm2.


as for the anchor winch.....unless you are running a long way....10mm2 twin would be a reasonable choice.....ya might get away with 6mm2.....but I recon 25mm2 might be a bit of overkill...... but there is no harm in that.

6mm automotive twin (4.6mm2) would probaly work and may not burn, but it may be a very sad thing.........there is nothing more pitifull than the sound of a winch motor starved for voltage & current.

cheers

[timddo]

sorry mate, How about we calulate it all properly and work on max 5% voltage drop?

So the basic setup is 8.2m of cable in total? Can you tell us what winch it is so I can look up the actual specs on it?


As for cables, perhaps peterbo3 might be able to help you out if you can handle not using twin.

Andy was only kidding mate.

I will need to allow for a few bends so 8.5 meters in length. South pacific 710S ( baby anchor winch).

Great idea any, Peterbo3 should have all the cables.

thanks

[finga]

In the civilised electrical world, we work on a rule of thumb of 10 amps per square mm of conductor.....with some corrections, for how and where the wire is used........and as Mr Wrigley says in the text...... often the limiting factor is the insulation not the wire.

Electricians worth their salt will know what current carrying capacities of wire are.
No rule of thumb should ever be involved. It's an exact science not rule of thumb.
The rule of thumb is what probably got Timdo's winch wired up in 2X2mm wires wired in parallel.
If in doubt consult the manual. One of which is the Olex cable manual.

If your wanting to figure out wire sizes in relation to current load and length work it out.
Work to 2-3 or up to 5% voltage drop and that will give you an answer.
I'm sorry but cable sizing does not work to a budget.
The cable size is either right or wrong. Once the cable size is found then you can shop around.

resistance = % x V x 1000
....................100 ........L x I
Please disregard the dots. It's the only way I could get the numbers and letters in roughly the right spot.

Now resistance is the resistance per 1000m figure you need to look for when you look up the table on page 96 of the Olex cable manual .
V is the voltage your working to
L is the length of cable
I is the current.
% is the percentage of voltage drop that is acceptable
So for Timdo:
voltage (V) of 12V
cable length (L) of say 8.5m
current (I) of 30A
% of say 5%

R= 5 x 12 x 1000
....100 .........8.5 x 30
R = 0.05 x 12 x 3.92
R = 2.35
Now that we have a number to work to we need a resistance that's lower then the number we have figured out.
So when we go to the table we see 6mm has a resistance per 1000m of 3.08 ohms. Not good as we're looking for 2.35
So we look at 10mm and we see it's got a resistance per 1000m of 1.83 ohms.
1.83 is lower then 2.35....we have a winner. Beauty
And then if we look at 16mm we see the figure of 1.15....better still and if you do the sums for a 3% voltage drop then you'll need the 16mm as you have to work to a calculated maximum resistance per 1000m of 1.41.

If you allow for things like heat build up and bad connections I'd be seriously considering the 16mm....especially as I personally like a 2-3% drop max on 12V dc.

[timddo]

guys

i have sourced some 16mm square 2 twin from springers at $15.40 a meter by 8.5 gives me $130. ( tinned too) I suppose it's worth it not to pull the anchor up by hand.

10mm square would be $93 or so.

Now the bloody connectors are only 6mm studs

[TheRealAndy]

Ok, so that unit only draws 12A for a maximum of 15minutes.

Given those values, 6mm2 is ample, 10mm2 is ideal. Votlage drop will be 0.6V (5.3%) and 0.37V(3.1%) respectivly.

Using the standard 8B&S cable from Bias and whitworths etc, Voltage Drop is 0.42V (3.5%)


So, if its wired with 6mm2 (not 6mm outer diameter) then I would leave it as is. If its smaller than that and you insist on rewiring, then go hit up peterbo3 for some 10mm2 cable and use that.


Now, do you need lugs?

[TheRealAndy]

Posted before I read your response. Dont buy from springers, PM peterbo3.

I should have plenty of crimps to suit 10mm2 cable with 6mm stud. Will check tonight. I also have a tool for crimping them properly

[MattChew]

Posted before I read your response. Dont buy from springers, PM peterbo3.

I should have plenty of crimps to suit 10mm2 cable with 6mm stud. Will check tonight. I also have a tool for crimping them properly

If you need some Tinned solder and a Butane torch just send me a pm.
Ta
Matt

[finga]

Ok, so that unit only draws 12A for a maximum of 15minutes.

Well done Andy for actually finding out what current is drawn.
I was working to the 30A as it was mentioned somewhere before.

It just goes to show to find out all the details forehand....and assume nothing.

[tigermullet]

Looks like there will be a re-wiring job for me. The chandlers advise that their 6mm single wire (tinned) is actually 4.59mm2 which means my wiring is way too light.

[oldboot]

OK.... cable rating is an exact science..... but it all works arround the base of 10 amps per square mm.......at least thats what all the tables I have in both manufacturers catalogues and the wiring rules work out to.....with correction factors and allowances .

At least if you understand that you have a clue if the figures you are seeing are in the ball park of being correct.

cheers

[finga]

OK.... cable rating is an exact science..... but it all works arround the base of 10 amps per square mm.......at least thats what all the tables I have in both manufacturers catalogues and the wiring rules work out to.....with correction factors and allowances .

At least if you understand that you have a clue if the figures you are seeing are in the ball park of being correct.

cheers

So this winch is rated at 12A.
So a 1.5mm cable will do the job??
Should be plenty seeing 1.5mm is good for 15A apparently.
Oh bugger it. Allow for some correction factors and allowances and go 2.5mm.
Now that's gotta be good as 2.5mm is good for 25A and we only need 12A.
That's over 100% allowances on the 10A per mm rule of thumb....and still wrong

Not even close to be in the ball park of been right according to what Andy has worked out.

I hate rule of thumbs....

[timddo]

So this winch is rated at 12A.
So a 1.5mm cable will do the job??
Should be plenty seeing 1.5mm is good for 15A apparently.
Oh bugger it. Allow for some correction factors and allowances and go 2.5mm.
Now that's gotta be good as 2.5mm is good for 25A and we only need 12A.
That's over 100% allowances on the 10A per mm rule of thumb....and still wrong

Not even close to be in the ball park of been right according to what Andy has worked out.

I hate rule of thumbs....

Ok. The website says 8 awg Min. Current Draw 12Am typical

So i'm getting 10mm2.

Problem solved.

Finga 1.5mm2 -- come on dude???? Websites says 8 AWG Min

[tigermullet]

I don't think Finga actually meant that!

This is been a beneficial education for me - not that I know much but am beginning to see the light.

Is this a great forum or what?

[deckie]

But But But..how much does it REALLY draw when the pick is stuck solid, you're pointing into 20knots of breeze, and you're in a bad mood coz of the gutless winch . Plus it isnt brand new anymore.

[tigermullet]

I wouldn't know, except that winches are not meant to be used in that manner. Boat power should be used to take the boat to above the anchor and to break it free. This is where a nifty little chain stopper comes in handy by taking the load off the winch at rest and on retrieval.