High Freq

Date 02-05-2006 13:29

I teach welding in a community college. My question concerns our TIG stations.I currently have 6 stations, all side by side. We hook the weld ground clamps low on the leg of the table to keep it out of the way. The tables themselves are not connected to an earth ground. As you know you can get shocked occasionally when welding AC with continous high frequency. I want to ground my tables to prevent shock from high frequency electricity without causing more problems. Can I hook all 6 tables to a common earth ground without problem or do they need to be individually grounded? In my weld lab. I may have students welding side by side with one welding AC and the next welding DCEN. I dont want current from one welder flowing through the next station and into that welder and causing more problems.
I suspect that all machines should have a seperate earth ground but would like some opinions.
Thank You

By Lawrence (*****)

Date 02-07-2006 21:45

I was hoping you would have gotten a responce by now.

I think you might be interested in ANSI Z49.1 2005 Section 11 and more specifically E11.3.6.3
Free PDF of the standard: http://www.aws.org/pr/jun17-2005.html
My understanding is that the greatest danger occurs when electrode holders of different polarities or AC come into contact when they are working on the same structure (which I think you would effectivly have if you grounded your workstations in a group)

The superimposed High frequency used in AC GTAW is no threat unless you have a pacemaker. The little blue arc is of such low amperage that the effect is negligable unless the open circuit voltage tries to follow it through you to complete the circuit.

I'm following your thread because I have thought about individually grounding my work stations in hopes of decreasing the occurance of arc-blow in SMAW. My shop is quite small with no choice but to stack power supplies in a circle, so there are plenty of EMF's to cause the arc blow. We have tried all the usual techniques (wrapping/moving the work clamp etc.) but sometimes we have to put the E6010 away and use AC and E6011 because the arc-blow just won't abate.

By aevald

Date 02-07-2006 22:37

Hello Lawrence, I too have been following this thread to see what some of the opinions are concerning the grounding issue as it is described here. In my facility we have 24 arc welding stations with all of the tables and booth structures built as one unit out of angle iron framework(thus they are essentially commonly grounded). We are using 2 Miller 8-paks and 8 XMT 304 multi-process power sources for welding machines. I also double in on some of the booths with LN-25's to do some innershield welding at times and also have about 6 other booths with access to CP 302's and SA22 feeders. Originally all of the arc welding power sources were commonly grounded to the booths(we use no earth ground rods in any of the booths, the only grounding to the machines is through the earth ground in the power panel, thus all of the machines are commonly grounded in a sense). After experiencing different levels of arc blow for a long time I finally went ahead and disconnected the common ground from the power sources and ran individual ground leads from all of the welding power sources and also the individual power modules in the 8-Pak to their own respective booths(in a sense they are still commonly grounded through the framework,however, they also have ground clamps that can be located relative to the welding that is going on), this made a drastic improvement in arc blow problems, however, it didn't solve the problem completely. I still find that on any given day it seems, depending on where students are welding and possibly what process they are running that there is still a certain amount of arc blow to contend with, having a good clean tight ground, welding away from the ground whenever possible and all of the other rules of thumb that apply to arc blow, still apply. I will be interested to see what else comes out of this thread. I also have 6 dedicated tig stations, however, they are only tied together by the panel earth ground that is part of the input power and have not experienced any odd sorts of shock issues or doubling up of current. Best regards, aevald

By dringge (*)

Date 02-12-2006 01:45

I was hoping this would generate a bit more input. Both replies are excellent. While the superimposed high frequency causes me no real problems I find it annoying to get a bit of a shock once in a while. I have seen articles and diagrams showing the importance of proper earth grounding to prevent problems. I have been trying to find one in particular to reference here but havent found it again.
One of the things that has come out of this is the common problem of arc blow in the weld lab. I can confess to having problems from time to time with arc blow. I have tried several fixes with limited success. I have 35 welders and 3 plasma cutters. We can generate plenty of magnetic fields. All stations are simply grounded through the machine ground, except for the cnc plasma which does have an earth ground.