I have googled unsuccessfully. I have data about voltage drops etc.
But what is acceptable?

Is there anywhere that I can find what are of wire I need, given my
expected current and length of wire?

I ask because (Hi. I'm troy McClure...You may recognise me from...) I
am setting up a welding traveller based on a Cobramatic push-pull
welder. I need to extend the wired from the power source to the
feeder, and also the erath electrode wire. I also may need to install
a solid wire from the feeder to the gun, rather than the water-fed one
that's there at present. While the water fed is superior, they cost a
small fortune, unless I can cobble one up, which may or may not be
worth the trouble.

I have asked a couple of welding shops, and had vastly (in?)different
replies, both between thenselves and from the wire that is already on
the welder.

Data

Welding current 220A max MIG
Distance from welder to feeder 5 metres 916 feet)
Distance from feeder to gun = 8 metres (25 feet)

Existing wire intended to go from welder to feeder
length = 2 metres (6.5 feet)
area = 70mm^2 !!!!!!

I am sure the welding shops were talking a lot less than this. I do
knwo that the same feeder is designed to provide power to a 400 Amp
gun, if required. So it's all swings and roundabouts.

Any help appreciated.

On Fri, 14 Jan 2005 14:12:07 +0800, Old Nick
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

hmm....unusually slow response.

HOWEVER. I realised (and meant to post) that it may well have nothing
to do with voltage drop, but simply the cable's ability to carry the
current without burning up the shop. Hence although the original cable
is short, to carry the 400A it has to be large.

I am going with 50mm^2. It is not that much more expensive and cannot
hurt.

I have googled unsuccessfully. I have data about voltage drops etc.
But what is acceptable?

Is there anywhere that I can find what are of wire I need, given my
expected current and length of wire?

On Sat, 15 Jan 2005 07:26:20 +0800, Old Nick
wrote:

On Fri, 14 Jan 2005 14:12:07 +0800, Old Nick
vaguely proposed a theory
......and in reply I say!:

remove ns from my header address to reply via email

hmm....unusually slow response.

HOWEVER. I realised (and meant to post) that it may well have nothing
to do with voltage drop, but simply the cable's ability to carry the
current without burning up the shop. Hence although the original cable
is short, to carry the 400A it has to be large.

I am going with 50mm^2. It is not that much more expensive and cannot
hurt.

Voltage drop is an issue with MIG, but you should be OK with 50 mm^2
and it certainly won't burn down the shop at 220 amps.

On Sat, 15 Jan 2005 01:13:30 -0600, Don Foreman
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

Voltage drop is an issue with MIG,

Yes. Well this was why I lpt fiorst to that conclusion.

I actually have alittle proggy that looks at this sort of stuff. I see
a 1.4 V drop over the 25metres total distance that I will use, at 220
A and 50mm^2.

but you should be OK with 50 mm^2
and it certainly won't burn down the shop at 220 amps.

OK. I feel safe G. But if VD (sorry!G) is an issue, then why have
the makers of this thing used 70mm^2 for a 2metre length? It seems way
overkill even at 400A, if I can get away with 50mm^2 over 13 metres
(X2 I might add allowing for the earth lead).

On Sat, 15 Jan 2005 17:31:32 +0800, Old Nick
wrote:

On Sat, 15 Jan 2005 01:13:30 -0600, Don Foreman
vaguely proposed a theory
......and in reply I say!:

remove ns from my header address to reply via email

Voltage drop is an issue with MIG,

Yes. Well this was why I lpt fiorst to that conclusion.

I actually have alittle proggy that looks at this sort of stuff. I see
a 1.4 V drop over the 25metres total distance that I will use, at 220
A and 50mm^2.

but you should be OK with 50 mm^2
and it certainly won't burn down the shop at 220 amps.

OK. I feel safe G. But if VD (sorry!G) is an issue, then why have
the makers of this thing used 70mm^2 for a 2metre length? It seems way
overkill even at 400A, if I can get away with 50mm^2 over 13 metres
(X2 I might add allowing for the earth lead).

I came up with about the same voltage drop. MIG voltage is typically
around 24 volts, so I figured 5% of that should not be a problem.

However, I note that the (factory) 10-foot ground lead on my Milller
210 is 3AWG, which is 5.827 mm dia. or 26.6 mm^2. Scaling that by
75/10 would suggest 200 mm^2!

One reason for using a spoolgun is to operate at significant distance
from the power supply. It may just be that welders using heavy
cables for minimum VD over long runs don't calculate cumulative VD in
the circuit but wouldn't appreciate seeing 2 meters of "wimpy wire"
at the feeder end.

On Sun, 16 Jan 2005 06:42:37 +0800, Old Nick
wrote:

I came up with about the same voltage drop. MIG voltage is typically
around 24 volts, so I figured 5% of that should not be a problem.

Hehe. It is when you NEED that 220A! G

A 5% drop in voltage won't affect max current much. In short-circuit
transfer (which is the case at 220 amps) current is set more by wire
speed.


However, I note that the (factory) 10-foot ground lead on my Milller
210 is 3AWG, which is 5.827 mm dia. or 26.6 mm^2. Scaling that by
75/10 would suggest 200 mm^2!

Not quite, because you have to factor in the electrode lead length as
well. It may not be as long (?) but....anyway it still leaves me with
100mm^2.

Now there's a question. These cables a _multi_ strand. Dioes that
gauge of the cable allow for that? So are your strands equivalent to
3AWG solid wire? I am assuming so.

Yes.

On Fri, 14 Jan 2005 14:12:07 +0800, Old Nick
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

rrrghh!

So I go to the shop, and buy my 50mm^2 cable, as it's cut and on the
bench, and as I write out the cheque, the guy says "You know rhis is
way overkill for your job?" _He_ was nearly overkilled.

I calmly (Calm...Calm) advised him that (a) his own staff had advised
me (b) it was better to spend the extra $50 and make sure....