Circuit Breaker Tutorial-why you should not use a 20A breaker.

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  • LCHIEN
    Internet Fact Checker
    • Dec 2002
    • 20913
    • Katy, TX, USA.
    • BT3000 vintage 1999

    #16
    Originally posted by atgcpaul
    However, I think NEC calls for most circuits to NOT carry more than
    80% of its maximum load. In this case, I would think a 20A circuit would be
    better suited.



    Paul
    If you read the article you sent me in detail, it says that the 80% rule applies to continuous loads, by definition continuous means more than 3 hours continuous load at that level. I doubt any of us uses their BT3 at continuous levels of 15Amps for more than 3 hours straight. Even if you leave the saw running while you select and feed new pieces of wood I would be surprised to find you could apply full load more than 50% of the time.

    I don't mean to cause panic or alarm and if you have a 20Amp breaker I don't mean for you to go and change it immediately.

    I am just suggesting that those who say you need a 20Amp breaker or say a 20Amp breaker will give better performance should be taken with a grain of salt.

    My reading of the technical information on breakers and my background in applying technical specifications to the design of systems and equipment says that a 15Amp breaker will be more than sufficient for the BT3000/BT3100 saw with the 15Amp motor. And that using a 20Amp breaker gives some window of opportunity for motor damage that a 15Amp breaker would not.

    As a post script, I would venture to say that running the BT3000/BT3100 continuously at 15 Amps for 3 hours would surely ruin the motor. I believe that although the designers did not so specify, that their intention with the universal motor was that 15Amp use would be intermittent, with duty cycles of 50% or less and duty periods of around a minute or so to rip a long board.
    Last edited by LCHIEN; 12-31-2006, 12:10 PM.
    Loring in Katy, TX USA
    If your only tool is a hammer, you tend to treat all problems as if they were nails.
    BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

    Comment

    • LCHIEN
      Internet Fact Checker
      • Dec 2002
      • 20913
      • Katy, TX, USA.
      • BT3000 vintage 1999

      #17
      Originally posted by Andrew Benedetto
      I am confused on this b/c the code does not change the gauge w.wire style. A contractor I know says that there is no advantage in resistance either way. Could you explain? I know some people who think that solid wire is better.
      Stranded wire of the same equivalent gauge is intended to have essentially the same resistance per foot characteristic.
      But, To qualify that,
      stranded wire is made of multiple strands of smaller gauge wire, usually 7 strands ( 6 around one), or 10, 16 19 or 26 strands which fill a round matrix nicely (otherwise it becomes lumpy and looks and handles awfully). The gauge of the fine wire is chosen to be at least 1/7 (for the 7 strand version) of the overall cross section of the wire your trying to build. You don't go under because then the reistsance will be too low.

      Because of the granualrity (e.g. limited choices) of standard fine sizes and the stranding choices, usually the stranded wire will have slightly more overall cross section and hence resistance. In my experience, this may amount from anywhere to 1 to 10% improved resistance (that's an off the cuff value, I didn't look it up). So in reality, the same gauge stranded wire may likely have less resistance because of the way its made. However, it's not something I would take to the bank. One because the difference is small, and two, because for a large gauge wire, you may find 7, 19 and 26-strand versions all with slightly varying (1-10%) less resistance compared to the solid.

      Theoretically, they can make in-between fine-gauge wires to make the resistance come out exact, but they don't (Standard wire dies, I guess). Note also stranded wire (before insulation) will always be larger diameter than solid of the same equiv gauge due to the interstices (air gaps) between the round components.
      Last edited by LCHIEN; 12-31-2006, 12:39 PM.
      Loring in Katy, TX USA
      If your only tool is a hammer, you tend to treat all problems as if they were nails.
      BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

      Comment

      • atgcpaul
        Veteran Member
        • Aug 2003
        • 4055
        • Maryland
        • Grizzly 1023SLX

        #18
        Originally posted by atgcpaul
        However, I think NEC calls for most circuits to NOT carry more than
        80% of its maximum load. In this case, I would think a 20A circuit would be
        better suited.



        Paul
        If you read my post again, I wasn't arguing to put the saw on a 20A circuit.
        The DC, however, is rated at 14A and with NEC's 80% suggestion, the DC should be on a 20A circuit.

        Per the article:

        "100%-rated devices. The NEC does recognize complete assemblies (including the OCPDs) that are listed for operation at 100% of their rating for continuous loads. This means that the equipment has undergone additional testing to verify that it can handle the additional heat rise associated with this level of operation.

        ...

        In summary, a CB either carries a standard rating (80%) or a 100% rating.
        The standard rating is subject to the NEC sizing rules we've just discussed.
        CBs that are 100%-rated are permitted to be loaded continuously at their full
        rating as long as the assembly is listed and conductors are properly
        connected."

        Now, I don't know if my CBs are rated for continuous use at 100%, but I
        have the same DC and I'm going to stay on the safe side and use the 80%
        rule.

        Paul

        Comment

        • MikeR
          Forum Newbie
          • Dec 2006
          • 86
          • Bayside, NY
          • Craftsman 21829

          #19
          Thank you Loring, valuable information indeed.

          I run the saw on a single dedicated 15A circuit and the vac on a separate one.

          So far, no problems.

          I didn't know about the surge and time lag thing. Another example of the treasures that probably exist here.

          Cheers,

          MikeR

          Comment

          • SARGE..g-47

            #20
            Interesting conversation going here. I have a 20 A circuit with outlets every five feet running down one side of my shop and another 20 a with same running down the other side. Both have #12 solid copper wire and 20 A outlets. I also have a 20 Amp 220 v I ran with #10 guage copper running over-head from the box in central rear to the front of shop where I attach my BS that could be up-graded to 30 A by my choice of wire if I pick up nay machines drawing over 20 Amps (ala MIni Max.. etc.. etc..)

            I run the BT on one of the 20 A's and the DC on the other as I will usually have another small, protable exhaust fan set behind the work to push fine particles of saw-dust away from me breathing them and towards the front of the shop where I want it till the leaf blower gets the call to remove it. In summer, fall and spring I just open the doors.

            All have been cleared upon connection by my certified electricialn after I laid them and originally suggeted by an electrical engineer friend when I presented him with what I intended to use them for and machine electrical draw data.

            Never had any problems with years of continous use so far.... But I learned something about getting involved in electrical conversations a long time ago. With the varied degree of expertise in the same conversation (Elec. Eng... Cert. Electricians and those of us that have different degrees of experience with running our own lines and circuits), it is difficult to get two of all those involved to agree on every single issue that gets tossed out!

            So... I my experience with these matters leads me to just state the obvious...... "I just don't know for absolute sure" and will remain on neutral ground until I do, letting those that are more qualified than me in electricity make the final call and certification in my personal dealing hoping that they are correct. Until then.. smoke alarms and care to make sure I stay within range of the current wiring I have installed will have to do! :>)

            Ya'll have fun reaching a conclussion.. I gotta go get busy in my shop on my wife's table before the smoke alarms go off and fire starts belching from between her beautiful lips. Now that's a 3 ALARM Blaze if I ever saw one and trust me... I've seen one and don't care for repeats. ha.. ha.. ha..ha..ha...

            Happy and prosperous New Year everyone...
            Last edited by Guest; 12-31-2006, 02:01 PM.

            Comment

            • maxparot
              Veteran Member
              • Jan 2004
              • 1421
              • Mesa, Arizona, USA.
              • BT3100 w/ wide table kit

              #21
              Originally posted by Andrew Benedetto
              I am confused on this b/c the code does not change the gauge w.wire style. A contractor I know says that there is no advantage in resistance either way. Could you explain? I know some people who think that solid wire is better.
              Most contractor would prefer to avoid running stranded wire. The reasons are economics. It requires special handling and more labor.
              it is most expensive to produce and therefore costs more. If you check manufacturers data sheets for like gauge wires of stranded and solid core you'll find that they are rated for the same current and voltage capacity. Further checking of stranded vs solid does show a resistant difference favoriing the stranded wire. Additionally as Loring stated stranded wire is available with different strand quantities as the strand number increases the resistance decreases.

              Remember we are talking about optimizing the supply circuit not just having it meet NEC.
              Longer circuit runs will put more demand on the cuicuit. Just as if your were to use an extension cord you would increase it's gauge for a longer cord, This precaution can be taken during the installation of new cicuits in your home or shop. Increased wire gauge and strands decreases resistance in the circuit and thereby allows the power to flow more easily. During long term peak demands on the circuit smaller gauge wires will tend to warm even get hot is overloaded (overloading is avoided with proper CB size) the warming effect is a result of resistance and the warmer the wire gets the more resistance and more heat. This may not be a problem for a few minutes of hard use during the winter. But lets change the equation and make it hours of hard use. Add in that it is occuring during the summer during peak electric use time. The electric company has browned out (cut it's supplied voltage) Under these conditions the work your saw has done many times before may cause the CB to break contact.

              Further consider this; NEC for most industrial situations requires metal conduit and in these type instalations stranded wire is common. As for needing pigtails the smart installer will avoid this extra connection point by tinning the stranded wire.
              Opinions are like gas;
              I don't mind hearing it, but keep it to yourself if it stinks.

              Comment

              • Crash2510
                Senior Member
                • Feb 2006
                • 830
                • North Central Ohio

                #22
                I think that maybe the problem with disregarding nec's 80% rule is that although it may not be in a day, week, or year ,but if you do this to the wire overtime it could eventually burn through.
                Phil In Ohio
                The basement woodworker

                Comment

                • LCHIEN
                  Internet Fact Checker
                  • Dec 2002
                  • 20913
                  • Katy, TX, USA.
                  • BT3000 vintage 1999

                  #23
                  Originally posted by Crash2510
                  I think that maybe the problem with disregarding nec's 80% rule is that although it may not be in a day, week, or year ,but if you do this to the wire overtime it could eventually burn through.
                  No, I pointed out earlier that the NEC current carrying capacity for 14 ga wire is something like 30-35-40 amps. With either a 15 or 20 Amp breaker the wire is very safe from melting insulation and "burning through" as you call it.

                  For load performance sake the wire is recommended to be no less than 14 ga.
                  Loring in Katy, TX USA
                  If your only tool is a hammer, you tend to treat all problems as if they were nails.
                  BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                  Comment

                  • maxparot
                    Veteran Member
                    • Jan 2004
                    • 1421
                    • Mesa, Arizona, USA.
                    • BT3100 w/ wide table kit

                    #24
                    Loring I don't mean to arguementative but I have put a constant 20 amp load on a 14 awg cable and have caused it to melt. I takes a while to heat up but it does.
                    Thankfully I was aware of the posibilty of a problem and was monitoring it carefully. It was temporary wiring to work during the winter using portable electric space heaters. Yes 14awg wire can handle over 15 amps but watch the duration and keep combustables away from the wire. Extension cords increase the hazzard.
                    Opinions are like gas;
                    I don't mind hearing it, but keep it to yourself if it stinks.

                    Comment

                    • niki
                      Senior Member
                      • Nov 2006
                      • 566
                      • Poland
                      • EB PK255

                      #25
                      Hi Loring

                      Can you please clarify something for me.

                      On many occasions I saw that the wire is for, say, "20 A - 110 V" or "20A - 220V"
                      From looking at the AWG table, the voltage is not a factor for choosing the correct wire gauge.

                      I think that any wire gauge can carry any Voltage but the wire thickness will dictate the amount of Amperes (flow) that the wire can stand without melting the insulation.

                      IMO, the same "20A -110V" wire, can carry also "20A - 1000V or more", or, I'm wrong.

                      So, what for is the Voltage marking on the wire.

                      Happy New Year
                      niki

                      Comment

                      • maxparot
                        Veteran Member
                        • Jan 2004
                        • 1421
                        • Mesa, Arizona, USA.
                        • BT3100 w/ wide table kit

                        #26
                        Originally posted by niki
                        So, what for is the Voltage marking on the wire.
                        It's the insulations safety rating.
                        Opinions are like gas;
                        I don't mind hearing it, but keep it to yourself if it stinks.

                        Comment

                        • niki
                          Senior Member
                          • Nov 2006
                          • 566
                          • Poland
                          • EB PK255

                          #27
                          Thank you so much Maxparot

                          In Europe the Voltage is 230V (in UK 240V) so I was not aware to the insulation safety rating.

                          niki

                          Comment

                          • Crash2510
                            Senior Member
                            • Feb 2006
                            • 830
                            • North Central Ohio

                            #28
                            Originally posted by maxparot
                            Loring I don't mean to arguementative but I have put a constant 20 amp load on a 14 awg cable and have caused it to melt. I takes a while to heat up but it does.
                            Thankfully I was aware of the posibilty of a problem and was monitoring it carefully. It was temporary wiring to work during the winter using portable electric space heaters. Yes 14awg wire can handle over 15 amps but watch the duration and keep combustables away from the wire. Extension cords increase the hazzard.
                            Sorry Loring I have to agree with Maxparot. Although it is capable of carrying the amps it just can't disipate the heat fast enough.

                            Although I am only 20 years old I have been doing electrical work with my father for 10 years and have seen wire "burn through" hundreds of times. I think you would be hard pressed to explain to them that the wire was capable of handling the amps when they have melted wires in their boxes.
                            Phil In Ohio
                            The basement woodworker

                            Comment

                            • Andrew Benedetto
                              Veteran Member
                              • Mar 2003
                              • 1071
                              • SoCal, USA
                              • Unisaw w. 52"Bies,22124CM & BT3K

                              #29
                              I run my BT3K on a 20A line I ran in thinwall w. 12 ga. I am thinking maybe a good power strip w. 15a breaker might be a good idea. Any thoughts? I do not like GFI's on motor curcuits otherwise I could add that in the line @15a.
                              Andrew

                              Comment

                              • LJR
                                Established Member
                                • Jan 2005
                                • 136
                                • .

                                #30
                                The breaker is meant to protect the wiring, not necessarily the device plugged into the circuit. It's possible to and we all do plug in something to the circuit that could never handle the full amperage capacity of that circuit (electric razor, hair dryer, those Glade plug in thingies).

                                All modern motors have some sort of internal overload protection and that includes the motors that Ryobi puts on their saws.

                                As Loring says he's not trying to get everyone to rewire their shop. He is suggesting that you take a look at what you're doing and trying to help us understand what a circuit breaker actually does.

                                Running your saw on a correctly wired 20 amp circuit is absolutely fine and safe to do. Running your saw on a correctly wired 15 amp circuit is absolutely fine and safe to do. I have chosen to run all 20 amp circuits in my shop because it gives me greater flexibility on placement of equipment when I change my mind about where to put equipment.

                                Comment

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