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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
Posted to sci.electronics.misc,sci.electronics.repair,rec.crafts.metalworking,rec.woodworking
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Fuses in place of motor "heaters"? (induction motor protection)
Looking to provide switching for 1-phase, 220 AC, 1/2 hp motor that doesn't
include use of a contactor. I appreciate the need for precise current limit (LRA) that a branch breaker can't provide. So, I choose to not have a contactor but instead, this, which provides the power-fail protection: http://www.amazon.com/Woodstock-D4160-110-Volt-Paddle- Switch/dp/B005W17HYY/ref=pd_sim_hi_1/191-4569239-2528519 This has a relay (rated 1/2 hp) that drops out on power fail, and has external connections for additional e-stop mushroom switch. But no provision for motor protection. Would 2 precisely-matched (ie, to the 1/4 amp), slow-blow HRC fuses be sufficient to protect this motor? Thanks. |
#2
Posted to sci.electronics.misc,sci.electronics.repair,rec.crafts.metalworking,rec.woodworking
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Fuses in place of motor "heaters"? (induction motor protection)
DaveC wrote:
Looking to provide switching for 1-phase, 220 AC, 1/2 hp motor that doesn't include use of a contactor. I appreciate the need for precise current limit (LRA) that a branch breaker can't provide. So, I choose to not have a contactor but instead, this, which provides the power-fail protection: http://www.amazon.com/Woodstock-D4160-110-Volt-Paddle- Switch/dp/B005W17HYY/ref=pd_sim_hi_1/191-4569239-2528519 This has a relay (rated 1/2 hp) that drops out on power fail, and has external connections for additional e-stop mushroom switch. But no provision for motor protection. Would 2 precisely-matched (ie, to the 1/4 amp), slow-blow HRC fuses be sufficient to protect this motor? Look at that switch again - it's a 110v switch, not a 220v switch. Hate to see you order the wrong one. You could fuse the circuit behind the switch but you'd have no way to ensure that both legs will drop out at the same time the way that a breaker does. You would not want to find yourself in a situation where one leg drops out but the other does not. What is the application for this motor that requires so much more precision than the circuit protection that a breaker would provide? -- -Mike- |
#3
Posted to sci.electronics.misc,sci.electronics.repair,rec.crafts.metalworking,rec.woodworking
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Fuses in place of motor "heaters"? (induction motor protection)
"DaveC" wrote in message
... Looking to provide switching for 1-phase, 220 AC, 1/2 hp motor that doesn't include use of a contactor. I appreciate the need for precise current limit (LRA) that a branch breaker can't provide. So, I choose to not have a contactor but instead, this, which provides the power-fail protection: http://www.amazon.com/Woodstock-D4160-110-Volt-Paddle- Switch/dp/B005W17HYY/ref=pd_sim_hi_1/191-4569239-2528519 This has a relay (rated 1/2 hp) that drops out on power fail, and has external connections for additional e-stop mushroom switch. But no provision for motor protection. Would 2 precisely-matched (ie, to the 1/4 amp), slow-blow HRC fuses be sufficient to protect this motor? Thanks. Why do you need two fuses for a single-phase motor? Do you know the motor's actual i-squared-t overcurrent limit requirement? http://www.copleycontrols.com/motion/pdf/IsqT.pdf When I ran a lab at Mitre an engineer kept asking me to buy him more and more Polaroid film for his scope camera. I finally asked him why and found that he was trying to discover the principles of how a fuse blows. He looked really sheepish and subdued when I handed him a Littelfuse pamphlet of current vs time curves. http://www.littelfuse.com/~/media/fi...ofuseology.pdf jsw |
#4
Posted to sci.electronics.misc,sci.electronics.repair,rec.crafts.metalworking,rec.woodworking
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Fuses in place of motor "heaters"? (induction motor protection)
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#5
Posted to sci.electronics.misc,sci.electronics.repair,rec.crafts.metalworking,rec.woodworking
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Fuses in place of motor "heaters"? (induction motor protection)
"Jim Wilkins" wrote in message ...
When I ran a lab at Mitre an engineer kept asking me to buy him more and more Polaroid film for his scope camera. I finally asked him why and found that he was trying to discover the principles of how a fuse blows. He looked really sheepish and subdued when I handed him a Littelfuse pamphlet of current vs time curves. http://www.littelfuse.com/~/media/fi...ofuseology.pdf When I worked one Summer at Bell Labs, one of the engineers told me he was trying to figure out how much detail the eye could see in color. What he didn't know (and I'd forgotten that I knew) was that this information was part of the design of the NTSC system. |
#6
Posted to sci.electronics.misc,sci.electronics.repair,rec.crafts.metalworking,rec.woodworking
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Fuses in place of motor "heaters"? (induction motor protection)
"William Sommerwerck" wrote in message
... "Jim Wilkins" wrote in message ... When I ran a lab at Mitre an engineer kept asking me to buy him more and more Polaroid film for his scope camera. I finally asked him why and found that he was trying to discover the principles of how a fuse blows. He looked really sheepish and subdued when I handed him a Littelfuse pamphlet of current vs time curves. http://www.littelfuse.com/~/media/fi...ofuseology.pdf When I worked one Summer at Bell Labs, one of the engineers told me he was trying to figure out how much detail the eye could see in color. What he didn't know (and I'd forgotten that I knew) was that this information was part of the design of the NTSC system. As a chemistry student I was expected to learn a lot of practical detail and hands-on procedure that I later noticed new electrical (and some mechanical) engineers often lacked. jsw |
#7
Posted to sci.electronics.misc,sci.electronics.repair,rec.crafts.metalworking,rec.woodworking
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Fuses in place of motor "heaters"? (induction motor protection)
qOn 2014-01-25, Jim Wilkins wrote:
"DaveC" wrote in message Why do you need two fuses for a single-phase motor? because it's got two live inputs, and either could develop a short to ground. -- For a good time: install ntp --- news://freenews.netfront.net/ - complaints: --- |
#8
Posted to sci.electronics.misc,sci.electronics.repair,rec.crafts.metalworking,rec.woodworking
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Fuses in place of motor "heaters"? (induction motor protection)
"Jasen Betts" wrote in message
... qOn 2014-01-25, Jim Wilkins wrote: "DaveC" wrote in message Why do you need two fuses for a single-phase motor? because it's got two live inputs, and either could develop a short to ground. For a good time: install ntp --- news://freenews.netfront.net/ - complaints: --- The panel circuit breakers protect the wiring from that. The separate fusing is for a motor overload condition. |
#9
Posted to sci.electronics.misc,sci.electronics.repair,rec.crafts.metalworking,rec.woodworking
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Fuses in place of motor "heaters"? (induction motor protection)
On 2014-01-25, Jim Wilkins wrote:
"Jasen Betts" wrote in message qOn 2014-01-25, Jim Wilkins wrote: "DaveC" wrote in message Why do you need two fuses for a single-phase motor? because it's got two live inputs, and either could develop a short to ground. The panel circuit breakers protect the wiring from that. The separate fusing is for a motor overload condition. Fuses ARE heaters. They have thermal action and the slow ones are meant for motors. I would say that fuses are "overload heaters for the poor". I spent some effort when replacnig electricals on my three phase bandsaw, and finally found a contactor with the exact heaters that the motor needed. Very happy about it. i |
#10
Posted to sci.electronics.misc,sci.electronics.repair,rec.crafts.metalworking,rec.woodworking
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Fuses in place of motor "heaters"? (induction motor protection)
"Jim Wilkins" Why do you need two fuses for a single-phase motor? ** Cos the AC supply is two phase. The OP is an American. They have spit phase power where 240VAC is split into a pair of 120V lines with a common neutral. While 120V appliances use one or the other, some ( usually high powered ) ones are rated at 220 /240 and connect across the pair. ...... Phil |
#11
Posted to sci.electronics.misc,sci.electronics.repair,rec.crafts.metalworking,rec.woodworking
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Fuses in place of motor "heaters"? (induction motor protection)
On 2014-01-25, Jim Wilkins wrote:
"DaveC" wrote in message ... Looking to provide switching for 1-phase, 220 AC, 1/2 hp motor that doesn't include use of a contactor. I appreciate the need for precise current limit (LRA) that a branch breaker can't provide. [ ... ] Would 2 precisely-matched (ie, to the 1/4 amp), slow-blow HRC fuses be sufficient to protect this motor? Thanks. Why do you need two fuses for a single-phase motor? In the UK, you don't, because 240 VAC comes with one side grounded. However, in the USA, 240 VAC is normally supplied with a grounded center tap, so if you have only one fuse -- or have two but only one blows, you still have 120 VAC live in the motor's housing, and potentially available for contact and personal zapping. :-) Do you know the motor's actual i-squared-t overcurrent limit requirement? http://www.copleycontrols.com/motion/pdf/IsqT.pdf When I ran a lab at Mitre an engineer kept asking me to buy him more and more Polaroid film for his scope camera. I finally asked him why and found that he was trying to discover the principles of how a fuse blows. He looked really sheepish and subdued when I handed him a Littelfuse pamphlet of current vs time curves. :-) http://www.littelfuse.com/~/media/fi...ofuseology.pdf And I'm not sure why he feels the need for precision current limiting on the motor. Most motors will handle a fairly wide range of time vs overcurrent exposures. (An exception is a permanent magnet DC servo motor which can be partially demagnetized by a sort spike over the rated current limit. Enjoy, DoN. -- Remove oil spill source from e-mail Email: | (KV4PH) Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#12
Posted to sci.electronics.repair,rec.crafts.metalworking
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Fuses in place of motor "heaters"? (induction motor protection)
On 1/25/2014 7:10 AM, Mike Marlow wrote:
DaveC wrote: Looking to provide switching for 1-phase, 220 AC, 1/2 hp motor that doesn't include use of a contactor. I appreciate the need for precise current limit (LRA) that a branch breaker can't provide. So, I choose to not have a contactor but instead, this, which provides the power-fail protection: http://www.amazon.com/Woodstock-D4160-110-Volt-Paddle- Switch/dp/B005W17HYY/ref=pd_sim_hi_1/191-4569239-2528519 This has a relay (rated 1/2 hp) that drops out on power fail, and has external connections for additional e-stop mushroom switch. But no provision for motor protection. Would 2 precisely-matched (ie, to the 1/4 amp), slow-blow HRC fuses be sufficient to protect this motor? May or may not, depending on the fuse characteristics. The fuse has to be slow-blow enough to not open when the motor starts (starting current is about 6x running current). But it has to open within the i-squared-t rating of the motor (as in Jim's post). The "overloads" in motor starters are matched to motor starting. And the settings in are much finer steps (or are continuous) compared to fuses. Many 1/2HP motors have internal overload protection ("thermally protected"). Look at that switch again - it's a 110v switch, not a 220v switch. Hate to see you order the wrong one. You could fuse the circuit behind the switch but you'd have no way to ensure that both legs will drop out at the same time the way that a breaker does. You would not want to find yourself in a situation where one leg drops out but the other does not. In the US, using the NEC, fuses are allowed. And a "controller" only has to open one of the supply wires. (You are right about the 110V rating on the amazon switch.) A "disconnect" has to open all the live supply conductors. What is the application for this motor that requires so much more precision than the circuit protection that a breaker would provide? Application is important. But a breaker provides little overload protection for a motor. For a hard-wired motor circuit (like central air conditioning) the breaker does not usually provide overload protection (that is provided at the motor). The breaker can be significantly larger than the rating of the wires, and provides short circuit protection. A breaker is large so it does not trip on the motor starting current. |
#13
Posted to sci.electronics.repair,rec.crafts.metalworking
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Fuses in place of motor "heaters"? (induction motor protection)
"bud--" May or may not, depending on the fuse characteristics. The fuse has to be slow-blow enough to not open when the motor starts (starting current is about 6x running current). But it has to open within the i-squared-t rating of the motor (as in Jim's post). ** Think you will have poor luck with a HRC fuse taking 6 time rated every time the motor starts or stalls and not nuisance blowing. A "motor start" circuit breaker is what is normally used. Slow, thermal characteristic at up to 6 times and then a very fast magnetic action at about 10 times. ..... Phil |
#14
Posted to sci.electronics.misc,sci.electronics.repair,rec.crafts.metalworking,rec.woodworking
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Fuses in place of motor "heaters"? (induction motor protection)
"DoN. Nichols" wrote in message
... On 2014-01-25, Jim Wilkins wrote: Why do you need two fuses for a single-phase motor? In the UK, you don't, because 240 VAC comes with one side grounded. However, in the USA, 240 VAC is normally supplied with a grounded center tap, so if you have only one fuse -- or have two but only one blows, you still have 120 VAC live in the motor's housing, and potentially available for contact and personal zapping. :-) I assumed it was wired with a 20A double-pole breaker at the panel protecting from shorts and a smaller fuse sized (how?) to blow before the motor burned out. jsw |
#15
Posted to sci.electronics.repair,rec.crafts.metalworking
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Fuses in place of motor "heaters"? (induction motor protection)
On 1/26/2014 2:18 AM, bud-- wrote:
... The breaker can be significantly larger than the rating of the wires, and provides short circuit protection. .... I don't think so! The breaker is there to protect the wires. If there is a load on the circuit greater than what the wires can handle, the breaker opens. You do not want the wires overheating and it doesn't take a short to do it. Bob |
#16
Posted to sci.electronics.repair,rec.crafts.metalworking
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Fuses in place of motor "heaters"? (induction motor protection)
On 1/26/2014 1:47 AM, Phil Allison wrote:
"bud--" May or may not, depending on the fuse characteristics. The fuse has to be slow-blow enough to not open when the motor starts (starting current is about 6x running current). But it has to open within the i-squared-t rating of the motor (as in Jim's post). ** Think you will have poor luck with a HRC fuse taking 6 time rated every time the motor starts or stalls and not nuisance blowing. Fuses are not usually used for motor overload protection in the US. There aren't enough fuse ratings to match to the motor running current except for relatively small motors. A "motor start" circuit breaker is what is normally used. Slow, thermal characteristic at up to 6 times and then a very fast magnetic action at about 10 times. .... Phil Time delay breakers can be up to 175% of the motor running current in the US. They often are used for short circuit protection of a motor circuit, but not for overload protection. There are even fewer sizes of breakers than fuses. |
#17
Posted to sci.electronics.repair,rec.crafts.metalworking
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Fuses in place of motor "heaters"? (induction motor protection)
On 1/26/2014 9:27 AM, Bob Engelhardt wrote:
On 1/26/2014 2:18 AM, bud-- wrote: ... The breaker can be significantly larger than the rating of the wires, and provides short circuit protection. ... I don't think so! The breaker is there to protect the wires. If there is a load on the circuit greater than what the wires can handle, the breaker opens. You do not want the wires overheating and it doesn't take a short to do it. Bob Under the US NEC the wires have to be 115% of the motor run current. A time delay breaker can be 175% of the motor run current. (Breakers that don't have a time delay can be even larger.) As stated, for a motor circuit, the breaker provides _short circuit protection_. Breakers can be large so they don't trip on normal motor starts. (I have seen an example for something like a 1/2HP motor where the breaker was twice the wire rating.) _Overload protection_ is usually at the motor (at the load end of the circuit). One common method is a motor starter with an 'overload' unit that is closely matched to the run current. Another is an internal thermal protector that disconnects the motor when it overheats. An internal thermal protector may be wired to drop out a motor starter. For welder circuits, the breaker can be even larger with respect to the wire rating. That can happen if the welder has a low "duty cycle". |
#18
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Fuses in place of motor "heaters"? (induction motor protection)
On 1/26/2014 12:15 PM, bud-- wrote:
On 1/26/2014 9:27 AM, Bob Engelhardt wrote: On 1/26/2014 2:18 AM, bud-- wrote: ... The breaker can be significantly larger than the rating of the wires, and provides short circuit protection. ... I don't think so! The breaker is there to protect the wires. ... ... for a motor circuit, ... Ah ... my mindset was residential branch circuit. |
#19
Posted to sci.electronics.repair,rec.crafts.metalworking
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Fuses in place of motor "heaters"? (induction motor protection)
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#20
Posted to sci.electronics.repair,rec.crafts.metalworking
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Fuses in place of motor "heaters"? (induction motor protection)
"bud--" Phil Allison wrote: "bud--" May or may not, depending on the fuse characteristics. The fuse has to be slow-blow enough to not open when the motor starts (starting current is about 6x running current). But it has to open within the i-squared-t rating of the motor (as in Jim's post). ** Think you will have poor luck with a HRC fuse taking 6 time rated every time the motor starts or stalls and not nuisance blowing. Fuses are not usually used for motor overload protection in the US. There aren't enough fuse ratings to match to the motor running current except for relatively small motors. A "motor start" circuit breaker is what is normally used. Slow, thermal characteristic at up to 6 times and then a very fast magnetic action at about 10 times. Time delay breakers can be up to 175% of the motor running current in the US. ** Blah, blah, blah... They often are used for short circuit protection of a motor circuit, but not for overload protection. ** Horse manure !!!!!!!!!! Overload protection is EXACTLY what circuit breakers are there for. You cab size them to protect a stalled or overloaded motor or just the supply cables. ..... Phil |
#21
Posted to sci.electronics.repair,rec.crafts.metalworking
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Fuses in place of motor "heaters"? (induction motor protection)
On 2014-01-26, bud-- wrote:
On 1/25/2014 7:10 AM, Mike Marlow wrote: DaveC wrote: Looking to provide switching for 1-phase, 220 AC, 1/2 hp motor that doesn't include use of a contactor. I appreciate the need for precise current limit (LRA) that a branch breaker can't provide. [ ... ] Would 2 precisely-matched (ie, to the 1/4 amp), slow-blow HRC fuses be sufficient to protect this motor? To the 1/4 A out of what rating? 1/4 A out of a 1/4 A fuse is a pretty big error. 1/4 A out of a 50 A fuse is a lot less. In other words, what kind of percentage? And the curves for fuses don't say *when* it will blow, they simply say that it must tolerate full load amps for N hours, and for each increment above that, they have to blow within a certain time. They can be quicker, but not slower. How are you going to find fuses that precisely matched? You can't really *know* that they are that precisely matched until you have tested them -- by which time they are now blown, and thus useless, except perhaps as a poor insulator. :-) May or may not, depending on the fuse characteristics. The fuse has to be slow-blow enough to not open when the motor starts (starting current is about 6x running current). But it has to open within the i-squared-t rating of the motor (as in Jim's post). The "overloads" in motor starters are matched to motor starting. And the settings in are much finer steps (or are continuous) compared to fuses. Many 1/2HP motors have internal overload protection ("thermally protected"). Some of those are thermal fuses (cooked off by the heat in the windings) buried in the windings. When that goes, you can't access it to replace it -- except by re-winding the motor. They don't re-set on their own. Enjoy, DoN. -- Remove oil spill source from e-mail Email: | (KV4PH) Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#22
Posted to sci.electronics.repair,rec.crafts.metalworking
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Fuses in place of motor "heaters"? (induction motor protection)
On 1/26/2014 11:00 PM, Phil Allison wrote:
"bud--" Phil Allison wrote: "bud--" May or may not, depending on the fuse characteristics. The fuse has to be slow-blow enough to not open when the motor starts (starting current is about 6x running current). But it has to open within the i-squared-t rating of the motor (as in Jim's post). ** Think you will have poor luck with a HRC fuse taking 6 time rated every time the motor starts or stalls and not nuisance blowing. Fuses are not usually used for motor overload protection in the US. There aren't enough fuse ratings to match to the motor running current except for relatively small motors. A "motor start" circuit breaker is what is normally used. Slow, thermal characteristic at up to 6 times and then a very fast magnetic action at about 10 times. Time delay breakers can be up to 175% of the motor running current in the US. ** Blah, blah, blah... They often are used for short circuit protection of a motor circuit, but not for overload protection. ** Horse manure !!!!!!!!!! Overload protection is EXACTLY what circuit breakers are there for. You cab size them to protect a stalled or overloaded motor or just the supply cables. The step between circuit breaker ratings is far too large to provide overload protection for motors. What I described is exactly what is in the US NEC and what practice is in the US. Must be another alwayswrong sock puppet. |
#23
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Fuses in place of motor "heaters"? (induction motor protection)
"boob = bull**** artist " Phil Allison wrote: A "motor start" circuit breaker is what is normally used. Slow, thermal characteristic at up to 6 times and then a very fast magnetic action at about 10 times. Time delay breakers can be up to 175% of the motor running current in the US. ** Blah, blah, blah... They often are used for short circuit protection of a motor circuit, but not for overload protection. ** Horse manure !!!!!!!!!! Overload protection is EXACTLY what circuit breakers are there for. You cab size them to protect a stalled or overloaded motor or just the supply cables. The step between circuit breaker ratings is far too large to provide overload protection for motors. ** FFS - asshole try LEARNING TO READ Thermal breakers come in any almost size you like and you fit them between the AC outlet and the load. Thermal/ magnetic breakers are not simply for "short circuit protection". They provide cable overload ( overtemp) protection. ****ing moron. .... Phil |
#24
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Fuses in place of motor "heaters"? (induction motor protection)
On 1/27/2014 4:58 PM, Phil Allison wrote:
"boob = bull**** artist" Phil Allison wrote: A "motor start" circuit breaker is what is normally used. Slow, thermal characteristic at up to 6 times and then a very fast magnetic action at about 10 times. Time delay breakers can be up to 175% of the motor running current in the US. ** Blah, blah, blah... They often are used for short circuit protection of a motor circuit, but not for overload protection. ** Horse manure !!!!!!!!!! Overload protection is EXACTLY what circuit breakers are there for. You cab size them to protect a stalled or overloaded motor or just the supply cables. The step between circuit breaker ratings is far too large to provide overload protection for motors. ** FFS - asshole try LEARNING TO READ Perhaps you could read. US NEC sizes breakers up to 175% of motor run current. Wire is 115% of motor run current. Thermal breakers come in any almost size you like and you fit them between the AC outlet and the load. What breaker would you use for overload protection for a motor with a run current of 16.3A. Breaker must be UL listed, able to withstand motor starting currents, and suitable for use as motor protection. Thermal/ magnetic breakers are not simply for "short circuit protection". They provide cable overload ( overtemp) protection. Not in the US NEC. And not the practice in the US. ****ing moron. You have such compelling arguments. |
#25
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Fuses in place of motor "heaters"? (induction motor protection)
"boob = bull**** artist"
They often are used for short circuit protection of a motor circuit, but not for overload protection. ** Horse manure !!!!!!!!!! Overload protection is EXACTLY what circuit breakers are there for. You cab size them to protect a stalled or overloaded motor or just the supply cables. The step between circuit breaker ratings is far too large to provide overload protection for motors. ** FFS - asshole try LEARNING TO READ Thermal breakers come in any almost size you like and you fit them between the AC outlet and the load. Thermal/ magnetic breakers are not simply for "short circuit protection". They provide cable overload ( overtemp) protection. Not in the US NEC. And not the practice in the US. ** You are one stupid, lying ass. WTF do you think AC supply circuit breakers are ****ing for? -------------------------------------------------------------------- You have such compelling arguments. ** While you have posted NONE at ALL !!!!!!!! **** off - you crazy ****ing nut case. ..... Phil |
#26
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Fuses in place of motor "heaters"? (induction motor protection)
On 1/28/2014 5:41 PM, Phil Allison wrote:
"boob = bull**** artist" They often are used for short circuit protection of a motor circuit, but not for overload protection. ** Horse manure !!!!!!!!!! Overload protection is EXACTLY what circuit breakers are there for. You cab size them to protect a stalled or overloaded motor or just the supply cables. The step between circuit breaker ratings is far too large to provide overload protection for motors. ** FFS - asshole try LEARNING TO READ Thermal breakers come in any almost size you like and you fit them between the AC outlet and the load. Thermal/ magnetic breakers are not simply for "short circuit protection". They provide cable overload ( overtemp) protection. Not in the US NEC. And not the practice in the US. ** You are one stupid, lying ass. More of the famous Allison logic. WTF do you think AC supply circuit breakers are ****ing for? You forgot to to answer the question. Maybe because you deleted it. "What [AC supply circuit] breaker would you use for overload protection for a motor with a run current of 16.3A. Breaker must be UL listed, able to withstand motor starting currents, and suitable for use as motor protection." That should be a trivial you. You have such compelling arguments. ** While you have posted NONE at ALL !!!!!!!! Only if you can't read !!!!!!!! **** off - you crazy ****ing nut case. Does you mommy approve of your language? |
#27
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Fuses in place of motor "heaters"? (induction motor protection)
bud-- wrote: Must be another alwayswrong sock puppet. No, this is a different character. A psychotic Aussie. |
#28
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Fuses in place of motor "heaters"? (induction motor protection)
Fred Abse wrote:
On Sun, 26 Jan 2014 08:13:56 -0500, Jim Wilkins wrote: "DoN. Nichols" wrote in message ... On 2014-01-25, Jim Wilkins wrote: Why do you need two fuses for a single-phase motor? In the UK, you don't, because 240 VAC comes with one side grounded. However, in the USA, 240 VAC is normally supplied with a grounded center tap, so if you have only one fuse -- or have two but only one blows, you still have 120 VAC live in the motor's housing, and potentially available for contact and personal zapping. :-) I assumed it was wired with a 20A double-pole breaker at the panel protecting from shorts and a smaller fuse sized (how?) to blow before the motor burned out. Panel breakers are there to protect the upstream wiring from excessive load current, not to protect the load. Matching the I-squared-t of a breaker, or fuse, to startup and running conditions of a motor is not trivial. Motors are subject to starting inrush currents sometimes tens of times the rated full-load current. Be guided by the data published by reputable manufacturers. There's plenty of it. My ac compressor unit says, use 20 amp breaker. The wiring said nothing. Greg |
#29
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Fuses in place of motor "heaters"? (induction motor protection)
On 1/29/2014 11:23 PM, gregz wrote:
Fred Abse wrote: On Sun, 26 Jan 2014 08:13:56 -0500, Jim Wilkins wrote: "DoN. Nichols" wrote in message ... On 2014-01-25, Jim Wilkins wrote: Why do you need two fuses for a single-phase motor? In the UK, you don't, because 240 VAC comes with one side grounded. However, in the USA, 240 VAC is normally supplied with a grounded center tap, so if you have only one fuse -- or have two but only one blows, you still have 120 VAC live in the motor's housing, and potentially available for contact and personal zapping. :-) I assumed it was wired with a 20A double-pole breaker at the panel protecting from shorts and a smaller fuse sized (how?) to blow before the motor burned out. Panel breakers are there to protect the upstream wiring from excessive load current, not to protect the load. Matching the I-squared-t of a breaker, or fuse, to startup and running conditions of a motor is not trivial. Motors are subject to starting inrush currents sometimes tens of times the rated full-load current. Be guided by the data published by reputable manufacturers. There's plenty of it. My ac compressor unit says, use 20 amp breaker. The wiring said nothing. The manufacturer tells you what size breaker will withstand the starting current and provide protection from manor failures. Overload protection is very likely a thermal trip on the compressor. Small fans are "impedance" protected. |
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Posted to sci.electronics.repair,rec.crafts.metalworking
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Fuses in place of motor "heaters"? (induction motor protection)
On Wed, 29 Jan 2014 14:28:16 -0600, bud-- wrote:
On 1/28/2014 5:41 PM, Phil Allison wrote: "boob = bull**** artist" They often are used for short circuit protection of a motor circuit, but not for overload protection. ** Horse manure !!!!!!!!!! Overload protection is EXACTLY what circuit breakers are there for. You cab size them to protect a stalled or overloaded motor or just the supply cables. The step between circuit breaker ratings is far too large to provide overload protection for motors. ** FFS - asshole try LEARNING TO READ Thermal breakers come in any almost size you like and you fit them between the AC outlet and the load. Thermal/ magnetic breakers are not simply for "short circuit protection". They provide cable overload ( overtemp) protection. Not in the US NEC. And not the practice in the US. ** You are one stupid, lying ass. More of the famous Allison logic. WTF do you think AC supply circuit breakers are ****ing for? You forgot to to answer the question. Maybe because you deleted it. "What [AC supply circuit] breaker would you use for overload protection for a motor with a run current of 16.3A. Breaker must be UL listed, able to withstand motor starting currents, and suitable for use as motor protection." That should be a trivial you. You have such compelling arguments. ** While you have posted NONE at ALL !!!!!!!! Only if you can't read !!!!!!!! **** off - you crazy ****ing nut case. Does you mommy approve of your language? For real horror to think he eats with that mouth. ?-) |
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