6mm wtin sheath cable

[TheRealAndy]

Why did I want to change the wiring? This thread! I bought 6mm (single wires not twin core) because I thought it was thick enough and the chandlery didn't have 8mm. After reading the first couple of posts on this thread I began to get the idea I had made a mistake and have realized just how complicated this whole business of wiring really is. Well, to me anyway.

Thanks for the tip about grabbing the wires after winching. I've already given it a go but cannot say why I did it. The wires were cool = no detectable heat. I'll try it again after giving the winch even more work. I guess, my main concern is with voltage drop and burning out the winch motor. I wasn't worried prior to this. Ignorance is bliss.

BTW, grabbing the wires for a heat test is not the recommended method of ascertaining if the cables are of sufficient current capacity but it does work!!! I think most insulation used for cars and boats is rated to 90°C (need to look at AS3008 to be certain) so you should know before it gets to that!!!


The voltage drop wont cause your motor to burn out, it will just stop it from working as well.

[tigermullet]

The voltage drop wont cause your motor to burn out, it will just stop it from working as well.

You beauty! In that case all is well. The winch works as expected - or even better than hoped. I will leave things alone - after all I anchor in shallow water - generally not more than 4 to 5 metres and let out 15 metres of chain unless it gets very windy. Being lazy, I don't shift position - often staying in the one spot for a couple of days. The winch won't have to work hard.

Thanks again for your response and advice.

[TheRealAndy]

You beauty! In that case all is well. The winch works as expected - or even better than hoped. I will leave things alone - after all I anchor in shallow water - generally not more than 4 to 5 metres and let out 15 metres of chain unless it gets very windy. Being lazy, I don't shift position - often staying in the one spot for a couple of days. The winch won't have to work hard.

Thanks again for your response and advice.

No problem.

I can beleive this thread actually managed to make 5 pages!

[timddo]

i found this formula to calculate voltage drop.

Formula 2 X L X A X I divided by cable sixe in mm2 ..

L = Length of cable , A = Amps being carried and I is the resistance of the cable ( Copper is 0.017 , Steel is 0.028 ) ...

So in theory i will get a voltage drop of .35 volts. ( using 8.5 meters of cable and 10mm2).

This has been a great learning curve. Andy's probably already covered this though

[oldboot]

Um.. sorry to be picky..... but 1.5mm2 or 15 amp flex will carry 15 amps regardless of voltage.
and more importantly

It will carry 15 amps the same distance with the same voltage drop regardless of the supply voltage involved.

How much voltage drop is acceptable is a whole different decision.
A matter which has been discussed, and i cant remember argueing with.


Remember too
in the world of DC, outside of the building industry, there are very few standards and all most without exception they are unenforceable.

There may be some legal requirements for boats under survey, but privately registered pleasure boats........ nup.

and if you think 20 to 25 amps on a 1.8mm2 wire is a joke..... check out the wiring in your almost any car.......you will die laughing.

Most local manufacturers dont even make 18 or 20 guage automotive cable..... but you will find it in your cars and mine and operating well over the 10 amps/mm2 and at quite high voltage drops.

measure the voltage at your stop lights..especilay with a trailer attached.....what a laugh.


cheers

[TheRealAndy]

Um.. sorry to be picky..... but 1.5mm2 or 15 amp flex will carry 15 amps regardless of voltage.
and more importantly

It will carry 15 amps the same distance with the same voltage drop regardless of the voltage involved.

How much voltage drop is acceptable is a whole different decision.
A matter which has been discussed, and i cant remember argueing with.


Remember too
in the world of DC, outside of the building industry, there are very few standards and all most without exception they are unenforceable.

There may be some legal requirements for boats under survey, but privately registered pleasure boats........ nup.

and if you think 20 to 25 amps on a 1.8mm2 wire is a joke..... check out the wiring in your almost any car.......you will die laughing.

Most local manufacturers dont even make 18 or 20 guage automotive cable..... but you will find it in your cars and mine and operating well over the 10 amps/mm2 and at quite high voltage drops.

measure the voltage at your stop lights..especilay with a trailer attached.....what a laugh.


cheers

Seriously, have a good think about what you just said.

[oldboot]

It has just occured to me that perhaps this whole thing is being "over thunk".

Phaps it is on one hand, but on the other hand some things are being overlooked.

In the world of the "Full Ticket Sparkie", the supply voltage is more or less fixed, and there is an expectation of no more than 10% voltage drop across the whole system..or something like that.

Now we move across to a boat or car with a "12 volt system".

If that vehicle has been sitting for some time without the motor running the supply voltage will be arround 12 to 12.5 volts, but as soon as we start the engine and run it for a while our supply voltage will come up to arround 13.5 to 15 volts depending on the charging system.

Then we start cranking some sort of heavy motor ( winch, starter motor).
If the engine isnt running the battery will be loaded down and the terminal voltage with drop ( how far good question).....10 volts would be not unreasonable engine cranking a car or 4 stroke inboard.

So how much battery terminal voltage drop will a winch cause.
In a car the alternator will be able to supply 40 amps pluss, but many of our outboards will only supply 8-15 amps..how much will that help.

so in short even without the voltage drop in the wires we may have dropped several volts.

So we need to think about heavier cables that we would on a fixed supply.

I can see how some of the "uneducated" would say FK the maths i'll just put the heaviest cable in that I can manage.....and I would say "I can not argue with that"

now a sad story
I went fishin with a mate, he had an average 16 foot runabout with 60Hp on the tail...all was great, a snoger bream caught..BUT when we got back to the ramp.

He trots out this cable with jumper clips to hook his winch up to his car battery.

anyway he starts pulling the boat on....as the load came on the progress stopped

so he starts up the car, and I have to keep the revs up while he winches on.....OH the sad and mournfull sound of the winch , even then the boat barely got on.

now the cable was 6mm automotive twin and arround 6 meters of it.....12m cable run.

combine the voltage drop in the battery and the voltage drop in the cable and the resistance in the clips and there was a real problem.

I recon it mught have cranked on with a good heavy cable and a better connection and no assistance from the alternator...maybe.

But the voltage drop in the cable was not the only issue.

So are the voltage drop figures in the building industry standards suitable.

There is very rarely any harm in using heavier cable.

cheers

[oldboot]

Seriously, have a good think about what you just said.

Um yeh I have.

voltage only appears in the volatge drop equasion as an output.

A given current, in a given wire, will always result in the same voltage droped and that is a fact.

basic ohms law.

The supply voltage is irrelivent in calculating the voltage dropped.

How much voltage drop is acceptable is a completly seperate issue, and an "engineeing decision" and not a fact.


cheers

[finga]

It has just occured to me that perhaps this whole thing is being "over thunk".
Sparky's worth their salt have to think otherwise things burn and people die

Phaps it is on one hand, but on the other hand some things are being overlooked.

In the world of the "Full Ticket Sparkie", the supply voltage is more or less fixed, and there is an expectation of no more than 10% voltage drop across the whole system..or something like that.
Seriously, have a good think about what you just said

Now we move across to a boat or car with a "12 volt system".
But the voltage drop in the cable was not the only issue.
True BUT it's on top of the hit parade.
It's a main issue as well as current carrying capacity and short circuit temperature rise.

A couple of quotes from AS 3008: Electrical Installations - Selection of cables.

1.1 SCOPE
This Standard sets out a method for cable selection for those types of electrical cables and
methods of installation that are in common use at working voltages up to and including
0.6/1 kV at 50 Hz a.c.
Three criteria are given for cable selection, as follows:
(a) Current-carrying capacity.
(b) Voltage drop.
(c) Short-circuit temperature rise.
and
2.2 SELECTION PROCESS
The following three main factors influence the selection of a particular cable to satisfy the circuit requirements:
(a) Current-carrying capacity Dependent upon the method of installation and the presence of external influences, such as thermal insulation, which restrict the operating temperature of the cable.
(b) Voltage drop Dependent upon the impedance of the cable, the magnitude of the load current and the load power factor.
(c) Short-circuit temperature limit Dependent upon energy produced during the
short-circuit condition.
The minimum cable size will be the smallest cable that satisfies the three requirements.

So as far as Australian Standards are concerned voltage drop is a big thing and one well worth considering.


So are the voltage drop figures in the building industry standards suitable.
Why aren't they suitable. A lot of stuff wired in the building industry is DC and around the 12-24V. And what better standard is there to use other then one as authoritative as Australian/New Zealand Standards.
You could also consider AS 1125:2001 for cable selection
There is very rarely any harm in using heavier cable.
Cost would be a big harm in a lot of circumstances.

cheers

Full Ticket Sparkie's have to think. They have to think about a lot of different things before a cable can be selected or the installation method of the cable is selected.
Rules of thumb do not work.
They never have and never will.
That's why it takes a fair period of time to do an apprenticeship.

[finga]

Um yeh I have.

voltage only appears in the volatge drop equasion as an output.

A given current, in a given wire, will always result in the same voltage droped and that is a fact.

basic ohms law.

The supply voltage is irrelivent in calculating the voltage dropped.

How much voltage drop is acceptable is a completly seperate issue, and an "engineeing decision" and not a fact.


cheers

Voltage drop for those in the trade is considered as a percentage of the supply voltage...never at a nominal voltage of say 7V
What percentage of the supply voltage is dropped if the calculated or measured Vd is say 7V when the supply voltage is 12V and then 240V??
"How much voltage drop is acceptable is a completly seperate issue, and an "engineeing decision" and not a fact".
Oh dear. Australian Standards are pretty factual. And a maximum of 5% would be about right.
I should know. I've issued a lot of defect notices with non compliance from AS 3000 and AS 3008 with a fair whack of them concerning cable selection.
I reckon Australian and New Zealand Standards would agree with their publications been factual.
Engineers have to work to minimum standards...what would they be??

[oldboot]

Full Ticket Sparkie's have to think. They have to think about a lot of different things before a cable can be selected or the installation method of the cable is selected.
Rules of thumb do not work.
They never have and never will.
That's why it takes a fair period of time to do an apprenticeship.

Um.....4 years and a certificate 3 competency.......just like a plumber.....or carpenter.......yeh I served a 4 year apprenticship too.

Funny I don't know how but the regulators seem to think plumbing is more dangerous than electricity......that is why the still inspect plumbers work... but lets not go there.

I don't question how much thinkin' an electrician should be doing.

What I am questioning is if the preconceptions of the 240V world translate across to the 12 volt world.

Yeh I do think about what I have posted......think on it, a supply voltage that is legesated to a standard, and should not ever vary too far beyond that standard in a correct instalation in normal operation.

A 12 volt automotive system supply could be as low as 8 volts and as high as 15 volts and not be considered faulty that is a variation of near 20%..even that not guaranteed by standard or legeslation.

In a normal low charge cranking situation the terminal voltage on a starter motor may be as low as 6 volts ( half nomonal supply) and still start the car...just.. the ignition system has to work and the engine management too.......and the whole system will probaly recover without harm

If we have 120 Volts on a 240V fridge motor we are certainly out of spec and have a real problem.


As far as the building standarsd being relivent to auto electrics and boats.

The wire table and the procedured will certainly apply, but they exist without the standard anyway, along with a whole pile of engineering expectations and work method requirements.

DC wiring systems in the building industry would be a very very small persentage, barely worth a chapter in AS300. It devotes more space to flexible cords.

Most of the larger institutions that work with extensivly DC have their own standards and practices that are far stricter than the building electrical standards.

when we are expecting large fluctuations in the supply voltage perhaps we should be considering much lower acceptable voltage drops in cables AND other improvements in our work methods and expectations to compensate.

So if 10% voltage drop is what is acceptable AND we have lost that with the battery sagging.....where does that leave the voltage drop in our cable.

ya see where I am going.

As far as cost being an issue......in the building industry, cable runs are relativly long and there is always cost preasure........another 50cents per meter could bust the budget......so many of the methods in the building electrical industry are cost motivated.
Interesting plumbers demand a higher labour rate in the market than electricians..... but who wants to work in S.... all day

In a boat or car we are mostly talking cable runs in the single digits....an extra couple of bucks a meter is not the problem here that it would be in the building trade.

SO $8 per meter V's $12 per meter over a 5 meter run......if it makes my anchor winch on my $35 000 boat work better...who cares..even $8 a meter V's $20 a meter.....for one of the most important things on a $35 000 boat..its a no brainer.


I ask you not to get upset about what I say but to think about the implications.

There are different considerations crossing over the disciplines.

cheers

[oldboot]

Voltage drop for those in the trade is considered as a percentage of the supply voltage...never at a nominal voltage of say 7V
What percentage of the supply voltage is dropped if the calculated or measured Vd is say 7V when the supply voltage is 12V and then 240V??
"How much voltage drop is acceptable is a completly seperate issue, and an "engineeing decision" and not a fact".
Oh dear. Australian Standards are pretty factual. And a maximum of 5% would be about right.
I should know. I've issued a lot of defect notices with non compliance from AS 3000 and AS 3008 with a fair whack of them concerning cable selection.
I reckon Australian and New Zealand Standards would agree with their publications been factual.
Engineers have to work to minimum standards...what would they be??

Remember the vast majority of any standard represent "wise engineering decisions" bassed on carefull consideration in context not facts.

I do understand but when the supply voltage is small and variable, the persentage is nothing more than a arbitary figure....an engineering decision or "a rule of thumb" if you like.....

combine the permissable supply variation with the acceptable voltage drop and 10% variation is more like it than 5%.

Like it or not AS 3000 is full of rules of thumb, possibly not recognised because they have been formalised, but rules of thumb all the same.

Remember not only the supply voltage but the supply tolerance of appliances and equipment on 240V mains is regulated by standard and legeslated by law......the system is pretty damn good.....if other areas were as sensibly regulated, life would be so much easier for so many of us.

In the 12 volt word, the supply tolerances of different items can vary wildly and there is no standard to regulate it.

If we are to do the "whole job", my maths we need to know what the supply tolerance is of that item.

Some "12 volt" items may run happliy at 5 or 6 volts, others may exhibit problems at 11.5, yet others will not run at best efficency with less than 13 volts..and there is seemingly no rhyme or reasn to it.

It occurs to me the best approach is to, do the best you can and run the heaviest cable that is practical and within reason...a philosophy that would send you broke in the building industry.
And it seem this works very well for those "uneducated" and willing to spend a little extra.

And in truth when we consider available wire sizes....even if we do the maths we probaly end up no different.

cheers

[finga]

Um.....4 years and a certificate 3 competency.......just like a plumber.....or carpenter.......yeh I served a 4 year apprenticship too.
In what??

What I am questioning is if the preconceptions of the 240V world translate across to the 12 volt world.
They do. Electrical theory is electrical theory and standards are standards.


A 12 volt automotive system supply could be as low as 8 volts and as high as 15 volts and not be considered faulty that is a variation of near 20%..even that not guaranteed by standard or legeslation.
8V dc is OK in the auto industry??

In a normal low charge cranking situation the terminal voltage on a starter motor may be as low as 6 volts ( half nomonal supply) and still start the car...just.. the ignition system has to work and the engine management too.......and the whole system will probaly recover without harm
You reckon??

As far as the building standarsd being relivent to auto electrics and boats.

The wire table and the procedured will certainly apply, but they exist without the standard anyway, along with a whole pile of engineering expectations and work method requirements.

DC wiring systems in the building industry would be a very very small persentage, barely worth a chapter in AS300. It devotes more space to flexible cords.
I dunno about that. Solar power seems to be catching on and I thought that was DC...as well as dc controlling of appliances and then there's dc lighting and ..... the list goes on. That's why there are tables in AS 3000 and 3008 that involve dc.
The installation of dc cabling should be regarded along the same lines as ac cabling.
DC is dealt with throughout both publications.
There are no specific chapters dealing with DC but in AS 3000:2007 there are a few clauses. Those clauses start at 7.5 and the title is Extra-Low Voltage Electrical Installations.
So you kinda get an idea of what the chapter is about.
Now clause 7.5.7 deals entirely with voltage drop and refers the reader to AS 3008.

Most of the larger institutions that work with extensivly DC have their own standards and practices that are far stricter than the building electrical standards.
But those 'in house' standards would be merely extensions of the AS 3000 and 3008 standards.
when we are expecting large fluctuations in the supply voltage perhaps we should be considering much lower acceptable voltage drops in cables AND other improvements in our work methods and expectations to compensate.
Who's expecting large fluctuations in supply voltage. I don't want large fluctuations so design things a bit better.
If you do some reading supply voltages are required to be within certain guidelines


So if 10% voltage drop is what is acceptable AND we have lost that with the battery sagging.....where does that leave the voltage drop in our cable.
Try 5% maximum voltage drop. If the battery is not up to the job then a rethink is needed
ya see where I am going....going to the shop to get a better battery I reckon

As far as cost being an issue......in the building industry, cable runs are relativly long and there is always cost preasure........another 50cents per meter could bust the budget......so many of the methods in the building electrical industry are cost motivated.
Interesting plumbers demand a higher labour rate in the market than electricians..... but who wants to work in S.... all day
Who cares who earns what??
Who does a plumber call when his anchor winch doesn't work??
Is this relavent knowing who gets paid what to make an anchor winch work correctly??
In a boat or car we are mostly talking cable runs in the single digits....an extra couple of bucks a meter is not the problem here that it would be in the building trade.
Maybe in a Peel 50 or my 3.7m tinny they'd be single digits.

SO $8 per meter V's $12 per meter over a 5 meter run......if it makes my anchor winch on my $35 000 boat work better...who cares..even $8 a meter V's $20 a meter.....for one of the most important things on a $35 000 boat..its a no brainer.
If it's so important to get things right why work to a rule of thumb??
Isn't a $35,000 boat worth 3 minutes of sums??
So why not use $40/m cable where $8/m cable will be sufficient for the job??
It's only a 5 m run.
By rule of thumb we only needed a 1.5mm cable to run the anchor winch.
That's all it needed. 12A....rule of thumb 1mm per 10 A...= 1.5mm with room to spare.

I ask you not to get upset about what I say but to think about the implications.
Implication are people might read the rule of thumb and go...beauty. Electric motor...40A it says in the book so 4mm cable will do.
And then wonder why the electric blows up and warranty is declined.
Implications of rules of thumb can injure people or at the very least cause material damage.


There are different considerations crossing over the disciplines.
Sparks are sparks and poo is poo.

cheers

All this is because you said waaaaay back the rule of thumb is 1mm in cable cross sectional area will carry 10 A.
That has proved to be utter crap.
Andy would know better then anyone about dc that's used in industry and the importance of correct cable sizing and installation design. He's an instrument fitter as well as a sparky dude.
I'm merely a sparky dude with a few extra tickets.

[finga]

And in truth when we consider available wire sizes....even if we do the maths we probaly end up no different.

cheers

That would have to be the biggest heap of male bovine excrement I've read in ages.
Why did they bother writing all those books and making all those rules and working out all those tables.
They could have just said...refer to your left thumb and be done with it. It'll all work.
Lucky it's a rule of thumb and not a rule of hand as the left AND right hand rules are already taken thanks to Mr Fleming.

Rule of thumb....1mm of cable = 10A load...goodo.
Crap. Think of the implications or have a good disclaimer when making statements like that.

Like I said before. I should like rule of thumbs.
They made me lots of money doing repairs to those rules of thumb's and gave me lots of pleasure righting defect notices to those who used rules of thumb's.

[murf]

great post my head now hurts, so many past memories flooding back and I haven't touched the AS3000 in 10years, I just looked behind me and it is still on the shelf feeding the cockroaches

I saved a couple of great little bits of this thread

cheers Murf