I am sizing up some wire to connect two 12V leisure batteries together, also
teminals, fuse holder etc.

I noted that the wire thicknesses were quoted in mm^2 so I went looking for
an explanation on how to relate wire thickness (diameter) to mm^2.

Found this:
http://www.learn-about-electronics.c...onductors.html
which said, amongst other things
"Here is another example. Assume that a conductor is 3/8 inch thick and 4
inches wide. The 3/8 inch can be expressed in decimal form as 0.375 inch.
Since 1 mil equals 0.001 inch, the thickness of the conductor will be 0.001
´ 0.375, or 375 mils. Since the width is 4 inches and there are 1,000 mils
per inch, the width will be 4 ´ 1,000, or 4,000 mils. "

Now is the mil completely different from the mm?
Or is something horribly wrong here?
Looks like the terminology here is mil = a thousandth of an inch.

Given that the UK spoken shorthand for a millimetre is a mil (as in 10 mil
spanner) there is enormous scope for confusion.

You say tomayto and I say tomarto?

Now trying to estimate the thickness of the conductor if the conductor plus
sheathing is about 6mm.

Cheers

Dave R
--
No plan survives contact with the enemy.
[Not even bunny]

Helmuth von Moltke the Elder

(\__/)
(='.'=)
(")_(")

"David WE Roberts" wrote in message
...
I am sizing up some wire to connect two 12V leisure batteries together,
also teminals, fuse holder etc.

I noted that the wire thicknesses were quoted in mm^2 so I went looking
for an explanation on how to relate wire thickness (diameter) to mm^2.

Found this:
http://www.learn-about-electronics.c...onductors.html
which said, amongst other things
"Here is another example. Assume that a conductor is 3/8 inch thick and 4
inches wide. The 3/8 inch can be expressed in decimal form as 0.375 inch.
Since 1 mil equals 0.001 inch, the thickness of the conductor will be
0.001 ´ 0.375, or 375 mils. Since the width is 4 inches and there are
1,000 mils per inch, the width will be 4 ´ 1,000, or 4,000 mils. "

Now is the mil completely different from the mm?
Or is something horribly wrong here?
Looks like the terminology here is mil = a thousandth of an inch.

Given that the UK spoken shorthand for a millimetre is a mil (as in 10 mil
spanner) there is enormous scope for confusion.

You say tomayto and I say tomarto?

Now trying to estimate the thickness of the conductor if the conductor
plus sheathing is about 6mm.

Cheers

Dave R
--
No plan survives contact with the enemy.
[Not even bunny]

Helmuth von Moltke the Elder

(\__/)
(='.'=)
(")_(")

Yeah well, going back to basics ..... !

area of a circle is pi * r^2 (where r = half of the diameter)

pi = 3.14159

r^2 = r x r

so the cross sectional area of your wire is 3.14159 x d/2 x d/2

where d is the diameter in mm of the wire

the result is in mm^2

"Phil Jessop" wrote in message
o.uk...

"David WE Roberts" wrote in message
...
I am sizing up some wire to connect two 12V leisure batteries together,
also teminals, fuse holder etc.

I noted that the wire thicknesses were quoted in mm^2 so I went looking
for an explanation on how to relate wire thickness (diameter) to mm^2.
snip
Now trying to estimate the thickness of the conductor if the conductor
plus sheathing is about 6mm.
Yeah well, going back to basics ..... !

area of a circle is pi * r^2 (where r = half of the diameter)

pi = 3.14159

r^2 = r x r

so the cross sectional area of your wire is 3.14159 x d/2 x d/2

where d is the diameter in mm of the wire

the result is in mm^2


Yeah, can do that and have also found a web site with a calculator.

The important part of the phrase was "plus sheathing".
I can calculate the cross sectional area of the (wire+sheathing) but this
doesn't give me the area of the conductor, but I don't want to disassemble
the current installation and strip back the insulation to get the true cross
section.

I guess if I assume that the sheathing is 5% of the diameter of the wire
that should be close enough.

Cheers

Dave R
--
No plan survives contact with the enemy.
[Not even bunny]

Helmuth von Moltke the Elder

(\__/)
(='.'=)
(")_(")

On Fri, 17 Jun 2011 19:23:28 +0100, David WE Roberts wrote:

I guess if I assume that the sheathing is 5% of the diameter of the wire
that should be close enough.

Depends what the cable was orgininally intended for. A wire designed
for use on low voltages the insulation may only be 0.5mm or less
thick. For mains maybe 2mm, high voltages 5mm or more. Thickness of
the insulator will also depend a bit on what that material is, though
these days it's nearly always PVC or similar.

The only real way of knowing the conductor size is to measure it.

--
Cheers
Dave.

"Dave Liquorice" wrote in message
ll.co.uk...
On Fri, 17 Jun 2011 19:23:28 +0100, David WE Roberts wrote:

I guess if I assume that the sheathing is 5% of the diameter of the wire
that should be close enough.

Depends what the cable was orgininally intended for. A wire designed
for use on low voltages the insulation may only be 0.5mm or less
thick. For mains maybe 2mm, high voltages 5mm or more. Thickness of
the insulator will also depend a bit on what that material is, though
these days it's nearly always PVC or similar.

The only real way of knowing the conductor size is to measure it.


Just to restate - this is for linking 12V leisure batteries together so it
is similar to the cable used in jump leads.
In fact, I am tempted to use some old jump leads where the crocodile clips
are broken.
However the cable quality in the cheaper jump leads is sometimes suspect so
this could be false economy.
Whatever, the cautious method of sizing the conductor is to pretend the
sheathing is conductor also and thus get a slightly oversize cable.
This would give a 28mm^2 conductor for a 6mm diameter cable.
[ According to http://www.sengpielaudio.com/calcula...ss-section.htm ]
From the Durite catalogue the nearest flexible starter cable is 25mm^2 to
carry 170 amp.

However given that the earth lead from the battery to the chassis is
protected by a 50 amp fuse (the 50 amp Maxi blade fuse in the Durite
catalogue is rated 50 amp continuous 100 amp blow) 170 amp cable seems a bit
over the top.
20mm^2/135 amp seems reasonable for 50 amp continuous (not that I'm likely
to be pulling anything like 600 watts) and a slightly slimmer cable will be
easier to route.

The existing cable does look remarkably slim compared to the usual
automotive starter cable - will check the external diameter in the car - so
perhaps I should be working back from the load the fuse will support instead
of trying to replicate the existing cable.

My original problem remains - I can't measure the conductor diameter on a
cable which is fully sheathed and with an integral ring connector at the end
also covered with insulation without removing some insulation and thus
damaging the existing cable.
Which I obviously don't want to do.

Anyway, the discussion is helping me to get my head around the issues, so
thanks to all.

Cheers

Dave R
--
No plan survives contact with the enemy.
[Not even bunny]

Helmuth von Moltke the Elder

(\__/)
(='.'=)
(")_(")

"David WE Roberts" wrote in message snip
However given that the earth lead from the battery to the chassis is
protected by a 50 amp fuse (the 50 amp Maxi blade fuse in the Durite
catalogue is rated 50 amp continuous 100 amp blow) 170 amp cable seems a
bit over the top.
20mm^2/135 amp seems reasonable for 50 amp continuous (not that I'm likely
to be pulling anything like 600 watts) and a slightly slimmer cable will
be easier to route.
snip

I've just confused myself again.
I assume that the rating shown on a fuse is the continuous load and not the
blow rating.

--
No plan survives contact with the enemy.
[Not even bunny]

Helmuth von Moltke the Elder

(\__/)
(='.'=)
(")_(")

On Sat, 18 Jun 2011 09:21:47 +0100, David WE Roberts wrote:

However given that the earth lead from the battery to the chassis is
protected by a 50 amp fuse (the 50 amp Maxi blade fuse in the Durite
catalogue is rated 50 amp continuous 100 amp blow) 170 amp cable seems a
bit over the top.

At low voltages loses in the cable become significant. V = I * R.

Say you are drawing 50A through the 170A rated cable which, for the
sake of argument, has a resistance of 0.01 ohm. That gives a volt
drop of:

50 * 0.01 = 0.5V (4% drop) device gets 11.5V not 12.

Lets assume that the 50A rated cable has three times the resistance:

50 x 0.03 = 1.5V (12.5% drop) device gets 10.5V not 12.

The more current you draw the worse the volt drop in the cables
becomes.

My original problem remains - I can't measure the conductor diameter on
a cable which is fully sheathed and with an integral ring connector at
the end also covered with insulation without removing some insulation
and thus damaging the existing cable.

This is LV stick a pin in it and measure how far the pin goes in. The
hole won't be a problem unless the cable is in a damp location. If
you are worried wrap a bit of self amalgamting tape around where the
pin went in.

--
Cheers
Dave.

On Sat, 18 Jun 2011 09:21:47 +0100, "David WE Roberts"
wrote:

Just to restate - this is for linking 12V leisure batteries together so it
is similar to the cable used in jump leads.
In fact, I am tempted to use some old jump leads where the crocodile clips
are broken.
However the cable quality in the cheaper jump leads is sometimes suspect so
this could be false economy.

Welding cable is often a good choice for battery linking.

http://www.weldingtorchparts.co.uk/c..._and_lugs.html

If you need a more flexible cable the stuff used for arc welding
torches is many strands of fine wire and has both low resistance and
flexibility, eg

http://www.fhbrundle.com/wcaa-08.htm

On Sat, 18 Jun 2011 09:21:47 +0100, "David WE Roberts"
wrote:


My original problem remains - I can't measure the conductor diameter on a
cable which is fully sheathed and with an integral ring connector at the end
also covered with insulation without removing some insulation and thus
damaging the existing cable.

Use a stanley knife to cut two rings round the cable an inch or so
apart. Make one cut longways and remove the insulation. Untwist the
lay of the cable to enable a check of individual stand size with
vernier caliper. Count number of strands.

Replace removed insulation. Cover with an overlap of half an inch back
to good insulation with adhesive lined heatshrink or self amagamating
tape.

Then look up the cable size online or report back here with the
dimensions


--

In article ,
Phil Jessop wrote:

"David WE Roberts" wrote in message
...
I am sizing up some wire to connect two 12V leisure batteries together,
also teminals, fuse holder etc.

I noted that the wire thicknesses were quoted in mm^2 so I went looking
for an explanation on how to relate wire thickness (diameter) to mm^2.

Found this:
http://www.learn-about-electronics.c...onductors.html
which said, amongst other things
"Here is another example. Assume that a conductor is 3/8 inch thick and 4
inches wide. The 3/8 inch can be expressed in decimal form as 0.375 inch.
Since 1 mil equals 0.001 inch, the thickness of the conductor will be
0.001 ´ 0.375, or 375 mils. Since the width is 4 inches and there are
1,000 mils per inch, the width will be 4 ´ 1,000, or 4,000 mils. "

Now is the mil completely different from the mm?
Or is something horribly wrong here?
Looks like the terminology here is mil = a thousandth of an inch.

Given that the UK spoken shorthand for a millimetre is a mil (as in 10 mil
spanner) there is enormous scope for confusion.

You say tomayto and I say tomarto?

Now trying to estimate the thickness of the conductor if the conductor
plus sheathing is about 6mm.

Yeah well, going back to basics ..... !

area of a circle is pi * r^2 (where r = half of the diameter)

Or pi * d^2 / 4

pi = 3.14159

r^2 = r x r

so the cross sectional area of your wire is 3.14159 x d/2 x d/2

which is what you've described here.


where d is the diameter in mm of the wire

the result is in mm^2

Assuming you start in mm in the first place.

That website above is, I guess, from the other side of the pond... They
seem to use the term 'mil' or 'mills' to represent thousandth of an inch.

It's not one I'm familair with, but maybe that's how it's done over there.

Gordon

On 17/06/2011 18:41, David WE Roberts wrote:
I am sizing up some wire to connect two 12V leisure batteries together,
also teminals, fuse holder etc.

I noted that the wire thicknesses were quoted in mm^2 so I went looking
for an explanation on how to relate wire thickness (diameter) to mm^2.

Found this:
http://www.learn-about-electronics.c...onductors.html
which said, amongst other things
"Here is another example. Assume that a conductor is 3/8 inch thick and
4 inches wide. The 3/8 inch can be expressed in decimal form as 0.375
inch. Since 1 mil equals 0.001 inch, the thickness of the conductor will
be 0.001 ´ 0.375, or 375 mils. Since the width is 4 inches and there are
1,000 mils per inch, the width will be 4 ´ 1,000, or 4,000 mils. "

Now is the mil completely different from the mm?
Or is something horribly wrong here?
Looks like the terminology here is mil = a thousandth of an inch.

Given that the UK spoken shorthand for a millimetre is a mil (as in 10
mil spanner) there is enormous scope for confusion.

You say tomayto and I say tomarto?

Now trying to estimate the thickness of the conductor if the conductor
plus sheathing is about 6mm.

Cheers

Dave R

To be fair the article does define a mil where there are 1,000 to the
inch. It's an American and not a European measurement. Here, as you
rightly say, mils generally refer to mm, but would still be written as mm.

On Jun 17, 6:52*pm, Fredxx wrote:
On 17/06/2011 18:41, David WE Roberts wrote:









I am sizing up some wire to connect two 12V leisure batteries together,
also teminals, fuse holder etc.

I noted that the wire thicknesses were quoted in mm^2 so I went looking
for an explanation on how to relate wire thickness (diameter) to mm^2.

Found this:
http://www.learn-about-electronics.c...onductors.html
which said, amongst other things
"Here is another example. Assume that a conductor is 3/8 inch thick and
4 inches wide. The 3/8 inch can be expressed in decimal form as 0.375
inch. Since 1 mil equals 0.001 inch, the thickness of the conductor will
be 0.001 0.375, or 375 mils. Since the width is 4 inches and there are
1,000 mils per inch, the width will be 4 1,000, or 4,000 mils. "

Now is the mil completely different from the mm?
Or is something horribly wrong here?
Looks like the terminology here is mil = a thousandth of an inch.

Given that the UK spoken shorthand for a millimetre is a mil (as in 10
mil spanner) there is enormous scope for confusion.

You say tomayto and I say tomarto?

Now trying to estimate the thickness of the conductor if the conductor
plus sheathing is about 6mm.

Cheers

Dave R

To be fair the article does define a mil where there are 1,000 to the
inch. *It's an American and not a European measurement. *Here, as you
rightly say, mils generally refer to mm, but would still be written as mm..

No, mil is and always has been 1/1000".

MBQ

On Fri, 17 Jun 2011 18:41:03 +0100, "David WE Roberts"
wrote:

Now is the mil completely different from the mm?
Or is something horribly wrong here?
Looks like the terminology here is mil = a thousandth of an inch.

Correct, in USA mechanical slang the mil is one thousandth of an inch.
Other abbreviations include point and thou (and the thou is
increasingly being used in the USA to reduce confusion).

Given that the UK spoken shorthand for a millimetre is a mil (as in 10 mil
spanner) there is enormous scope for confusion.

Oh yes, as the Hubble telescope found out.

On 17/06/2011 19:59, Peter Parry wrote:
On Fri, 17 Jun 2011 18:41:03 +0100, "David WE Roberts"
wrote:

Now is the mil completely different from the mm?
Or is something horribly wrong here?
Looks like the terminology here is mil = a thousandth of an inch.

Correct, in USA mechanical slang the mil is one thousandth of an inch.
Other abbreviations include point and thou (and the thou is
increasingly being used in the USA to reduce confusion).

Given that the UK spoken shorthand for a millimetre is a mil (as in 10 mil
spanner) there is enormous scope for confusion.

Oh yes, as the Hubble telescope found out.



Never mind.
Just have a pint of beer instead...

--
R

On 17/06/2011 19:59, Peter Parry wrote:
On Fri, 17 Jun 2011 18:41:03 +0100, "David WE Roberts"
wrote:

Now is the mil completely different from the mm?
Or is something horribly wrong here?
Looks like the terminology here is mil = a thousandth of an inch.

Correct, in USA mechanical slang the mil is one thousandth of an inch.
Other abbreviations include point and thou (and the thou is
increasingly being used in the USA to reduce confusion).

Not just in the USA. My father went through an apprenticeship and on
upwards here in the UK and mil was (and in some areas still is) in
perfectly common UK useage.

SteveW

On Fri, 17 Jun 2011 22:07:24 +0100, Steve Walker
wrote:

On 17/06/2011 19:59, Peter Parry wrote:
On Fri, 17 Jun 2011 18:41:03 +0100, "David WE Roberts"
wrote:

Now is the mil completely different from the mm?
Or is something horribly wrong here?
Looks like the terminology here is mil = a thousandth of an inch.

Correct, in USA mechanical slang the mil is one thousandth of an inch.
Other abbreviations include point and thou (and the thou is
increasingly being used in the USA to reduce confusion).

Not just in the USA. My father went through an apprenticeship and on
upwards here in the UK and mil was (and in some areas still is) in
perfectly common UK useage.

It was used for many years by the GPO for adjustment and specification
of relay and electromagnet springs and contact spacings in telephone
and telex exchange (as well as some subscribers' apparatus)..

Spring pressures were measured in grams and spacial dimensions in mils
(thousandths of an inch) for literally billions of relay-type stuiff.

Mind you - size of wire used in cable and jumper wire was expressed in
pounds (weight) per mile (of copper).

I should imagine that the reason for tis was that it was easier for a
local GPO stores to determine how much wire was on a particular hank
by weighing it than by flaking it all out to measure its length.

6¼ lb equated more or less to 25 swg

--
Frank Erskine

On 17/06/2011 19:59, Peter Parry wrote:
Oh yes, as the Hubble telescope found out.

Actually, no. Hubble's problem wasn't units.

http://en.wikipedia.org/wiki/Hubble_...of_the_problem

AKA

http://tinyurl.com/673ultu

You're thinking of Mars Climate Orbiter.

http://en.wikipedia.org/wiki/Mars_Climate_Orbiter

Andy

David WE Roberts wrote:
I am sizing up some wire to connect two 12V leisure batteries together,
also teminals, fuse holder etc.

I noted that the wire thicknesses were quoted in mm^2 so I went looking
for an explanation on how to relate wire thickness (diameter) to mm^2.

Found this:
http://www.learn-about-electronics.c...onductors.html
which said, amongst other things
"Here is another example. Assume that a conductor is 3/8 inch thick and
4 inches wide. The 3/8 inch can be expressed in decimal form as 0.375
inch. Since 1 mil equals 0.001 inch, the thickness of the conductor will
be 0.001 ´ 0.375, or 375 mils. Since the width is 4 inches and there are
1,000 mils per inch, the width will be 4 ´ 1,000, or 4,000 mils. "

Now is the mil completely different from the mm?
Or is something horribly wrong here?
Looks like the terminology here is mil = a thousandth of an inch.

Given that the UK spoken shorthand for a millimetre is a mil (as in 10
mil spanner) there is enormous scope for confusion.

You say tomayto and I say tomarto?

Now trying to estimate the thickness of the conductor if the conductor
plus sheathing is about 6mm.

Cheers

Dave R


You would have a hard time guessing conductor size from od of insulation.
for instance auto jumper leads often cheat with very thick insulation to
fool you into thinking that they are heavy duty.

On Sat, 18 Jun 2011 18:20:07 +1000, F Murtz
wrote:

You would have a hard time guessing conductor size from od of insulation.
for instance auto jumper leads often cheat with very thick insulation to
fool you into thinking that they are heavy duty.


Cables often have thinner insulation if they use something better than
PVC. Raychem's PVDF cables are a case in point. Tiny overall
diameter, cost a packet and will run at 140 deg C for years.

I'd never guess what was inside a cable. A vernier caliper is about 10
quid from one of the cheapy supermarkets/ebay


--