breaker needed for 4.5HP motor?

[James Baker SD]

I have a Laguna bandsaw that came with a 3HP motor. I put it on a 20A breaker and everything was fine. I recently upgraded the motor to the Baldor 4.5HP motor that Laguna was offering. It still seems quite happy with the 20A breaker, but I was wondering if I should upgrade the breaker (and replace the wires in the conduit) to 30A for this motor. Thanks.

James

[Paul McGaha]

James,

Check the FLA (Full Load Amps) rating on the nameplate of the motor. Multiply FLA x 1.25. The wire size has to be large enough to handle the FLA plus 25% spare.

As for the wiring #12 Wire is good for 20 Amps or less, #10 is good for 30 Amps or less, #8 is good for 40 Amps or less.

Say for example your FLA is 28 Amps. 28 Amps x 1.25 = 35 Amps. The wire you use has to be good for at least 35 Amps. In this case you would use #8 Wire.

For the circuit breaker, You need to provide a large enough breaker to allow the motor to start while still protecting the wire. Usually you use a 20 Amp Breaker to protect #12 Wire, 30 Amp Breaker for #10 Wire, 40 Amp Breaker for #8 Wire. In the case of the example I'd use a 40 Amp Breaker.

In summary, wire size for 125% of the FLA. Breaker size large enough to allow the motor to start and still protect the wiring.

Hope this is helpful.

PHM

[James Baker SD]

James,

Check the FLA (Full Load Amps) rating on the nameplate of the motor. Multiply FLA x 1.25. The wire size has to be large enough to handle the FLA plus 25% spare.


PHM

Hi PauL:

I just looked at the motor. It does not have a spec labeled as FLA; just "Amps 18.2". It is located right under the "Volts 230" spec. Can I assume that 18.2 is the number to multiply by 1.25? Thanks.

James

[Steven Wayne]

Hi PauL:

I just looked at the motor. It does not have a spec labeled as FLA; just "Amps 18.2". It is located right under the "Volts 230" spec. Can I assume that 18.2 is the number to multiply by 1.25? Thanks.

James

That's correct. How long is the run from the panel to the bandsaw? Provided the distance isn't extreme, you would want to run 10ga wire and use a 30a circuit breaker.

[James Baker SD]

That's correct. How long is the run from the panel to the bandsaw? Provided the distance isn't extreme, you would want to run 10ga wire and use a 30a circuit breaker.

Probably about 8'. Just on the other side of a double door, but has to go up a bit to get over the top of the door and then back down.

[Jim Neeley]

James,

I'm no code junkie but the National Electric Code has special rules for motors that seem to defy the logic that would apply for other loads. Steve's advice is what I would recommend as well.

I have one of the new "5hp" Delta Unisaws whose motor nameplate FLA is 20. Their owners manual recommends installing #10 wire and hooking it to a 40A breaker or a 30A slow-blow fuse but provides it with a 240V 20A plug. This left me scratching my head and opening my code book.

The code is very lenient on what you *can* do with motors assuming they have their own overload protection, if it is required to make it operate. In general we must size the breaker so as to "protect the downstream wiring" but for qualifying motors (motors containing overload protection) this is not the case. The code permits you to use a breaker UP TO the result of multiplying the FLA by 2.25 and rounding up to the next available breaker size. IN your case, that'd be 50A. That said, it also says you should use the smallest breaker on which the unit will run. I would install a 30A and only move up to a 40 if the breaker still popped, even then knowing you could go to a 50A if necessary.

I understand this sounds crazy but motors have a tremendous inrush current, typically on the order of 6x the nameplate rating, for a fraction of a second on start-up. This is what causes some breakers to trip on start-up or only *sometimes* trip on start-up.


.

[Rick Christopherson]

Hi PauL:

I just looked at the motor. It does not have a spec labeled as FLA; just "Amps 18.2". It is located right under the "Volts 230" spec. Can I assume that 18.2 is the number to multiply by 1.25? Thanks.

James

You're fine with a 20 amp breaker. The 125% rule is to protect the breaker from constantly operating at its maximum capacity, but your saw hardly ever operates at this level. This 125% is not to protect the wire, but to protect the breaker. The rule doesn't apply if you get a breaker rated for 100% load. But in your case, your motor will only reach FLA infrequently and for very short periods.

[Paul McGaha]

You're fine with a 20 amp breaker. The 125% rule is to protect the breaker from constantly operating at its maximum capacity, but your saw hardly ever operates at this level. This 125% is not to protect the wire, but to protect the breaker. The rule doesn't apply if you get a breaker rated for 100% load. But in your case, your motor will only reach FLA infrequently and for very short periods.

The above statement is completely wrong.

Advise you creekers to size your wire and breakers just the way I said to in post #2 in this thread.

PHM

[Curt Harms]

I have a Laguna bandsaw that came with a 3HP motor. I put it on a 20A breaker and everything was fine. I recently upgraded the motor to the Baldor 4.5HP motor that Laguna was offering. It still seems quite happy with the 20A breaker, but I was wondering if I should upgrade the breaker (and replace the wires in the conduit) to 30A for this motor. Thanks.

James

If it works, why screw with it? As long as you don't upsize the breaker without upsizing the wire, you're not at risk of a fire or anything like that. If the breaker trips, then worry about it. Not an expert but I think breakers do wear out so I wouldn't want too many trips. That's how I'd handle it. Just because a motor has a FLA rating doesn't mean it runs at that load ALL THE TIME.

[John Lanciani]

The above statement is completely wrong.

Advise you creekers to size your wire and breakers just the way I said to in post #2 in this thread.

PHM

Just because I'm curious, could you please share your credentials? There is a ton of misguided information in this thread.

[Kent A Bathurst]

As long as you don't upsize the breaker without upsizing the wire, you're not at risk of a fire or anything like that. If the breaker trips, then worry about it.

I'm not sending my dog into the other fight, but I can confirm this. If you put a 30a breaker on 12ga wire, you have crossed the line.....the wire can nuke out before the breaker throws.

[Paul McGaha]

Just because I'm curious, could you please share your credentials? There is a ton of misguided information in this thread.

Master Electrician, State of Virgina and Maryland. I'm currently one of the lead estimators for one of the largest electrical contractors in the US. I've worked in the electrical field since 1977.

PHM

[Kent A Bathurst]

Show-off.

[Paul McGaha]

Show-off.

I'm not meaning to be a show off. Woodworking is a hobby for me and I make the dumbest of the dumb mistakes routinely.

Electrical work though is something that I do have a lot of experience with. There may be 2 very different point of views at work here.

Some may simply be looking at this as how can I get the tool to run for the least amount of money and time spent?

The way I (and I would think everybody else in the electrical industry) look at this is how to install the wiring for the saw that will meet code requirements in every way and pass an electrical inspection by the local jurisdiction, and will not under any circumstances over heat and cause a fire.

PHM

[Kent A Bathurst]

I was poking fun, of course. Your credentials were asked for, you answered - they are impeccable. Thanks for the expert info on the OP.