4.5 HP Needs a 30 Amp Breaker?

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Flameproof suit on.
Laguna says 30 Amp breaker on 220 Volt service is needed for the LT16HD (4.5 HP Baldor motor).
My quick calc shows 4.5 HP on 220V is ~3375 Watts or about 15.3 Amp.
Is the start-up draw 30% higher than the run draw?
I have 220V 20A service and 10-3 wiring installed over about a 20' span and wonder if I need to go up to a 30 Amp breaker.
I could just plug it in, crank it up, and see if the breaker pops :-).
Flameproof suit off.
Regards.
Tom
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I would imagine at least 30% more. That said, I have the same saw and run it on my 30 amp Dryer Circuit at the same time that the dryer is running with no sign of voltage drop. The saw starts the same whether the dryer is running or not.

If you get into resawing wider boards you may blow the breaker on a 20 amp. On a side note, I can run my 22/44 drum sander that requires a 20 amp circuit and my 1100 CFM Dust Collector on a 15 amp circuit but on wider boards I will blow a breaker. Both running off of the 20 amp washer circuit works great.

I would be suprised if it blows on start up, it'll blow in the middle of a resaw job. ;~)
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You think they are trying to scare off customers by demanding too large a circuit? Seems like an odd sales strategy.

Better do a slower calc. Probably about 23a.

No, about 200% higher.

Sounds like a simple solution.

Yeah, but since you know it will, why not do it properly?

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Don't doubt you're right as I just used:
E=IR or I=E/R
W=I^2R or I*(E/R)*R
therefore W=EI
so 220V*20A = 4400 watts (avaialble)
1HP (electrical) = .746KW (source IEEE handbook circa 1968) 4.5HP= 4.5*746 = 3357 watts (required)
Obviously I missed something like adjusting for efficiency.
Don't have the saw yet so I can't read the plate on the motor.
In any case, thanks for the input.
Regards.
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wrote:

Those are calcs based on Ohm's law which is for DC. This AC. You have to include Power Factor. There's also efficiency. Both will yield a higher current than your calcs.
Bob
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That's assuming 100% efficiency, which you're not going to get. Figure *at*least* 20A, probably more.

No, it's even worse than that.

The manufacturer recommends a 30A circuit. 10-3 wire will support a 30A circuit. A 30A double pole breaker will cost about ten bucks, and take you fifteen minutes, tops, to swap in.
Doesn't sound like a difficult decision to me.

Yes, you could. Or you could spend the ten bucks and fifteen minutes, and put in the correct breaker.
Your choice. :-)
--
Regards,
Doug Miller (alphageek at milmac dot com)
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First of all, it won't hurt the wiring if the circuit breaker is too small. Instead, you will eventually get tired of tripped breakers.
The Delta manual shows that a 5 HP motor can draw up to 28 amperes. Frankly, I expect that Baldor knows more about the requirements of their motors than any of us. Hence, I would follow their instructions.
Incidentally, my table saw has a 1 HP repulsion-induction motor which is rated at 11 amperes. Despite this, I have tripped a 20 ampere circuit breaker while I was ripping some wood.
Jim
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The motor in my central A/C unit draws 30 amps once it's running, but needs 123 amps (at 240V!) for a few seconds to get started.
So yeah, go with the manufacter's recommendation, not pure math.
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writes:

You are so right. When I mentioned 28 amperes, I intended that to mean the current that flows after the motor gets started. Jim
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Tom B wrote:
> Laguna says 30 Amp breaker on 220 Volt service is needed for the > LT16HD (4.5 HP Baldor motor).
So what is the problem?
SFWIW, momentary inrush can be as high as 2.5 times running current.
Lew
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Tom B wrote:

Sounds reasonable.

That would be wrong. I'd guess closer to 20A after standard motor efficiency and power factor. My 3HP motor is about 13A.

Easily. Sometimes much more. On dedicated motor circuits you can sometimes use breakers up to 4x the "normal" breaker size to cover startup draw.

Likely, yes.

One option, certainly.
Chris
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most power tools don't draw a huge amount of power starting up because the load is not a lot. now what a real power sucker going to my larger cyclone and that thing draws some real power getting going. far more then any other tool in my shop.
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Steve knight wrote:

A high startup current of a motor is caused by the motor's windings providing a direct short across the line. After the initial surge the motor produces a counter voltage, known as a counter electro motive force (EMF), as a result of the collapsing magnetic field around the coils as the voltage cycles. This counter EMF acts as a resistance limiting the current once it has been started.
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Jack Novak
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Tom B wrote:

What does the spec. plate on the motor indicate?

According to Leeson, "the starting current, usually 450 to 575% of rated current," http://www.iprocessmart.com/leeson/leeson_singlephase_article.htm

Ayup.
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Jack Novak
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Thanks to all for the responses.
Net/net - why be pound foolish? Spend $3K on a saw, blades, base, etc and not spend a few bucks and a few scary minutes (I hate doing 220 in the breaker box, though I lived with it overseas for years) on a circuit for it? Case of the dumbs.
Though I do like the idea of using the dryer (or stove) circuit - HMMM.
No, last thing I need is to have to explain to SWMBO that my new high $$ toy fouled up her kingdom's smooth operation. That could get really expensive! New breaker it is.
Regards.
Tom
On Fri, 04 May 2007 09:31:07 -0500, Tom B

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Tom, I tapped into the dryer wall outlet and attached an extra 220 volt outlet within a few inches of the dryer outlet. I used the more standard outlet plug set up so that I could run my Planer and Table Saw from that outlet also. I run a 30' 10-3 extension cord from the outlet to the tool. This way the dryer stays plugged in all the time and the "Kingdom" runs smoothly. ;~)
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Leon:
Thanks. Good idea but our drier is in the house, 80' from the gara-shop.
In any case, I put in a new breaker this evening, so all is well - no damage, no sparks, got volts. TS runs fine on it and I'll use the same outlet for the BS when it arrives. One at a time of course. Only one of me so having both saws going at once makes zero sense. Dust collector is on a separate 220 circuit.
Reagrds.
Tom
On Fri, 4 May 2007 16:49:53 -0500, "Leon"

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Tom B wrote:

It's NBD, IF you approach it right.
Remove load center cover.
Pop out existing c'bkr with a rocking motion disconnecting c'bkr from L/C bus bar.
Change out c'bkr with it in your hand and disconnected from L/C.
Pop c'bkr back in place with a rocking motion such that c'bkr contacts contact bus bar last.
Replace L/C cover.
If the above scares you, stick flash light in mouth, shut off main c'bkr in L/C, the do as above.
Lew
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Lew:
Thanks. I'm a CS. I shut the mains down, checked voltage across the bus bars, replaced 20 amp with a 30 amp, backed off and reset the mains. All done, no sparks.
The work I do for a living is on the theorectical side of circuits that couldn't draw an amp in a millenium without frying. But I can wire a light switch!
Regards.
On Fri, 04 May 2007 21:52:15 GMT, Lew Hodgett

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Note that putting a 30 amp breaker on wire that isn't rated for 30 amps is, at least in most (if not all) US cities, illegal. Make sure the wire is able to carry the current, else it poses a fire hazard. (the breaker protects the wire, not your tool)
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