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

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  • lcm1947
    Veteran Member
    • Sep 2004
    • 1490
    • Austin, Texas
    • BT 3100-1

    #31
    Well I for one appreciate the thread and understand this was just at attemp educate us so thank you Loring, I sure didn't know that about circuits. I thought I had to have all 20 amp service out in the garage and spent good money getting it out here. Had I known a 15 amp curcuit would do for most of my bench top tools I could have saved some money and worry. That's why this forum is so great. I learn tons of stuff just like this. Thanks for the thread Loring.
    May you die and go to heaven before the Devil knows you're dead. My Best, Mac

    Comment

    • MBG
      Senior Member
      • Apr 2003
      • 945
      • Chicago, Illinois.
      • Craftsman 21829

      #32
      (You'll have to excuse me because I'm a mechanical engineer.)

      But, this is all good info but not practical in practice. As I have been told over-and-over is that a fuse or circuit breaker is for the protection of the wire. To be cautious you may want to add a secondary breaker at the device (my Delta TS has internal overload protection) but think of all the other things in your house that are not rated for full amperage the circuit allows.

      So I would suggest to be smart. If you have dedicated circuits for every tool, yes install a breaker at the tools rating. Most of us don't have the capability of separate circuit for every tool so in that case where the breaker is above the tools rating make sure the tool is protected at the tool independently.

      Comment

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

        #33
        That is my suggestion, a good quality power strip w. overload breaker built in . I do not think my BT3K has an overload breaker like on induction motors. I use such a set up on my large generator, have the strip bolted to the frame. Correct me if I am wrong.
        Andrew

        Comment

        • lcm1947
          Veteran Member
          • Sep 2004
          • 1490
          • Austin, Texas
          • BT 3100-1

          #34
          I know or at least I think I know that it is not s good idea to add any length of extension cord to run any device. Now I know it's ok to some degree but if you can avoid it you should, right? At least that's my understanding being a insurance agent anyway. OK, now my question. Is it a good idea to add one of these power strips to each tool where they do not have a built-in protector? I've for years have been avoiding them whenever and wherever I could. Is my thinking or understanding wrong?
          May you die and go to heaven before the Devil knows you're dead. My Best, Mac

          Comment

          • eezlock
            Senior Member
            • Feb 2006
            • 997
            • Charlotte,N.C.
            • BT3100

            #35
            circuit breakers...

            Originally posted by LCHIEN
            Seems to me like Circuit breakers are commonly used by everyone and little understood by most. I will explain Circuit breakers and why you should not use a 20A breaker with your BT3x saw.

            Technical basis for this tutorial comes from the Square-D company that makes circuit breakers used in their panels for industrial and residential uses. These are designed to the same guidelines of the National Electrical code as other manufacturers' breakers so the operation should be the same.

            I think the typical person thinks circuit breakers are black and white devices. That is, for a 15A breaker that if the current is 14.9 amps it will continue to conduct and if the current rises to 15.1 Amps it will open up and disconnect the circuit.

            But in reality, circuit breakers are both time and current sensitive. This is a very useful thing because it allows us to use devices which vary in current pull so that the average is 15 amps and have peaks (say when your saw encounters a knot, or when a motor or light bulb turns on) very much in excess of 15 amps.

            If you look at the end of the reference document, it has trip-point curves for the breakers , time vs. normalized current (e.g. the rated, or handle current is considered to be "1"). The curves and the text say that the circuit breaker should conduct the rated "handle" current (e.g. the value marked on the handle) pretty much forever if the ambient temperature is less than 40°C (~104°F). If the current is over about 1.5 times the rated current for longer than 10-100 seconds the breaker will eventually trip.

            The curves approach the rated current when the time exceeds 10-100 seconds, this is because one trip mechanism is a bimetal element that is heated by the current flow. The element takes time to heat up to the trip point, allowing brief overcurrent surges since the heating takes time. And, devices shifting quickly from 10-20 amps and back but averaging 15 will also work forever.

            The other feature of the curve is that around 9-10 times the rated current (about 135 Amps in this 15A breaker example), the breaker trips within one AC cycle (a few milliseconds) due to the electromagnetic trip element based solely on current. This is sufficient to let motor and light bulb starting curges through.

            Between the two portions of the curve, like from 1.5x to 9x the rated current, the time it takes to trip decreases from 10 seconds to less than .3 of a second.

            Thus you see that circuit breakers will trip immediately on gross overcurrent levels starting around 9x the rating, but allow brief, surges in the 1-10 second or more range. this is consistent with motors which can stand brief surges without overheating due to the thermal mass of the motor.

            If you understand how these work, the people who put a 20A breaker on their dedicated circuit for their BT3100/BT3000 are just fooling themselves and taking a risk that the saw will melt down when overloaded. A 15A breaker for the BT3100/BT3000 is more than sufficient, given the leeway designed into the breakers. A 15A breaker is more than sufficient, allowing current surges consistent with startup and brief surges in operation associated with knots and feeding inconsistencies and other short term irregularities which do not exceed 15A on average. It will also protect the 15A-rated motor properly since the saw itself does not use any current overload protection.


            Reference:
            http://ecatalog.squared.com/techlib/...01&action=view
            Loring...you are right again! #14 gauge wire---15 amps, #12 wire---20 amps
            You can underfuse a wire/cable, but never, never, never overfuse it under any circumstances. It will cause a fire in a heartbeat! eezlock

            Comment

            • eezlock
              Senior Member
              • Feb 2006
              • 997
              • Charlotte,N.C.
              • BT3100

              #36
              tripping breaker...

              Originally posted by Sawatzky
              I had my saw plugged into a 15 amp circuit. It was always tripping, especially in hot weather. I used no extension cord either. Even if I had other devices plugged into the same circuit (the circuit powered additional plugs in my garage) but did not turn them on, the circuit still tripped when I ran my BT. I added a 20 amp circuit because of advise on this forum. I now plug my BT and miter saw (both with 15 amp motors) into this outlet. I have not had any problems. Will I really damage my tools? If so, how do I avoid tripping the breaker all the time?
              Might want to check those tools that keep tripping the breaker...sounds as if there is a problem somewhere. That problem could be a weak breaker
              in the panel, if it is an old one, been installed for several years, and has tripped several times under a heavy load...the spring mechanism is getting weak. I would test it by hand, if that breaker does not have a strong positive
              snapping action when you turn it off and back on...it is weak, just replace
              it with a new proper sized one. eezlock

              Comment

              • eezlock
                Senior Member
                • Feb 2006
                • 997
                • Charlotte,N.C.
                • BT3100

                #37
                power cord size...

                Originally posted by lcm1947
                I wasn't sure either so just went out and copied what my actual DC says and I quote;

                Central Machenery Model 45378, DC- 2 HP 70 Gal.,
                Motor 2 HP, 20 amps Peak,
                Single phase, 60 Hz
                110 volts,
                RPMs 3450,
                Power cord 5 1/2" 16 AWG x 3C gauge.

                I wonder why ours differs so much. I bought mine about 2 years ago maybe that's it? Also the 16 AWG power cord puzzles me. 16 AWG? Sure seems light to me.
                Mac, I would see what length cord is there (maximum) and go to nearest
                HD or Lowe's and get a #12 awg cord (stranded type)and new grounded plug install it and throw that piece of crap cord in the trash where it belongs, #16awg cord is not much heavier than a stupid lamp cord you would use in the house! eezlock

                Comment

                • JimD
                  Veteran Member
                  • Feb 2003
                  • 4187
                  • Lexington, SC.

                  #38
                  Interesting thread.

                  I agree, I think, with Lorings main point that a 15A circuit is sufficient for the BT3100.

                  I also agree with the points LJR made, however. If we depend on the circuit breaker to protect our BT3100 we are likely to be sorry regardless of whether it is a 15A or a 20A circuit. 15 will trip a little sooner but it seems to me there is a good chance the saw will be dead regardless. Many of us have determined that the weak link of the BT3100 is the belts (at least for a "jamb-up" situation). The belts melt before the motor can overheat and fail.

                  Lastly, I put a 20A circuit in my shop because at the time I was using a contractor style saw with a full 1 hp induction motor and I still have an identical motor on my planner/jointer. I used it in my last house on a 15A circuit but it would trip regularly. Part of that problem was the fact that the circuit ran from the basement panel to the second floor bathrooms and back to the basement outlet I was using. A more reasonable circuit run while leaving it 15A might have solved the problem but I just put in a 20A. If you want to gain a slight amount of margin in protecting equipment, a 15A may be a better way to go but watch the circuit length. I am still happy with my 20A but I found Lorings post interesting, as usual.

                  I forgot, stranded wire can have a bit lower resistance because electicity wants to flow on the surface of the conductor, not evenly across the cross section. The effect is significant on large very high voltage conductors but I don't know how big it is on house sized wires.

                  Jim

                  Comment

                  • footprintsinconc
                    Veteran Member
                    • Nov 2006
                    • 1759
                    • Roseville (Sacramento), CA
                    • BT3100

                    #39
                    20 amp?

                    loring, well, its a very interesting post that you started! i was just contemplating this myself since i read on another thread about the person who was burning wood while trying to rip. he had his shop vac on aswell on the same circuit. I have that very problem aswell. my solution was to go to 20amp circuit so that i could now use both machines at the same time.

                    my one car garage has three outlets, that are connected with all the outlet on the outside of my house and they are inturn connected to the kitchen ones. that is what the builder told us. he said if there is no power in the garage or outside, make sure none of the bathroom or kitchen test have tripped.

                    so i thought, that i would install a 20amp in the box and then run a wire from there to the one in the garage, and then disconnect it from the other circuit.

                    now that i have read all these post, i am confused as what to do. really really confused. any advice?
                    _________________________
                    omar

                    Comment

                    • LCHIEN
                      Internet Fact Checker
                      • Dec 2002
                      • 20914
                      • Katy, TX, USA.
                      • BT3000 vintage 1999

                      #40
                      Originally posted by footprintsinconc
                      loring, well, its a very interesting post that you started! i was just contemplating this myself since i read on another thread about the person who was burning wood while trying to rip. he had his shop vac on aswell on the same circuit. I have that very problem aswell. my solution was to go to 20amp circuit so that i could now use both machines at the same time.

                      my one car garage has three outlets, that are connected with all the outlet on the outside of my house and they are inturn connected to the kitchen ones. that is what the builder told us. he said if there is no power in the garage or outside, make sure none of the bathroom or kitchen test have tripped.

                      so i thought, that i would install a 20amp in the box and then run a wire from there to the one in the garage, and then disconnect it from the other circuit.

                      now that i have read all these post, i am confused as what to do. really really confused. any advice?
                      Well, yes, that's the discussion thread that made me write this one.

                      A new 20A circuit is not enough for saw and Vac, typcially (and this depends on the size of the vac) Vacs take 10 amps by themselves as I pointed out in the other thread leaving only 10a for your saw. Less than ideal.

                      What I would do if I were you,
                      Run the Vac on the existing circuits and run a new circuit of 15A just for the saw. IT's real lousy that they hooked the kitchen circuits to the garage shared. Even if you do as I recommend, your wife running a toaster or electric frying pan while you are running the vac can trip your breaker.

                      Probably the builder saved $5 on a second GFCI and $7 on a breaker by sharing it on the kitchen and garage on a single circuit! Instead of a GFCI and breaker each for two circuits.
                      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

                      • footprintsinconc
                        Veteran Member
                        • Nov 2006
                        • 1759
                        • Roseville (Sacramento), CA
                        • BT3100

                        #41
                        Thanks! that's a good idea. i dont know anything about electricity, so my common sense takes a dump at topics like this. now i just have to get into the attic and figure out a route .....
                        _________________________
                        omar

                        Comment

                        • gjat
                          Senior Member
                          • Nov 2005
                          • 685
                          • Valrico (Tampa), Florida.
                          • BT3100

                          #42
                          I AM NOT AN ELECTRICIAN, but I've managed industrial/commerical electrical projects for 20+ years. I'm looking at my UGLY's Electrical Reference book since I don't want to get up to get my NEC.

                          You want the breaker to be the weak link in the circuit. Not the wire, not your tool. NEVER put a 20a breaker on 14ga wire. That is NEC.

                          Wire is rated by 'ampacity' (amp compacity). How it is installed, it's environment, insulation, etc., determines it's ampacity. When wire can't dissapate heat, it will melt through the insulation. In 'Optimal' conditions, which is free air, the ampacity of a single #14 conductor is 25 amps, but NEC code states that is should NEVER be protected by more than a 15amp breaker. It's a SAFETY thing. Not convenience, not to save a few bucks.

                          I've seen lot's of 120v things burn up, catch fire, etc., before the breaker trips. Breakers fail all the time. Don't risk it! Do things properly and safely.

                          Comment

                          • footprintsinconc
                            Veteran Member
                            • Nov 2006
                            • 1759
                            • Roseville (Sacramento), CA
                            • BT3100

                            #43
                            i should have asked before, so with the new wire that i am going to put in dedicated for the table saw, its going to have a 15amp breaker. what guage wire should it be? its going to have a 60' run by the time i get from the breaker to my shop and i live in phoenix, so its burning hot in the summer, especially in the attic!
                            _________________________
                            omar

                            Comment

                            • LCHIEN
                              Internet Fact Checker
                              • Dec 2002
                              • 20914
                              • Katy, TX, USA.
                              • BT3000 vintage 1999

                              #44
                              Originally posted by gjat
                              I AM NOT AN ELECTRICIAN, but I've managed industrial/commerical electrical projects for 20+ years. I'm looking at my UGLY's Electrical Reference book since I don't want to get up to get my NEC.

                              You want the breaker to be the weak link in the circuit. Not the wire, not your tool. NEVER put a 20a breaker on 14ga wire. That is NEC.

                              ....
                              YES! That sort of goes w/o saying. I was attempting to make the point that, given wire big enough to carry 20 Amps, it would still be advisable to put a 15A breaker on your saw circuit.

                              As for wire gauges, there are reasons to use heavier gauge wire than the NEC suggests for the current. Such as to minimize the voltage drop on long runs. NEC's sugestions are for fire prevention by melting of the insualtion as you suggest. In this case, wire heats up carrying current due to the Resistance times Current squared product. The power per foot dissipated is constant down the whole wire. Even though 200 ft of wire dissipates twice as much total power as a 100 ft wire, the local heating per unit distance is the same. Unable to dissipate power "down the line" because the adjoining wire is the same temp, all power must be dissipated to the sides.
                              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

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