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Thread: Miller Shopmaster 300 Wiring help

  1. #1
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    Miller Shopmaster 300 Wiring help

    New to forum, but not new to welding (over 10 years experience.) I just purchased a miller shopmaster 300 that has been completely rebuilt. I just need to know what breaker is needed to run in the electrical panel and also what type of disconnect I will need? I will be hooking it up directly to the disconnect as I will not have to move it around my shop it will stay in one place. It is set up to run on 220v. Any help is appreciated.
    Manual for the welder based on serial number below.
    https://www.millerwelds.com/files/ow.../O318A_MIL.pdf

  2. #2
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    Re: Miller Shopmaster 300 Wiring help

    From the manual you posted. Looks like it requires a 125amp CB/Fuse.


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  3. #3
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    Re: Miller Shopmaster 300 Wiring help

    ok, what about a quick disconnect? non fused or something like a time delayed fuse and what size? Manual doesn't state what kind.

  4. #4
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    Re: Miller Shopmaster 300 Wiring help

    2-9. Electrical Service Guide
    60 Hz 50 Hz
    Input Voltage 200 230 460 575 220 380 415
    Input Amperes At Rated Output 105 91.2 45.6 36.4 88.2 51 46.8
    Max Recommended Standard Fuse Or Circuit
    Breaker Rating In Amperes 150 125 70 50 125 80 70
    Min Input Conductor Size In AWG/Kcmil 4 6 8 10 6 8 8
    Max Recommended Input Conductor Length In
    Feet (Meters) [116 (35)][103 (31)][271(83)][284(87)][99(30)][194(59)][232 (71)]
    Min Grounding Conductor Size In AWG/Kcmil 6 ,6, 8, 10, 6, 8. 8
    Reference: 1996 National Electrical Code (NEC). S-0092J

    Grid didn't copy well from the service manual But it calls for a 125 amp standard fuse or circuit breaker. This allows operation to 300 amps. You can get away with a smaller service if you stay below 200 amps of welding current.

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