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I need to add a 220/240-volt (single-phase) circuit to my shop for a bandsaw. Does a typical circuit breaker allow for a circuit draw above the breaker’s rated output during the first few moments a motor is starting? The bandsaw’s motor is listed as 220volt 15.3 amp. (Supposed to be 3 hp but its European made so who really knows) If I have an electrician (my wife won’t let me near the box) wire a 20 amp 2 pole circuit breaker (type MP) to the Crouse/Hinds load center (100amp service at the panel) will the breaker blow during startup. My understand was that motors often draw 2-3 times their amp rating at startup. At the same time, I don’t want to put a 50amp breaker in if all I needed was 20-amp service to this machine. It could take a while for a 15 amp motor to draw enough to blow a 50 amp circuit breaker that large and seems to sort of negate any benefit of having a breaker in the first place.
The local code calls for a GFCI breaker in the unfinished basement. (It is damp down there at times) JCrocker
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You will have no problems with a 20 amp breaker. That is the first time I have ever heard of a motor drawing that much to start. I have a 1 1/2 and two 2 hp motors that run just fine on a 15 amp braker.
Scott
*I agree with Scott - that sounds safe. The rule of thumb is that you want the circuit to have a capacity 20% greater than your maximum load. You've got just about 25%.Also, make sure that you're wiring is correctly sized at b 12 gauge and no smaller. Most household 15amp applications use 14 gauge, which can overheat and cause fires when used for 20 amps. Many people throw a larger amp breaker in when smaller one keeps tripping - a VERY bad idea, certain to lead to a visit from the fire department.If you do step up to, say a 30amp breaker, then you should increase the wire gauge appropriately, in this case 10 gauge.Scott, I'm assuming you're also using 220v, not 110v as a 2hp motor at 220v is about 12amps and a 1.5hp at 220v is about 10 amps. In this situation running one tool at a time is a safe load for 15amps, but both is not a good idea (I bring this up mainly to illustrate a point). The amperage is double at 110v, which isi waytoo much. In reality, these motors operate at a lower amperage in typical use, but we should always use the maximum rating for load calculations.Best,SethPS. Are you sure about GFCI for a 220v application? You may want to ask your local planning department/buiding inspection department as this is often the case on 110v household circuits, but not for 220v circuits. I'm fairly certain about this, but check. You can ask about GFCI or arc breakers, but these are very pricey items. Also, you'd get a better response to your post if it were not in the Gallery. This section is generally for posting work/pictures. I'd post this in the main forum in the future.Disclaimer - i Never take electrical advice over the internet! Codes vary from locale to locale. Make sure to consult a licensed electrical for your specific application. Whew, now my insurance agent can sleep again tonight!
*Ya I have everything wire seperate that way I never have to worry.As Seth metioned you should always check local code. Most of the people at your local electrial shop can tell you just what you need for your area.Scott
*Here's something you might be interested in. http://www.baldor.com/products/perfdata.asp?1=1&page=1&catalogonly=1&catalog=L3606&product=AC+Motors&family=General+Purpose%7Cvw%5FACMotors%5FGeneralPurpose&phase=1&hp=3&rpm=2800%2D3600It's a link to a basic 3 HP motor on Baldor's website. (They supposedly make really good motors) They list the startup current for a 3HP motor as being 86A. They list the full load current as being 14.5-15A @ 230V. Since they don't say whether that startup current is with the motor wired for 115V or 230V, I have to assume that it doesn't matter.I don't think that your bandsaw will trip the breaker. I think they know about startup currents when they're designing circuit breakers. Anything with an inductive load (i.e. transformers, motors, some lighting circuits) will draw an initial inrush of up to 8X the operating current.By my way of thinking, you can do one of three things:1) Talk to the electrician when he/she comes over to install the service. He/she will know what to do. Just make sure you let him/her know that you're operating a 3 HP motor off of this circuit and you don't want nuisance tripping at startup.2) Find out whether they make time delay circuit breakers. I work in the electrical industry, and we use time delay fuses for larger transformers and motors so that the inrush current doesn't blow fuses that would otherwise be acceptable. If they do make these, that's what you need.3) Install a 30A circuit. This will be OK for that motor. In addition to that, you can operate other machinery you have at 220V and use half the current (and thus save on electricity costs) You will also find that sometimes the equipment seems more powerful when it is wired for 220V, but this is mostly for the machines that run close to the limit of whatever circuit you have them on. For instance, a tablesaw that would draw 20 A full load on a 115V 20A circuit might seem more powerful on a 220V circuit because the inrush and full-load currents don't pull down the system voltage as much. If it were me, I'd run these options past the electrician. The best solution would be to have a time-delay (or "Slo-blo") circuit breaker on a 30A circuit. It's a pretty easy matter to rewire a motor for 220. Even if you don't want to take that route, you'd be prepared if you ever bought another high-power piece of machinery.
*Well, I wired the 220V circuit in my shop with 10 gauge wire and a 40 amp breaker. I have a 1.5hp planer and a 1.5 hp DC running at the same time; both on the 220V circuit. I also occasionally use a welder on that circuit.I installed a separate breaker box in the shop that ties directly to the main meter. I did not want the shop going through the house main breaker box. The local power company came out and disconnected the meter while I made the connections. Most power companies will do this free of charge. A GFCI circuit was not required in my case, nor was a licensed electrician. I did install a ground rod for the shop. I also installed a dis-connect box at the site where the shop line ties into the main meter.If you think that some day you might want additional equipment on that circuit, then I would use 10 gauge wire. Use the 20 amp breaker till that time, then switch it out for a larger breaker. also, 1 HP = 749 Watts. At 220V, that would be roughly 4 amps, considering PF loses, etc. Would be 8 amps using 110V. Startup current can be as much as 1.5 times normal load current. That really depends on the particular piece of equipment you are using.PS - I have a degree in Electrical Engineering (as if that might lend any credibility).
*A small tip - if you do pull 10 gauge wire through conduit pulling i stranded THHN instead of solid THHN is a heck of a lot easier (esp. at long lengths with a bunch of 90s). Just twist the unjacketed end before making connections or use a wire nut and a piece of solid when connecting to the outlet (usually just the ground screw is small and difficult to clamp stranded down with - the hot and neutral aren't as big a pain.) Or leave an 1/8 inch of jacket on the end after stripping to hold the wire together.These methods have saved me a bunch of frustration in the past.Seth
*>>have at 220V and use half the current (and thus save on electricity costs)No savings. You pay for electiciy by the watt--actually kilowatt. Double the voltage, halve the amperage equal same wattage.
*Yup.. P=ExI or P=RxI(2) or P=E(2)/R (Ohms Law) Of course you must realize that this is all based on Electron Theory so if someone is seeing a savings in Kilowatt consumption, we can't actually prove them wrong. I tried to argue that with my Teacher when I'd miscalculate a test question answer...Didn't work.
*Actually, using 220V will save power. 1) the current is half as much, resulting in less resistance loss in the line and the motor. The additionl torque given by using 220V for a motor will keep it running closer to rated speed, again effectively reducing the current draw. Current goes up as speed drops and reverse torque increases. Have you ever tripped the circuit breaker on your TS motor when the blade binds up??
*Mike, I'm probably wrong but I thought the reduction in current was due to the voltage being equal on both sides of the stator. I guess thats the same as reducing overall resistance since the 110v drop is now across only half the field. That would mean that the each leg would now encounter only half as much resistanct and the applied constant voltage would be higher. For some reason I still think that it has to balance to create the same HP. Probably just my stuborn brain unwilling to admit that it has absoulutely no idea what its talking about...LOL..
*Steve - The HP rating stays the essentially the same whether wired for 220 or 110. The 220 windings draw about 1/2 the current as do the 110 windings. Ever notice that a 220 motor does not get as hot as a 110 motor of the same HP rating? Big industrial shops will use 440V 3 phase motors which are very efficient in converting input power to output power. 110V motors are pretty crude, really, in comparison.
*You may be able to get away with the 20 amp/12 awg circuit but you won't be able to run anything else. If you want to expand by adding a DC which would be running at the same time, you would be out of luck. On the other hand it takes very little more effort to install 30 amp/10 awg. This would allow you to expand in the future and gives you some additional headroom for startup.TDF
*i Steve - The HP rating stays the essentially the same whether wired for 220 or 110. The 220 windings draw about 1/2 the current as do the 110 windings. Ever notice that a 220 motor does not get as hot as a 110 motor of the same HP rating? Big industrial shops will use 440V 3 phase motors which are very efficient in converting input power to output power. 110V motors are pretty crude, really, in comparison. Ther are no "240 volt windings" in a 120/240 volt motor.(Ignoring the staring windings) there are two 120 volt coils. They are either wired in series for 240 or parallel for 120. Each of the coils has the same voltage and the same current, regarless of the operating voltage.b THE MOTOR DOES NOT KNOW IF IT IS WORKING ON 120 OR 240. IT WILL RUN AT THE SAME TEMPATURE AND SUPPLY THE SAME POWER.
*From: ftp://rtfm.mit.edu/pub/usenet/news.answers/electrical-wiring/part2Subject: Is it better to run motors at 110 or 220? Theoretically, it doesn't make any difference. However, there is a difference is the amount of power lost in the supply wiring. All things being equal, a 110V motor will lose 4 times more power in the house wiring than a 220V motor. This also means that the startup surge loss will be less, and the motor will get to speed quicker with 220V. And in some circumstances, the smaller power loss will lead to longer motor life. This is usually irrelevant unless the supply wires are more than 50 feet long.
*> Well, I wired the 220V circuit in my shop with 10 gauge wire and a 40 amp breaker.FYI, that's a code violation; 30A is the largest breaker you can use with 10 guage wire.And yes, assuming adequate supply wiring, it makes no difference whether a dual voltage motor is wired for 110 or 220.On the original question, you could wire the circuit with 10 gauge wire, with a 20A breaker. That way, you could just swap the breaker to 30A ones if you have problems with blowing the 20A's.In general, you want to use as small a breaker as possible as long as they don't trip. The smaller the breaker the better they do protecting the motor.Also, if this is a dedicated circuit just for the bandsaw, NEC doesn't required GFCI, even on concrete floors. For local code, YMMV.
*Crocker, just curious, did you put a dual 20 amp breaker in or a dual 40 amp. If its a dual 40, as BarryO says, you probably have a code violation and a potential fire problem that your insurance won't cover.Steve
*Here's the plan so far: 1) Use 10-gauge wire (careful not to stress wire coming out of box or crimp wire with staples, wire nice and flat, not along bottom or top of flr joist, labled with destination) 2) Use a two-pole (Murray or other MP type) GFCI Breaker.3) 20 AMP or 30 AMP (electrician makes the final call) 4) If we go 30 AMP, I rewire the bandsaw motor's plug and outlet box to 30 AMP NEMA specifications, because my motor's plug is the smaller 20 AMP. (what a total pain) 5) If 20 AMP, then use the motor's existing plug and use a conforming 20 AMP receptacle (outlet)Note: This is a dedicated line, nothing else in the shops runs on 220 volt. The posts on circuit breakers and motor loads were very informative. I think that manufacturers should have this information listed (IMO those HP games discredit the industry and don't serve anyone) I also spoke with the bandsaw manufacturer and they said a 20 AMP would probably be fine (they sell the bandsaw with a 20 amp cord and plug and spec a 20 amp breaker in their brochure and on their web site) but they said the saw would draw more current (up to 22.5 - 23 AMP) when resawing hardwoods and really "recommend a 25 AMP or 30 AMP" breaker (The loads mentioned sound similar to the info on the Delta Unisaw/Baldor motor posted by "SMAUG" above.) The GFI is the controversial decision. Some of the posts argue that these GFCI breakers are problematic when used with motors and their seems to be a lot of variability from one manufacturer to another, add to that the fact the first ones on the market were not the best, and they aren't cheep. However, my concern is that one-day I will move out and this 220 line will be there. With a walk out basement (unfinished throughout/ dirt floor in one section) I began to wonder if the next owner might run a paint sprayer with a compressor outside, or a contractor might plug in a piece of equipment. Last year I had cellulose (sp?) blown into the walls and the contractor was hunting all over for a 220. People do really stupid things, I can't control that. IF a GFCI prevents one accident I'll live with the expense. If the GFCI false trips I'll go back to a straight breaker, easy enough. The comments were really helpful! There were some references to back issues of Fine Homebuilding so I went to the library and read those. I also picked up a few books on electrical wiring. Now if only I can figure out the difference between ground and neutral. JC
*Crocker, sounds to me like you've got the situation well under control. Let us know how it turns out so we can learn from what you find works best.S
*Crocker,I can't see why you would need to rewire the plug on the bandsaw. Use the appropriate outlet for the plug and be done with it. Just because you've got a 30amp circuit doesn't mean that all, or any of the devices on that circuit have to be outletted and plugged for 30amps. It's the amount that the i device draws that determine the type of outlets/plugs, not the maximum amperage of the circuit.Any seconds on this or am I off base?Best,SethMy understanding of neutral v. ground (with the help of Rex Cauldwell, i Wiring a House:About neutral . . . All electrical current must make a complete loop. The current starts at the utility transformer and must therefore return to the transformer; the neutral is simply the return part of that loop. This too eventually will be grounded, but at a great distance from your outlets.A ground is a means of providing the least amount of resistance (shortest distance, quickest path) from your devices to a 0 volt ground. Resistance is bad. Too much resistance in the conductors and you've got problems.By phyics a current will follow the path of least resistance. You're ground provides that in a jiffy, whereas the neutral is a much longer path with greater resistance.
*I was concerned about misleading someone by putting 20 amp outlet on a 30 amp circuit. True, the bandsaw's motor would not cause any problems running under this senario, but could it cause problems somewhere in the future? Electrical wiring seems to have an unwritten language, "big thick wire, lost of AMP, etc." I also picked up this dandy:"A circuit breaker is not there to protect your motor, it is to protect the line. The bandsaw's motor protect itself with a fuse." I am still reading the manual to find out about the fuse.And I should pass along this from gem from a friend:"If you do it yourself and have a fire that traces back to electrical, and it's not to code, your homeowners insurance may not pay out." We had a long thread about this in this form and another in the Fine Home Building breaktime. No, one, including several insurance adjusters have ever seen a policy that would not pay in a case like this. If you have one please post the contract wording. " Also you mentioned that motor is from Europe. They have 50Hz 220V over there as opposed to 60Hz 240V here. If the machine was built for export to the US it should have the correct motor for our power. If not the motor will run too fast and may overheat and burn out." The "new hormonized" European supply voltage is 230V -10% +6% (i.e. 207.0 V-243.8 V). That range was "picked" to cover both the continental standard of 220 and the UK standard of 240 volts. Starting next year the motors will be labeled for 207 to 253 volts. The US/Canadain standard is 228 - 252V, except 228 - 240 in California. See http://users.metro2000.net/~purwinc/seec2_2.htm And due to the lower magnetizing currents on 60hz the motors will work better with the slightly higher voltages. Yes, the motor does will 6/5 faster on 60 Hz than 50Hz. In most WW applications this is of little difference. THE MOTOR WILL NOT BURN OUT. "The local code calls for a GFCI breaker in the unfinished basement. (It is damp down there at times)" Nec code 210-8 (a5) require receptacles in unfinished basements be GGFCI protected. But there are two specific exclusions. 1) "Receptacles that are not readily accessible." (ceiling) 2) "A single receptacle or a duplex recptacle for two appliances located within dedicated space for each appliance located within the dedicated space for each appliance that in normal use, is not easily moved from one place to another, and that is cord and plug connected in accordance with sections ...." You local code make be slightly different. But this is a real exception and is needed in basements for things like freezers and sump pumps. But your saw should also fall into to that exception. Yes, most breakers have an inverse time/current curve that will withstand a large over current for a short time period. Based on the motor label you are safe with a 20 amp circuit. But the code specs for a 3 hp motor calls out a 17 amp load and with you figure in the 80% derating factor that forces you to 30 amps. Now you are not staring with a load and most of the time the saw is loafing away so that 20 amps is OK and many, many 3 hp cabinet saws are wired to 20 amp circuits. But go ahead and spend the extra $10 and put in a 30 amp circuit. Bill
*Happens to be that the electrical inspector for my town was just here for a project Im' working on and I asked him. He said, don't change any plugs. You need a 20 amp circuit with 20 amp breaker for the 20 am plug and a 30 amp breaker for a 30 amp breaker with a 30 amp plug (Sounds kinda obvious now.) You shouldn't mix 20 and 30 amp outlets on a 30 amp circuit as there are risks when running a 20 amp device as it won't trip at 20 amps.Hope that's useful.Seth
*Seth, Thanks for confirming that you don't mix these. Interested to know though, if I were to change from a 20 Amp breaker with a 10/2 wire(three wires) (even though 12/2 would meet code requirement) and later switched to a the breaker to 30 AMP would I need 10/3 (four wire) to wire in the receptacle? All the 30 amp receptacles I have seen have hookups for 4 wires (like a dryer) as opposed to the 220 20 AMP receptacles that use just three wires.
*Crocker,My 30amp tools such as my table saw PM66 3hp only use three wires. I think most 220 tools do. I pull two 10 gauge hots and 10 gauge ground. That's it. Dryers and stoves use a neutral therefore needing a fourth.Seth
*CrockerFor 30A service, use NEMA 6-30R and 6-30P straight blade plugs and receptacles, or L6-30R and L6-30P twist lock plugs and receptacles. Both types are 2-pole, 3-wire, 250V devices, and they are rated 3 AC hp. You may have to go to a real electrical supply house, or better yet, hire an electrician. Article 210-24 of the NEC permits only 30A receptacles on a circuit with 30A overcurrent protection (breaker or fuse). Mixing 20A devices on such a circuit is not allowed, and certainly not smart. Article 210-8 of the NEC requires GFCI protection on "125-volt, single-phase , 15- and 20-ampere receptacles installed in the locations specified below..." I'm not aware of any requirement for GFCI's on 240V circuits of this type. But as always, don't take electrical advice from the internet; talk to the local authorities and/or tradesmen.
*Thomas,Do you run 20-ampere or 30-ampere in your shop? Do you find the service acceptable? Does the tablesaw motor every trip the circuit? By comparison, a 3hp Baldor has a FLA of 15 and lists the follwing load characteristics:Rated Load 25% = 7.00 amp = 3558 rpmRated Load 50% = 9.00 amp = 3526 rpmRated Load 75% = 11.5 amp = 3496 rpmRated Load 100% = 14.5 amp = 3457 rpmRated Load 125% = 18.0 amp = 3407 rpmRated Load 150% = 21.8 amp = 3356 rpmDoes this mean that when the saw is straining to cut a 12/4 oak beam the rpms will drop to 3356 and the load will exceed the capacity of the 20 amp breaker and trip the circuit? Fishing,J Crocker
*J. CrockerI have a 20A circuit for my Unisaw (nameplated 3hp, 230V), and I've never tripped the breaker. I also don't do any really heavy work for extended periods. Check the nameplate on the motor. Most TEFC single phase motors of that size have a 1.0 service factor; 1.15 is the highest I've seen in that size and type. If you work it harder than continuous rated x service factor for more than short periods of time, you'll burn up the motor, unless it has proper overload protection (ie a motor starter or internal thermal; as posted before, the circuit breaker is not there to protect the motor, just the wiring, and consequently your home and your life, although the NEC does allow an exception if the load in intermittent in nature - perhaps like a home shop saw?). To answer your question directly, that's pretty much what would happen if you work it to 150%, ie 4.5 hp, if the motor doesn't burn up first. Personally I'd leave it at 20A and be done with it, but as someone else wrote, spend the extra $10 and use 10 gauge wire. And, of course, don't take electrical advice from the internet; ask your local electrical building inspector and/or licensed electrician. Hope this helps.T. Kanzler
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