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Old 12-03-2014, 06:23 AM   #21
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While I have never done it, it would seem to me that with a 50 and a 100 amp breaker, both would trip around 110 amps. With parallel circuits of equal wire gauge size, the current would flow equally over each conductor (path of least resistance). When the 50 amp breaker saw 55 amps +/-, it would trip sheading its load to the 100 amp breaker which would now trip with a 110 amp load.

Ted
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Old 12-03-2014, 08:15 AM   #22
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Our Warn DC1200 hoist lists max draw at 100 amps and 1200 lbf. It is part of a davit system, not the factory boom and mast from Krogen. Does your lifting system have 2 winches?
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Old 12-03-2014, 09:14 AM   #23
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Per NEC 240.8: "Fuses and circuit breakers shall be permitted to be connected in parallel where they are factory assembled in parallel and listed as a unit. Individual fuses, circuit breakers, or combinations thereof shall not otherwise be connected in parallel."
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Old 12-03-2014, 11:08 AM   #24
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Yes Larry, it has two winches. I only operate one at a time. These are the "Rule" winches.


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Old 12-03-2014, 11:35 AM   #25
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Quote:
Originally Posted by High Wire View Post
We use series breakers in a nuclear power plant for motor loads that penetrate primary containment. One breaker is setup specifically to protect the motor. Because its a motor, there are design conditions that must be met and verified through periodic testing. The other breaker is sized specifically to prevent damage to the primary containment penetration and has completely different design and testing requirements. Neither breaker alone can meet both sets of requirements and both must operate independantly. Other than that, I can honestly say that in 40+ years in the electrical field, I've never seen 2 breakers used for one load that werent mechanically ganged together to trip at the same time until this post. Me thinks the installer was more of a mechanical guy.
Wow! Archie you sure brought back memories of an earlier life for me....countless hours sitting in front of an old SR76 or EPOCH test set shooting penetration breakers during refueling outages! Nice to know there are a few old power nukes still afloat.
Back OP's subject...I agree this was probably something configured by a "boatyard electrical expert", and lacks basis in both theory and application....Replace the two breakers with one that is properly sized for the load.
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Old 12-03-2014, 12:35 PM   #26
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Thanks all! I will go ahead and replace that breaker combination, but will wait until I replace the winches as the new ones may have a different requirement. They won't be used much in the next few months anyways.

The setup seemed odd, even for this electrical lightweight!

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Old 12-03-2014, 03:37 PM   #27
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>Thanks all! I will go ahead and replace that breaker combination, but will wait until I replace the winches as the new ones may have a different requirement.<

The CB are usually sized to protect the wiring , not the user.

A slow blow fuse works best for that.
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