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#1
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Amperage for 5HP table saw?
What amperage breaker does one need for a 5HP table saw on a 240V
single phase circuit? My logic: Typically, single phase 5HP 240V (or 230V) motors are rated at 19.8 or 20 A. Given that a circuit is supposed to be loaded 80% (look it up in the NEC sometime), this means a 25 A breaker would be borderline sufficient, and that a 30A breaker should be generous. With a slow breaker (not a fuse), there should be no problems with the startup surge of the motor tripping the breaker. The reason I'm asking is that I've recently read a few posts claiming that a 5HP tool needs a 40A or even 50A breaker. There are a few reasons not to do that. First, it requires 8 gauge wire (for 40A) or 6 gauge wire (for 50A), which is considerably harder to work with. Second, it requires a different connector, which means less flexibility in moving tools around. For this reason, I had been planning to make all the 240 V outlets be twist-look 30A outlets in my soon-to-be-built shop. Third, it is unsafe to use too large a breaker: If something goes wrong, there is more current around to fry things or start a fire. While we are it it. I have converted on of our waterpumps (a 1.5HP pump) from single-phase to three-phase motor, with a VFD (or inverter) driving it. This gives me a really nice slow start, with no current surges (which is vital when running on a generator). I'm planning to convert my drill press similarly, one of these days. This would give me the ability to run at variable speed (within a range of maybe a factor of two), without having to change belts, and it would again remove the startup surge and the mechanical stress associated with it. This brings up the following question: Is there a point using a 3-phase tablesaw motor on an inverter? There is no point running a tablesaw at reduced speed, is there? So the only point would be slow start (which is not worth the extra couple hundred $$$ for the inverter). Also, in principle, one can buy 3 HP inverters that run on single-phase 240V, but if the single-phase motor on the table saw has a service factor 1, a nominal 3 HP inverter will not be quite sufficient. Does anyone know whether electronic VFD inverters with single-phase input and 5HP capacity even exist? I haven't seen one yet. -- The address in the header is invalid for obvious reasons. Please reconstruct the address from the information below (look for _). Ralph Becker-Szendy _firstname_@lr _dot_ los-gatos _dot_ ca.us |
#2
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Amperage for 5HP table saw?
Hello Ralph,
the big point in using an inverter on the TS is not the speed (except you want to cut steel on your saw), but the inherent motor break in the inverter. My saw was spinning for close to a minute with a heavy dado stack on after switching it off. With the inverter, it comes to an instant stop. Regards Matthias schrieb im Newsbeitrag news:1078204646.761648@smirk... Is there a point using a 3-phase tablesaw motor on an inverter? There is no point running a tablesaw at reduced speed, is there? So the only point would be slow start (which is not worth the extra couple hundred $$$ for the inverter). |
#3
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Amperage for 5HP table saw?
In article 1078204646.761648@smirk,
wrote: What amperage breaker does one need for a 5HP table saw on a 240V single phase circuit? 5 HP is 3725 watts. At 240v, this is a 15.52A draw, assuming 100% efficiency. at 80% efficiency, you've got a 19.4A draw @ 240V. My logic: Typically, single phase 5HP 240V (or 230V) motors are rated at 19.8 or 20 A. Given that a circuit is supposed to be loaded 80% (look it up in the NEC sometime), "No more than 80%", for permanently attached loads, yup. this means a 25 A breaker would be borderline sufficient, and that a 30A breaker should be generous. Yup. 30A is "more than sufficient". With a slow breaker (not a fuse), there should be no problems with the startup surge of the motor tripping the breaker. The reason I'm asking is that I've recently read a few posts claiming that a 5HP tool needs a 40A or even 50A breaker. At 120V, yup. not at 240. There are a few reasons not to do that. First, it requires 8 gauge wire (for 40A) or 6 gauge wire (for 50A), which is considerably harder to work with. Second, it requires a different connector, which means less flexibility in moving tools around. For this reason, I had been planning to make all the 240 V outlets be twist-look 30A outlets in my soon-to-be-built shop. Third, it is unsafe to use too large a breaker: If something goes wrong, there is more current around to fry things or start a fire. While we are it it. I have converted on of our waterpumps (a 1.5HP pump) from single-phase to three-phase motor, with a VFD (or inverter) driving it. This gives me a really nice slow start, with no current surges (which is vital when running on a generator). I'm planning to convert my drill press similarly, one of these days. This would give me the ability to run at variable speed (within a range of maybe a factor of two), without having to change belts, and it would again remove the startup surge and the mechanical stress associated with it. This brings up the following question: Is there a point using a 3-phase tablesaw motor on an inverter? There is no point running a tablesaw at reduced speed, is there? So the only point would be slow start (which is not worth the extra couple hundred $$$ for the inverter). Also, in principle, one can buy 3 HP inverters that run on single-phase 240V, but if the single-phase motor on the table saw has a service factor 1, a nominal 3 HP inverter will not be quite sufficient. Does anyone know whether electronic VFD inverters with single-phase input and 5HP capacity even exist? I haven't seen one yet. They, and even bigger ones, do exist. You *don't* want to see the price tag, however. |
#4
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Amperage for 5HP table saw?
In article 1078204646.761648@smirk,
wrote: What amperage breaker does one need for a 5HP table saw on a 240V single phase circuit? My logic: Typically, single phase 5HP 240V (or 230V) motors are rated at 19.8 or 20 A. Given that a circuit is supposed to be loaded 80% (look it up in the NEC sometime), this means a 25 A breaker would be borderline sufficient, and that a 30A breaker should be generous. With a slow breaker (not a fuse), there should be no problems with the startup surge of the motor tripping the breaker. Using Ohm's law this is a relatively simple question to answer... 1 horsepower = 745.7 watts Power (watts) = I (amperage) x E (voltage) When you have two values for the variables in the equation you can figure out the third. P 3728.5 (watts 1 HP x 5) Therefore I = --- or I = ------ E 230 volts 230 volts = 16.21 amps 240 volts = 15.53 amps Using the "80% rule", a 20 amp breaker should not exceed a continuous load above 16 amps. It seems to me, that with the proper type of "slow" breaker, you should be OK with a 20 amp breaker. Joe PS I am not an electrician or an electrical engineer. In fact, I have never even played one on TV. |
#5
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Amperage for 5HP table saw?
That only works for an ideal motor. Unfortunately, they do not exist in real life. You need to adjust for power factor and
efficiency. P = (HP * 746) / (pf * eff) So with an efficiency of 80% (.8) and a Power factor of 90% (.9), 1 horsepower = 1036 Watts For the 5 HP example I = (5 * 746) / (.9* .8) / 230 = 22.5. amps Using the 80 % rule on breaker sizing, 22.52/.8 = 28.23, so a 30 amp breaker will be required. -- Al Reid "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." --- Mark Twain "Joe McDonald" wrote in message ... In article 1078204646.761648@smirk, wrote: What amperage breaker does one need for a 5HP table saw on a 240V single phase circuit? My logic: Typically, single phase 5HP 240V (or 230V) motors are rated at 19.8 or 20 A. Given that a circuit is supposed to be loaded 80% (look it up in the NEC sometime), this means a 25 A breaker would be borderline sufficient, and that a 30A breaker should be generous. With a slow breaker (not a fuse), there should be no problems with the startup surge of the motor tripping the breaker. Using Ohm's law this is a relatively simple question to answer... 1 horsepower = 745.7 watts Power (watts) = I (amperage) x E (voltage) When you have two values for the variables in the equation you can figure out the third. P 3728.5 (watts 1 HP x 5) Therefore I = --- or I = ------ E 230 volts 230 volts = 16.21 amps 240 volts = 15.53 amps Using the "80% rule", a 20 amp breaker should not exceed a continuous load above 16 amps. It seems to me, that with the proper type of "slow" breaker, you should be OK with a 20 amp breaker. Joe PS I am not an electrician or an electrical engineer. In fact, I have never even played one on TV. |
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Amperage for 5HP table saw?
In article ,
Joe McDonald wrote: Using Ohm's law this is a relatively simple question to answer... 1 horsepower = 745.7 watts Alas, this assumes 100% efficiency, which saws are not. For example, my 2HP saw is rated to draw 9A @ 220 or 1980W, considerably more then the 1492W ideal rating. It is this that makes me shy from 2HP+ tools; don't wanna run 220 all over the shop. Though a 2HP DC is calling me... Paul K |
#7
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Amperage for 5HP table saw?
A 30 Amp breaker should be O.K. for a table saw, I had real problems when I
was trying to run a 5HP 24" planer/thicknesser because the mass is so large it takes that much longer to get up to speed. Your 20 Amp running load is right, but the startup Amps are round 2 to 2 1/2 times that. Bernard R wrote in message news:1078204646.761648@smirk... What amperage breaker does one need for a 5HP table saw on a 240V single phase circuit? My logic: Typically, single phase 5HP 240V (or 230V) motors are rated at 19.8 or 20 A. Given that a circuit is supposed to be loaded 80% (look it up in the NEC sometime), this means a 25 A breaker would be borderline sufficient, and that a 30A breaker should be generous. With a slow breaker (not a fuse), there should be no problems with the startup surge of the motor tripping the breaker. The reason I'm asking is that I've recently read a few posts claiming that a 5HP tool needs a 40A or even 50A breaker. There are a few reasons not to do that. First, it requires 8 gauge wire (for 40A) or 6 gauge wire (for 50A), which is considerably harder to work with. Second, it requires a different connector, which means less flexibility in moving tools around. For this reason, I had been planning to make all the 240 V outlets be twist-look 30A outlets in my soon-to-be-built shop. Third, it is unsafe to use too large a breaker: If something goes wrong, there is more current around to fry things or start a fire. While we are it it. I have converted on of our waterpumps (a 1.5HP pump) from single-phase to three-phase motor, with a VFD (or inverter) driving it. This gives me a really nice slow start, with no current surges (which is vital when running on a generator). I'm planning to convert my drill press similarly, one of these days. This would give me the ability to run at variable speed (within a range of maybe a factor of two), without having to change belts, and it would again remove the startup surge and the mechanical stress associated with it. This brings up the following question: Is there a point using a 3-phase tablesaw motor on an inverter? There is no point running a tablesaw at reduced speed, is there? So the only point would be slow start (which is not worth the extra couple hundred $$$ for the inverter). Also, in principle, one can buy 3 HP inverters that run on single-phase 240V, but if the single-phase motor on the table saw has a service factor 1, a nominal 3 HP inverter will not be quite sufficient. Does anyone know whether electronic VFD inverters with single-phase input and 5HP capacity even exist? I haven't seen one yet. -- The address in the header is invalid for obvious reasons. Please reconstruct the address from the information below (look for _). Ralph Becker-Szendy _firstname_@lr _dot_ los-gatos _dot_ ca.us |
#8
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Amperage for 5HP table saw?
"Paul Kierstead" wrote in message news In article , Joe McDonald wrote: Using Ohm's law this is a relatively simple question to answer... 1 horsepower = 745.7 watts Alas, this assumes 100% efficiency, which saws are not. For example, my 2HP saw is rated to draw 9A @ 220 or 1980W, considerably more then the 1492W ideal rating. It is this that makes me shy from 2HP+ tools; don't wanna run 220 all over the shop. Though a 2HP DC is calling me... you guys are starting to get there, but whats so hard about looking on the motor for the current rating or calling the manufacturer and getting a power factor curve for it if you insist on going that route? randy |
#9
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clarification
i didnt mean to come off as an ass, but now that i read it, i kind of do..
all i mean is that if you want to start doing the math, there are many factors involved. the load conditions on startup. the load conditions during running. and none of these are simple to calculate but most motor manufactures will provide charts. but in any case, if you cant run your 5horse motor on a 30 amp circuit, something is wrong. randy |
#11
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Amperage for 5HP table saw?
I sought advice from a couple of Electrical Engineers at work. They assured me that: 1. The NEC allows a 40 Amp breaker on #10 wire IF the wire is only feeding an electric motor that is hard-wired, AND there are no other loads on the circuit. Are you sure about that one. All of the references I am aware of limit the overcurrent device to 30A on a #10 wire. Anyone know for sure? -- Al Reid |
#12
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Amperage for 5HP table saw?
Somebody wrote: I sought advice from a couple of Electrical Engineers at work. They assured me that: 1. The NEC allows a 40 Amp breaker on #10 wire IF the wire is only feeding an electric motor that is hard-wired, AND there are no other loads on the circuit. "Al Reid" asks: Are you sure about that one. All of the references I am aware of limit the overcurrent device to 30A on a #10 wire. Anyone know for sure? It is all a function of the insulation used. The function of the c'bkr is to protect the insulation on the wire, not the wire itself and most definitely not the motor. Don't have my code book handy to verify; however, the use of a #10 conductor on a 5HP/240V/1PH motor even if legal, would at best be considered a bad installation. The difference between the I^2*R heat losses of that #10 vs the lower heat losses of a #8 would soon consume any material savings made during installation. After that, the power company would be laughing all the way to the bank. Personally, I'd use #6 wire /w/ a 2P-40A c'bkr for a 5HP/240V/1PH motor. SFWIW, have designed and sold the equipment to build more than a few electrical distribution systems during my career. HTH -- Lew S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland) Visit: http://home.earthlink.net/~lewhodgett for Pictures |
#13
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Amperage for 5HP table saw?
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#14
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Amperage for 5HP table saw?
"Lew Hodgett" wrote in message hlink.net... Somebody wrote: I sought advice from a couple of Electrical Engineers at work. They assured me that: 1. The NEC allows a 40 Amp breaker on #10 wire IF the wire is only feeding an electric motor that is hard-wired, AND there are no other loads on the circuit. "Al Reid" asks: Are you sure about that one. All of the references I am aware of limit the overcurrent device to 30A on a #10 wire. Anyone know for sure? It is all a function of the insulation used. No, it's not. Theampacity may be higher than 30 A, but code limits the evercurrent device to 30A. See the tables in section 310. Section 310 states that #14 = 15A, #12=20A and #10=30A. I agree that the rated ampacities may, however, be greater than those limits. My question is, can anyone cite the section of the NEC that allows a larger overprotection that is stated in section 310? I have never ran across that exception and I have been an Electrical Engineer for 24 years working in, among other areas, electrical construction engineering. I am still looking at the code book. The function of the c'bkr is to protect the insulation on the wire, not the wire itself and most definitely not the motor. Don't have my code book handy to verify; however, the use of a #10 conductor on a 5HP/240V/1PH motor even if legal, would at best be considered a bad installation. The difference between the I^2*R heat losses of that #10 vs the lower heat losses of a #8 would soon consume any material savings made during installation. After that, the power company would be laughing all the way to the bank. Personally, I'd use #6 wire /w/ a 2P-40A c'bkr for a 5HP/240V/1PH motor. SFWIW, have designed and sold the equipment to build more than a few electrical distribution systems during my career. HTH -- Lew S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland) Visit: http://home.earthlink.net/~lewhodgett for Pictures |
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Amperage for 5HP table saw?
"Al Reid" wrote in message ...
I sought advice from a couple of Electrical Engineers at work. They assured me that: 1. The NEC allows a 40 Amp breaker on #10 wire IF the wire is only feeding an electric motor that is hard-wired, AND there are no other loads on the circuit. Are you sure about that one. All of the references I am aware of limit the overcurrent device to 30A on a #10 wire. See the disclaimer attached to my post. No, I'm not sure, because I didn't look it up myself; but I'm satisfied those guys knew what they were talking about. I'm comfortable with it. But then, I'm known for taking risks and living on the ragged edge. I used to hang off cliffs on ropes and ride motorcycles really fast. I don't have a guard on my tablesaw blade. And I used PVC pipe for airline. Don't do what I do. Do what makes YOU comfortable. DonkeyHody If ignorance is bliss, why aren't more people happy? |
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Amperage for 5HP table saw?
DonkeyHody writes:
1. The NEC allows a 40 Amp breaker on #10 wire IF the wire is only feeding an electric motor that is hard-wired, AND there are no other loads on the circuit. Are you sure about that one. All of the references I am aware of limit the overcurrent device to 30A on a #10 wire. See the disclaimer attached to my post. No, I'm not sure, because I didn't look it up myself; but I'm satisfied those guys knew what they were talking about. I'm comfortable with it. But then, I'm known for taking risks and living on the ragged edge. I used to hang off cliffs on ropes and ride motorcycles really fast. I don't have a guard on my tablesaw blade. And I used PVC pipe for airline. Don't do what I do. Do what makes YOU comfortable. Comfort is not the point. If you run an undersized wire, you're risking problems with the system that might become critical. If that system is part of your house wiring, failure could be fatal. I very much doubt the NEC allows a 40 amp breaker on 10 gauge wire, though many odd things are possible. I don't have even my old copies here to check, but your best source for a check will be your local building inspection office. After all, they have to pass your installation. Another point: most electrical engineers of my acquaintance know very little about NEC and building codes in general. They have no need to know, unless their speciality is in some area of construction. I've seen guys who can do a superb job of designing transport wiring systems for production lines that I would let wire the last motorcycle I had...and that was a bike without a headlight or taillight. Charlie Self "There is nothing wrong with America that cannot be cured with what is right in America." William J. Clinton http://hometown.aol.com/charliediy/m.../business.html |
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Amperage for 5HP table saw?
In article , Charlie Self
wrote: If you run an undersized wire, you're risking problems with the system that might become critical. If that system is part of your house wiring, failure could be fatal. I'm anything but an electrician, but I learned early that the breaker is there to protect the wire, 'cause when wires fail houses burn. djb -- Is it time to change my sig line yet? |
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Amperage for 5HP table saw?
I have a Left Tilt Unisaw with a 5 HP, single phase 230V, TEFC motor. It
uses the full voltage motor starter (GPE). I have the saw connected to a 30 A breaker. The saw starts right up and has never tripped the breaker when starting or in use. While waiting for delivery of the saw, I talked to Delta technical support. They said I would need a 40 Ampere Slo-Blow Fuse. But as noted in earlier email, there is no such beast at Home Depot. Once I had the saw, I looked at rating of the motor starter. I was rated for 18-25 A devices. And I did verify that the motor was rate at 5 HP. |
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Amperage for 5HP table saw?
wrote in message news:1078204646.761648@smirk... What amperage breaker does one need for a 5HP table saw on a 240V single phase circuit? My logic: Typically, single phase 5HP 240V (or 230V) motors are rated at 19.8 or 20 A. I have a true 5 HP motor that is rated at 25 amps @ 230 volt. I did a quick check through a Grainger catalog and found only one 5 HP motor under 20 amps @ 230 volt. Most were 22-23 amps. Greg |
#20
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clarification
"xrongor" wrote in message news:PU31c.100625$Xp.434279@attbi_s54... i didnt mean to come off as an ass, but now that i read it, i kind of do.. all i mean is that if you want to start doing the math, there are many factors involved. the load conditions on startup. the load conditions during running. and none of these are simple to calculate but most motor manufactures will provide charts. but in any case, if you cant run your 5horse motor on a 30 amp circuit, something is wrong. randy Delta states a requirement of a 40 amp slow blow fuse for protection on their 5 HP Unisaw. It may run on a 30 amp circuit, but I would not bet on it! Greg |
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Amperage for 5HP table saw?
" Don't have my code book handy to verify; however, the use of a #10
conductor on a 5HP/240V/1PH motor even if legal, would at best be considered a bad installation. The difference between the I^2*R heat losses of that #10 vs the lower heat losses of a #8 would soon consume any material savings made during installation. After that, the power company would be laughing all the way to the bank. Personally, I'd use #6 wire /w/ a 2P-40A c'bkr for a 5HP/240V/1PH motor. Lew, The plate on my 5 HP motor indicates that it draws 20 Amps at full load. If it was a motor that operated for extended periods at full load, or on a long wire, I'd agree with your thinking on the I squared R loss. But my table saw will rarely load the 5 HP motor, and the run of #10 wire is less than 20 feet. Since I have a pretty good feel for the tradeoffs involved, I elected to use the smaller wire, not because of cost, but because it's easier to pull. Others may certainly choose another path. DonkeyHody Even an old blind hog finds an acorn every now and then. |
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Amperage for 5HP table saw?
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#23
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clarification
"Greg O" wrote in message ... "xrongor" wrote in message news:PU31c.100625$Xp.434279@attbi_s54... i didnt mean to come off as an ass, but now that i read it, i kind of do.. all i mean is that if you want to start doing the math, there are many factors involved. the load conditions on startup. the load conditions during running. and none of these are simple to calculate but most motor manufactures will provide charts. but in any case, if you cant run your 5horse motor on a 30 amp circuit, something is wrong. randy Delta states a requirement of a 40 amp slow blow fuse for protection on their 5 HP Unisaw. It may run on a 30 amp circuit, but I would not bet on it! well, i cant vouch for that particular motor, but imho a 40 amp slow blow fuse on a 5hp table saw motor is kind of like saying, ok, once the thing catches on fire and explodes and the blade has spun out of control and the power wires are actually touching and welding together, we better stop supplying current to it g i would bet that saw has internal protection that blows long before that fuse does. randy |
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Amperage for 5HP table saw?
Are you sure about that one. All of the references I am aware of limit the overcurrent device to 30A on a #10 wire. Anyone know for sure? It is all a function of the insulation used. No, it's not. Theampacity may be higher than 30 A, but code limits the evercurrent device to 30A. See the tables in section 310. Section 310 states that #14 = 15A, #12=20A and #10=30A. I agree that the rated ampacities may, however, be greater than those limits. My question is, can anyone cite the section of the NEC that allows a larger overprotection that is stated in section 310? I have never ran across that exception and I have been an Electrical Engineer for 24 years working in, among other areas, electrical construction engineering. I am still looking at the code book. Well shucks. Y'all made me get out of my chair and go look it up. Check out Section 430, Part D - Motor Banch-Circuit Short-Circuit and Ground-Fault Protection. Paragraph 430-52 (b) All Motors. "The motor branch-circuit and ground-fault protective device shall be capable of carrying the starting current of the motor." (c) Rating or Setting. (1) "A protective device that has a rating or setting not exceeding the value calculated according to the values given in Table 430-152 shall be used." EXCEPTION NO. 1 (Paraphrased) Exception 1 allows you to go to the next size up if you are between sizes. EXCEPTION NO. 2 (Quote) "Where the rating specified in Table 430-152 as modified by Exception 1, is not sufficient for the starting current of the motor:" "(a) The rating of a nontime-delay fuse or a time-delay Class CC fuse shall be permitted to be increased, but shall in no case exceed 400% of the full-load current. "(b) The rating of a time-delay (dual element)fuse shall be permitted to be increased but shall in no case exceed 225% of the full-load current. "(c) The rating of an inverse-time circuit breaker shall be permitted to be increased but shall in no case exceed 400 percent for full-load currents of 100 amperes or less or 300 percent for full-load currents greater than 100 amperes." The commentary in the handbook states: (Quote) "It should be noted that it is not necessary to size the branch-circuit conductors to the percentages (150 to 300) permitted for the branch-circuit short circuit and ground-fault protective devices." . . . "During a short-circuit or phase-to-ground condition, the extremely high current causes the protective fuses or circuit breakers to open the circuit. Excess current flow caused by an overload condition passes through the overload protective device at the motor controller, thereby causing the device to open . . ." DonkeyHody Even a dumb old country boy gets it right once in a while. |
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Amperage for 5HP table saw?
"DonkeyHody" wrote in message m... Are you sure about that one. All of the references I am aware of limit the overcurrent device to 30A on a #10 wire. Anyone know for sure? It is all a function of the insulation used. No, it's not. Theampacity may be higher than 30 A, but code limits the evercurrent device to 30A. See the tables in section 310. Section 310 states that #14 = 15A, #12=20A and #10=30A. I agree that the rated ampacities may, however, be greater than those limits. My question is, can anyone cite the section of the NEC that allows a larger overprotection that is stated in section 310? I have never ran across that exception and I have been an Electrical Engineer for 24 years working in, among other areas, electrical construction engineering. I am still looking at the code book. Well shucks. Y'all made me get out of my chair and go look it up. Check out Section 430, Part D - Motor Banch-Circuit Short-Circuit and Ground-Fault Protection. Paragraph 430-52 (b) All Motors. "The motor branch-circuit and ground-fault protective device shall be capable of carrying the starting current of the motor." (c) Rating or Setting. (1) "A protective device that has a rating or setting not exceeding the value calculated according to the values given in Table 430-152 shall be used." EXCEPTION NO. 1 (Paraphrased) Exception 1 allows you to go to the next size up if you are between sizes. EXCEPTION NO. 2 (Quote) "Where the rating specified in Table 430-152 as modified by Exception 1, is not sufficient for the starting current of the motor:" "(a) The rating of a nontime-delay fuse or a time-delay Class CC fuse shall be permitted to be increased, but shall in no case exceed 400% of the full-load current. "(b) The rating of a time-delay (dual element)fuse shall be permitted to be increased but shall in no case exceed 225% of the full-load current. "(c) The rating of an inverse-time circuit breaker shall be permitted to be increased but shall in no case exceed 400 percent for full-load currents of 100 amperes or less or 300 percent for full-load currents greater than 100 amperes." The commentary in the handbook states: (Quote) "It should be noted that it is not necessary to size the branch-circuit conductors to the percentages (150 to 300) permitted for the branch-circuit short circuit and ground-fault protective devices." . . . "During a short-circuit or phase-to-ground condition, the extremely high current causes the protective fuses or circuit breakers to open the circuit. Excess current flow caused by an overload condition passes through the overload protective device at the motor controller, thereby causing the device to open . . ." Well, now you caught me without my code book but that seems to imply that it is a dedicated, hardwired motor, being supplied by a motor controller that incorporates both instantaneous (like an MCP) and overload protection AND that it pertains to the wiring between the motor controller and the motor. I could be wrong, but I doubt you could convince a residential electrical inspector to pass an installation with #10 wire being protected by a 40A breaker. -- Al Reid DonkeyHody Even a dumb old country boy gets it right once in a while. |
#26
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Amperage for 5HP table saw?
Well, now you caught me without my code book but that seems to imply that it is a dedicated, hardwired motor, being supplied by a
motor controller that incorporates both instantaneous (like an MCP) and overload protection AND that it pertains to the wiring between the motor controller and the motor. I could be wrong, but I doubt you could convince a residential electrical inspector to pass an installation with #10 wire being protected by a 40A breaker. Al, That section is specifically NOT about the factory installed wire between the factory installed motor controller and the motor. I went to the trouble to look up the reference for you and even took the time to quote chaper and verse. I'm not going to type the whole chapter for you. If you want to argue context, at least go to the trouble to read the chapter so you'll know what your're talking about. Now I remember why I mostly just lurk here. DonkeyHody We should be careful to get out of an experience only the wisdom that is in it - and stop there; lest we be like the cat that sits down on a hot stove-lid. She will never sit down on a hot stove-lid again---and that is well; but also she will never sit down on a cold one anymore. Mark Twain |
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Amperage for 5HP table saw?
Hey DonkeyHody, don't get your drawers in a knot!! I thought we were having a discussion. As anyone that has dealt with the NEC or
other NFPA publications, interpretation is everything. And I have found that there is no universal interpretation of all aspects of the code. I was merely expressing my doubts as to the wisdom of violating the 30A on a #10 wire rule in section 310. Most inspectors get hung up un that one and usually don't budge. Perhaps, my designs are too conservative, however, I have never had one rejected by a PE review before installation or by an inspector during/after installation. Also, I started my comment by stating that I did not have my code book in front of me. -- Al Reid "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." --- Mark Twain "DonkeyHody" wrote in message m... Well, now you caught me without my code book but that seems to imply that it is a dedicated, hardwired motor, being supplied by a motor controller that incorporates both instantaneous (like an MCP) and overload protection AND that it pertains to the wiring between the motor controller and the motor. I could be wrong, but I doubt you could convince a residential electrical inspector to pass an installation with #10 wire being protected by a 40A breaker. Al, That section is specifically NOT about the factory installed wire between the factory installed motor controller and the motor. I went to the trouble to look up the reference for you and even took the time to quote chaper and verse. I'm not going to type the whole chapter for you. If you want to argue context, at least go to the trouble to read the chapter so you'll know what your're talking about. Now I remember why I mostly just lurk here. DonkeyHody We should be careful to get out of an experience only the wisdom that is in it - and stop there; lest we be like the cat that sits down on a hot stove-lid. She will never sit down on a hot stove-lid again---and that is well; but also she will never sit down on a cold one anymore. Mark Twain |
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Amperage for 5HP table saw?
Given that a breaker exists only to protect the wire connected to it and
that is fact: 1) a 30A breaker connected to and protecting #10 wire will give (by your NEC code) 30 x 80% = 24 amps of continues current 2) You must get the FLA off the nameplate of the motor. Motors are ALL built with different efficiciencies and housing structures - therefore the only accurate current draw is that which was tested at the factory on their design model. Motors, at startup typically drew about 6 x FLA at startup, but today motors can easily hit 12 x FLA at startup because of lighter housing, thinner internal wiring etc - in otherwords the motors have been cheapened up. 3) If you motor nameplate, and it read 22 amps FLA - then you'd have 2 amps left over and you are good to go. If the motor nameplate on the other hand said 26 amps FLA you need to revisit the breaker/wire combination. It will still work but likely it will trip, maybe not for hours (only the breaker trip curve could answer that question) - the code can't stop you from attaching a 35 amp load to a 30 amp breaker combo - it just won't stay live very long. The code derates by 20% to give you the easily calculated values that allow you to enjoy continuous power on a circuit. The derating comes from the fact that circuit breakers are thermal devices (BTW so are fuses) in that they have as part of their protection system, a bimetallic element that works on heat principles. Once you put a breaker in an enclosure, heat can build up and trip the breaker. Enclosure are build with minimum cubic inches of "cooling space" and in conjunction with the 20% derating rule offer you a product that can supply current on a continuous basis. Put that product in the boiler room of a ship, where the ambient temp is high and the breaker will trip sooner. Same applies to a "hot" woodworking shop - this is why the 20% derating. If you want to spend the money, you can buy 100% rated breakers which are certified as such and you can draw 100% of the current. These breakers start at 400Amp and go to 6000Amp. Anyway, I digress - don't try to re-engineer some that has been designed for you and enforced by the NEC: 12A circuit = 15A breaker + #14 wire 16A circuit = 20A breaker + #12 wire 24A circuit = 30A breaker + #10 wire 32A circuit = 40A breaker + #8 wire Once you pick the right size "service" - make sure you have the proper device to protect your motor - the upstream breaker has nothing to do with that - but that a lot more typing and I'm not good at that. Regards John wrote in message news:1078204646.761648@smirk... What amperage breaker does one need for a 5HP table saw on a 240V single phase circuit? My logic: Typically, single phase 5HP 240V (or 230V) motors are rated at 19.8 or 20 A. Given that a circuit is supposed to be loaded 80% (look it up in the NEC sometime), this means a 25 A breaker would be borderline sufficient, and that a 30A breaker should be generous. With a slow breaker (not a fuse), there should be no problems with the startup surge of the motor tripping the breaker. The reason I'm asking is that I've recently read a few posts claiming that a 5HP tool needs a 40A or even 50A breaker. There are a few reasons not to do that. First, it requires 8 gauge wire (for 40A) or 6 gauge wire (for 50A), which is considerably harder to work with. Second, it requires a different connector, which means less flexibility in moving tools around. For this reason, I had been planning to make all the 240 V outlets be twist-look 30A outlets in my soon-to-be-built shop. Third, it is unsafe to use too large a breaker: If something goes wrong, there is more current around to fry things or start a fire. While we are it it. I have converted on of our waterpumps (a 1.5HP pump) from single-phase to three-phase motor, with a VFD (or inverter) driving it. This gives me a really nice slow start, with no current surges (which is vital when running on a generator). I'm planning to convert my drill press similarly, one of these days. This would give me the ability to run at variable speed (within a range of maybe a factor of two), without having to change belts, and it would again remove the startup surge and the mechanical stress associated with it. This brings up the following question: Is there a point using a 3-phase tablesaw motor on an inverter? There is no point running a tablesaw at reduced speed, is there? So the only point would be slow start (which is not worth the extra couple hundred $$$ for the inverter). Also, in principle, one can buy 3 HP inverters that run on single-phase 240V, but if the single-phase motor on the table saw has a service factor 1, a nominal 3 HP inverter will not be quite sufficient. Does anyone know whether electronic VFD inverters with single-phase input and 5HP capacity even exist? I haven't seen one yet. -- The address in the header is invalid for obvious reasons. Please reconstruct the address from the information below (look for _). Ralph Becker-Szendy _firstname_@lr _dot_ los-gatos _dot_ ca.us |
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