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Old 09-06-2010, 05:27 PM   #31
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grounding the workpiece you're welding


Here is the entire ansi welding saftey standard from the free download over on the american welding society website. I don't have time today to sort through it but maybe it will lead us to our answer about grounding the work piece.
But as you said it does require it in the small section of that standard I qouted earlier.....

http://files.aws.org/technical/facts/Z49.1-2005-all.pdf

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Old 09-06-2010, 05:33 PM   #32
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grounding the workpiece you're welding


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btw, NEC 630.15 clearly states that the secondary of the welder shall not be considered as premises wiring fro the purpose of applying article 250 (Grounding and Bonding).

that would support your statement that the grounding must be separate of the work conductors.
HMMMM nice find and I agree it supports my understanding for grounding the workpiece.
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Old 09-06-2010, 05:47 PM   #33
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grounding the workpiece you're welding


My art work isn't quite as nice as Stubbie's but I hope it gets the point across.
A simple welder is nothing but transformer and this transformer provides isolation between the primary and secondary winding. In other words, there is no current path between the two sides. The primary side has 240V and a ground - an equipment ground. The secondary side, the welding side, has no connection to anything other than what the work clamp, sometimes called a ground, and the electrode - the transformer isolates the primary from the secondary side. If you leave the work clamp disconnected and touch the electrode to earth ground, there will be no current flow. You cannot strike an arc.
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Old 09-06-2010, 06:00 PM   #34
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grounding the workpiece you're welding


Some really nice windings you drew there a7ecorsair ...

Ok here is my issue and maybe some one can clear it up for me. Current wants to return to its source so it does that over the electrode lead thru the workpiece to the work lead then back to the welder (source). If I ground the workpiece or metal work table to lets say building steel which could be part of the grounding system of the premise wiring. If the work lead clamp would for some reason come off the work piece would I not have another path to the source and thereby energizing building steel and egc's so on and so forth?? Would not the welder possibly continue the arc even if the welding clamp was disconnected?
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Old 09-06-2010, 08:26 PM   #35
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grounding the workpiece you're welding


With the work clamp disconnected and not touching anything there is no current path on the secondary side at all. The winding insulation electrically separates the primary side and the secondary side so there is no way the current can go any where.
Since it is a transformer the only difference between the two secondary poles, the work clamp and electrode holder, is the polarity of instantaneous voltage. With the welder on and neither the clamp nor the electrode touching anything it will have an open circuit voltage of maybe 30 volts but no current flow. I can then connect the work clamp to anything or the electrode to anything but not both or I will start welding.
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Old 09-06-2010, 11:17 PM   #36
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grounding the workpiece you're welding


I'm not sure if that would be correct. In a warehouse building steel is almost always part of the grounding electrode system of the premise wiring and grounded to the utility neutral. If the work lead clamp came off the work piece it would open the welding circuit to the welder then current would flow to the welder power source.. the welder transformer.. over the separate ground.... Just like a ground fault. If you would ground the work lead , metal work table or work itself to building steel or some other low impedance path you could open the breaker protecting the welding circuit immediately on loss of the work clamp connection.

The other benefit I see is maintaining voltage potential with other grounded objects like the metal work table. In the event you had some kind of failure in the welder this would limit the voltage between the work piece and ground.

Now if I don't have the work piece grounded and the work clamp comes off the work piece the breaker will not open and an open circuit will exist with a 'hot electrode' at open circuit voltage which is a bit higher than when you are actually welding. If I don't turn the power supply off at the welder and grab the work clamp and somehow manage to touch the electrode also or a bare area on the welding cable to the electrode stinger then it would be possible everything being right to complete the welding circuit and get zapped.

I only think this way because you have to determine why the ansi standard in safety requires this separate ground lead. So this is what I have to think is going on ... whether it is right or wrong is still possibly a mystery at this point.
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Old 09-07-2010, 01:02 AM   #37
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grounding the workpiece you're welding


OK just before calling it a night I found this in the miller weld technical library so lets see if we can sort this out later ... time to call it a day

1. The Power Source and Primary Power Line
Grounding the Equipment
Welders must be concerned at all times about the possibility of electrical shock. Wet working conditions must be avoided, because water is an excellent conductor and electricity will always follow the path of least resistance. Even a person's perspiration can lower the body's resistance to electrical shock. Standing on a dry rubber mat or, when welding outdoors, standing on a dry board is always advisable. Poor connections and bare spots on cables further increase the possibility of electrical shock, and therefore, daily inspection of these items is also recommended.
Aside from these more obvious shock hazards, equipment operators should routinely inspect for proper ground connections. A proper ground connection is always necessary because it provides a safety connection from a welding machine frame to the earth. Connections typically used for grounding an engine-driven welding machine include a cable connected from a ground stud on the welding machine to a metal stake placed in the ground.
The workpiece being welded and the frame or chassis of all electrically powered machines must be connected to a good electrical ground. This can be accomplished by connecting it to a properly grounded building frame or other appropriate ground. Chains, wire ropes, cranes, hoists and elevators must never be used as grounding connectors.
The work lead is not the grounding lead. The work lead connects the work terminal on the power source to the workpiece. A separate lead is required to ground the workpiece or power source.
When arc welding equipment is properly grounded according to the National Electrical Code, and to ANSI Z49.1 "Safety in Welding and Cutting" standards, a voltage may safely exist between the electrode and any conducting object. Examples of conducting objects include buildings, power tools, work benches, welding power source cases and workpieces. Never touch the electrode and any metal object unless the welding power source is off.
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Old 09-07-2010, 08:57 AM   #38
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grounding the workpiece you're welding


Quote:
Originally Posted by Stubbie View Post
If the work lead clamp came off the work piece it would open the welding circuit to the welder then current would flow to the welder power source.. the welder transformer.. over the separate ground....
Look back at my sketch and note that the work clamp is not connected to the welder frame nor the EGC. Therefore, there is no path for current flow on the secondary side unless both the work clamp and electrode complete the circuit. And, unless the insulation in the transform windings has failed, there is no path to the primary side.

Quote:
Just like a ground fault. If you would ground the work lead , metal work table or work itself to building steel or some other low impedance path you could open the breaker protecting the welding circuit immediately on loss of the work clamp connection.
Nope, loose the work clamp and it just stops welding.
FYI - A welder is really an impedance matching transformer. The primary being high impedance and the secondary low impedance. This will actually support a short circuit on the secondary side without tripping the breaker.
I can weld a car frame with the car sitting on its rubber tires and I'm sure you're heard about welding underwater... Have you heard of someone using a welder to thaw a frozen pipe?

Quote:
The other benefit I see is maintaining voltage potential with other grounded objects like the metal work table. In the event you had some kind of failure in the welder this would limit the voltage between the work piece and ground.
Yes, the work piece can be "grounded" but think about this:
Would welding current flow to the EGC? No, the current has to return to the same place it originated - the secondary winding.
Quote:
Now if I don't have the work piece grounded and the work clamp comes off the work piece the breaker will not open and an open circuit will exist with a 'hot electrode' at open circuit voltage which is a bit higher than when you are actually welding.
Yes, you will have open circuit voltage between the electrode and the work clamp but there is no open circuit voltage between the EGC and and the electrode.
Quote:
If I don't turn the power supply off at the welder and grab the work clamp and somehow manage to touch the electrode also or a bare area on the welding cable to the electrode stinger then it would be possible everything being right to complete the welding circuit and get zapped.
Yup, you could based on the open circuit voltage of the secondary.

Update:
I just did some testing with my Lincoln 225 AC welder.
Open circuit on the secondary is 83 volts AC. Electrode to EGC with work clamp isolated is 2 VAC - maybe some stray AC
With the welder on and the work clamp isolated, the electrode can be touched to any grounded metal with out any current flow or sparks.

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Old 09-07-2010, 01:07 PM   #39
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grounding the workpiece you're welding


Ok I'm getting closer to understanding... like everything your new to sometimes it takes a while to digest thru all the different opinions. But I tend to agree with you. It appears the major benefit is maintaining close to equal voltage potentials around the work area.

Let me show you the comment I found from an experienced electrician that that just had me thinking otherwise.

Quote:
We need some clarification and interpreation on this conflict:
NEC NFPA 70 Article 630-15: "Objectionble current in welding output circuit"

ANSI Z49.1
11.3.2 The Work. The work piece or metal upon which the welder welds shall be grounded independent of the welding leads to a good electrical ground., unless a qualified person assures it is safe to work on ungrounded work piece.

Miller O&M manual Section 8 (OMB-356) recommends to connect the work piece to a building to address AC High Frequency.

Grounding and Arc Welding Safety:
Grounding the workpiece has similar benefit to grounding the welding machine enclosure. When the workpiece is grounded, it is at the same potential as other grounded objects in the area. In the event of insulation failure in the arc welding machine or other equipment, the voltage between the workpiece and ground will be limited.

Question:
If we follow the code and removed the ground wire connection between table and building ground and totally isolate weld table, how do you address difference in potential and AC high frequency that needs to dissipate to ground and can sometimes cause electric shock
Answer

Quote:
The problem whit all this, is many don't understand that current only wants to return to source, each time you have installed a transformer in a system, it creates a new source, even a welder is a source, and the current it provides will try to return to it.

I have worked in many weld shops as an electrician, and I have seen the results of bonding the work piece to the building independent of the weld leads. the HF AC used in some types of welders only returns to the source that created it, the welder supply.
The problem with bonding the work piece to the building or the building grounding system, is the two paths that the welding current can take, if the welder lead connection to the work piece is lost for any reason (and it happens all the time), then all the current will try to return to the welder power supply via the building through the grounding system or the EGC's of the electrical system (which can have disastrous consequences).

There are two ways to stop this from happening, one is to bond the work lead to the building at the welder power supply, then the bonding of the work piece to the building that is close to the welder power unit will provide a low impedance path back to the welder power supply in the event of a loss of a connection of the work lead.

even with this arrangement, I have seen 600-1200 amp welding blow bolts apart on the building frame, melt stiffener cables that hold the building square.

so we went to just bonding the work lead to the building at the power supply, and not using any other parallel connection, we lowered the connection loss rate of the work lead to the work, by lugging and bolting the work lead to a waste plate that is welded to the work each time, then cut off after the welding is done.
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Old 09-07-2010, 08:24 PM   #40
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grounding the workpiece you're welding


There are some good points in this but there are a few that are questionable. I'm sure the welding manufactures have to point out any possible circumstance so the lawyers don't get a hold of something in a law suit.
This is by far the most accurate comment:
Quote:
Grounding and Arc Welding Safety:
Grounding the workpiece has similar benefit to grounding the welding machine enclosure. When the workpiece is grounded, it is at the same potential as other grounded objects in the area. In the event of insulation failure in the arc welding machine or other equipment, the voltage between the workpiece and ground will be limited.
This too is accurate. The welder secondary is the new source and is isolated from the primary.
Quote:
The problem whit all this, is many don't understand that current only wants to return to source, each time you have installed a transformer in a system, it creates a new source, even a welder is a source, and the current it provides will try to return to it.
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Old 09-07-2010, 09:36 PM   #41
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grounding the workpiece you're welding


Yeah I agree with that . Anyway I learned something that I didn't know and that is always a plus.
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Old 09-08-2010, 07:33 AM   #42
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grounding the workpiece you're welding


Quote:
Originally Posted by a7ecorsair View Post
FYI - A welder is really an impedance matching transformer. The primary being high impedance and the secondary low impedance. This will actually support a short circuit on the secondary side without tripping the breaker..
The load on an arc welding circuit is the arc itself and is of a very low resistance or impedance. If you accidentally touch the electrode to the work, the arc extinguishes and you get a dead short. Either the impedance of the secondary itself is high enough that even a dead short won't draw enough secondary circuit current to overheat it (impedance protected), or a low enough load resistance will cause enough current to flow in the primary to trip the breaker.

If the work clamp comes off the work piece then the current flow stops unless there is a fault in the secondary winding or other part of the secondary circuit. Now if the work clamp falls and lands on metal structure such as a catwalk and also the work piece is grounded, then the secondary circuit could be completed again. The welding current from the work clamp could possibly travel far and wide to get back to the work piece via a workpiece grounding cable and clamp and restrike the arc and return up into the hand held electrode.

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