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Circuit Breaker issue Miller Bobcat 225NT

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  • Circuit Breaker issue Miller Bobcat 225NT

    The Solid State Ignition Module on my BlueStar 2E isn't putting out enough spark to run anymore so the Bobcat 225 NT sitting in the shop has been put into service. After actually using the NEWER welder in the field, I'm wondering why I didn't change it out sooner.

    Here is the use and conditions I had issues with the circuit break breaker on the 120V POWER outlet. Service Rig setup over well in feed yard. Ambient Temperature above 95 degrees F. Using 12/3 25' extension cord while running Bosch 1492 Hot Air Heat Gun. I was making my wire splice attaching my Submersible Pump Drop Cable to the motor lead of the pump I was preparing to set. 4 pieces of heavy duty 3M heat shrink. This gun can make 1000 degree hot air pulling 14.5Amps. When using on the BlueStar2E, it could stall out the generator on startup. It pulled pretty heavy. On the Bobcat225NT, I was able to get it going without to any issue. HOWEVER, as I was nearing completion of making the splice, still shrinking my heat shrink, the hot air gun cut out, NO POWER. The 20A Breaker on the power receptacle had tripped. I swapped the cord to the secondary plug, restarted my heat gun and finished my splice.

    After doing a search through Allied Electronics, I found the type and style of Circuit Breaker that is installed on the Bobcat. Turns out that at Ambient Temperatures above 73.5 Degrees F, the circuit breaker, a THERMAL OVERLOAD style, is DERATED. at 95 degrees and with a 14.5A load, it will trip out. Now I am looking at REPLACING the 20A breaker with either a 25A or 30A breaker to reduce or stop the nuisance tripping in High Temperatures in the field.

    This unit is old enough, it has standard duplex 20A receptacles in the panel. I have had the panel off before to replace the aluminum rivets from Miller with BRASS SCREWS, WASHERS, AND NUTS to ensure tight bonded connection to the frame of the unit. My other option is to modify the unit and install PLUG TYPE DUAL ELEMENT TIME DELAY FUSES on the power outlets.

    This situation reminds me of the NEC Chart for FUSES and CIRCUIT BREAKERS in my Franklin Electric Application and Installation Manual. Fast Blow fuses and Circuit Breakers had to have a HIGHER AMP RATING than DUAL ELEMENT TIME DELAY fuses because of the INRUSH CURRENT at STARTUP on the motor. For 0.6 seconds, in a Single Phase 230V motor and control, the START CURRENT is 3X the normal running current. For a motor pulling 10A, the start current is 30A for that 0.6 seconds at startup. That BLOWS 30A NON fuses and trips 30A Breakers. BUT, a 20A Dual Element Time Delay fuse will work on the 10A load of the motor.

    I have basically solved my particular problem through the analysis of the problem and sizing of breakers and fuses from the NEC Chart in my Motor Application book...To ensure no further nuisance tripping of the power circuit on the generator of my welder, I will need to install the 30A Breaker so I don't have to DERATE the output on a HOT SUMMER DAY in West Texas while making my motor splice with my heat gun.
    '77 Miller Bluestar 2E on current service truck
    '99 Miller Bobcat 225NT for New Service Truck
    '85 Millermatic 200 in Shop

    '72 Marquete 295 AC cracker box in Shop
    '07 Hypertherm Powermax 1000 G3 Plasma Cutter in Shop
    Miller Elite and Digital Elite Hoods

  • #2
    Just make the circuit a 30amp deal with 10g wires and then you'll not have to worry about the wiring either.
    Ed Conley
    http://www.screamingbroccoli.net/
    MM252
    MM211
    Passport Plus w/Spool Gun
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    Miller 125c Plasma 120v
    O/A set
    SO 2020 Bender
    You can call me Bacchus

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