Electrical query

[skotl]

I was in the garage this afternoon, re-running the wire through the feed cos I accidentally let it slacken and it bird-nested and I got to thinking.

The current carries down the 0.8 mm wire and returns through the dirty great earth cable. So why do we need an earth cable that substantial when physics suggests that the energy down the source path (the 0.8mm wire) is the same as the energy on the return (excepting the loss through heat)?

 

[Paul.]

The welding current dosen't go down the wire, its applied in the torch through the contact tip,

 

[skotl]

Ah! That makes more sense - ignore me, then

 

[Robotstar5]

If you open the harness up you'll see a cable of similar csa (cross sectional area) to the earth cable, this carries the current to the contact tip.

 

[normspanners]

When you put welding current through a length of .8 it gets pretty warm pretty quick I have had the scars when running couple of metres of roller damage wire through and you didnt realise the end has shorted on the earth !!! it glows in less than blink, then you grab it to snip it, and F*** IT you stupid T**t comes out unaided.
I have cut foam with that method by adjusting the volts with the wire pulled tight and the wire feed switched off get the wire hot but not glowing and pull the foam through it.

 

[chunkolini]

Ahem
I remember thinking this.
I was welding tiny little components and they were sat on my blackboard not the metal workbench. The return lead was to heavy and messed up the arrangement.
So I made up a jump lead out of a bike gear cable and small crocodile clip.
For some reason I held it in my left hand, wrapped around the hand to steady it.
Can you see what comes next?
Yelp yelp yelp, a lovely puff of smoke from around my hand, and a foot of yellow charring, no real damage.
What kind of idiot does things like that?
Now I use the return lead from my plasma cutter and it works a treat.
Norm, you are almost as stupid as me.

 

[500e]

I never wear any rings or watch to work.
There was this lad a battery & a metal watch strap, it was not pleasant, hospital & skin grafts !!!.
Chunk, we have all done almost the same as you, connected earth to a small part then held it & welded, as soon as you start to press trigger you know it is going to hurt, the poor lads watch welded itself between + & earth

 

[skotl]

Thanks chaps. It's obvious now that I've looked at the trunk!

As it happens, I snipped the wire after the birds nest and pulled the trigger to evacuate the remains of the wire but the flapping end caught the earth - decent sized spark (not MIG-level spark) and a whiff of smoke. Let go of the trigger, grabbed the 0.8mm and...


....


....

OWW! It was bloody hot!

This is all part of the learning experience of understanding how the welders work

 

[pedrobedro]

It's all to do with the path of least resistance. You want the welding wire to get hot and melt but the earth wire to stay cool and in one piece.

 

[thestig]

ive used 5 metre lengths of angle iron tacked together as an earth.

 

[BrokenBiker]

on my machine in work I have the earth lead bolted to the table.

on my home machines I have a few arrangements, some 16mm multi strand cable stripped of its insulation to wrap around round stuff and clamp to that, a 400A rated aluminium clamp, a 3rd hand tool made from a big bit of aluminium block with solid copper bars sticking out to form the legs and finger and a bit of 16mm cable bolted on through a crimp.

they all have their uses, just have to make sure they are substantial enough to not melt when you hit the trigger

 

[Robotstar5]

ive used 5 metre lengths of angle iron tacked together as an earth.

I've seen some one use a hooped access ladder to save running the cable to the top of a building

 

[BrokenBiker]

I've seen some one use a hooped access ladder to save running the cable to the top of a building

that sounds like something my pikey uncle would try.

I have actually seen him try to weld a car with an ac stick welder.

my cousin is a fabricator and had been doing work on his morris minor pick up project, making a crane arm to go in the bed.

he had been welding plates in to support the crane, and for some reason had bolted the earth lead to the car. the bolt wouldn't come out when my uncle though he would have a go at his cavalier.

instead of finding my cousin and seeing if he could sort it out, he simply reversed his cavalier up until it was in contact with the morris and thought he could start welding...unfortunately it didn't go well.

he tried to start an arc, big flash from between the cars where they were touching, big burn marks on the paint and a hole in the Morris...

 

[Robotstar5]

he tried to start an arc, big flash from between the cars where they were touching, big burn marks on the paint and a hole in the Morris...

definately pikey!

 

[BrokenBiker]

I wouldn't expect anything else from him. he is supposedly a builder (cowboy) and once fitted new windows to the local social club. however he isn't the best at reading, or cutting things square, and cut the aperture about 4cm too wide, and then stuffed the gap with newspaper and covered with a strip of plaster board.