amp question


Old 04-15-05, 08:47 AM
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amp question

i just bought a 15 amp dewalt 7" circular saw $129.99...i use it on a 15 amp line,with a 3.5 amp pond pump running 24/7...i never trip the breaker,it seem hard to believe a 7 inch saw can use 15 amps....can anyone explain why its rated at 15 amps,and is the a hazzard using this saw on a 15 amp line that already is using 3.5 amps sure the pump is 3.5 true amps by the cost on my electric bill in the spring and summer months....thanks
p.s the saw isnt used everyday,just typical home owner projects ....
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Old 04-15-05, 09:20 AM
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I would not worry about it......if you do have breakers and it does not trip then it is simply not pulling enough to cause the breaker to trip... I do find it hard to figure the circular saw drawing 15 amps....but regardless the breaker would trip if their was a problem so you should be fine...saw away...let the OCPD do it's job.
Old 04-15-05, 09:54 AM
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The 15A rating is probably the start-up current drawn by the motor. This means that for the brief period of time after the motor starts until the blade reaches full speed, the saw may peak at 15A. The actual running current is probably about one-third of that or 5A.
Old 04-15-05, 10:05 AM
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The 15 amp rating on your saw is likely using the same logic as they use when advertising HP ratings on consumer air compressors.
They use the amperage of the motor before it stalls and smokes rather than the countinuous hp it can develop without overheating.

I have a rebranded Campbell Hausfield air compressor that is labelled as having a 5 Hp motor and draws 15 amps at 220 volts.
My other compressor has an industrial 3 hp motor on it and it draws 14 amps at 220 volts.

Yours is just a case of misleading advertising.
To determine the correct amperage for your saw you would need to put it under a load that it could operate continuously at without overheating and then have someone read the current draw with an ammeter.
Old 04-15-05, 10:48 AM
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A 1 HP motor wired for 120v would draw 16 amps. It is doubtful that a hand-held circular saw has a motor that is just shy of 1 HP. I also believe it is marketing. It has also become popular to put a HP rating on vacuum cleaners. It is boastful but not accurate.

Old 04-15-05, 11:54 AM
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My 5hp compressor motor pulls around 25 amps, takes a size 2 starter and is on a 60a breaker. I've seen the overrated jobs (sometimes referred to as "peak" hp) run off the contacts in the pressure switch.
Old 04-15-05, 01:07 PM
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That 15 amp rating would be when the saw was under load. Just running the saw it would not use 15 amps. Cutting a four inch thick piece of lumber and almost stalling the saw would likely draw 15 amps.
Old 04-15-05, 01:13 PM
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Joed has the answer.
If the saw has 15 amps on the rating plate then it is a 15 amp motor, under full load. An SPF 2by will not even come close to maxing out the motor.
This is not like a company label, like Craftsman shop vacs stataing 6HP (with a 120 plug on the 16ga cord).
Old 04-15-05, 01:30 PM
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thanks guys for the replies...for a dewalt it wasnt an expensive saw,and i figured it couldnt possibly trip a 15 amp breaker.just wanted to double check with you guys to make sure i wasnt putting my electric in an sort of danger....thanks again and have a nice weekend
Old 04-16-05, 10:08 AM
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I dont see why a saw cant run 15 amps. My vacuum runs at somethin like 13 amps. There's a toaster in another thread that runs at 15 amps . . .

And ya gotta figure that that saw blade better be running a lot faster than a vaccum to cut through thick hard material, using more power.
Old 04-16-05, 08:43 PM
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I agree, the 15 amp is probably the full load amps, or rather, the maximum current the saw will draw. Locked rotor amps may be double that. Most direct drive saws aren't very powerfull, they rely instead on the momentem of the blade to continue cutting, which is why they are so easy to stall. A belt drive saw on the other hand, would hardly even bog down where a direct drive would stall.

Shoot, my coffee maker draws nearly 15 amps right by itself (as shown on the kill-a-watt) when all 3 warmers and the boiler is going at the same time.
Old 04-17-05, 06:17 AM
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Mechanical work is required to cut wood. Power is nothing more than the rate at which work is being performed. It takes more power to quickly saw a thick piece of oak than to cut a 1 by 2 piece of pine. The saw motor turns the blade by getting it's power from the electrical line. You will need to pull more amps while quickly cutting that thick piece of oak than while cutting a thin piece of pine. Just because a motor is rated at 15 amps doesn't mean that it will always draw that current. The rated current is just the maximum amount of current that the motor is safely capable of using. Yes, there's some salesmanship (hype) involved in coming up with that maximum current rating. You might have a saw that can use 15 amps for, say, 30 seconds and then must have a cooling off period of 1 minute. Another saw might use 15 amps continuously and doesn't require a cooling off period. Obviously, you would say that the second example is a much more robust saw. However, you would probably pay a high price for that capability. The typical home owner doesn't need to cut that much wood, but a factory or saw mill might. It all comes down to what you need and what you are willing to pay for.

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