HF interference and grounding

[dutchman]

I’ve been reading the manual for my new 2nd hand tig welder and it states the following:

Electrical conductors within 50 ft (15.2m) of the
welder should be enclosed in grounded rigid metallic
conduit or equivalent shielding, wherever possible.
Flexible metallic conduit is generally not suitable.

This is to reduce HF interference.
I have a large metal cupboard (6 foot high) located 1m away from the workbench. Does this mean I need to ground it with a non-flexible bar? I dont't see why a cable wouldn't do it.

Is HF interference really a big problem, also when welding 1.5mm steel (at low amperage)?

 

[rtbcomp]

I think it's saying the shielding should be rigid and not flexible - the actual bonding to ground only has to conduct electrcity so a bit of cable should be fine.

Unless you've got sensitive elctronic equipment in the cupboard I don't see why it needs to be grounded.

 

[Robotstar5]

Slightly off the thread but will HF affect heart pacemakers?, at work we have HF spot welding equipment and it has a warning label about pacemakers.

 

[rtbcomp]

I think the answer is in the question! Really the only person who can answer that is an expert in the field.

 

[snowcat]

About 10 years ago a friend of mine was working on an MOD site, The MOD were haveing problems with some of there ground radars and guidance systems, convinced it was activty from a hostile source they sent out some of there top bods with huge backpacks and ariels to try and triangulate the source of the signal, problem was everytime they got near everything would go back to normal, After 3 days they finaly infultrated the hostile source, My mate Tiging up some pipes for them...

 

[malcolm]

I've got an old Miller Syncrowave with HF (generated the old way with spark gaps). The manual says much the same about HF interference. I didn't take any special measures and things seem to be OK. I have a computer in the garage about 8m from the TIG and it's not broken, though it's probably not been switched on while I've been welding.

 

[matt1978]

HF (High Frequency voltage) is an air borne contaminant and can effect some sensitive electrical equipment. In most workshop scenarios it doesn't make any difference at all apart from sometimes your radio will make a funny noise as if its not tuned in.

In environments that use a lot of equipment and computers and telephones such as Hospitals, usually forbid the use of any welders using HF.

On normal DC tig welding there is generally not a problem as HF is only used to ignite the arc, once this is done the HF is no longer used. However on most AC welders, especially old ones, definitely the ones from China and a fair few European Inverters (Not Lorch ) HF is used all the time when welding on AC mode. This is because the machine cannot switch from positive to negative quick enough and the arc wants to extinguish at the zero point. A HF overlay is used to keep the arc going when it passes from positive to Negative and thru the zero point.

Good quality inverters switch the arc so fast that the arc doesn't get chance to go out at the zero point and therefore Aluminium can be welded without the need for any HF, and could be used on Lift arc mode in any sensitive environments

Lorch use up to 14,000 volts on their HF to help guarantee perfect ignition, but the downside is you can't afford to use cheap torches where the insulation is not great as it can get back into the welding machine via the Dinze sockets.

 

[dutchman]

Thanks for the info about HF and the shielding, very useful. I don't know why, but my Lincoln invertec seems to have HF switched on all the time when in Tig mode (dc only machine).


I also have another question, about the earth ground.

The manual states:
The work piece must be connected to an earth
ground close to the work clamp, using one of the
following methods:

a) A metal underground water pipe in direct contact
with the earth for ten feet or more.
b) A 3/4” (19mm) galvanized pipe or a 5/8” (16mm)
solid galvanized iron, steel or copper rod driven
at least eight feet into the ground.
The ground should be securely made and the grounding
cable should be as short as possible using cable
of the same size as the work cable, or larger.
Grounding to the building frame electrical conduit or a
long pipe system can result in re-radiation, effectively
making these members radiating antennas.


As I understand this text, the work clamp must be in direct connection with the earth ground. This would mean that the clamp is not connected to the machine, sounds rather strange…
Or does it mean that an extra connection should be made from the earth ground to the work piece?
Can anyone help me out on this??

 

[irondarren]

The IFL fusion AC/DC unit has a AC noise reduction circuit, not sure if they mean actual noise in terms of decibels or noise as in terms of interference. I guess its all due to the electromagnetic pulse created by the spark, but i have been told it doesnt do mobile phones much good.

 

[matt1978]

The IFL fusion AC/DC unit has a AC noise reduction circuit, not sure if they mean actual noise in terms of decibels or noise as in terms of interference. I guess its all due to the electromagnetic pulse created by the spark, but i have been told it doesnt do mobile phones much good.

AC Noise reduction will mean the DB Level.

Welding machine manufacturers and Welding distributors are supposed to tell you to wear ear protection when welding Aluminium over a certain amperage (150 Amps I think) as when welding above this, the noise exceeds the safe level (80 DB, again I think) and ear protection should be worn.

I think that there will be quite a few lawsuits in the future because of this. Its a loophole in the law where joe public can sue, for not using common sense, such is most of the case with this where there's blame theres a claim culture.

 

[irondarren]

Matt where are those photos of the welding on the s3 you were going to share with the forum?

 

[dutchman]

The work piece must be connected to an earth
ground close to the work clamp

After reading the sentence over and over it seems to me that the second interpretation is better (the extra connection), but am not sure…

Just shoot if you have any ideas.

 

[matt1978]

Matt where are those photos of the welding on the s3 you were going to share with the forum?

Sorry mate,

I was hectic last week, should have a little spare time this week, I will do them then. I got some 6mm CrNi and 3mm Alu blanks for samples coming in on Monday.

 

[matt1978]

The work piece must be connected to an earth
ground close to the work clamp

After reading the sentence over and over it seems to me that the second interpretation is better (the extra connection), but am not sure…

Just shoot if you have any ideas.

Some old school machines had a separate return for the HF, is was a thin piece of wire (about 3mm) with a Crocodile clip on the end, this was used as well as the main welding return lead.

Modern welders only use the Welding return cable (Earth socket), so as long as thats connected to the work piece that you want to weld then you should be fine.

 

[Drains]

Dutchman, the advice re grounding is generic, and applies in theory to all welding sets:- in case the earth lead becomes detached from the machine, but you're standing in a puddle (or otherwise making a good contact), you will end up being the earth. Zap. If you have an extra ground earth, you will be safe.

It is sound advice, but generally ignored (by me too). Lincoln are fulfilling their obligations by telling you how it should be done.

 

[rtbcomp]

.....applies in theory to all welding sets:- in case the earth lead becomes detached from the machine, but you're standing in a puddle (or otherwise making a good contact), you will end up being the earth. Zap. If you have an extra ground earth, you will be safe.

That would only apply if the welding return is connected to ground in the welding unit.

 

[Drains]

That would only apply if the welding return is connected to ground in the welding unit.

Which it is, isn't it? (I'm happy to be wrong btw)

 

[rtbcomp]

Which it is, isn't it? (I'm happy to be wrong btw)

Doubt it - if you were welding something that was earthed and the welding return (aka earth) came disconnected (e.g. the clamp slips off) then the welding current would try to go down the earth cable of the mains lead, and take the ring main out as well.

Also you can't have the earth connected to either of the terminals on a gas/gasless MIG because you have to swap polarity depending on the wire type you're using.

 

[snowcat]

As I understand a poor work return and a damp enviroment can cause the return through you, It is listed as a protential hazard in My AWS book, The FOS book and BOCs Safety pack.

 

[rtbcomp]

As I understand a poor work return and a damp enviroment can cause the return through you, It is listed as a protential hazard in My AWS book, The FOS book and BOCs Safety pack.

Although the welding voltage is low, I guess there could be high voltage spikes which could give you a shock, but these would be between the torch and return. If the return is connected to earth, either directly or through dampness, your feet are connected likewise and the torch is connected to your hand by dampness, dirty torch, no gloves etc. you could get a shock. That would be another argument for keeping earth (ground) and return seperate, standing on a dry surface and keeping torch and gloves in good condition.