single phase vs. 3 phase

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That system makes sense. In household mains, is it a two-wire system, with the normal potential 240V to earth (ground)?
Do you have a safety (fault) ground (earth)?
Kevin
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wrote:

Cable is three core; live (red), neutral (black), earth, where earth is a bare wire inside the overall jacket.
We have two systems of wiring.
Radials are wired with a low-value fuse or breaker at the panel, appropriate to what's connected to the circuit and the cable it's wired in. Most of Europe uses this system.
The UK has fused plugs throughout, so you can have an appropriate fuse for each appliance, plugged into high capacity sockets. This also allows us to use our "ring main" system, which is the best way to do house wiring I've seen.
Each floor (up to a maximum floor area per ring) has a ring of heavy (2.5mm^2) cable laid in a loop, supplied by a 32A breaker. You can hang as many sockets off this as you like. Each appliance then has its own cable and fused plug, up to a max of 13A per appliance. Although there's not much call for these, you can have 3kW on a portable appliance and plug it into any socket in any house in the country. It's a good system.
Although the ring main was originally developed to save copper post-war, it's also a key part of our national passion for tea drinking. A kitchen kettle is 3kW of sheer rapid boiling power and we'd never be seen dead with that American abomination of the warm, damp, Liptons bag in a cup.
We never went for aluminium wiring. Thank goodness.
We're not allowed sockets or light switches in bathrooms. However "bathroom" literally meant a room with a bath in it, and shower rooms never came under this rule. Recently things have changed and there's now a more sensible system based on zones (is it reachable from the bath or shower ?) and sockets are permitted with some rules.
Earth leakage breakers (RCD) came in in the early '70s but weren't used widely until 1990-ish. Now all new fitments have a 100mA breaker on the main panel and individual circuits may have 30mA RCDs where useful (external sockets, kitchens, etc.) Better designed systems use split load panels, where only half the circuits share the common ground fault RCD, so that the lights and freezer don't go off if the garden pond pump springs a leak.

Yes. All cable is three core, and everything gets bonded, right down to the lampshades. There are also rules for wet rooms like kitchens where metalwork must have supplementary bonding.
I sincerely believe that UK house wiring (to current standards) is the world's best system for doing it. It's a simple system, but it's efficient on materials and the standardisation amongst appliances is a great convenience.
-- Die Gotterspammerung - Junkmail of the Gods
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On Sun, 26 Oct 2003 01:40:10 +0100, Andy Dingley

Sure, if you like being nibbled by the 'lectricity.
==================================================================== -=Everything in Moderation,=- NoteSHADES(tm) glare guards -=including moderation.=- http://www.diversify.com ====================================================================
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While the grounded (aka neutral) conductor in premises wiring is indeed typically insulated, the original poster was refering to the service drop, where in most cases the grounded conductor (neutral) is uninsulated.
scott
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Are you referring to neutral supported cable as it comes overhead to your home?
writes:

shop. 3

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Premises Wiring == Within the premises. Service Drop == From the utility company to the service entrance Service Entrance == Meter base and premises disconnect.
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Rico wrote...

Careful! Let's not get neutral and ground wires confused.
Jim
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In the US, on the utility side, neutral is ground. They don't have to conform to NEC rules. They are regulated by the NESC
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Three phase power is more efficient. Typically 3 phase power is only available in commercial and industrial locations. One doesn't usually find it in a residence. Three phase motors require a magnetic motor starter with short circuit and overload protection.
Ms Leslie

the
little
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"Leslie Gossett" wrote in message

In commercial/industrial even single phase equipment can require the same. It's not just because it's 3-phase.
Just for the record..... Jon Veeneman
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Correct on everything but the starter. Overload protection is a good idea for any motor, but you don't need it for either single phase or three phase.
John Martin
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Did they just repeal part III of article 430 and not tell me. I hate it when that happens. ;-) It's true that a high percentage of motors, particularly those sold retail, have internal overload protection (check the labels on the motor) but it still needs to be there somewhere. The branch circuit breaker is sized to the starting current, not the full load current and can typically be 250% of what the motor will safely run at. (see table 430-52) That can also be more than twice the regular ampacity of the wire feeding the motor. (stuff like 40a breakers on 14ga wire<legal>). It is the overload protection that keeps this safe.
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Greg:
I'm not an electrician, and don't have easy access to the National Electrical Code. Are you really telling me that the Code requires overload protection for every motor? Because if you are, I guess I've seen an awful lot of machines that don't appear to meet that requirement.
I just took a look at all of the motors in my shop. All of those, at least, that I could read the labels on without pulling them off the machine or resorting to a mirror.
three phase horizontal mill, static converter
single phase 220V table saw thickness planer dust collector
single phase 110V drill press metal shaper wood shaper wood/metal band saw wood lathe metal lathe
None of the motor labels that I could see said anything about overload protection. The only machine that I know has it is the table saw, but that is a manual starter with heater coils. Am I missing something on the labels? I do remember a few motors with reset buttons, but not of these have them.
I have on a few occasions run the bandsaw hard enough to kick the overload. 1 HP Baldor motor, 12 amps at 110V. It kicks the 20 amp breaker, though, not anything in the motor.
John Martin
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It may say "thermally protected" or something similar or there could be a pop out button on the tool itself. There are some exceptions to the rule for small, cord and plug connected, fractional HP motors but most motors will have some kind of overload protection.
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Greg:
The Delco motor on my metal lathe does say "Thermotron" on the label, but other than the "40 degree" rise rating on most of the motors, there is nothing referring to any overload or thermal protection on any of the others. No pop out buttons, either. These range from a big old GE motor probably from the 1920s to a Baldor from the mid-1980s. Oh, and in my earlier email I forgot the 110V scroll saw and jointer.
On those of the motors that I've had apart for cleaning or new bearings, the only obvious switches that I recall seeing were the centrifugal starting switches.
If I'm reading you right, you are saying that:
1. Most of these motors do incorporate internal overload protection, even though they don't mention it.
2. The electrical code requires that these machines be equipped with overload protection in addition to the circuit breaker.
Looking at a circa 1985 McMaster Carr catalog. Capacitor start single phase motors. Copy states "Enclosed motors with rubber mount feature automatic thermal protection - not for use where unexpected restarting might be a hazard". That copy, though, leads me to believe that the motors offered which were not enclosed, or were not rubber mounted, had no thermal protection. And only a few of those offered were enclosed and rubber mounted.
Not trying to be a PITA, I'd just like to know. Thanks.
John Martin
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You have me curious now. As I said there is an exception for small motors used intermittantly, basically like drill motors and such but even those Chinese $15 box fans have a thermal fuse. I haven't really looked at my tools but I know my Makita side grinder, Sears table saw and drill press have protection. In the case of the fractional HP induction motors like my drill press uses the thermal is in the windings. That is a cradle mount motor like you were talking about tho. he table saw has a pop out in the frame of the saw, The Makita has a button on the end. Article 430 can usually get a fist fight started at an inspector meeting so I am not surprised that there can be confusion with cord and plug consumer products. If something get's a U/L listing we are pretty much stuck with it, whether it meets the letter of the NEC or not.

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WARNING!!! OT, long boring code dissertation
OK I did some looking. The first thing you need to define is "Continuous duty motor"
***NEC2002 430.22(E) Note: Any motor application shall be considered as continuous duty unless the nature of the apparatus it drives is such that the motor will not operate continuously with load under any condition of use. ***
***NEC2002 430.32 Continuous-Duty Motors. (A) More Than 1 Horsepower. Each continuous-duty motor rated more than 1 hp shall be protected against overload by one of the means in 430.32(A)(1) through (A)(4).
OK that's a slam dunk
Now how about a non-continuous duty motor
***NEC2002 430.33 Intermittent and Similar Duty. A motor used for a condition of service that is inherently short-time, intermittent, periodic, or varying duty, as illustrated by Table 430.22(E), shall be permitted to be protected against overload by the branch-circuit short-circuit and ground-fault protective device, provided the protective device rating or setting does not exceed that specified in Table 430.52. Any motor application shall be considered to be for continuous duty unless the nature of the apparatus it drives is such that the motor cannot operate continuously with load under any condition of use. If a motor is selected for duty-cycle service (short-time, intermittent, periodic, or varying), it can be assumed that the motor will not operate continuously, due to the nature of the apparatus or machinery it drives. Therefore, prolonged overloads are rare unless mechanical failure in the driven apparatus stalls the motor; in this case, however, the branch-circuit protective device would open the circuit. The omission of overload protective devices for such motors is based on the type of duty and not on the time rating of the motor. ***
IF the branch circuit O/C device <fuse/breaker> is sized properly for the motor and the motor can't be locked on (I.E.trigger control with no "lock on" button) you can do without overload protection. Bear in mind this limits the size of the motor you can use. If it's too small the typical 15/20a branch circuit O/C device will not adequately protect the motor. That's why we see thermal fuses in those cheap fans. This was written, assuming you would size the branch circuit to a particular motor.
If you have more than one motor on a branch circuit they must have overload protection.
***NEC2002 430.53 Several Motors or Loads on One Branch Circuit. Two or more motors or one or more motors and other loads shall be permitted to be connected to the same branch circuit under conditions specified in 430.53(D) and in 430.53(A), (B), or (C). (A) Not Over 1 Horsepower. Several motors, each not exceeding 1 hp in rating, shall be permitted on a nominal 120-volt branch circuit protected at not over 20 amperes or a branch circuit of 600 volts, nominal, or less, protected at not over 15 amperes, if all of the following conditions are met: (1)    The full-load rating of each motor does not exceed 6 amperes. (2)    The rating of the branch-circuit short-circuit and ground-fault protective device marked on any of the controllers is not exceeded. (3)    Individual overload protection conforms to 430.32. Two or more motors or one or more motors and other loads may be connected to the same 120-volt, 15- or 20-ampere, single-phase lighting circuit as long as each motor is rated not more than 1 hp, the full-load rating of each motor does not exceed 6 amperes, and the rating of the branch-circuit protective device is not exceeded. The requirements for overload protection, as provided in 430.32, must be applied in all cases, regardless of the number (one or more) of motors or the type of branch circuit. ***
This brings is to something more relevant to what we use.
***NEC2002 430.42 Motors on General-Purpose Branch Circuits. Overload protection for motors used on general-purpose branch circuits as permitted in Article 210 shall be provided as specified in 430.42(A), (B), (C), or (D). (A) Not Over 1 Horsepower. One or more motors without individual overload protection shall be permitted to be connected to a general-purpose branch circuit only where the installation complies with the limiting conditions specified in 430.32(B) and (D) and 430.53(A)(1) and (A)(2). (B) Over 1 Horsepower. Motors of ratings larger than specified in 430.53(A) shall be permitted to be connected to general-purpose branch circuits only where each motor is protected by overload protection selected to protect the motor as specified in 430.32. Both the controller and the motor overload device shall be approved for group installation with the short-circuit and ground-fault protective device selected in accordance with 430.53 (C) Cord-and-Plug Connected. Where a motor is connected to a branch circuit by means of an attachment plug and receptacle and individual overload protection is omitted as provided in 430.42(A), the rating of the attachment plug and receptacle shall not exceed 15 amperes at 125 volts or 250 volts. Where individual overload protection is required as provided in 430.42(B) for a motor or motor-operated appliance that is attached to the branch circuit through an attachment plug and receptacle, the overload device shall be an integral part of the motor or of the appliance. The rating of the attachment plug and receptacle shall determine the rating of the circuit to which the motor may be connected, as provided in Article 210. *** You see why someone could get confused?? Basically I wouldn't want anything that didn't have some kind of overload protection unless it was a throw away tool or something you only run intermittantly with a trigger. Certainly any kind of a free standing tool like a planer, jointer or table saw that has an on/off switch requires O/L protection because it is capable of "continuous duty". IMHO ... and that is how the fist fights begin at the inspector meetings ;-)
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you aren't likely to have 3 phase power unless you are in an industrial zoned area. your home would be single phase.
dave
Mike B wrote:

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Mike, discussions of 3-phase may well be moot if you're in the US. It's what industrial users of 5+ HP motors use, and not normally available to residential customers. This is probably a good thing to examine http://www.woodweb.com/knowledge_base/When_is_threephase_power.html
It's like having current at 180Hz providing a more constant push, though at the same potential (power) as single. You can get a converter to generate a close clone to 3-phase, but it's going to use enough power to negate any gain you might make. For lathes and such, varying the phase angle in the converter is used to control speed without a significant loss of torque above a minimum speed.
BTW, capacitor starters generate pulses to get a single-phase motor running, then cut out. Capacitor run motors use an interboost from the run capacitor to get greater output from a smaller motor.

the
little
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Lots of larger offices and most all factories are fed with 3 phase because it's cost effective and more efficient. Smaller buildings and residential are fed with single phase. 220 is single phase. Your wise in utilizing it. Upgrading to 3-phase power would require a whole new "service entrance", main panel, and perhaps "line work" to replace the line transformer feeding your location. Heck, you might not even have it available at the pole in your location. If you're situation is substantial, and your so inclined, call up a local electrical contractor that advertises "commercial and industrial" and talk to their service department manager. I'm sure he'd be glad to talk with you and clarify the finer points. If you two figure out it's worth a look-over he'll come by or send someone over to eyeball the location to see if it's feasible and makeup a quote. It's that easy.
Hope this helps, Jon Veeneman

the
little
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