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I have a 5hp 230 single phase Leeson motor on my bandsaw. I ran a 30' circuit from a 30amp breaker in the panel to a NEMA 14-30 plug using 10AWG wire. From there, I have a 10-foot 10AWG cord to the saw. The connections are two loads and a ground, no neutral. Every time I turn on the bandsaw, the breaker pops immediately. I checked that the saw turned freely.

I had previously connected a dryer cord to it, also 10 feet long and 10AWG. The connection was two loads and a neutral. The saw ran fine. However, there was no blade so only the bottom wheel had to be turned. The dealer, Laguna, specifies that it is 30 amp. Any ideas how I can fix it?

Update

When I turn on the breaker, I can hear a solenoid clicking. When I turn the start switch, the blade starts to move before the breaker trips.

Plate on the motor Plate on the motor

The 30 amp breaker 30amp breaker

Update 2

I went back to the 10-30 cord and my 30amp dryer circuit. The connections are load, load, neutral as far as I can tell looking in the main panel. It works fine. It did take a few seconds to come up to speed. I put the 14-30 cord back on. The connections are load, load, ground. It still has the same problem. I tried the neutral on the new cord and got the same result.

I even read the manual. The spec for the LT18 bandsaw, which I have, is for a 30amp breaker. It also specifies that it has a 4.5hp motor so it may be out of date as it was written in 2008.

I did one more test. I hot wired the plug directly to the breaker in the panel using 10AWG wire I had left over. I got the same result. Could it be the breaker itself? I had previously used it for a 15amp motor and a 20amp, one at a time.

More images

The tripped 30amp breaker is for the bandsaw. sub panel The circuit box at the bandsaw. circuit box at the bandsaw

The wiring diagram from the manual. The image says LT16 HD. The manual is for the entire range of their Italian bandsaws.

Wiring Diagram

This is the breaker for my dryer. This is one on which the bandsaw works. The wire from it looks like 10AWG at most. Dryer Breaker

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  • Have you checked for a short from a hot to ground inside the saw somewhere? The instatrip makes it sound like that; also -- what make/model is the breaker in question?
    – ThreePhaseEel
    Commented Sep 28, 2018 at 3:48
  • Wiring diagram/pictures and nameplate?
    – SomeoneSomewhereSupportsMonica
    Commented Sep 28, 2018 at 5:57
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    Also, a 5HP motor is going to be drawing 25A+ line current. At start, it's going to be ~7x that - 175A ish. That could be enough to operate the magnetic trip. If it were in IEC-land, I'd recommend going to a D curve breaker, or a larger circuit. I don't know what the US equivalent is - HACR?
    – SomeoneSomewhereSupportsMonica
    Commented Sep 28, 2018 at 6:01
  • Can you post a picture of the nameplate on the saw? Also, any reason not to hardwire with a disconnect rather than a cord and plug?
    – batsplatsterson
    Commented Sep 28, 2018 at 9:33
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    @curt - You might have another problem here, a NEMA 14-30 plug and receptacle is only rated for 2 HP, at 5HP you're way over.
    – batsplatsterson
    Commented Sep 29, 2018 at 15:19

2 Answers 2

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NEC Table 430.245 states to size 5HP motor for 28A at 230V. Add 25% for start up and the circuit should be sized for 35 amps minimum. That would be #8 copper conductors with a 40A or 45A breaker.

The only way you could verify it is to check the amperage with an ammeter at start up and see if it is over 30A. That's probably is what is tripping your breaker.

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  • 1
    I called Laguna. Their support person said I needed a 60amp breaker. That seems over the top to me.
    – curt
    Commented Sep 28, 2018 at 22:23
  • See update 2 above. Could it be because I'm not using the neutral? Laguna told me to use the ground.
    – curt
    Commented Sep 29, 2018 at 1:54
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    @curt -- can you post a face-on shot of the breaker please?
    – ThreePhaseEel
    Commented Sep 29, 2018 at 1:56
  • Tried the neutral: same result.
    – curt
    Commented Sep 29, 2018 at 6:09
  • I agree with RME your breaker and wire size is undersized, you need 125% of the FLA of the motor to calculate wire size, if the motor trips on start up you are allowed to increase the breaker size to get the motor running see NEC article 430.52 and table 430.52 . standard motors commonly draw 3-5× there FLA on startup but this only lasts for a few seconds. Most inverse time breakers and fuses can hold through the in rush as it is very short this is why code allows larger breakers than the wire size would normally support.
    – Ed Beal
    Commented Sep 29, 2018 at 19:13
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The problem was a bad breaker. I bought the one shown below to replace it. The saw works fine. Thanks all for your help on this.

New Breaker Packaging

Panel Information:

enter image description here

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4
  • Eh, that's the wrong breaker for your panel most likely, can you post a picture of the labeling on the panel door though?
    – ThreePhaseEel
    Commented Sep 29, 2018 at 22:05
  • confirmed you have the wrong breaker -- you need a Murray MP230, not what you have!
    – ThreePhaseEel
    Commented Oct 2, 2018 at 22:11
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    @ThreePhaseEel, thanks for catching that. All my other breakers are Crouse-Hinds MHxxx, mostly 20amp single throw. Would a Murray MH230 be a valid replacement? The Challenger breaker looks identical to the Crouse-Hinds.
    – curt
    Commented Oct 4, 2018 at 0:29
  • A Murray MH230 works -- Murray went through a few changes of ownership and renaming to get their current home (under the Siemens umbrella)
    – ThreePhaseEel
    Commented Oct 4, 2018 at 1:10

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