How to melt an extension cord (Oh, it's an electrical, question alright!)

trubble2rubble · Feb 15, 2007

Welder is about to stick weld an assembly together when he is called away. The welder (Miller 320A, 220V 1 phase) is switched off, and he puts the grounding clamp on a nearby bandsaw (110v)which is plugged into an outlet via an extension cord. A few minutes later, a hot, plasticky smell is detected and smoke is seen pouring from an electric box on the bandsaw. The bandsaw is unplugged, and after the smoke disapates the grounding lug on the bandsaw plug has melted plastic around it, and the extension cord is fried along it's entire length. After it cools down, the bandsaw actually works as before. Where did the juice come from? Something like the grounding clamp being neutral instead of ground, or is there something wrong with the Miller 320?

Thanks,
t2r

Bill Simmons · Feb 15, 2007

I do not have the answer but it is a good question. Be sure the problem is not in the bandsaw. I would use a volt meter to make the following measurements: Check band saw by measureng AC volts from frame to ground, should be 0 volts. Then measure voltage from ground lead of welder to ground. There may be a voltage but I am not sure what it would be. I do not think the ground lead of a welder is ground since it typically allows for the reversal of polarity. But I would not expect much current to be available unless there was a leakage problem in the welder. See if there is a spark when touching a well grounded item with the ground electrode. If you have a clamp on amp meter measure the current through the ground lead with it connected to ground. These readings may provide further clues.

Timw · Feb 15, 2007

Either the saw or the welder is wired wrong. Also possible the wall plugs are wired wrong. Either way if you don't know how to troubleshoot this get someone who does. Sounds like a very dangerous condition, someone could get fried!

macona · Feb 15, 2007

The output of the welder should be isolated from the mains through its transformer. Measure from each output stud to case of the welder, you shouldnt get more than a couple volts. If you do something is wrong inside the machine. Send it in for repair.

Sea Farmer · Feb 18, 2007

Is this why the manual for my Lincoln Invertec tells me to ground the frame of the welder?

anchorman · Feb 18, 2007

I hate to sound preachy, but you should not be leaving any sationary equipment (like a bandsaw) hooked up permanently through an extension cord. especially if you have employees, and fall under osha rules. Violates the spirit and the letter of the national electric code, and could get you some trouble from the firemarshall. If you don't have an outlet where the bandsaw is set up, you should have one installed. Go ahead and have the existing outlets and the bandsaw and welder checked out while your electrician is there.

It used to be with some welders that the manual said to ground the work clamp to the frame of the welder in addition to having a ground rod at the work table, connected to the work. That would explain any output from the welder. Newer miller welders at least the ones I have books for, do not call for the work terminal to be grounded to the frame of the machine.

Listen to Timw and find an electrician to check this out. if you don't already know the basics of how to trouble shoot electrical problems, you should find someone who does. If you want to know how to trouble shoot them, get that someone to show you. It's pretty simple stuff, but there is not a whole bunch of room for error.

anchorman · Feb 18, 2007

Sea Farmer, any equipment with exposed metal parts and hooked to the mains is required to be grounded properly. Saves many lives. as any shorts to the frame get taken by a low impedance path to ground instead of through you.

That said, the work clamp is not necessarily supposed to be grounded to the frame. Called for in some cases, not called for in others. I would be interested if anyone knows if there are requirements about that these days, and would be interested in knowing/discussing the pros and cons of both setups (grounded work clamp and ungrounded work clamp) with someone who is an expert on these things.

macona · Feb 19, 2007

Actually the frame is grounded through the ground lug on your power wire. You should not need to add an additional ground line.

Whoever said a bandsaw is a stationary piece of equipment? Mine cam with wheels and I move it where I need it.

One of my customers melted a power cable off one of their control box for the arc gouging system they bought. Still havnt figured out why.

Chris999 · Feb 19, 2007

The only problem here by what you have described was the person that was doing the welding. The ground lug needs to be attached to the WORK, not some convenient grounded object! What happened is that all the welding current (potentially 320A) was routed through the bandsaw ground lead and back to the welder output circuitry through the welder's input wiring ground. A 12 or 14 ga. 110 volt cord cannot handle that kind of current without turning into a flaming mess.
A welder's output circuit needs to be a closed loop, this case was not.
This was a very serious mistake and I'd check the welder's input ground wiring as it may be damaged as well.

macona · Feb 19, 2007

Chris, reread the initial post. The welder was off and when the ground clamp was set on the bandsaw it burned up its ground lead. There is something VERY wrong in the welder. My best guess is somehow the primary and secondary windings of the transformer have come into contact, this brings the whole output of the transformer at a bias depending on the point it shorted.

Chris999 · Feb 20, 2007

...Oh Krap! Note to self: Do not post stuff to teh interweb after a few beers.
My bad. Sorry.
Now I'm gonna have to sit down and scribble out some possible circuit diagrams to come up with a possible solution. Maybe get hold of a Megger tester and test whether the transformer insulation has broken down and the primary windings have shorted to the secondary or to the iron core?

macona · Feb 20, 2007

Nah. There is something wrong with the welder. Take it to them and have it fixed. That is if it is something more than a buzz-box. In that case trash it and buy a new one.

JacobS · Feb 20, 2007

Check out the wiring in the wall/conduit also. If the extension cord is fried, your other wiring may be also. If it's the same gauge wire, it would be in the same condition.

anchorman · Feb 20, 2007

Still think if the work clamp is grounded to the frame, as it sometimes is, that a wiring fault within the bandsaw could also be the problem. If this was the case, the frame, table and all exposed parts of the bandsaw could be a potential killer. if not, macona's advice seems pretty sound as usual.

chuckey · Feb 26, 2007

Sounds like the saw has its frame at neutral and the welder has its secondary ground ,actually earthed. Why? If the saw was grounded, as the welder was not on, there could be NO output voltage or neutral at all. If the saw had neutral on its frame, it would have up to 6V but at a huge current available (no fuses on neutral wires). So earthing this neutral, would not cause any fuse to blow and the current would be limited by the resistance of the earth only.
Check out your wiring.
Frank

mjk · Feb 28, 2007

New to this part of the forum but I'll add.
Have the wiring the bandsaw was hooked up to checked out also. If the "cord" was fried, chances are the hard wiring going back to the circuit breaker is damaged. The circuit breaker also should be checked.
I was always told never attach a welding machines ground clamp to a piece of machinery unless it is disconnected from the power source.

dem45133 · Feb 28, 2007

Wow... I agree with all the checks and verifies... could be serious issues left that it caused.

My uncle was a master electrician for GM for 48 years... he knows his stuff. I'll send this thread to him... maybe he has some ideas. Electric can do some very weird things when someting isn't right... It also kills indescriminantly!

Dave

anchorman · Feb 28, 2007

Unless you are dealing in High Voltage, High frequency AC, there is ver little strange stuff that electricity will do. And even with the HV/HF it does follow rules, just not the ones most of us are accustomed to. Electricity follows simple laws... Everyone who has anything to do with it should learn them.

most basic is that no current can flow without completeing the circuit. So if current is flowing, find the path along which it is flowing, and the problem should and can almost always be easily solved from there... Not a huge mystery, just a lack of knowledge and patience on most people's part. It's all science.

bdx · Apr 8, 2007

Sounds like the earth wire has went live, hence the burning along the entire cable length. Phase has contacted earth. Good stuff, scary tho! Polarity on plug / socket well worth checking, if incorrect, assuming the live is only fused, one can appreciate there is no fuse protection. A tight kink in a dodgey cable which shorts phase to earth can also cause burning and not blow the fuse due to the high impedance. There u go, a wee bit late, but im only new to the forum. Its realy a crude way to use heated cable!!

boilermakerwelder · May 11, 2007

I know it's a little late to reply but here goes. Maybe the welder wasn't really turned off untill ( oh sh-- ) after the smoke,or has a bad switch that only shutof 1/2 of the 220v. My best guess is the extension cord was damaged or pulled to hard and the ground wire was disconected at the plug or at the machine.without a ground a 220v motor will run.

How to melt an extension cord (Oh, it's an electrical, question alright!)

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