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#1
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Breaker on #6 copper
I am putting in a subpanel for my workshop. I need another 240v line, so I
am ripping out the two 120v lines and the 240v line I have already put in and replacing them all with a subpanel. Wish I had done it right the first time, but that boat has sailed. I am running #6 copper. As I read it, it is good for 55a, and since there is no 55a breaker, I can use a 60a. Is that correct? On the other hand; the most I will ever ever use at one time is a bandsaw and DC, which draw 27a together (which is why I need another 240v). I happen to have a 30a breaker. Any reason not to just use that? It is over the 80% rule, but I presume that applies to the wire rather than to the breaker. If it trips, I can always replace it. The #6 was only a few dollars more than the #8; so what the heck... |
#2
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Breaker on #6 copper
60 is fine
"Toller" wrote in message ... I am putting in a subpanel for my workshop. I need another 240v line, so I am ripping out the two 120v lines and the 240v line I have already put in and replacing them all with a subpanel. Wish I had done it right the first time, but that boat has sailed. I am running #6 copper. As I read it, it is good for 55a, and since there is no 55a breaker, I can use a 60a. Is that correct? On the other hand; the most I will ever ever use at one time is a bandsaw and DC, which draw 27a together (which is why I need another 240v). I happen to have a 30a breaker. Any reason not to just use that? It is over the 80% rule, but I presume that applies to the wire rather than to the breaker. If it trips, I can always replace it. The #6 was only a few dollars more than the #8; so what the heck... |
#3
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Breaker on #6 copper
"Toller" wrote in message ... I am putting in a subpanel for my workshop. I need another 240v line, so I am ripping out the two 120v lines and the 240v line I have already put in and replacing them all with a subpanel. Wish I had done it right the first time, but that boat has sailed. I am running #6 copper. As I read it, it is good for 55a, and since there is no 55a breaker, I can use a 60a. Is that correct? 100 foot run in dry condition good up to 65 amp. (ITE ret.) 3 wire conduit size 1" On the other hand; the most I will ever ever use at one time is a bandsaw and DC, which draw 27a together (which is why I need another 240v). I happen to have a 30a breaker. Any reason not to just use that? It is over the 80% rule, but I presume that applies to the wire rather than to the breaker. If it trips, I can always replace it. The #6 was only a few dollars more than the #8; so what the heck... |
#4
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Breaker on #6 copper
Toller wrote:
I am putting in a subpanel for my workshop. I need another 240v line, so I am ripping out the two 120v lines and the 240v line I have already put in and replacing them all with a subpanel. Wish I had done it right the first time, but that boat has sailed. I am running #6 copper. As I read it, it is good for 55a, and since there is no 55a breaker, I can use a 60a. Is that correct? No. Use a 50A breaker (or less). On the other hand; the most I will ever ever use at one time is a bandsaw and DC, which draw 27a together (which is why I need another 240v). I happen to have a 30a breaker. Any reason not to just use that? It is over the 80% rule, but I presume that applies to the wire rather than to the breaker. If it trips, I can always replace it. The 80% applies to the breaker, so with a 30A breaker you can only run 24 A continuous load. And maybe you might also want to run some lights, a vacuum, a radio, a charger for some handheld tools, etc.? The #6 was only a few dollars more than the #8; so what the heck... |
#5
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Breaker on #6 copper
RBM,
60 is fine Is the OP wrong that the #6 line is rated for only 55 amps or are you saying that a 60 amp breaker is safe with wire that will fail at 55 amps. Something is wrong here. Dave M. |
#6
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Breaker on #6 copper
M Q wrote:
Toller wrote: .... I am running #6 copper. As I read it, it is good for 55a, and since there is no 55a breaker, I can use a 60a. Is that correct? No. Use a 50A breaker (or less). I should clarify my comments here. The ampacity of the #6 wire depends upon the type of wire. OP didn't say what type. If it is a type that has a 55 A ampacity, then use 50 A breaker. Other types of #6, may have ampacities of 65, 75, or other. |
#7
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Breaker on #6 copper
In article k.net, "David Martel" wrote:
RBM, 60 is fine Is the OP wrong that the #6 line is rated for only 55 amps or are you saying that a 60 amp breaker is safe with wire that will fail at 55 amps. Something is wrong here. Nothing is wrong at all. The NEC specifically permits going up to the next higher standard breaker size when the rated ampacity of the wire (55A in this case) does not correspond to any standard breaker size. -- Regards, Doug Miller (alphageek at milmac dot com) It's time to throw all their damned tea in the harbor again. |
#8
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Breaker on #6 copper
In article AW%si.115$zg3.49@trnddc04, M Q wrote:
Toller wrote: I am running #6 copper. As I read it, it is good for 55a, and since there is no 55a breaker, I can use a 60a. Is that correct? No. Use a 50A breaker (or less). Wrong. Please familiarize yourself with the NEC before attempting to answer electrical questions. A 60A breaker is perfectly fine: "Devices Rated 800 Amperes or Less. The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met ..." [2005 NEC, Article 240.4(B)] The conditions can be summarized as not a multiple-receptacle circuit, no matching standard breaker, and next size up not 800A. On the other hand; the most I will ever ever use at one time is a bandsaw and DC, which draw 27a together (which is why I need another 240v). I happen to have a 30a breaker. Any reason not to just use that? It is over the 80% rule, but I presume that applies to the wire rather than to the breaker. If it trips, I can always replace it. The 80% applies to the breaker, so with a 30A breaker you can only run 24 A continuous load. And maybe you might also want to run some lights, a vacuum, a radio, a charger for some handheld tools, etc.? The #6 was only a few dollars more than the #8; so what the heck... -- Regards, Doug Miller (alphageek at milmac dot com) It's time to throw all their damned tea in the harbor again. |
#9
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Breaker on #6 copper
In article , "Toller" wrote:
I am putting in a subpanel for my workshop. I need another 240v line, so I am ripping out the two 120v lines and the 240v line I have already put in and replacing them all with a subpanel. Wish I had done it right the first time, but that boat has sailed. I am running #6 copper. As I read it, it is good for 55a, and since there is no 55a breaker, I can use a 60a. Is that correct? Correct; this is specifically permitted under Article 240.4(B). On the other hand; the most I will ever ever use at one time is a bandsaw and DC, which draw 27a together (which is why I need another 240v). I happen to have a 30a breaker. Any reason not to just use that? It is over the 80% rule, Remember that the "80% rule" applies only to circuits serving a continuous load, which is defined as "a load where the maximum current is expected to continue for three hours or more." [2005 NEC, Article 100] This usage probably doesn't meet that definition. but I presume that applies to the wire rather than to the breaker. Actually, it applies to both (see Article 210.19(A)(1) [wire] and 210.20(A) [breaker]), but, as noted above, this installation doesn't appear to meet the definition of a continuous load anyway, so it doesn't matter. -- Regards, Doug Miller (alphageek at milmac dot com) It's time to throw all their damned tea in the harbor again. |
#10
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Breaker on #6 copper
In article LO0ti.318$V53.117@trnddc08, M Q wrote:
I should clarify my comments here. The ampacity of the #6 wire depends upon the type of wire. OP didn't say what type. If it is a type that has a 55 A ampacity, then use 50 A breaker. Other types of #6, may have ampacities of 65, 75, or other. Clarifed or not, your comments are still wrong. It's perfectly OK to use a 60A breaker on a conductor with a listed ampacity of 55A, under Article 240.4(B). Likewise, if the listed ampacity is 65A, a 70A breaker may be used, and if the listed ampacity is 75A, an 80A breaker may be used -- all because standard breaker sizes do not include 55, 65, or 75 amps. -- Regards, Doug Miller (alphageek at milmac dot com) It's time to throw all their damned tea in the harbor again. |
#11
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Breaker on #6 copper
On Sat, 04 Aug 2007 13:55:20 GMT, Toller wrote:
I am putting in a subpanel for my workshop. I need another 240v line, so I am ripping out the two 120v lines and the 240v line I have already put in and replacing them all with a subpanel. Wish I had done it right the first time, but that boat has sailed. I am running #6 copper. As I read it, it is good for 55a, and since there is no 55a breaker, I can use a 60a. Is that correct? Yes, it is correct. I did the same thing, ran a 60a circuit to my garage, and I regret to this day that I did not make it a 100A circuit. Spend a few more bucks and get a 100A circuit. You can then buy some large equipment (welding, plasma cutters) and run them inexpensively. i On the other hand; the most I will ever ever use at one time is a bandsaw and DC, which draw 27a together (which is why I need another 240v). I happen to have a 30a breaker. Any reason not to just use that? It is over the 80% rule, but I presume that applies to the wire rather than to the breaker. If it trips, I can always replace it. The #6 was only a few dollars more than the #8; so what the heck... |
#12
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Breaker on #6 copper
"Doug Miller" wrote in message .. . In article , "Toller" wrote: I am putting in a subpanel for my workshop. I need another 240v line, so I am ripping out the two 120v lines and the 240v line I have already put in and replacing them all with a subpanel. Wish I had done it right the first time, but that boat has sailed. I am running #6 copper. As I read it, it is good for 55a, and since there is no 55a breaker, I can use a 60a. Is that correct? Correct; this is specifically permitted under Article 240.4(B). On the other hand; the most I will ever ever use at one time is a bandsaw and DC, which draw 27a together (which is why I need another 240v). I happen to have a 30a breaker. Any reason not to just use that? It is over the 80% rule, Remember that the "80% rule" applies only to circuits serving a continuous load, which is defined as "a load where the maximum current is expected to continue for three hours or more." [2005 NEC, Article 100] No, I can't see ever running the bandsaw for 3 hours. Thanks |
#13
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Breaker on #6 copper
In article , "Wade Lippman" wrote:
"Doug Miller" wrote in message . .. Remember that the "80% rule" applies only to circuits serving a continuous load, which is defined as "a load where the maximum current is expected to continue for three hours or more." [2005 NEC, Article 100] No, I can't see ever running the bandsaw for 3 hours. Thanks And even if you were, it's very unlikely that it would be pulling maximum current the entire time. -- Regards, Doug Miller (alphageek at milmac dot com) It's time to throw all their damned tea in the harbor again. |
#14
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Breaker on #6 copper
"Doug Miller" wrote in message ... In article k.net, "David Martel" wrote: RBM, 60 is fine Is the OP wrong that the #6 line is rated for only 55 amps or are you saying that a 60 amp breaker is safe with wire that will fail at 55 amps. Something is wrong here. Nothing is wrong at all. The NEC specifically permits going up to the next higher standard breaker size when the rated ampacity of the wire (55A in this case) does not correspond to any standard breaker size. -- Regards, Doug Miller (alphageek at milmac dot com) That doesn't make sense to me at all. Why allow the breaker to trip at a higher rating than the wire? Conceivably the wire would fail without the breaker ever tripping. That presumes the wire rating of 55 A means it is only capable of carrying 55A at 120V |
#15
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Breaker on #6 copper
Doug Miller wrote:
In article AW%si.115$zg3.49@trnddc04, M Q wrote: .... Wrong. Please familiarize yourself with the NEC before attempting to answer electrical questions. A 60A breaker is perfectly fine: "Devices Rated 800 Amperes or Less. The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met ..." [2005 NEC, Article 240.4(B)] The conditions can be summarized as not a multiple-receptacle circuit, no matching standard breaker, and next size up not 800A. Mea Culpa. I was wrong on two points. Thanks for correcting me. I will now slink off with my tail between my legs. |
#16
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Breaker on #6 copper
In article , "Eigenvector" wrote:
"Doug Miller" wrote in message .. . Nothing is wrong at all. The NEC specifically permits going up to the next higher standard breaker size when the rated ampacity of the wire (55A in this case) does not correspond to any standard breaker size. That doesn't make sense to me at all. Whether it makes sense to you or not, it *is* the Code. Article 240.4(B), to be exact. Why allow the breaker to trip at a higher rating than the wire? Conceivably the wire would fail What do you mean by "fail"? Melt? Start a fire? Neither will happen as a result of applying a 60A breaker on a 6AWG copper conductor. without the breaker ever tripping. That presumes the wire rating of 55 A means it is only capable of carrying 55A at 120V The vast majority of the time, a typical circuit with 60A overcurrent protection isn't going to be carrying anywhere near 60A. In any event, the difference between 60A and 55A on a #6 wire is not going to mean the difference between the wire igniting vs. not igniting. I imagine that the NFPA (authors of the NEC) decided that five amps on a wire that size wasn't enough to worry about. You could always ask them. -- Regards, Doug Miller (alphageek at milmac dot com) It's time to throw all their damned tea in the harbor again. |
#17
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Breaker on #6 copper
"Eigenvector" wrote in message . .. "Doug Miller" wrote in message ... In article k.net, "David Martel" wrote: RBM, 60 is fine Is the OP wrong that the #6 line is rated for only 55 amps or are you saying that a 60 amp breaker is safe with wire that will fail at 55 amps. Something is wrong here. Nothing is wrong at all. The NEC specifically permits going up to the next higher standard breaker size when the rated ampacity of the wire (55A in this case) does not correspond to any standard breaker size. -- Regards, Doug Miller (alphageek at milmac dot com) That doesn't make sense to me at all. Why allow the breaker to trip at a higher rating than the wire? Conceivably the wire would fail without the breaker ever tripping. That presumes the wire rating of 55 A means it is only capable of carrying 55A at 120V My cottage had a 23a water heater on #12 for 35 years before I found it and replaced it with #10. That is about the worst possible thing, since it comes on at full draw, and stays on for a long period of time; yet nothing happened. Code is rather conservative, which prevents many fires. And don't forget, the wire is 90degree and the panel and breaker are 75degree; yet the 55a limit is as though they were 60degree. So the extra 5 amps is not a big deal. |
#18
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Breaker on #6 copper
You're also presuming that the heat generated by pulling 60 amps through a
#6 copper wire would cause it to reach it's flash point. I'm pretty confident that the NEC has figured in considerable leeway "Eigenvector" wrote in message . .. "Doug Miller" wrote in message ... In article k.net, "David Martel" wrote: RBM, 60 is fine Is the OP wrong that the #6 line is rated for only 55 amps or are you saying that a 60 amp breaker is safe with wire that will fail at 55 amps. Something is wrong here. Nothing is wrong at all. The NEC specifically permits going up to the next higher standard breaker size when the rated ampacity of the wire (55A in this case) does not correspond to any standard breaker size. -- Regards, Doug Miller (alphageek at milmac dot com) That doesn't make sense to me at all. Why allow the breaker to trip at a higher rating than the wire? Conceivably the wire would fail without the breaker ever tripping. That presumes the wire rating of 55 A means it is only capable of carrying 55A at 120V |
#19
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Breaker on #6 copper
"M Q" wrote in message news:6u6ti.353$V53.338@trnddc08... Doug Miller wrote: In article AW%si.115$zg3.49@trnddc04, M Q wrote: ... Wrong. Please familiarize yourself with the NEC before attempting to answer electrical questions. A 60A breaker is perfectly fine: "Devices Rated 800 Amperes or Less. The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met ..." [2005 NEC, Article 240.4(B)] The conditions can be summarized as not a multiple-receptacle circuit, no matching standard breaker, and next size up not 800A. Mea Culpa. I was wrong on two points. Thanks for correcting me. I will now slink off with my tail between my legs. You got better treatment than I did from him. |
#20
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Breaker on #6 copper
In article , "Eigenvector" wrote:
"M Q" wrote in message news:6u6ti.353$V53.338@trnddc08... Doug Miller wrote: In article AW%si.115$zg3.49@trnddc04, M Q wrote: ... Wrong. Please familiarize yourself with the NEC before attempting to answer electrical questions. A 60A breaker is perfectly fine: "Devices Rated 800 Amperes or Less. The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met ..." [2005 NEC, Article 240.4(B)] The conditions can be summarized as not a multiple-receptacle circuit, no matching standard breaker, and next size up not 800A. Mea Culpa. I was wrong on two points. Thanks for correcting me. I will now slink off with my tail between my legs. You got better treatment than I did from him. If I offended you, I'm sorry - it was unintentional. -- Regards, Doug Miller (alphageek at milmac dot com) It's time to throw all their damned tea in the harbor again. |
#21
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Breaker on #6 copper
Toller wrote:
I am putting in a subpanel for my workshop. I need another 240v line, so I am ripping out the two 120v lines and the 240v line I have already put in and replacing them all with a subpanel. Wish I had done it right the first time, but that boat has sailed. I am running #6 copper. As I read it, it is good for 55a, and since there is no 55a breaker, I can use a 60a. Is that correct? On the other hand; the most I will ever ever use at one time is a bandsaw and DC, which draw 27a together (which is why I need another 240v). I happen to have a 30a breaker. Any reason not to just use that? It is over the 80% rule, but I presume that applies to the wire rather than to the breaker. If it trips, I can always replace it. The #6 was only a few dollars more than the #8; so what the heck... If you have a 30A breaker already, use it. If it ever trips (or just before you sell the house), replace it with a 60A. Bob |
#22
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Breaker on #6 copper
Well good greif! the damn wire will handle about 3 times what they say they
will. thats why. s "Eigenvector" wrote in message . .. That doesn't make sense to me at all. Why allow the breaker to trip at a higher rating than the wire? Conceivably the wire would fail without the breaker ever tripping. That presumes the wire rating of 55 A means it is only capable of carrying 55A at 120V |
#23
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Breaker on #6 copper
On Aug 4, 7:30 pm, "Eigenvector" wrote:
"Doug Miller" wrote in message ... In article k.net, "David Martel" wrote: RBM, 60 is fine Is the OP wrong that the #6 line is rated for only 55 amps or are you saying that a 60 amp breaker is safe with wire that will fail at 55 amps. Something is wrong here. Nothing is wrong at all. The NEC specifically permits going up to the next higher standard breaker size when the rated ampacity of the wire (55A in this case) does not correspond to any standard breaker size. -- Regards, Doug Miller (alphageek at milmac dot com) That doesn't make sense to me at all. Why allow the breaker to trip at a higher rating than the wire? Conceivably the wire would fail without the breaker ever tripping. That presumes the wire rating of 55 A means it is only capable of carrying 55A at 120V- Hide quoted text - - Show quoted text - A couple of the posts here seem to make the assumption that a wire with a 'rated safe' ampacity of 50 amps (i.e. that it can carry 50 amps under normal conditions of voltage drop and length of run etc.) will immediately heat up and burn off if it is made to carry 55 amps for intermittent periods of time. Not so. A 50 amp rated wire (say #6AWG) can probably carry twice that even if getting a bit warm and with a certain amount of voltage drop. And anyone who has ever dealt with an emergency situation where one presses into service whatever reasonable size conductors are available and has a good feel for the basics of electrical resistance, current flow and voltage drop will understand that. In this case we are discussing 'normal' domestic workshop conditions to meet safety and code requirements. With only one or two people working a maximum home workshop load is unlikely to be close to the rated capability. The statement "is only capable of carrying 55 amps" is probably only true in regard to maximum current that could be carried continuously. The reference 'is only capable of carrying 55 amps "at 120V", is superfluous. We are considering current here, not voltage. For example: Today we had two people working on a friends personal vehicle in our domestic garage; the maximum load at any one time was, intermittently; 1) A small wire welder maximum about 20 amps (@230 volt) 2) A sander/grinder or hand drill, maximum 5 amps (@120 volt). 3) A halogen lamp. 2.5 amps (@ 120 volt) Total (intermittently) 27.5 amps, plus maybe another light that was on. Maximum 30 amps say all fed from a panel wired with #6AWG and a 50 amp (Square D) breaker from the main house panel about 40 cable feet distant. Nothing blinked or went dim etc. Caught fire or popped a breaker. |
#24
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Breaker on #6 copper
On Sat, 04 Aug 2007 22:58:03 GMT, "Wade Lippman"
wrote: And don't forget, the wire is 90degree and the panel and breaker are 75degree; yet the 55a limit is as though they were 60degree. So the extra 5 amps is not a big deal. I don't understand any of the 3 degree things. |
#25
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Breaker on #6 copper
On Sat, 04 Aug 2007 20:38:19 -0700, terry
wrote: The reference 'is only capable of carrying 55 amps "at 120V", is superfluous. We are considering current here, not voltage. Absolutely. The heat, if any, generated by the current flowing through the wire is totally dependant on how much current is flowing, and unrelated to the voltage applied to the whole circuit. I think this will help a few people and won't help others at all. E=IR (Remember that. ) In other words: EMF=Current times resistance. In other words, in this case: Voltage = 55 amps x R (resistance) Power = Voltage x Amps. (Remember this.)In other words, in this case: Watts = voltage x 55 amps. But the voltage in the formula above is not the 110 or 220 that comes from the wall. It's the voltage drop from one end of the wire to the other, which is small, because the resistance of the wire is small. The total voltage drop of an appliance plugged in to a wall is 110 or 220 or whatever, but almost all of that voltage drop is in the appliance, and not in the cord going to it. It's the saw or washer or water heater or mixmaster that is designed to do the work, and the wire to it is designed to have low resistance and not impeded the electrficity getting to the appliance. But, in this case we're talking about running 6 gauge wire with a 60 amp breaker, even though the wire is rated at only 55 amps. So how much heat (power or watts, iirc) will be generated in that wire if the current goes up to just shy of 60 amps, even though it is rated at 55 amps. Look at the formulas at the top, and then continue he Since voltage = 55 amps x R, then: Watts = 55 amps x R x 55 amps. In other words: Watts = (55 amps) squared x R. Where R is the resistance of the wire feedinn the appliance. This is not the number of watts given off by a lightbulb, if there is a lightbulb in the appliance, or used by the motor if there is a motor in it. It's the number of watts given off by the wire feeding the appliance. And it is totally unrelated to the voltage applied to the appliance** **Except insofar as if higher voltage were applied, more current woudl go through the same resistance wire and appliance. |
#26
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Breaker on #6 copper
In article , mm wrote:
On Sat, 04 Aug 2007 22:58:03 GMT, "Wade Lippman" wrote: And don't forget, the wire is 90degree and the panel and breaker are 75degree; yet the 55a limit is as though they were 60degree. So the extra 5 amps is not a big deal. I don't understand any of the 3 degree things. Temperature rating of the insulation (some insulating materials can withstand higher temperatures than others). -- Regards, Doug Miller (alphageek at milmac dot com) It's time to throw all their damned tea in the harbor again. |
#27
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Breaker on #6 copper
"mm" wrote in message ... On Sat, 04 Aug 2007 20:38:19 -0700, terry wrote: The reference 'is only capable of carrying 55 amps "at 120V", is superfluous. We are considering current here, not voltage. Absolutely. The heat, if any, generated by the current flowing through the wire is totally dependant on how much current is flowing, and unrelated to the voltage applied to the whole circuit. That is not quiet right! "voltage drop" in the line times current equals watts which generate heat in or on the line so voltage does have some effect. I think this will help a few people and won't help others at all. E=IR (Remember that. ) In other words: EMF=Current times resistance. EMF= Electro Motive Force In other words, in this case: IxR=E Voltage = 55 amps x R (resistance) Power = Voltage x Amps. (Remember this.)In other words, in this case: Watts = voltage x 55 amps. But the voltage in the formula above is not the 110 or 220 that comes from the wall. It's the voltage drop from one end of the wire to the other, which is small, because the resistance of the wire is small. The total voltage drop of an appliance plugged in to a wall is 110 or 220 or whatever, but almost all of that voltage drop is in the appliance, and not in the cord going to it. It's the saw or washer or water heater or mixmaster that is designed to do the work, and the wire to it is designed to have low resistance and not impeded the electrficity getting to the appliance. But, in this case we're talking about running 6 gauge wire with a 60 amp breaker, even though the wire is rated at only 55 amps. So how much heat (power or watts, iirc) will be generated in that wire if the current goes up to just shy of 60 amps, even though it is rated at 55 amps. Look at the formulas at the top, and then continue he Since voltage = 55 amps x R, then: Watts = 55 amps x R x 55 amps. In other words:can you make simple (E=Volts) x (I=Curent) =(W=Watts) Watts = (55 amps) squared x R. Where R is the resistance of the wire feedinn the appliance. This is not the number of watts given off by a lightbulb, if there is a lightbulb in the appliance, or used by the motor if there is a motor in it. It's the number of watts given off by the wire feeding the appliance. And it is totally unrelated to the voltage applied to the appliance** **Except insofar as if higher voltage were applied, more current woudl go through the same resistance wire and appliance. And for any General use #6 wire three in conduit is rated for 65 Amps. |
#28
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Breaker on #6 copper
Tony wrote:
"mm" wrote in message ... On Sat, 04 Aug 2007 20:38:19 -0700, terry wrote: The reference 'is only capable of carrying 55 amps "at 120V", is superfluous. We are considering current here, not voltage. Absolutely. The heat, if any, generated by the current flowing through the wire is totally dependant on how much current is flowing, and unrelated to the voltage applied to the whole circuit. That is not quiet right! "voltage drop" in the line times current equals watts which generate heat in or on the line so voltage does have some effect. .... Well, yes and no...depends on whether it is a constant current or constant voltage source (or another way to consider it is in regards to the chicken and egg )... For a power circuit fed from the grid, one can consider it a constant voltage source. There is current flow through the circuit only because there is a voltage drop from that source to the neutral. How much voltage drop is in the wiring depends on the resistance of the wiring, that is correct. But how much current flows through the wire depends on the _total_ resistance from the source back to the neutral (assuming a series circuit, the current through each component is the same), not just the wire. So, given that there is a fixed voltage supply and for a particular piece of equipment on the circuit in the shop, the current will also be (nearly) constant and the voltage drop across the wiring will be determined by that current. Consequently, of the wiring loss, the situation looks more like a current source rather than a voltage source. But then again, one can analyze it as if there were a fixed voltage impressed over the cable and arrive at the same numerical result... V = IR P = VI = (IR)I = I^2 R Which is more fundamental; the VI or I-squared R form? All depends on point of view... .... |
#29
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Breaker on #6 copper
In article pFkti.3844$J13.1918@trnddc02, "Tony" wrote:
And for any General use #6 wire three in conduit is rated for 65 Amps. That is incorrect -- the ampacity depends on the insulation. Type TW or UF 6AWG conductors, for example, have an ampacity of 55A. -- Regards, Doug Miller (alphageek at milmac dot com) It's time to throw all their damned tea in the harbor again. |
#30
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Breaker on #6 copper
"Doug Miller" wrote in message et... In article , "Eigenvector" wrote: "M Q" wrote in message news:6u6ti.353$V53.338@trnddc08... Doug Miller wrote: In article AW%si.115$zg3.49@trnddc04, M Q wrote: ... Wrong. Please familiarize yourself with the NEC before attempting to answer electrical questions. A 60A breaker is perfectly fine: "Devices Rated 800 Amperes or Less. The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met ..." [2005 NEC, Article 240.4(B)] The conditions can be summarized as not a multiple-receptacle circuit, no matching standard breaker, and next size up not 800A. Mea Culpa. I was wrong on two points. Thanks for correcting me. I will now slink off with my tail between my legs. You got better treatment than I did from him. If I offended you, I'm sorry - it was unintentional. -- Regards, Doug Miller (alphageek at milmac dot com) Don't worry about, I have thin skin lately. But back to my question, which was more out of interest than contesting a ruling. The 5 extra amps is more than just the wire, what about the device at the other end of that wire - it'll be taking on an additional 5 amps too. Maybe not important, if it has its own fuses, they'll blow too. I was just curious is all. Now this next part is just my mind asking questions, not making personal attacks. A lot of people are firing back claiming the wire can handle 65 A, 60 A, 2000A, whatever, those current carrying capacities aren't advertised on the wire bundle, so how would an electrician know that? I'm presuming an electrician isn't schooled at the same level as an Electrical Engineer. So looking at a wire and being able to tell the ampacity of it seems liberal to me. When they allow higher breaker sizes it also tells me that the NEC conventions are largely anecdotal or arbitrary as opposed to calculated or theoretical values - which is even more worrisome to me. I would expect them to state restrictions and rules more along the lines of "This is the theoretical limit of this particular wire, plus a safety margin of 1.5 - you may not use something higher than this value" Rather than, "Just use the next highest one, they don't make the correct one for it." If they were to state something like that, I would also expect them to qualify it by stating the reason why they make that allowance. Like I said, just me asking questions. |
#31
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Breaker on #6 copper
Eigenvector wrote:
SNIP A lot of people are firing back claiming the wire can handle 65 A, 60 A, 2000A, whatever, those current carrying capacities aren't advertised on the wire bundle, so how would an electrician know that? I'm presuming an electrician isn't schooled at the same level as an Electrical Engineer. So looking at a wire and being able to tell the ampacity of it seems liberal to me. When they allow higher breaker sizes it also tells me that the NEC conventions are largely anecdotal or arbitrary as opposed to calculated or theoretical values - which is even more worrisome to me. I would expect them to state restrictions and rules more along the lines of "This is the theoretical limit of this particular wire, plus a safety margin of 1.5 - you may not use something higher than this value" Rather than, "Just use the next highest one, they don't make the correct one for it." If they were to state something like that, I would also expect them to qualify it by stating the reason why they make that allowance. Like I said, just me asking questions. Indeed, electricians are required to know all those fine details. To get some feel for the breadth of Code issues, look at Mike Holt's pages which include a very busy forum on Code issues: http://www.mikeholt.com/Newsletters/Newsletters.htm Jim |
#32
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Breaker on #6 copper
Eigenvector wrote:
.... A lot of people are firing back claiming the wire can handle 65 A, 60 A, 2000A, whatever, those current carrying capacities aren't advertised on the wire bundle, so how would an electrician know that? I'm presuming an electrician isn't schooled at the same level as an Electrical Engineer. So looking at a wire and being able to tell the ampacity of it seems liberal to me. When they allow higher breaker sizes it also tells me that the NEC conventions are largely anecdotal or arbitrary as opposed to calculated or theoretical values - which is even more worrisome to me. I would expect them to state restrictions and rules more along the lines of "This is the theoretical limit of this particular wire, plus a safety margin of 1.5 - you may not use something higher than this value" Rather than, "Just use the next highest one, they don't make the correct one for it." If they were to state something like that, I would also expect them to qualify it by stating the reason why they make that allowance. Like I said, just me asking questions. The electrician doesn't have to know what the theoretical current-carrying capacity of a conductor is -- all he has to do is learn the basic rules of NEC (or whatever particular code variant he is working under). The NEC is a product of the NFPA which is a nonprofit organization formed initially by a bunch of insurance underwriters for the purpose of trying to bring some order into common practice and to reduce the prevelance/frequency of fires owing to poor practice (and, given the time in which they started, not in small part, to define what good practice entailed.) The code is pragmatic and not intended as a technical treatise or engineering specification. That saic, there are bases for each rule and reasons for the rule and the exceptions to the rules. As others have said, the tendency is to make the rules conservative with respect to actual practices that would be an imminent and immediate danger. Code is written by committee of member representatives and is, for the most part, a volunteer activity. For an overview of the Code development process, see the following link... http://www.nfpa.org/categoryList.asp?categoryID=161& URL=Codes%20and%20Standards/Code%20development%20process Having served on another Standards committee subcommittee in the past with similar rules, it is a protracted process to say the least... -- |
#33
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Breaker on #6 copper
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#34
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Breaker on #6 copper
Eigenvector wrote:
When they allow higher breaker sizes it also tells me that the NEC conventions are largely anecdotal or arbitrary as opposed to calculated or theoretical values - which is even more worrisome to me. I would expect them to state restrictions and rules more along the lines of "This is the theoretical limit of this particular wire, plus a safety margin of 1.5 - you may not use something higher than this value" Rather than, "Just use the next highest one, they don't make the correct one for it." If they were to state something like that, I would also expect them to qualify it by stating the reason why they make that allowance. Like I said, just me asking questions. Like most "regulations," there is no requirement that a "reason" be given. Often the regulation is arbitrary and based on emotional satisfaction rather than science (silicone breast implants, arsenic levels in municipal water systems). Other times, like having a licensed electrician (or union member), be responsible for changing a light bulb, the underlying reason is political or economic. Sometimes, like the regulations prohibiting PEX in California, the regulation is merely a pride issue. |
#35
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Breaker on #6 copper
Doug: no disrespect to you are any one ales in this forum,
I have no degree to speak of so I am not going to contradict you But from my understanding insulation do not have anything to do with wire Ampacity or in the other words capacity to carry amount of current. Wire insulation rating is for soly purpose where that wire can be used to be able to carry it's rated current. example # 10 wire insulated with rubber is good up to maximum 140 Deg. F regardless if is carrying 30 amps. or 10 amps. because at that temp. rubber will start to melt. I use lot of glass cover wire and Teflon but # 10 wire is good only for up 30 amps. higher amperage requires larger conductor 8 or 6 whatever I may need so I don't see insulation been factor here I am sorry that is the way I see it Tony www.cas-environ.com "Doug Miller" wrote in message . net... In article pFkti.3844$J13.1918@trnddc02, "Tony" wrote: And for any General use #6 wire three in conduit is rated for 65 Amps. That is incorrect -- the ampacity depends on the insulation. Type TW or UF 6AWG conductors, for example, have an ampacity of 55A. -- Regards, Doug Miller (alphageek at milmac dot com) It's time to throw all their damned tea in the harbor again. |
#36
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Breaker on #6 copper
In wire sizes 10-12-14, the NEC limits the ampacity to 30-20-15 regardless
of insulation type, but in larger sizes the NEC allows different amperages depending upon insulation type, as well as other factors "Tony" wrote in message news:OPpti.3043$dD3.1679@trnddc07... Doug: no disrespect to you are any one ales in this forum, I have no degree to speak of so I am not going to contradict you But from my understanding insulation do not have anything to do with wire Ampacity or in the other words capacity to carry amount of current. Wire insulation rating is for soly purpose where that wire can be used to be able to carry it's rated current. example # 10 wire insulated with rubber is good up to maximum 140 Deg. F regardless if is carrying 30 amps. or 10 amps. because at that temp. rubber will start to melt. I use lot of glass cover wire and Teflon but # 10 wire is good only for up 30 amps. higher amperage requires larger conductor 8 or 6 whatever I may need so I don't see insulation been factor here I am sorry that is the way I see it Tony www.cas-environ.com "Doug Miller" wrote in message . net... In article pFkti.3844$J13.1918@trnddc02, "Tony" wrote: And for any General use #6 wire three in conduit is rated for 65 Amps. That is incorrect -- the ampacity depends on the insulation. Type TW or UF 6AWG conductors, for example, have an ampacity of 55A. -- Regards, Doug Miller (alphageek at milmac dot com) It's time to throw all their damned tea in the harbor again. |
#37
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Breaker on #6 copper
In article , "Eigenvector" wrote:
But back to my question, which was more out of interest than contesting a ruling. The 5 extra amps is more than just the wire, what about the device at the other end of that wire - it'll be taking on an additional 5 amps too. No, actually, they won't. A device draws whatever it draws. A 1200W heater, for example, pulls 10A at 120V whether the circuit it's on has a 15A breaker or a 100A breaker. Maybe not important, if it has its own fuses, they'll blow too. I was just curious is all. Nope; see above. Now this next part is just my mind asking questions, not making personal attacks. A lot of people are firing back claiming the wire can handle 65 A, 60 A, 2000A, whatever, those current carrying capacities aren't advertised on the wire bundle, so how would an electrician know that? I'm presuming an electrician isn't schooled at the same level as an Electrical Engineer. So looking at a wire and being able to tell the ampacity of it seems liberal to me. You don't tell the ampacity just from looking at the wire. Well, you might if you have NEC Table 310.16 memorized, but it's the table that tells you, not the wire. When they allow higher breaker sizes it also tells me that the NEC conventions are largely anecdotal or arbitrary as opposed to calculated or theoretical values - which is even more worrisome to me. It should be worrisome if your conclusion were correct; fortunately, it's not. It's important to remember that the Code allows going up *one*, and only one, breaker size, and then only if the listed ampacity does not correspond to a standard breaker size. For instance, a wire with a listed ampacity of 50A may *not* be breakered at 60A, because 50A is a standard breaker. I would expect them to state restrictions and rules more along the lines of "This is the theoretical limit of this particular wire, plus a safety margin of 1.5 - you may not use something higher than this value" Rather than, "Just use the next highest one, they don't make the correct one for it." There isn't really any difference between the two situations, and the latter is much more convenient to implement in practice. If they were to state something like that, I would also expect them to qualify it by stating the reason why they make that allowance. Like I said, just me asking questions. Perhaps the most important thing that you're missing here is the part of 240.4(B) that says "provided all of the following conditions are met" -- conditions which I only summarized in my earlier posts in this thread. It seems to me that it's time to quote the first one in full, and comment on it: "(1) The conductors being protected are NOT part of a multioutlet branch circuit supplying receptacles for cord-and-plug-connected portable loads." [emphasis added] Let's examine the possibilities under which the bump is permitted by this condition: 1) Circuit has no receptacles at all. That means it's feeding either a subpanel, or direct-wired stationary equipment. In the former case, the load will depend on which circuits in the subpanel are in use, and is unlikely to ever be at maximum. In the latter case, the load is precisely known, and the safety (or lack thereof) is readily determined. 2) Circuit has a single receptacle, or multiple receptacles, for cord-and-plug-connected NON-portable equipment. Again, the actual load can be readily determined: you know what's going to be used on the circuit, because it's sitting right next to the outlets, and it isn't going anywhere. A circuit supplying outlets for a table saw and a 5HP air compressor would be a good example of this category. 3) Circuit has a single receptacle for cord-and-plug-connected portable equipment. It is unlikely that any Code-compliant circuits can exist in this category: the *lowest* listed ampacity that would be permitted to be bumped is a 55A conductor breakered at 60A; it is a Code violation to install a receptacle with a rating lower than that of the overcurrent device on any circuit over 20A; and any load which requires a 60A (or higher) rated receptacle is highly unlikely to meet anyone's definition of "portable". In short, this means that the bump up to the next higher breaker size is limited to circumstances in which the load is either limited, or more or less fixed, and readily predictable. -- Regards, Doug Miller (alphageek at milmac dot com) It's time to throw all their damned tea in the harbor again. |
#38
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Breaker on #6 copper
In article OPpti.3043$dD3.1679@trnddc07, "Tony" wrote:
Doug: no disrespect to you are any one ales in this forum, I have no degree to speak of so I am not going to contradict you But from my understanding insulation do not have anything to do with wire Ampacity or in the other words capacity to carry amount of current. Well, I'm sorry, but your understanding is incorrect. Ampacity depends on multiple factors, and insulation is one of them. I'll try to explain. Wire insulation rating is for soly purpose where that wire can be used to be able to carry it's rated current. Exactly. And the rating depends on the type of insulation (among other things) -- this is laid out clearly in Table 310.16 of the National Electrical Code. example # 10 wire insulated with rubber is good up to maximum 140 Deg. F regardless if is carrying 30 amps. or 10 amps. because at that temp. rubber will start to melt. Which is exactly why wires with rubber insulation are limited to carrying currents low enough to *not* heat the wire up that much. Wires insulated with materials capable of withstanding higher temperatures are allowed to carry more current because they can get hotter without damaging the insulation and creating a hazard. I use lot of glass cover wire and Teflon but # 10 wire is good only for up 30 amps. higher amperage requires larger conductor 8 or 6 whatever I may need so I don't see insulation been factor here The insulation *isn't* a factor for AWG10 and smaller wires, because the NEC specifically limits the allowable breaker rating for AWG10, 12, and 14 conductors to 30A, 20A, and 15A respectively, regardless of what insulating material is used. For wires AWG8 and larger, the ampacity *does* depend on the insulation. For example, AWG8 wires with Type TW insulation are limited to 40A -- but with Type THHN insulation, the allowable ampacity is 55A. I am sorry that is the way I see it Tony www.cas-environ.com "Doug Miller" wrote in message .net... In article pFkti.3844$J13.1918@trnddc02, "Tony" wrote: And for any General use #6 wire three in conduit is rated for 65 Amps. That is incorrect -- the ampacity depends on the insulation. Type TW or UF 6AWG conductors, for example, have an ampacity of 55A. -- Regards, Doug Miller (alphageek at milmac dot com) It's time to throw all their damned tea in the harbor again. |
#39
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Breaker on #6 copper
HeyBub wrote:
.... Like most "regulations," there is no requirement that a "reason" be given. Often the regulation is arbitrary and based on emotional satisfaction rather than science (silicone breast implants, arsenic levels in municipal water systems). Other times, like having a licensed electrician (or union member), be responsible for changing a light bulb, the underlying reason is political or economic. Sometimes, like the regulations prohibiting PEX in California, the regulation is merely a pride issue. Some of those _may_ have some merit, but I'm doubtful of most... W/ the NEC, there is a very long and involved process of building the Code and while it isn't required (nor even very meaningful) to publish every nuance of "why" underlying the actual code provisions, there are defensible reasons for them and there has to be sufficient basis to win the approval of a sizable number of participants. At last time I looked there were some 80,000 members of the NFPA and the NEC had something otoh 5,000(!) peer reviewers. With that many folks involved, anything _too_ arbitrary or one-side simply isn't going to fly. It may appear arbitrary, but like most things, the details are far more complex than they may appear from the outside. -- |
#40
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Breaker on #6 copper
dpb wrote:
Eigenvector wrote: ... A lot of people are firing back claiming the wire can handle 65 A, 60 A, 2000A, whatever, those current carrying capacities aren't advertised on the wire bundle, so how would an electrician know that? I'm presuming an electrician isn't schooled at the same level as an Electrical Engineer. So looking at a wire and being able to tell the ampacity of it seems liberal to me. When they allow higher breaker sizes it also tells me that the NEC conventions are largely anecdotal or arbitrary as opposed to calculated or theoretical values - which is even more worrisome to me. I would expect them to state restrictions and rules more along the lines of "This is the theoretical limit of this particular wire, plus a safety margin of 1.5 - you may not use something higher than this value" Rather than, "Just use the next highest one, they don't make the correct one for it." If they were to state something like that, I would also expect them to qualify it by stating the reason why they make that allowance. Like I said, just me asking questions. The electrician doesn't have to know what the theoretical current-carrying capacity of a conductor is -- all he has to do is learn the basic rules of NEC (or whatever particular code variant he is working under). The NEC is a product of the NFPA which is a nonprofit organization formed initially by a bunch of insurance underwriters for the purpose of trying to bring some order into common practice and to reduce the prevelance/frequency of fires owing to poor practice (and, given the time in which they started, not in small part, to define what good practice entailed.) The code is pragmatic and not intended as a technical treatise or engineering specification. That saic, there are bases for each rule and reasons for the rule and the exceptions to the rules. As others have said, the tendency is to make the rules conservative with respect to actual practices that would be an imminent and immediate danger. Code is written by committee of member representatives and is, for the most part, a volunteer activity. For an overview of the Code development process, see the following link... http://www.nfpa.org/categoryList.asp?categoryID=161& URL=Codes%20and%20Standards/Code%20development%20process Having served on another Standards committee subcommittee in the past with similar rules, it is a protracted process to say the least... Which one? Nice description, I quite generally agree. IIRC the chemical industries forced a change from "hazardous" wiring to "classified" wiring. And I think the health care industries forced more significant changes to the chapter on health care facilities. Both examples quite old but there are probably still 'aberrations'. The process in general works pretty well. A few of the steps for NEC revision: Proposed changes are submitted by anyone. A panel makes decisions on the proposals and the results are published in the "Report on proposals" - ROC. The public makes comments on the proposed changes. The panel makes decisions using the comments and the results are published in the "Report on comments" -- ROC. There are a few more steps. The ROP and ROC are available (when I last looked) on the internet. Reading them can be interesting. You get the logic for the change (and occasionally lack of logic). When a proposed change fails you may get the logic (or lack of logic) for why the code is written as it is. -- bud-- |
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