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| Woodworking (rec.woodworking) Discussion forum covering all aspects of working with wood. All levels of expertise are encouraged to particiapte. |
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#1
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3-wire electrical circuit serving both 110 and 220V loads?
I know I'm going to get the "DAGS" for this question, but I just came from
there, and I didn't see this specific information. Lots of debate about how much current the neutral wire carries, though :-) With a 3-wire circuit, is it okay to wire both 120V and 240V outlets on that same circuit? I know it's *possible* by using the two hots for 240 and either hot and neutral for 120, but is it recommended? Maybe this is the main reason for this type of circuit, so I didn't see reference to it on Google. Much of the discussion I read was on balancing the load, which could imply using the 3-wire circuit with all 120V outlets. I've got a dust collector coming soon, and the extra 6-7 continuous amps is going to result in some frequent breaker trips when I start a saw or planer. Looked at my electrical service, and found there's an unused double-pole 30A breaker, feeding an unused dryer outlet (house had a gas dryer when I moved in). That should give me the 2 hots for a 3-wire circuit. My thought on this type of circuit is to wire one outlet at 240V (re-wire DC motor to 220V), and the rest wired at 120V. With that 30A breaker and 10 AWG wire, should have no problem handling the loads from a DC and air cleaner running, and startup surge from another tool. An electrician would be a good idea, too. Hopefully I can find someone willing to consult with me; I can do the wiring myself. But I'm hoping to get some idea if this is the way I want to go so I can cost materials. Won't get an electrician or the inspector on the phone until next week. TIA |
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#2
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"Keith Carlson" wrote in message
news:%zEyd.245829$V41.11293@attbi_s52... I've got a dust collector coming soon, and the extra 6-7 continuous amps is BTW, I read a lot trying to decide on a 1.5 - 2 HP dust collector. Finally put whatever specs and prices etc. into a spreadsheet to compare them side by side. (Ended up going with a Penn State unit). If anyone else is shopping dust collector, and would find this info useful, I'll be happy to email the sheet. (Hey, I'm a relative newbie, but I'm trying to contribute *something*). It's kinda interesting how they line up by price. The Harbor Freight unit is way below anything in price, even adding on $67 for a felt bag upgrade. There's a Grizzly and Jet at the high end. But most of them fall right into a $330-350 range (including shipping and upgrade of bag if it comes with a 30 micron bag). |
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#3
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If the breaker is double pole and the cable is 4 wire you can do it.
Don't share the neutral and ground! They even make a combo 120/240v duplex receptacle for this. |
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#4
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Hello Keith,
I am just passing by and noticed your post , I am an electrician. I do not know what level of experiance you have so let me start with some warnings, if you know understand what you are doing ignore the next few lines  (re-wire DC motor to 220V) I am not sure what you mean here D.C. is NOT a.c.! Unless there is some transformer-rectifier setup you didn't mention this just wont work, AT ALL.You will end up in flames.Realize you are saying rewire a ?Voltage Direct Current motor to 220Voltage Alternating Current...these are different beast. With that 30A breaker and 10 AWG wire, should have no problem handling the loads from a DC and air cleaner running, and startup surge from another tool. O.k. that is pretty reasonable there are many appliances that run on 220VAC and use one hot and a neutral to get 120VAC and use that for the timer, controls, or whatever. Really there is no reason to have put in a neutral wire in if you weren't needing to use it for that very purpose, ok you can use it for a 3way or 4way circuit, but that only holds for small wire...think about it. If you don't already know the transformer outside your house sends 3 wires. Grounding is done near your house. This is what you get fromthe transformer: L1-N-L2 L1 and L2 are the ends of the winding and N is the center tap that they ground. It is therefore in the middle between the two legs so between L1-N there is 120VAC and between N-L2 there is 120V and between L1-L2 there is 220VAC DIFFERENCE cause it is really all about potential difference between points Also you might be fooled into thinkingNeutral is ground it is not . DO NOT use it as such it can be a lethal mistake. The only real problem that I see is this: You have 30 amp double pole breaker. You want to use 220 for *whatever* You want to use 120 for *whatever else* what if the 120v appliance or tool messes up and starts pulling a higher load until it burns up ... The breaker would stop it huh....Nope not always, not if it didn't exceeded the 30 amp breakers capacity. Which is why you should run a seperate line for your 120v loads and your 220v loads that are not related.It is just a lot safer , also ground everything especially on a motor load, it will help reduce staitc and noise on the line as well. In this case I would run a new line, but I am an electrician Oh and by the way always check your local electrical codes they are always diffent and can sometimes surprise you! Hth, M.E.Farmer |
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#5
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This type of setup is common on a stove, right? 240 for the stove heating
elements, and 110 for the lights/clock? Personally, I'm thinking of this for my tablesaw/router (router built into tablesaw wing). It would be handy to just have one cordt to trip over, rather than two. But I don't know if you can get 4 wire extension cables. Haven't switched my saw over to 240 yet, so that hasn't been a problem. And since I'm wiring my garage up with 20 amp circuits, I might not bother. Clint "Greg" wrote in message ... If the breaker is double pole and the cable is 4 wire you can do it. Don't share the neutral and ground! They even make a combo 120/240v duplex receptacle for this. |
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#6
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There is no argument at all. In a two-wire 115V circuit, the current
carried by the neutral is exactly the same as that carried by the hot wire. In a three-wire 230V circuit, there is a property called phase angle or J-factor. This results in current flowing in both directions at the same time (this is not exactly a true statement but a convenient way to consider current flow in a three-wire circuit). As the current on one phase increases from zero to some positive value, the current in the other phase is decreasing from its positive value to zero. The vector sum of the currents on the neutral is exactly the same as the total of both phases. Because of the phase angle, however, that does not mean twice the current. It never exceeds the total current of each phase individually. Confusing? Yes. One has to study alternating current and understand plane geometry and simple trigonometry to comprehend it. "Keith Carlson" wrote in message news:%zEyd.245829$V41.11293@attbi_s52... I know I'm going to get the "DAGS" for this question, but I just came from there, and I didn't see this specific information. Lots of debate about how much current the neutral wire carries, though :-) With a 3-wire circuit, is it okay to wire both 120V and 240V outlets on that same circuit? I know it's *possible* by using the two hots for 240 and either hot and neutral for 120, but is it recommended? Maybe this is the main reason for this type of circuit, so I didn't see reference to it on Google. Much of the discussion I read was on balancing the load, which could imply using the 3-wire circuit with all 120V outlets. I've got a dust collector coming soon, and the extra 6-7 continuous amps is going to result in some frequent breaker trips when I start a saw or planer. Looked at my electrical service, and found there's an unused double-pole 30A breaker, feeding an unused dryer outlet (house had a gas dryer when I moved in). That should give me the 2 hots for a 3-wire circuit. My thought on this type of circuit is to wire one outlet at 240V (re-wire DC motor to 220V), and the rest wired at 120V. With that 30A breaker and 10 AWG wire, should have no problem handling the loads from a DC and air cleaner running, and startup surge from another tool. An electrician would be a good idea, too. Hopefully I can find someone willing to consult with me; I can do the wiring myself. But I'm hoping to get some idea if this is the way I want to go so I can cost materials. Won't get an electrician or the inspector on the phone until next week. TIA |
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#7
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Sorry...neglected to answer your original question. I believe the NEC
frowns on connecting across one phase of a 230V circuit to get 115V. That WOULD double the current on the neutral and result in a potential overload. "Chuck Hoffman" wrote in message ... There is no argument at all. In a two-wire 115V circuit, the current carried by the neutral is exactly the same as that carried by the hot wire. In a three-wire 230V circuit, there is a property called phase angle or J-factor. This results in current flowing in both directions at the same time (this is not exactly a true statement but a convenient way to consider current flow in a three-wire circuit). As the current on one phase increases from zero to some positive value, the current in the other phase is decreasing from its positive value to zero. The vector sum of the currents on the neutral is exactly the same as the total of both phases. Because of the phase angle, however, that does not mean twice the current. It never exceeds the total current of each phase individually. Confusing? Yes. One has to study alternating current and understand plane geometry and simple trigonometry to comprehend it. "Keith Carlson" wrote in message news:%zEyd.245829$V41.11293@attbi_s52... I know I'm going to get the "DAGS" for this question, but I just came from there, and I didn't see this specific information. Lots of debate about how much current the neutral wire carries, though :-) With a 3-wire circuit, is it okay to wire both 120V and 240V outlets on that same circuit? I know it's *possible* by using the two hots for 240 and either hot and neutral for 120, but is it recommended? Maybe this is the main reason for this type of circuit, so I didn't see reference to it on Google. Much of the discussion I read was on balancing the load, which could imply using the 3-wire circuit with all 120V outlets. I've got a dust collector coming soon, and the extra 6-7 continuous amps is going to result in some frequent breaker trips when I start a saw or planer. Looked at my electrical service, and found there's an unused double-pole 30A breaker, feeding an unused dryer outlet (house had a gas dryer when I moved in). That should give me the 2 hots for a 3-wire circuit. My thought on this type of circuit is to wire one outlet at 240V (re-wire DC motor to 220V), and the rest wired at 120V. With that 30A breaker and 10 AWG wire, should have no problem handling the loads from a DC and air cleaner running, and startup surge from another tool. An electrician would be a good idea, too. Hopefully I can find someone willing to consult with me; I can do the wiring myself. But I'm hoping to get some idea if this is the way I want to go so I can cost materials. Won't get an electrician or the inspector on the phone until next week. TIA |
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#8
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remember that watts x volts =amps total your watts x if 240 take it times
240 if 120 take x 120 this will give you a idea if your over loaded your breaker and yes a neutral dose carry some voltage if your circuit are unbalanced the amps will go up on the neutral it's also the return of current. some 240 stuff doesn't take a neutral "Keith Carlson" wrote in message news:%zEyd.245829$V41.11293@attbi_s52... I know I'm going to get the "DAGS" for this question, but I just came from there, and I didn't see this specific information. Lots of debate about how much current the neutral wire carries, though :-) With a 3-wire circuit, is it okay to wire both 120V and 240V outlets on that same circuit? I know it's *possible* by using the two hots for 240 and either hot and neutral for 120, but is it recommended? Maybe this is the main reason for this type of circuit, so I didn't see reference to it on Google. Much of the discussion I read was on balancing the load, which could imply using the 3-wire circuit with all 120V outlets. I've got a dust collector coming soon, and the extra 6-7 continuous amps is going to result in some frequent breaker trips when I start a saw or planer. Looked at my electrical service, and found there's an unused double-pole 30A breaker, feeding an unused dryer outlet (house had a gas dryer when I moved in). That should give me the 2 hots for a 3-wire circuit. My thought on this type of circuit is to wire one outlet at 240V (re-wire DC motor to 220V), and the rest wired at 120V. With that 30A breaker and 10 AWG wire, should have no problem handling the loads from a DC and air cleaner running, and startup surge from another tool. An electrician would be a good idea, too. Hopefully I can find someone willing to consult with me; I can do the wiring myself. But I'm hoping to get some idea if this is the way I want to go so I can cost materials. Won't get an electrician or the inspector on the phone until next week. TIA |
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#9
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It is not recommended. Anything confusing is dangerous, and this is
confusing. However, if you lose the 30a breaker, it is possible. You cannot use a 30a breaker because the 120v circuit will not be rated for 30a. You must get a 20a breaker and use #12 for all of it. (I am assuming #12 is adequate, which might not be true if your run is too long and the current is too high; you have to check that first) If 20a will cover the DC and whatever you want to also run on it, you can do it. Otherwise you can't. Overall it is a better idea to run two circuits. Did anyone mention that you will need 12/3 wire for the combination circuit but only 12/2 for the separate circuits? It is probably just as easy to run two 12/2 as one 12/3. That was funny about not being able to change DC to AC. |
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#10
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Hello,
sorry that just isn't right I'm sure you meant ; P=I*E Or rearranged : Watts = Amps*Voltage Amps = Watts / Voltage Voltage = Amps / Watts etc.. But even that isn't fully all of the story if you are talking AC power and Inductive loads..... then you deal with Impedance and other fun things (power factor), long story short ... it's complex. Hth, M.E.Farmer |
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#11
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I think DC = Dust Collector...
Maybe AC = Air Cleaner? Clint wrote in message oups.com... Hello Keith, I am just passing by and noticed your post , I am an electrician. I do not know what level of experiance you have so let me start with some warnings, if you know understand what you are doing ignore the next few lines (re-wire DC motor to 220V) I am not sure what you mean here D.C. is NOT a.c.! Unless there is some transformer-rectifier setup you didn't mention this just wont work, AT ALL.You will end up in flames.Realize you are saying rewire a ?Voltage Direct Current motor to 220Voltage Alternating Current...these are different beast. With that 30A breaker and 10 AWG wire, should have no problem handling the loads from a DC and air cleaner running, and startup surge from another tool. O.k. that is pretty reasonable there are many appliances that run on 220VAC and use one hot and a neutral to get 120VAC and use that for the timer, controls, or whatever. Really there is no reason to have put in a neutral wire in if you weren't needing to use it for that very purpose, ok you can use it for a 3way or 4way circuit, but that only holds for small wire...think about it. If you don't already know the transformer outside your house sends 3 wires. Grounding is done near your house. This is what you get fromthe transformer: L1-N-L2 L1 and L2 are the ends of the winding and N is the center tap that they ground. It is therefore in the middle between the two legs so between L1-N there is 120VAC and between N-L2 there is 120V and between L1-L2 there is 220VAC DIFFERENCE cause it is really all about potential difference between points Also you might be fooled into thinkingNeutral is ground it is not . DO NOT use it as such it can be a lethal mistake. The only real problem that I see is this: You have 30 amp double pole breaker. You want to use 220 for *whatever* You want to use 120 for *whatever else* what if the 120v appliance or tool messes up and starts pulling a higher load until it burns up ... The breaker would stop it huh....Nope not always, not if it didn't exceeded the 30 amp breakers capacity. Which is why you should run a seperate line for your 120v loads and your 220v loads that are not related.It is just a lot safer , also ground everything especially on a motor load, it will help reduce staitc and noise on the line as well. In this case I would run a new line, but I am an electrician Oh and by the way always check your local electrical codes they are always diffent and can sometimes surprise you! Hth, M.E.Farmer |
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#12
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Correction
Or rearranged : Watts = Amps*Voltage Amps = Watts / Voltage Voltage = Watts / Amps Sorry for the screw up. M.E.Farmer |
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#13
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#14
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#15
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In article , "Chuck Hoffman" wrote:
Sorry...neglected to answer your original question. I believe the NEC frowns on connecting across one phase of a 230V circuit to get 115V. That WOULD double the current on the neutral and result in a potential overload. Utter nonsense. It would do nothing of the sort. In a circuit wired as he described, with (for example) a 10A load at 240V and a 15A load at 120V, the current in the neutral conductor is 15A. (The 240V load places *no* current on the neutral.) Now add a 17A load at 120V on the opposite leg. One hot leg is drawing 10 + 15 = 25A. The other is drawing 10 + 17 = 27A. And the current in the neutral is 17 *minus* 15 = 2A. -- Regards, Doug Miller (alphageek-at-milmac-dot-com) Get a copy of my NEW AND IMPROVED TrollFilter for NewsProxy/Nfilter by sending email to autoresponder at filterinfo-at-milmac-dot-com You must use your REAL email address to get a response. |
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#16
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"Keith Carlson" wrote in message news:%zEyd.245829$V41.11293@attbi_s52... I know I'm going to get the "DAGS" for this question, but I just came from there, and I didn't see this specific information. Lots of debate about how much current the neutral wire carries, though :-) Agreed, this is a confusing issue. But there are lot of people with experience on the rec. With a 3-wire circuit, is it okay to wire both 120V and 240V outlets on that same circuit? I know it's *possible* by using the two hots for 240 and either hot and neutral for 120, but is it recommended? Maybe this is the main reason for this type of circuit, so I didn't see reference to it on Google. Much of the discussion I read was on balancing the load, which could imply using the 3-wire circuit with all 120V outlets. Yes, mixing 120V and 240V is possible, and many circuits are designed this way. That is why (almost) all 240V installations have a neutral wire. If you used only 240V loads, there would be no need for that neutral wire. If you want to mix 240V and 120V on the same circuit, at least 4 wires will be needed. Call them L1, L2, N, and G (for Line1, Line2, Neutral, and Ground). The "3-wire" terminology was confusing. Hence 3-wire with ground is common, if a bit of a mouthful. My tablesaw and jointer have 3 prongs on their plugs (L1, L2, and G) -- no neutral is needed, since only the 240V motor is used. My bandsaw has 3 prongs (L1, N, and G) If, however, I wanted to add a 120V light bulb at a 240V tool, 4 prongs would be needed (L1 L2 N & G). I would need to add the neutral wire to carry the 120V current. That's a hassle, which is why most people would just run a separate plug.  I've got a dust collector coming soon, and the extra 6-7 continuous amps is going to result in some frequent breaker trips when I start a saw or planer. Looked at my electrical service, and found there's an unused double-pole 30A breaker, feeding an unused dryer outlet (house had a gas dryer when I moved in). That should give me the 2 hots for a 3-wire circuit. My thought on this type of circuit is to wire one outlet at 240V (re-wire DC motor to 220V), and the rest wired at 120V. With that 30A breaker and 10 AWG wire, should have no problem handling the loads from a DC and air cleaner running, and startup surge from another tool. Even if the startup surge would cause the current to exceed the breaker rating, the breaker probably would not open. Circuit breakers have what is called a time-current curve, which tells you how long a circuit breaker can carry excess current before it opens. Most breakers will carry 2x or 3x their rated current (ex: 30 or 45A on a 15A breaker) for ten seconds or so before they open; even short time delay models will do it for a second or so, which covers the startup surge. Google on "circuit breaker time current curve" to check it out for yourself. Once you go above this level, the breaker will trip very quickly. For example, when a hot wire shorts to the neutral or ground, a current of many time the rated current occurs (10x? 20x?), and the breaker trips within milliseconds. The general idea is that larger overcurrents trip quickly, but that 2x or 3x currents can run for a long time. This protects the wiring, which is one of the reasons for circuit breakers; a "shorted curcuit" level of overcurrent would damage wires quickly, but lower overcurrents would take a long time to overheat the wiring. An electrician would be a good idea, too. Hopefully I can find someone willing to consult with me; I can do the wiring myself. But I'm hoping to get some idea if this is the way I want to go so I can cost materials. Won't get an electrician or the inspector on the phone until next week. Calling qualified help is never a bad idea, but this sounds like a simple project. And this group will be helpful. Matthew TIA |
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#17
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Clint wrote:
This type of setup is common on a stove, right? 240 for the stove heating elements, and 110 for the lights/clock? Yes, and electrical dryers as well. At least NEC used to (I don't have a very recent copy to check current, maybe someone else will) allow the bare wire to be used as neutral in this specific instance (under some other specific circumstances as well, basically being a single dwelling). Actually, in a range, the burners typically only draw 110 as well until they're turned to "hi"... |
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#18
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"Matthew" wrote:
My tablesaw and jointer have 3 prongs on their plugs (L1, L2, and G) -- no neutral is needed, since only the 240V motor is used. My bandsaw has 3 prongs (L1, N, and G) If, however, I wanted to add a 120V light bulb at a 240V tool, 4 prongs would be needed (L1 L2 N & G). I would need to add the neutral wire to carry the 120V current. That's a hassle, which is why most people would just run a separate plug. Or a step-down transformer inside the machine. Not that that's not a hassle in its own way. The best suggestion I ever saw was just put two bulbs in series. Or, I suppose, find a source for 240V bulbs (they must exist). |
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#19
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"Doug Miller" wrote in message
m.... Utter nonsense. No, it isn't. Look at my simplified description of the current in a two-phase circuit for a clue that I know what I'm talking about. |
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#20
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Doug Miller wrote: In article , "Chuck Hoffman" wrote: Sorry...neglected to answer your original question. I believe the NEC frowns on connecting across one phase of a 230V circuit to get 115V. That WOULD double the current on the neutral and result in a potential overload. Utter nonsense. It would do nothing of the sort. In a circuit wired as he described, with (for example) a 10A load at 240V and a 15A load at 120V, the current in the neutral conductor is 15A. (The 240V load places *no* current on the neutral.) Now add a 17A load at 120V on the opposite leg. One hot leg is drawing 10 + 15 = 25A. The other is drawing 10 + 17 = 27A. And the current in the neutral is 17 *minus* 15 = 2A. Right on Doug, Exactly thats the idea behind LOAD BALANCING! if the are equal there is no current on the neutral. The whole idea of the neutral is a 0 volt refrence only We really try to achieve 0 volts potential across the neutral it is technically a ground wire of sorts but is not the GROUND wire . It isn't magic if you look at how they send it too you from the 'pole pig' transformer they send L1 and Neutral (ever seen the ground wires running down the light pole? That's were they ground the neutral at on there side) and then L2. This is a simplification and is only meant to help illustrate the idea. Please look into it if you want to verify any of this. ['pole pig' transformer step down] the v's are windings and the = is the seperator between the windings. M1-vvvvvvvvvvvvvvvvvvv-M2 13.8kv or some other mains voltage ====================== L1-vvvvvv-N-vvvvvv-L2 240v split phase | | | |---240v---------| | | | L1--120v-N--120v--L2 Excuse my ascii. The legs L1 and L2 are 180 degrees out of phase with each other that means one should be at -120 and the other at +120 . Notice that the Neutral is at the middle...that gives you a ZERO volt refrence to ground. Why is it needed well we need a reference to ground so we can use our appliances and not be subject varying voltage levels from ground. A simple 240v circuit could actually be floating 1000v above earth ground but between legs only have a potential of 240v but since there is no ground reference it could be 1000v above earth ground from just 1 leg, that would hurt a bit Once again it is all a bit complex. One could study for years and still be confused. And ponder this, what is electricity, is it the just the flow of electrons .... or is it more to it, like maybe the electrons are just buckets that travel the circuit slowly tranfering 'photonic energy', hint they are never consumed in the circuit yet we do get power from the circuit M.E.Farmer |
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#21
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wrote in message
oups.com... Hello Keith, I am just passing by and noticed your post , I am an electrician. I do not know what level of experiance you have so let me start with some warnings, if you know understand what you are doing ignore the next few lines (re-wire DC motor to 220V) I am not sure what you mean here D.C. is NOT a.c.! Unless there is Thanks, M.E. Sorry for the confusion. As someone else noted, I meant Dust Collector, not direct current. Made an assumption about the audience of that post. The dust collector has a 110/220V motor, pre-wired for 110. I believe it's a straightforward task to re-wire for 220. I don't believe it comes with a 220V plug, though; I'd need to add that. The only real problem that I see is this: You have 30 amp double pole breaker. You want to use 220 for *whatever* You want to use 120 for *whatever else* what if the 120v appliance or tool messes up and starts pulling a higher load until it burns up ... I was just thinking about this on the way to pick up pizza. With 10AWG wire, I'd have a circuit capable of 30A, but the cords from all the tools are 110V/15A. (leaving out the Dust Collector for a moment). Those will plug into 20A receptacles, so say I wire 20A receptacles on the 120V outlets. Now suppose the planer or whatever manages to load down and wants to pull something like 28 amps. The circuit breaker says "no problem". Could run that way all day and it wouldn't trip. But what about that receptacle that's rated for 20A?? Are the connections or conductors inside it going to overheat? Might be some risk there, not to mention the tool itself like you say. I should go look at my reference book; NEC probably doesn't allow a 20A rated receptacle on a circuit protected to 30A. Then there's 120V/30A receptacles. Haven't looked, but probably cost more than the 20's. The 110V/15A plugs won't fit in them, so I'd have to change plugs on the tools. Even then I have to consider how likely it is that I'll have situations where the tool wants to pull more than its rated current. The 3-wire circuit starts to look like more trouble than it's worth. It sounded like a slick idea at first, because I have the breaker, and I'd be able to run 3 wires + ground in my conduit. (Finished walls, and I'm not going to tear them up, so I'll be running EMT and individual wires inside). I am going to ask a local electrician, but starting to think about the original plan of a simple 2-wire 20A circuit. Then go with 220V, on a separate circuit, on the dust collector if it's needed. |
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#22
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"toller" wrote in message
... It is not recommended. Anything confusing is dangerous, and this is confusing. Saw quite a bit of this debate on various NGs. Some felt it's dangerous because someone will screw up the neutrals at a later time, or a future homeowner might replace the double pole breaker with two, and put them both on the same leg of the service. Others thought, anyone qualified to work on the wiring or panel should not be confused by this type of circuit. However, if you lose the 30a breaker, it is possible. You cannot use a 30a breaker because the 120v circuit will not be rated for 30a. You must get a 20a breaker and use #12 for all of it. (I am assuming #12 is adequate, which might not be true if your run is too long and the current is too high; you have to check that first) This might be my downfall. It's not going to be practical to use 30A outlets so the whole circuit can be considered 30A rated. If 20a will cover the DC and whatever you want to also run on it, you can do it. Otherwise you can't. It's looking more like that's what I'll do... back to the original plan and see how it goes. My thinking, though, was that now on a 15A circuit, I'll have the breaker trip sometimes on starting a machine. Table saw - about 10% of the time. Miter saw - maybe 15% of the starts. Planer - probably 1/3 of the starts trip the breaker. So I was thinking 20A circuit. But now add the dust collector, drawing 6A continuous (12 on startup). Now I've got about 14A "headroom" for other motors to start. Overall it is a better idea to run two circuits. Did anyone mention that you will need 12/3 wire for the combination circuit but only 12/2 for the separate circuits? It is probably just as easy to run two 12/2 as one 12/3. Yeah, I knew that. I'm running the wiring in EMT conduit though, so I don't have to tear up finished walls. I thought I read somewhere that you can't run more than one circuit in the same conduit run. If that's true, two circuits means more cost. I suppose another option is replace the 30A breaker with a 20A double-pole, make it a 20A, 120/240V circuit. Could still use the 20A receptacles then. Anyway, talked to my neighbor who referred me to another neighbor who's an electrician. I may be able to get some inexpensive guidance from him. That was funny about not being able to change DC to AC. |
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"Matthew" wrote in message
... "Keith Carlson" wrote in message news:%zEyd.245829$V41.11293@attbi_s52... Ground). The "3-wire" terminology was confusing. Hence 3-wire with ground is common, if a bit of a mouthful. Yeah, this is what I was talking about: 2 hot wires, 1 neutral, 1 grounding wire. In my HP Richter book, they called it a "3-wire" or "split-wire" circuit. "3-wire" sounded less confusing to me. Don't know how common that term is in sparky-land. Even if the startup surge would cause the current to exceed the breaker rating, the breaker probably would not open. Circuit breakers have what is called a time-current curve, which tells you how long a circuit breaker can carry excess current before it opens. Most breakers will carry 2x or 3x their rated current (ex: 30 or 45A on a 15A breaker) for ten seconds or so before they open; even short time delay models will do it for a second or so, which covers the startup surge. Google on "circuit breaker time current curve" to check it out for yourself. Once you go above this level, the breaker will trip very quickly. For example, when a hot wire shorts to the neutral or ground, a current of many time the rated current occurs (10x? 20x?), and the breaker trips within milliseconds. The general idea is that larger overcurrents trip quickly, but that 2x or 3x currents can run for a long time. This protects the wiring, which is one of the reasons for circuit breakers; a "shorted curcuit" level of overcurrent would damage wires quickly, but lower overcurrents would take a long time to overheat the wiring. Hmm. I do have trouble tripping the breaker on the current (present) 15A circuit. Could be that the breaker is old and trips easier? From what you're saying, starting up a TS or planer shouldn't draw a high current long enough to trip the breaker. |
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In article , "Chuck Hoffman" wrote:
"Doug Miller" wrote in message om.... Utter nonsense. No, it isn't. Look at my simplified description of the current in a two-phase circuit for a clue that I know what I'm talking about. I read that. And you don't. -- Regards, Doug Miller (alphageek-at-milmac-dot-com) Get a copy of my NEW AND IMPROVED TrollFilter for NewsProxy/Nfilter by sending email to autoresponder at filterinfo-at-milmac-dot-com You must use your REAL email address to get a response. |
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In article nDKyd.6899$k25.6498@attbi_s53, "Keith Carlson" wrote:
I was just thinking about this on the way to pick up pizza. With 10AWG wire, I'd have a circuit capable of 30A, but the cords from all the tools are 110V/15A. (leaving out the Dust Collector for a moment). Those will plug into 20A receptacles, so say I wire 20A receptacles on the 120V outlets. Now suppose the planer or whatever manages to load down and wants to pull something like 28 amps. The circuit breaker says "no problem". Could run that way all day and it wouldn't trip. But what about that receptacle that's rated for 20A?? Yep, that's a problem. Hence toller's statement that your 120V circuit isn't rated for 30A. Technically, that's not exactly correct: there's no reason that you can't have a 120V 30A circuit, as long as the wire is 10ga copper or larger. But you're probably not going to find any receptacles that you can plug a 15A or 20A tool into, that are rated for 30A. Are the connections or conductors inside it going to overheat? Not if you don't feed current through it to some downstream load, *and* the load you have plugged into that outlet never overloads. But if either of those conditions occurs, yes, there is indeed a risk of overheating and fire. Might be some risk there, not to mention the tool itself like you say. I should go look at my reference book; NEC probably doesn't allow a 20A rated receptacle on a circuit protected to 30A. Right, it doesn't. Then there's 120V/30A receptacles. Haven't looked, but probably cost more than the 20's. The 110V/15A plugs won't fit in them, so I'd have to change plugs on the tools. Right on both counts. Even then I have to consider how likely it is that I'll have situations where the tool wants to pull more than its rated current. Not relevant -- you have the same issue with a 20A rated receptacle on a 20A circuit. The 3-wire circuit starts to look like more trouble than it's worth. It sounded like a slick idea at first, because I have the breaker, and I'd be able to run 3 wires + ground in my conduit. (Finished walls, and I'm not going to tear them up, so I'll be running EMT and individual wires inside). Have you considered that when you rewire the dust collector for 240V, it will pull only half as many amps? This may enable you to run the DC on a 20A circuit, which you could wire with 12/3 and then add standard 15A or 20A 120V receptacles. (Code *does* permit 15A-rated receptacles on 20A circuits.) -- Regards, Doug Miller (alphageek-at-milmac-dot-com) Get a copy of my NEW AND IMPROVED TrollFilter for NewsProxy/Nfilter by sending email to autoresponder at filterinfo-at-milmac-dot-com You must use your REAL email address to get a response. |
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In article XiLyd.552464$wV.437490@attbi_s54, "Keith Carlson" wrote:
Hmm. I do have trouble tripping the breaker on the current (present) 15A circuit. Could be that the breaker is old and trips easier? From what you're saying, starting up a TS or planer shouldn't draw a high current long enough to trip the breaker. Yes, that could very easily be the case. Breakers are cheap; replace it and see what happens. -- Regards, Doug Miller (alphageek-at-milmac-dot-com) Get a copy of my NEW AND IMPROVED TrollFilter for NewsProxy/Nfilter by sending email to autoresponder at filterinfo-at-milmac-dot-com You must use your REAL email address to get a response. |
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#27
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On Thu, 23 Dec 2004 23:18:38 GMT, "Chuck Hoffman"
wrote: "Doug Miller" wrote in message om.... Utter nonsense. No, it isn't. Look at my simplified description of the current in a two-phase circuit for a clue that I know what I'm talking about. Right church, wrong pew. All the stuff you wrote about phase angle and AC circuits, etc. seems to be okay, however, you liberally sprinkled in terms that in the real world of electrical wiring just aren't true. Let's take a look. There is no argument at all. In a two-wire 115V circuit, the current carried by the neutral is exactly the same as that carried by the hot wire. True. You should have stopped there. In a three-wire 230V circuit, there is a property called phase angle or J-factor. This results in current flowing in both directions at the same time I don't recall J-factor in the NEC. That could be me, though. (this is not exactly a true statement but a convenient way to consider current flow in a three-wire circuit). And since it's not, you should have left it alone. As the current on one phase increases from zero to some positive value, the current in the other phase is decreasing from its positive value to zero. Here's the crux of the problem. In electrical systems (the stuff the power company provides) current is delivered in three phases. In the average house, however (and that is what the discussion is about), power is delivered from only one phase of the three phase system. It is run through a center tap transformer which yields two "hot" legs that are 180° out of phase and a common return leg. All three of these wires, however, are delivered from a single phase. There is no two phase power. It's either three phase or single phase. No electrician calls either hot leg a "phase." The vector sum of the currents on the neutral is exactly the same as the total of both phases. Yeah, you could say that...if you wanted to answer the question of "what time is it?" by telling us how to build a clock. Because of the phase angle, however, that does not mean twice the current. Phase angle, as a concept, is perfectly suited for all sorts of theoretical discussions but is unnecessarily complex in single phase wiring. The only "angle" to consider is the 180° that each leg of the single phase power feed to house is out of to each other. It never exceeds the total current of each phase individually. Correct (except for that "phase" thing), but you sure took the long way around to get to it, and lost half the pack doing it. Confusing? Yes. One has to study alternating current and understand plane geometry and simple trigonometry to comprehend it. Please. Opposite legs have opposite values (because they are 180° out of phase) and the current is additive. It's simple arithmetic (albeit incorporating negative numbers). Sorry...neglected to answer your original question. I believe the NEC frowns on connecting across one phase of a 230V circuit to get 115V. Given that stoves and dryers sometimes do that very thing, I believe you're wrong...unless you could cite the section in which they "frown" upon it. That WOULD double the current on the neutral and result in a potential overload. This is the part that Doug describes as utter nonsense. And he's right. The ONLY current on the neutral would result from the connection across one LEG of the 230V circuit (to get 115V). There is NO current in the "neutral" of a 230V circuit because there is no "neutral" in a 230V circuit. - - LRod Master Woodbutcher and seasoned termite Shamelessly whoring my website since 1999 http://www.woodbutcher.net |
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For the critics, I've been in electronics for 40-some years and have been a
technical school instructor. And I worked for an electric utility. I do, in fact, know what I'm talking about. My late father-in-law was a union electrician and he didn't fully understand AC. He could follow the code, pull wires, bend conduit, install boxes, switches and outlets, etc., but he had no clue about the physical properties of electricity. Now let's talk about your comments. First you say: "Phase angle, as a concept, is perfectly suited for all sorts of theoretical discussions...." It is far more than theory, I'm afraid. It's an important consideration when working with multi-phase circuits. Then you say: "Opposite legs have opposite values (because they are 180° out of phase)" That seems diametrically opposed to your first disdainful comment. It is, however, precisely the point I was making. You also said: "I don't recall J-factor in the NEC. I've known people who could recite the NEC chapter and verse but had no clue about the physical properties of electricity or AC circuit analysis. Do you really understand alternating current and its physical properties ? Or are you like my father-in-law? "LRod" wrote in message ... On Thu, 23 Dec 2004 23:18:38 GMT, "Chuck Hoffman" wrote: "Doug Miller" wrote in message om.... Utter nonsense. No, it isn't. Look at my simplified description of the current in a two-phase circuit for a clue that I know what I'm talking about. Right church, wrong pew. All the stuff you wrote about phase angle and AC circuits, etc. seems to be okay, however, you liberally sprinkled in terms that in the real world of electrical wiring just aren't true. Let's take a look. There is no argument at all. In a two-wire 115V circuit, the current carried by the neutral is exactly the same as that carried by the hot wire. True. You should have stopped there. In a three-wire 230V circuit, there is a property called phase angle or J-factor. This results in current flowing in both directions at the same time I don't recall J-factor in the NEC. That could be me, though. (this is not exactly a true statement but a convenient way to consider current flow in a three-wire circuit). And since it's not, you should have left it alone. As the current on one phase increases from zero to some positive value, the current in the other phase is decreasing from its positive value to zero. Here's the crux of the problem. In electrical systems (the stuff the power company provides) current is delivered in three phases. In the average house, however (and that is what the discussion is about), power is delivered from only one phase of the three phase system. It is run through a center tap transformer which yields two "hot" legs that are 180° out of phase and a common return leg. All three of these wires, however, are delivered from a single phase. There is no two phase power. It's either three phase or single phase. No electrician calls either hot leg a "phase." The vector sum of the currents on the neutral is exactly the same as the total of both phases. Yeah, you could say that...if you wanted to answer the question of "what time is it?" by telling us how to build a clock. Because of the phase angle, however, that does not mean twice the current. Phase angle, as a concept, is perfectly suited for all sorts of theoretical discussions but is unnecessarily complex in single phase wiring. The only "angle" to consider is the 180° that each leg of the single phase power feed to house is out of to each other. It never exceeds the total current of each phase individually. Correct (except for that "phase" thing), but you sure took the long way around to get to it, and lost half the pack doing it. Confusing? Yes. One has to study alternating current and understand plane geometry and simple trigonometry to comprehend it. Please. Opposite legs have opposite values (because they are 180° out of phase) and the current is additive. It's simple arithmetic (albeit incorporating negative numbers). Sorry...neglected to answer your original question. I believe the NEC frowns on connecting across one phase of a 230V circuit to get 115V. Given that stoves and dryers sometimes do that very thing, I believe you're wrong...unless you could cite the section in which they "frown" upon it. That WOULD double the current on the neutral and result in a potential overload. This is the part that Doug describes as utter nonsense. And he's right. The ONLY current on the neutral would result from the connection across one LEG of the 230V circuit (to get 115V). There is NO current in the "neutral" of a 230V circuit because there is no "neutral" in a 230V circuit. - - LRod Master Woodbutcher and seasoned termite Shamelessly whoring my website since 1999 http://www.woodbutcher.net |
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Chuck Hoffman wrote:
"I don't recall J-factor in the NEC. I don't know much about the NEC, but I do understand polyphase circuits (4 years of EE in college). I don't think I've ever heard the term J-factor. What is it? |
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On Fri, 24 Dec 2004 17:14:26 GMT, "Chuck Hoffman"
wrote: For the critics, I've been in electronics for 40-some years and have been a technical school instructor. And I worked for an electric utility. I do, in fact, know what I'm talking about. I, also have been in electronics for more than 40 years. I have a pretty good idea of what I'm talking about, too. I've known all sorts of people over those years; some with the golden finger who didn't even need schematics to fix complex equipment but who couldn't pour **** out of a boot with the instructions on the heel. I've known people that couldn't pass a Morse code exam if it was sent one character every two minutes but who could teach brilliantly. And now I know someone with more background and experience perhaps than I have who can't explain a simple concept involving a single phase, two pole, center-tapped electrical circuit without complicating it beyond measure, and then when trying the simple answer gets it completely WRONG. Now let's talk about your comments. First you say: "Phase angle, as a concept, is perfectly suited for all sorts of theoretical discussions...." It is far more than theory, I'm afraid. It's an important consideration when working with multi-phase circuits. Then you say: Excuse me, but when you're discussing phase angles, AC circuits, impedance, etc., THEORY is EXACTLY what you're talking about. Or, to be even more precise, anything involving the movement of electrons is electrical theory. Want me to prove my point? Let's discuss current flow; electron or conventional current? "Opposite legs have opposite values (because they are 180° out of phase)" That seems diametrically opposed to your first disdainful comment. It is, however, precisely the point I was making. But the issue at hadn is a special circumstance; it is the set of properties that becomes simple, additive arithmetic when the phase angle is 180°. It uniquely occurs in the center tapped, two pole circuit that is residential house wiring. Discussion of other phase angles overly complicates the simple additive (albeit with negative numbers) process required to understand and calculate resultant current in a two pole, shared neutral circuit. You also said: "I don't recall J-factor in the NEC. I've known people who could recite the NEC chapter and verse but had no clue about the physical properties of electricity or AC circuit analysis. Do you really understand alternating current and its physical properties ? Yes, I'm afraid I do. But with all your experience and expertise, explain this: That WOULD double the current on the neutral and result in a potential overload. That was your response to a question about running a 120V load on one half of a 240V circuit. I said then: This is the part that Doug describes as utter nonsense. And he's right. The ONLY current on the neutral would result from the connection across one LEG of the 230V circuit (to get 115V). There is NO current in the "neutral" of a 230V circuit because there is no "neutral" in a 230V circuit. And I stand by that question; how do you explain this? You should have left well enough alone. - - LRod Master Woodbutcher and seasoned termite Shamelessly whoring my website since 1999 http://www.woodbutcher.net |
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This has become an obvious standoff and it will serve no purpose to continue
it. "LRod" wrote in message ... On Fri, 24 Dec 2004 17:14:26 GMT, "Chuck Hoffman" wrote: For the critics, I've been in electronics for 40-some years and have been a technical school instructor. And I worked for an electric utility. I do, in fact, know what I'm talking about. I, also have been in electronics for more than 40 years. I have a pretty good idea of what I'm talking about, too. I've known all sorts of people over those years; some with the golden finger who didn't even need schematics to fix complex equipment but who couldn't pour **** out of a boot with the instructions on the heel. I've known people that couldn't pass a Morse code exam if it was sent one character every two minutes but who could teach brilliantly. And now I know someone with more background and experience perhaps than I have who can't explain a simple concept involving a single phase, two pole, center-tapped electrical circuit without complicating it beyond measure, and then when trying the simple answer gets it completely WRONG. Now let's talk about your comments. First you say: "Phase angle, as a concept, is perfectly suited for all sorts of theoretical discussions...." It is far more than theory, I'm afraid. It's an important consideration when working with multi-phase circuits. Then you say: Excuse me, but when you're discussing phase angles, AC circuits, impedance, etc., THEORY is EXACTLY what you're talking about. Or, to be even more precise, anything involving the movement of electrons is electrical theory. Want me to prove my point? Let's discuss current flow; electron or conventional current? "Opposite legs have opposite values (because they are 180° out of phase)" That seems diametrically opposed to your first disdainful comment. It is, however, precisely the point I was making. But the issue at hadn is a special circumstance; it is the set of properties that becomes simple, additive arithmetic when the phase angle is 180°. It uniquely occurs in the center tapped, two pole circuit that is residential house wiring. Discussion of other phase angles overly complicates the simple additive (albeit with negative numbers) process required to understand and calculate resultant current in a two pole, shared neutral circuit. You also said: "I don't recall J-factor in the NEC. I've known people who could recite the NEC chapter and verse but had no clue about the physical properties of electricity or AC circuit analysis. Do you really understand alternating current and its physical properties ? Yes, I'm afraid I do. But with all your experience and expertise, explain this: That WOULD double the current on the neutral and result in a potential overload. That was your response to a question about running a 120V load on one half of a 240V circuit. I said then: This is the part that Doug describes as utter nonsense. And he's right. The ONLY current on the neutral would result from the connection across one LEG of the 230V circuit (to get 115V). There is NO current in the "neutral" of a 230V circuit because there is no "neutral" in a 230V circuit. And I stand by that question; how do you explain this? You should have left well enough alone. - - LRod Master Woodbutcher and seasoned termite Shamelessly whoring my website since 1999 http://www.woodbutcher.net |
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I think one of the problems in this thread is the confusion of using
"phase" to refer to both true phases as in 3-phase versus the 180-deg phase difference between the two hot legs of a single-phase AC circuit. I don't know when it became prevelant or popular (if it actually is or whether it's still fairly isolated) to refer to the two hots as two "phases" but I spent a significant amount of time trying to break my hired hand of the misconception over the last year. He was trained as an aircraft mechanic and was/is pretty darn good w/ hydraulics, mechanics, most simple wiring, controls, etc., but apparently was taught this as gospel regarding single phase AC power... |
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On Fri, 24 Dec 2004 13:40:40 -0600, Duane Bozarth
wrote: I think one of the problems in this thread is the confusion of using "phase" to refer to both true phases as in 3-phase versus the 180-deg phase difference between the two hot legs of a single-phase AC circuit. I don't know when it became prevelant or popular (if it actually is or whether it's still fairly isolated) to refer to the two hots as two "phases" but I spent a significant amount of time trying to break my hired hand of the misconception over the last year. He was trained as an aircraft mechanic and was/is pretty darn good w/ hydraulics, mechanics, most simple wiring, controls, etc., but apparently was taught this as gospel regarding single phase AC power... Yes. It even confuses tech school teachers with 40+ years in electronics who work for the power company...if you can believe that. I think it's isolated. I remember years ago when I was "educated" about it. All my prior knowledge of AC theory didn't count for squat while my friend who educated me was pounding it into my head. Oddly, one of the things he kept saying was, "the power company won't like hearing you call it 'two phase.'" - - LRod Master Woodbutcher and seasoned termite Shamelessly whoring my website since 1999 http://www.woodbutcher.net |
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I think one of the problems in this thread is the confusion of using "phase" to refer to both true phases as in 3-phase versus the 180-deg phase difference between the two hot legs of a single-phase AC circuit. I don't know when it became prevelant or popular (if it actually is or whether it's still fairly isolated) to refer to the two hots as two "phases" As I understand it, everything is pretty much the same whether you have true 240v (one 240v hot and a 0v neutral) or "2 phase" 240v (two 120v hots 180 degrees out of phase). Everything will work identically. (With the understanding you would need a 120v "neutral" in the first instance to get 120v to H-N) However 3 phase electricity is very different. Or so I have heard. I think that is why 240v is not called "2 phase"; it can be thought of as 1 phase, but is completely different than 3 phase. |
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Chuck Hoffman wrote:
This has become an obvious standoff and it will serve no purpose to continue it. Respectfully there is no standoff you are wrong. there is only a single PHASE in household power supplies unless you have a huge shop and have 3 phase power(rare). What you haven't noticed was the fact that it is a SINGLE phase that is SPLIT by a transformer with the center tapped to ground for reference. Not 2 phases , just a split-phase.........DO NOT CONFUSE! I don't really understand the difficulty if you have 40 years of electronics you should have played with tranformers a little by now. Oh wait a minute this isn't electronics........ Leave it to ELECTRICIANS. I also know electronics and love to build things but when I started in the electrical field I discovered most of electronics is diffrent than electrical even the symbols( capacitors (electronics) look like open-contacts ( electrical) and it took many years to sort it all out (oh yes I just knew that electronics would help me....bahh). Just to qualify myself I have wired many 3 phase transformers and motors and know what the difference in a delta, wye or delta-wye transformer, and can wire them correctly too. M.E.Farmer Family full of electricians even my mother. |
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On Fri, 24 Dec 2004 22:47:19 GMT, "toller" wrote:
I think one of the problems in this thread is the confusion of using "phase" to refer to both true phases as in 3-phase versus the 180-deg phase difference between the two hot legs of a single-phase AC circuit. I don't know when it became prevelant or popular (if it actually is or whether it's still fairly isolated) to refer to the two hots as two "phases" As I understand it, everything is pretty much the same whether you have true 240v (one 240v hot and a 0v neutral)... In the U.S. I don't believe there is any such thing. Household supply is obtained from a single phase of a three phase system. For all intents and purposes, when the power grid appears in your neighborhood, forget about two of those phases. You will never be involved with them. Only single phase is getting into your house. The single phase current is transformed from a fairly high voltage off the feeders to 240V from the output of a center tapped transformer up on the pole. With regard to that 240V, there is no neutral. The 240V comes from the two secondaries of the transformer. And there is no + or -. This is AC, not DC. It is 240V across the two poles. Our well known 120V supply comes, as you know, from one hot leg and the center tap of the transformer. Either hot leg will work. Here is the most important thing: ALL of this; the 240V, and each 120V is developed from the same single phase of the three phase system. It is single phase power. There is no "two phase" power. ...or "2 phase" 240v (two 120v hots 180 degrees out of phase). There is no "two phase" power. The two legs or poles are 180° out of phase, as you say, because they come off the opposite legs of the secondary of the transformer. They are NOT two phases of the three phase system. It is single phase. All of the current in your house comes from the same, SINGLE phase of the three phase system. However 3 phase electricity is very different. Or so I have heard. Yes and no, but I will leave that discussion to those with experience with it. I have none. I think that is why 240v is not called "2 phase"; it can be thought of as 1 phase, It IS single phase. There's no "thinking" about it. but is completely different than 3 phase. Sigh. Yes, you have stated a tautology. - - LRod Master Woodbutcher and seasoned termite Shamelessly whoring my website since 1999 http://www.woodbutcher.net |
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In real "two phase" the phases are 90 degrees out and it is a 4 wire service.
Topology is like the 4 poles of a compass. |
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"LRod" wrote in message
but is completely different than 3 phase. Sigh. Yes, you have stated a tautology. 54 degrees? -- www.e-woodshop.net Last update: 11/06/04 |
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On Sat, 25 Dec 2004 01:33:37 +0000, LRod wrote:
The single phase current is transformed from a fairly high voltage off the feeders to 240V from the output of a center tapped transformer up on the pole. With regard to that 240V, there is no neutral. The 240V comes from the two secondaries of the transformer. And there is no + or -. This is AC, not DC. It is 240V across the two poles. It is 240VAC, but it is similar to differential signaling (each wire wioth equal but opposite instaneous voltage & current) as in twisted pair ethernet vs. AC with a ground reference as in coax TV cable (the ground stays at a zero volt reference and the voltage on the center conductor varies symetrically positive and negative in relation to the ground). - Doug -- To escape criticism--do nothing, say nothing, be nothing." (Elbert Hubbard) |
Linear Mode
