Working in a Mobile Home Factory, the M/C in the house traveling down the line has to be open due to testing, I installed from the load center power boxes down the line with 20 amps GFCI with a 5 miliamp protection, would this be enough to keep our employees working around the m.c from the required PPE?

M/C = Metal Clad or something else?

Arc Flash is not current restricted, its voltage restricted. You'd have to give more specifics for a good analysis. What safety precautions other than the GFI are being used, ie, caution tape, barriers, employee training, etc. Can you set up a test transformer and test at 24VAC instead of 120/240?

The m/c is meter center. To hook up a house on line, we drop a pig tail or extension cord from the meter box using a DP 20 amp GFCI breaker. The breaker trips at very little resistance.

A GFCI trips on an imbalance on the line and netrual, has nothing to do with arc flash protection or reduction.

I would look for a different method of testing. Can you not use 48VAC or some other low voltage 24VAC, 'This would be under 50V and out of arc flash range.