I am building a fab/welding table. This table will have a swing arm
lamp in one of the back corners of the table. The lamp fixture is an
old one off of a machine w/ steel ball/socket design for the pivots.
If I add a ground lead to the lamp asm (by default also ground the
welding table), will welding interfere w/ the GFI outlet that I will
be plugging the lamp into? Welding (curently, can't justify a TIG) is
via A/C bussbox and 110v MIG (also plugged into the GFI outlet).
The same happens to me. Of the four separate GFI circuits in my shop, one
trips only when I TIG. The other three almost never trip with use of any
tool or the similar lamp that I have mounted to my welding bench.
GFI (and security lights) are susceptible to the HF used with TIG.
It helps to eliminate any ground loops. In particular, have the workpiece
grounded to the welder -- and no other ground connection. In the case of a
metal welding table, if that is grounded to the welder then try NOT to have
any other ground connection, as thru the frame of the lamp clamped to the
table to the gnd of the GFI. OK to ground the lamp thru it's 3-wire plug,
but insulate it from the metal welding table. Connect the welder's ground
as near as possible to the welding site.
I have no problem with GFI's or security lights, even with TIG. (Miller
Ditto for the VFD (Variable Frequency Drive; synthesizes
variable frequency 3-phase from 230v single phase) on
my Delta wood-turning lathe. Pops GFCI every time.
Delta sells a ferrite donut with the leads wrapped
around it that is supposed to fix this, but it didn't
help with my situation. I plan to (but haven't yet)
try increasing the number of wraps to see if it will
work. My guess is that the power supply draws some
kind of spike when starting up that trips the GFCI.
Or maybe there is some kind of capacitive coupling
between one side of the hot leads and ground. The
ferrite donut should reduce any differential-mode
spike between the hot leads (which is what a GFCI
is supposed to detect).
"Peter W. Meek"
That GFCI receptacle has a balanced current transformer inside that
is VERY sensitive - If it thinks that there's more than a 3 Milli-amp
leakage to ground (power going out on the hot wire that is not coming
back on the white wire) it trips.
Problem is, when you are welding and the light is close, or shares a
common ground through the inverter-fed equipment chassis or the
welding table, you get induced currents in the light cord that can
fool the GFCI into thinking there's a problem when there really isn't.
If it likes to trip out on you, either cheat and run a cord from a
non-GFCI outlet, or put one in dedicated for that purpose.
You could also build a transformer-isolated work light - get a
Malibu Light transformer to make some 12 VAC, and then use any
landscaping light fixture to make your work light. You can easily go
from 10W up to 75W with an MR-16 prefocused reflector lamp, and you
can have your choice of beam spreads with a half-dozen steps between
Very Narrow Spot to Very Wide Flood.
Oh, and if you have a refrigerator or freezer in the garage, make
sure it is on a dedicated appliance circuit that you have installed
for the task - NOT on the GFCI-protected garage receptacle circuit
like the current codes call for. You do NOT want to come home from a
2-week vacation to find that GFCI tripped and the freezer thawed out,
and a biology experiment is going on inside...
Do you have the donut next to the VFD or next to the power plug ?
The antenna is at the VFD and the donut shortens the effective length.
Might just move it around and see what happens.
Peter W. Meek wrote:
Good point. I put the donut in a box with a
power cord and a receptacle. I plugged the
full length of the lathe's power cord into
the receptacle (so as to not modify the lathe).
I will try moving the donut closer to the VFD.
"Peter W. Meek"
Building a new house with a shop at:
Ground Fault Interrupter. They function by measuring the current on
the hot and neutral wires. If the currents differ by greater than a set
amount (typically 3 mA), they trip open the circuit. The assumption being
that the current difference is due to a fault (short) to ground.