[AT] Wire size for welder?? Help welder people!

[Dean VP]

Greg:


Your suggestion of wire size IMHO is pushing the limits of common sense.
Unless one knows that John is going to be normally welding at less than
maximum output all of the time, #10 gauge wire is inadequate for the job and
will eventually or almost immediately cause some problems. The 25' run comes
into play here heavily. We also don't know the incoming wiring size to the
breaker or the rating of the overall supply. Just too many unknowns require
one to select higher than may be minimally required. The cable getting warm
is just a small part of the problem. What will affect performance of the
welder is voltage drop. Now if the nominal 220v supply is already low then
additional voltage drop in the 25' cable, breaker and connections will even
be more noticeable. 

As an old and now obsolete EE and one who designed many electronics circuits
and products in the early years of his career including power supplies, it
is very important for long term reliability and safety, to over design a
bit. When one worst case tolerances circuits and allows all worst case
variables to happen at once it is amazing what the real circuit requirements
are. For example if a resistor has to nominally dissipate 50 Watts. Design
in a 100 watt resistor. Safety is always the primary concern and then long
term reliability. It is never wise to skimp on wire size when hooking up to
a welder which costs 10 to 20 times what the wire costs not considering what
the building it is in costs. 

Let me provide an example, I personally experienced, what the cost is of an
under designed electrical circuit could be.  This is in the mid 60's. I was
sent to Lockheed Martin Marietta, GA to help get customer acceptance of a
$7,000,000 Hybrid Computer facility that my company had sold and installed.
I had been responsible for a portion of the design but not the total system
design. 

Upon entering the computing facility late one evening when the computing lab
was vacant, all 4 analog computers and one digital computer were running but
not being used, I noticed an unusual smell.  To this day I remember the
smell and I said to my escort:  "I smell Allen Bradley".  The smell of a
Carbon resistor over heating is very unique!  There was row after row on
large 6' tall cabinets all filled with electronic equipment. It was an air
conditioned room and the smell seemed like it was everywhere. We frantically
opened door after door trying to find the location of the source of the
smell. Eventually, I opened one door and flame shot out over 4' high.
Fortunately we were able to contain the damage to one cabinet. 

I spent another 3 1/2 weeks getting the system repaired and accepted but we
really wanted to know why this had happened. Upon returning to the lab at
the home office we did a detailed design analysis of the purchased
commercial power supply that had been the cause of the fire. After much
analysis we determined that one underrated resistor in the design was being
overstressed and the body of the resistor had been mounted in contact with
the Printed Circuit Board. The resistor had gotten so hot that it lit the
PCB on fire. This was in the days when fire resistant PCB's were not
commonly used like they are today. But here was the case where the circuit
had not been properly worst case designed. A lousy $0.50 or $2.00 resistor
could wipe out a $7,000,000 facility along with a potential hazard to human
life. I have never forgotten that lesson. 

I am probably known as being very frugal on this list but when it comes to
this kind of stuff, I will spend money freely to avoid endangering
facilities and humans. In this area it does not pay to try to "just get by"!

BTW, all of these Power Supplies were immediately replaced in all installed
systems. Ok, rant over!  :-)


Dean A. Van Peursem
Snohomish, WA 98290

I'm a walking storeroom of facts..... I've just lost the key to the
storeroom door 


www.deerelegacy.com

http://members.cox.net/classicweb/email.htm



-----Original Message-----
From: at-bounces at lists.antique-tractor.com
[mailto:at-bounces at lists.antique-tractor.com] On Behalf Of Greg Hass
Sent: Tuesday, December 07, 2004 9:00 PM
To: Antique tractor email discussion group
Subject: Re: [AT] Wire size for welder?? Help welder people!

John:

At the risk of being arrested by the "correct police", I will give what I 
consider to be a "common sense" approach.
First of all, that amperage rating is only at the very top end of the usage 
scale.  I have a 150-amp wire welder and a 250-amp AC/DC stick welder.  I 
have been running both of them on a no.10 wire since I built the shop 10 
years ago, and have never had a problem with the wires getting warm, 
although I did use a 50-amp breaker (on the advice of a licensed 
electrician) to take care of the sudden amperage jolt when striking an 
arc.  A big thing in my favor, however, is that my biggest run is 25 feet 
from breaker box to welder.  If you are already wired for a welder, I would 
say go ahead and try it because if you are properly fused the worst that 
could happen is that you would trip a breaker or blow a fuse.  I would 
guess that most of the welding jobs you would do would draw less than 30 
amps anyhow.  If you want to be correct, I would go with a no. 6 copper or 
no. 4 aluminum entrance cable or Romex, whichever it's called in your 
area.  (Aluminum must always be one size bigger than copper to carry the 
same amperage.)  No. 8 copper would be sufficient for 45 amps, however in 
our area it is next to impossible to find and costs more than no.6, which 
is why I recommended going with the heavier cable.  Just an opinion.

Greg Hass

_______________________________________________
AT mailing list
http://www.antique-tractor.com/mailman/listinfo/at