I’m finally moving my stationary equipment from the tiny old shop to the slightly larger new shop, about 80 feet away. To do this, I need to re-route the old wire and extend it. What’s there now is #10 stranded, three wires, in 1″ conduit, ending in a sub-panel. The new shop is about 800 feet from the main panel. There is a splice in a junction box about halfway between the main panel and the old shop.
What I need is enough 220V power for the DC (9 amps peak) and bandsaw OR tablesaw (12.5 amps). Lights and 110V tools are powered from a separate (existing) feed. (I’m the only worker, so there is never a need to run both saws at once – I could install a single receptacle to make sure it can’t happen.)
I’m considering running one 220V circuit to power both tools. I’d put a 30A breaker at the main panel, a 20A breaker at the shop sub-panel, and turn on the DC first, then the BS or TS. Is the #10 stranded wire, 800 feet long with a splice in it, big enough for that load? (The DC probably runs at no more than 4 or 5 amps once it’s started, and even the BS probably runs under 10.)
Alternatively, I might have enough wire to pull 6 wires through the existing conduit, but I’m afraid some of the spools are short and so there might be two splices in each wire (before the sub-panel). But that way I could have the DC on its own dedicated circuit, and just swap plugs for the BS and TS. Then I’d never have more than 12.5 amps on one circuit… and maybe I could also move the compressor… but there are those splices to worry about.
Finally, can I wire-nut the splices, or is there a better option?
I know I really ought to just run new, unspliced #6 all the way from main to sub, but that isn’t going to happen until I sell more furniture, so I need a temporary solution that won’t burn my shop down. I already have a bunch of this #10 stranded THHN wire, and according to what I have read it should carry 30A. So I figure as long as I keep a 20A breaker at the shop, I shouldn’t be heating things up too badly. What do you electrical experts think?
“Everything should be made as simple as possible, but no simpler.” A. Einstein
Replies
Don't wire it with splices. 800' is a long way to go and you're not going to be able to use 10ga, especially stranded. Cross sectional area and length of run determines the current handling capability of a wire. Don't skimp on this or your tools will fail prematurely. There are charts out there for wire gauge. Use them and you shouldn't have any problems. You'll also need a grounding spike at the new shop. Call a friend who is an electrician for help with wire gauge, grounding, breaker size, circuit layout, etc. You will probably need a subpanel in the new shop. Long runs = voltage drop, especially under load.
Ohm's Law power formula states that P=IxE. If the device(let's use a saw as the device) is rated at 3HP, that's peak draw. With 746 watts/HP, (3)(746)=2238 Watts. At 220V, the current derived is 10.17A, P/E=I or, 2238W/220V. That's just the saw. Add the DC, lights, a fan when it's hot and anything else you may need to run. There isn't any reason to run 120V out there from the house. You can get that from the subpanel. My house is a duplex with 2x100A service panels. My garage has a 60A subpanel. The electric company ran 2ga for the feed from the pole, about 100'. When the wires heat up from current draw, they resist more, lowering the voltage, increasing the current. If the device is going to draw 3HP(2238W), at 200V it'll draw 11.19Amps. Add more equipment running and it drops more.
I guess my post was too long, or I didn't make some things clear... I already know all of that. The charts for wire guage say #10 will carry 30A (as I mentioned already). And I will be running far less than that, probably no more than 15A at any given moment. And I already have a subpanel at the shop, and a grounding spike. And the HP ratings on the motors are meaningless, I quoted the actual amperage draw specs which are a lot more reliable. And I'm not running lights, fan, or anything else on this circuit - those are already on another line. All I want to know is whether the #10 stranded, with the splices, is safe with a current of less than 20A. Maybe I can redefine my questions:1. How much voltage drop can I expect over 800 feet of #10 stranded, with two splices, assuming a current of 15A at constant load?2. Is that configuration likely to develop enough heat to either shorten motor life, or degrade the wire insulation?"Everything should be made as simple as possible, but no simpler." A. Einstein
http://www.albionworks.net
From: [email protected] (James Roche)
Newsgroups: rec.woodworking,misc.consumers.house,news.answers,rec.answers,misc.answers
Subject: rec.woodworking Electric Motors Frequently asked Questions
Followup-To: poster
Reply-To: [email protected]
Approved: [email protected]
Frequency: monthly
Archive-name: woodworking/motors
Last-modified: 3/17/94
Copyright (c) 1994 by James J. Roche. All rights reserved.
This article answers many of the frequently asked questions about electric
motors.
Motors:
There are many kinds of motors, but this article considers only two
kinds used frequently in woodworking tool applications: universal AC/DC
motors and single-phase induction motors. Universal motors have brushes
and commutators and are used for portable tools like routers, skilsaws,
and electric drills. Single-phase induction motors have no brushes,
run only on AC electrical power, and are usually found on stationary
tools such as table saws, drill presses, planers, and jointers.
There are exceptions to this: some stationary tools use universal
motors.
Horsepower: Motor horsepower is the most misunderstood (and misused)
electric motor rating. Neither motor, universal or induction, produces
usable horsepower unless it is slowed down (by applied mechanical load)
from no-load speed. For induction motors, this slowdown is called
"slip", and the horsepower "developed" by a motor increases with slip
(to a simple approximation). This is why induction motors are
typically rated at 3450 rpm (two pole motor) or 1750 rpm (four pole
motor). The rating speed allows for slip from the "synchronous"
speeds of 3600 and 1800 rpm, respectively. Universal motors do not
have a synchronous speed, but have a maximum no-load speed that depends
upon the voltage applied to the motor.
Most motors can put out a lot more maximum horsepower than they can
sustain continuously. By forcing more mechanical load on the motor,
slowdown is increased and so therefore is the output horsepower.
Mechanically, horsepower is torque times rpm, and increasing the
mechanical load means that the rpm is slowed slightly and the drag
torque is increased to obtain more torque times rpm. Electrically,
horsepower is volts times amps, and by conservation of energy, the
mechanical output horsepower must be balanced by electrical input
horsepower. Since the voltage is relatively constant, this means that
as a motor is loaded, the input current increases. But the electrical
winding impedance has a resistive component, so that higher current
means more power dissipated in the windings. In fact, the motor
windings heat up proportional to the square of the motor current.
Except for specially designed motors, the current that a motor can
sustain continuously without burning out its windings is a fraction
of the current at maximum load.
Unscrupulous vendors sometimes publish maximum "developed" horsepower
to make their products seem more capable than they really are.
Developed horsepower may be two to five times the continuous duty
rating of a motor. Such products should be examined to discover the
continuous duty rating to compare with other, more conservatively
rated products.
When the talk is of developed horsepower, the meaning is "peak" which
for an induction motor is typically the local peak of the torque curve
near synchronous speed. A typical induction motor torque curve is:
|
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.
|.
| .
Dev. _ . .
| . . .
| . . .
| . . .
| . .
Rated _ . .
|
| .
|
| .
|
Torque | .
|
|
| .
|__________________________________________________________._
|
0 RPM 1800 or 3600
As you can see, the curve is very steep in the operating region and in
fact, the observed operation is typically that once you load the motor
past the local maximum torque, the speed jumps to the corresponding
point on the initial portion of the curve or simply stops. The actual
operation depends upon the shape of the curve near 0 RPM.
The Rated HP is typically the torque level at which the motor can be run
continuously without exceeding the temperature at which the winding
insulation beaks down. Since there is thermal mass involved, you can
operate the motor at higher than rated torque for less than 100% of
the time and not exceed this temperature if the motor is cool preceding
the run etc. etc. etc.
Typically, two motors with different rated HP develop different HP in a
ration close to the same as the difference in rating.
The story is somewhat different for a universal motor such as is used on
most hand held tools. In these motors, for a given input voltage, the
torque goes up as the speed goes down. The more you load them, the slower
they run until they stall, at which point their torque is a maximum.
In this case, the developed horsepower is a the point along the torque
curve where the speed X torque is a maximum. As with the induction motor,
the rated horsepower means you can run the motor there at 100% duty cycle.
Again, you can load the motor more and it will produce more torque but you
may only do this on a limited basis.
The final word is heat. If you exceed the winding insulation temperature
rating, you will fail the insulation and ruin the motor ( or pop the
thermal cutout if so equipped).
Application areas: Universal motors are compact, have high starting
torque, can run at high rpm, and deal well with rapidly varying
loads. They are often used with triac or thyristor speed controls.
This makes them ideal for portable power tools. Single-phase
induction motors are efficient, have a limited rpm selection,
are relatively heavy and bulky, and are almost maintenance-free.
They work well in stationary tools that run at one rpm or that have
a variable-speed transmission.
Voltage: Both kinds of motors are supplied in popular mains voltages
(115 or 230) but only induction motors are supplied with winding
taps that allow either voltage to be selected. As far as the motor
is concerned, there is no difference in efficiency when selecting
either 115 or 230 volts. This is because such motors have two
identical sets of windings that are connected in parallel for the lower
voltage and in series for the higher. Neither connection results
in the individual windings seeing a different voltage. However,
inadequate wiring can make a difference to motor operation, because
higher current at 115 volts may give unacceptable wiring voltage drops
in some shops or garages. Some wiring voltage drop is expected and
built into the motor rating. Nominal pole transformer output (to
your house) is about 120/240 volts. Motors are rated for 115/230
volt operation, which allows for 5/10 volts wiring voltage drop.
More voltage drop than this can cause low starting torque and
overheating at rated load.
115 or 230 volt operation makes no difference to your power company
either. The watt-hour meter at your electrical entry measures watts
regardless of the voltage used. Your power company does not give
you a single watt for free, and your PUC (Public Utility Commission)
won't let the power company charge more than the legal rates.
Watt-hour meter accuracy is a matter of law in most States.
Current: Motors have a nominal current rating which is supposed to be
the current at rated horsepower and rated voltage. A motor will not
draw exactly rated current except in the unlikely circumstance that
the voltage applied is exactly the rated voltage and the load applied
is exactly the rated horsepower. As a matter of fact, most woodworking
tools spend much of their life spinning without applied load and drawing
only a small fraction of nameplate rated current. When the tool begins
to cut, motor current varies widely depending upon cutting load. In
some tools which have relatively small motors, motor current may approach
several times rated current as the tool is momentarily loaded close
to stall or breakdown torque. An exception to this wide variation
would be something like the motor driving the fan on a dust
collection system; such motors operate at about rated horsepower all
the time because the fan presents a constant load.
For both universal and single-phase induction motors, the full-load
current is given by
I = (746 * hp) / (eff * pf * voltage)
where eff is efficiency, pf is power factor, and the others are
obvious. In AC systems, the voltage and current waveforms are
(nominally) sine waves and may differ in phase from each other
by an angle called the phase angle. There are 360 phase angle
degrees in one sinusoidal cycle. Power factor is the cosine of
the phase angle, and for motors this angle is normally between
zero and 90 degrees, current lagging voltage. In DC systems,
there is no phase angle, and power factor is defined as 1.0.
Typical values for single-phase induction motors running at 115
volts AC are pf = 0.8 and eff = 0.9. This gives a rule-of-thumb
value for amps/horsepower at 115 volts of
9 amps / horsepower
This figure is probably OK for rule-of-thumb comparison of induction
and universal motors or reasonability checks as long as you
remember that it is based on typical values.
If you are contemplating operating a 115 volt universal motor
on DC, performance should be slightly better at 115 volts DC
than it was on AC. The proper voltage to use is 115 volts DC.
This is because AC voltages are given as RMS values, which
are their power-equivalent DC values. The tool will actually
endure less voltage stress under DC operation because the
peak voltage experienced under DC is 0.707 times the AC peak
voltage. Switches and contacts, however, may not last as long.
Starting current can be as much as ten times rated motor current.
This is usually not a problem for the circuit breaker feeding the
motor, because modern circuit breakers are typically rated to trip
instantaneously at about ten times breaker nameplate rating. For
currents less than the instantaneous value, the breaker trips due
to internal heater elements which mimic the heatup characteristics
of the wiring the breaker is supposed to protect. Since starting
currents last only a second or two (unless the motor is jammed),
motors usually will not trip circuit breakers on starting current if
the breaker is rated at higher current than the motor nameplate
current. This may not be true if you start the motor on a circuit
which is already loaded close to rating.
A motor may trip your circuit breaker on time-overcurrent (the
heaters) even if the motor nameplate current rating appears to be
within the breaker rating. This can happen if you continuously
overload the motor; motor current will then be several times the
nameplate rating. There may be other signs of this. The motor may
become extremely hot (spit sizzles on the casing). This is General
Electric's way of telling you to slow down.
Breakdown torque: Single-phase induction motors, unless they are
designed for torquemotor operation, have a "breakdown" torque rating.
This refers to the motor torque-versus-rpm curve, which has a peak
torque somewhere between zero rpm and rated rpm. If the motor is
running and load is applied, the motor slows and torque increases
until breakdown torque is reached. At this point, further rpm
reduction causes a reduction of motor-supplied torque, and the motor
rpm reduces rapidly to zero (it "breaks down"). This is why a saw,
for instance, appears to suddenly stall as it is overloaded.
Ventilation: Most motors have one of two kinds of ventilation: fan-
cooled open housing, or totally enclosed, fan-cooled (TEFC) housing.
In the former type, a fan attached to the motor shaft draws air
through the internal parts of the motor and blows it out of
ventilation slots cut into the motor housing. Most universal motors
are of this type because of the need to cool the brushes and to
exhaust brush carbon dust and commutator copper fragments. In the
TEFC type, the motor housing is completely enclosed and no air
gets to the internal parts of the motor. Instead, internal heat
is conducted through the metal housing to fins, where air blown
by an external fan removes the heat. Some induction motors have
this kind of (more expensive) ventilation and they are often used
in applications where excessive dust or flammable conditions exist.
Drive gear: Surprisingly enough, even though many people will look
at motor horsepower rating, they often completely ignore the drive
gear attaching the motor to its load. The drive gear is often a clue
to the real power rating of the motor-drive combination. It's
difficult to determine the rating of enclosed gears, but v-belts
can give an immediate visual clue. While larger pulleys increase
a v-belt rating, a nominal rule of thumb is about one horsepower
per 1/2 inch v-belt. Two 5/8 v-belts on large pulleys may be good
for 4 or 5 horsepower. One small belt on a motor which "develops"
3 horsepower is cause for some suspicion. Actual belt drive ratings
can be found in manufacturers handbooks (see Gates, for example) or
in Machinery's Handbook.
Motor Starters: Motor starters are big relays mounted in expensive
metal boxes with heater overloads matched to the motor they start.
They serve two purposes: 1) The relay contacts are heavy duty and
are rated for the motor starting current. Delicate contacts, such
as those on a pressure switch, will fail if used directly to
start a large motor. Delicate contacts are therefore wired to
operate the motor starter relay rather than the motor. 2) Wall-
mounted circuit breakers are designed to protect building wiring,
not motors plugged into wall receptacles. If your electrical box
circuit breaker trips before your motor burns up, it is incidental,
not on purpose. However, motor starters are designed to trip on
heater overload before the motor they start burns up.
How much horsepower: This question is often asked and has no easy
answer. This is because the amount of horsepower you need depends
upon your patience, your preferences, and the way you use the
machine in question. Here are some pros and cons. A larger
horsepower motor (and associated drive gear) has a thicker shaft
and is typically more robust than a smaller horsepower motor. It
responds to overloads and hard cuts more strongly, and may not stall
in your application. It does not use very much more power, since
electric motors use only power demanded plus some motor losses (which
are somewhat larger for higher rated motors). On the down side, the
initial expense of the motor and drive gear is greater. Higher
horsepower often requires 230 volt wiring. The motor and associated
drive gear and mountings are heavier. A smaller horsepower motor
is cheaper, lighter, and may run on 115 volts. For a careful worker,
the torque supplied may be sufficient. On the down side, the tool
may stall more often and wet wood may be impossible to cut. The
drive gear may be less robust and may require more maintenance. If
the tool is operated in overload, the 115 volt circuit breaker may
trip.
Call a licensed electrical contractor! Get a professional opinion and not bad advice from non-electrical trades people. Your main concern should be voltage drop from your existing service to your shop (800 feet away). The National Electrical Code has a section on wire resistance and voltage drop calculations. Also be advised of the local codes in your area. Anytime you have a sub feed panel it is a code requirement to feed it with a four wire circuit. This circuit consists of two 120 volt legs, one neutral wire and an equipment ground. By the way, it's a code violation to drive a seperate ground rod at the shop. PLEASE seek profesional help to keep you out of trouble, safe, and in compliance with the codes for insurance purposes.Good luck!
Delbert
http://www.hydroponics.net/learn/is-220-volts-more-efficient.asp
Thanks for the link for the voltage drop calculation. It beats doing the math and looking up the data in the NEC.
Delbert
we are you doing with those grow lights??
Dont answer its just a joke.
Edited 2/1/2005 12:24 am ET by TURNSTYLER
I didn't know it was a code violation to drive a ground stake at the shop. I have a new garage and a fourth wire(ground), staked at the garage, was required by the inspector since the new service was run in plastic conduit. If it had been run in metal conduit, the fourth wire apparently wasn't required, but the panel in the garage would need to be bonded, anyway.
"I cut this piece four times and it's still too short."
The code has two requirements. One for a "main service panel" another for a "sub feed panel. When you have a sub feed panel, that sub feed panel is bonded with the equipment ground wire which runs from the main service panel location. The code requires that the main service panel be grounded to a ground rod. Article 250 NEC2002 covers these requirements. Your Main service panel and the sub feed panel should have been bonded by a seperate equipment grounding conductor. This may not have been the case in your installation. The person having the final say is "always" the Authority Having Jurisdiction.
Delbert
What am I missing here?AlbionWood asked if he could use 10 ga stranded wire over 800 feet and expect to get at least 20 amps.It sounds as though some of you are saying no, and if that's the case, what guage wire must he run for his purpose?
The big issue here is the 800 feet between the breaker panel and the shop. Any wire has a certain amount of resistance per foot, so the longer the wire the more resistance it has. In general, the larger the wire the less resistance per foot. So, for long lengths the wire size has to be increased to keep the wire's resistance from causing an excessive drop in voltage at the far end.Voltage drop on a branch circuit should be kept at 3% or less to keep your power tools happy. There are a number of voltage drop calculators available online, the one I like to use is at http://www.electrician.com/vd_calculator.html. For a 10 gauge wire 800 feet long, a fully loaded 240VAC 20 amp circuit would have a voltage drop of almost 17% at the far end. In other words, if he put a 20 amp load on the circuit at the far end, the voltage would drop from 240VAC to 199VAC. In this example the wire size would have to be increased all the way to 2 gauge to get the voltage drop below 3%.Now, if the load were only 3 amps at the far end, the voltage drop on an 800 foot long 10 gauge wire at 240VAC would be only 2.5%, which is fine. So, the size of the wire will depend on the size of the anticipated load.
Edited 2/1/2005 10:56 am ET by Stuart
Finally, a useful response! The calculator at least gives me a quantitative comparison for voltage drops at various gauges and amps. It still doesn't address the splice issue, so I'll have to do some more digging around to find that; but to me it looks as if I can safely run one tool at a time on one circuit. (90% of the time, the current will only be a few amps.) So I should pull a new line for the DC and a new line for the saws. I'd love to run #2 all the way out, but for the same amount of money I could either buy several dozen replacement motors, or a new shop closer to the pole.Where does the 3% value for power-tool happiness come from? The utility power around here fluctuates more than that."Everything should be made as simple as possible, but no simpler." A. Einstein
http://www.albionworks.net
The 3% voltage drop requirement is from the National Electric Code (section 210.19a of the 2002 edition, to be exact.)
As far as splices go, of course it would be best not to have any but they are OK if done correctly. Assuming your wire will be in a buried conduit, the splices will have to be in an accessible junction box and the box has to be big enough to allow enough space for the splices. If the boxes are above grade, wire nuts are OK - I assume these boxes would be located out in the yard somewhere between your panelboard and the shop; you can mount them on a post or something similar that securely locates them high enough above the ground so they don't get wet or get run over by the lawn mower, and the boxes need to be weatherproof. If you're planning on using some sort of box or handhole that's at grade level, instead of wire nuts you'll need some sort of weatherproof splice rated for use in that environment. Those weatherproof splices can be tricky to do right, so you'd probably be better off with junction boxes above grade. There are also splice kits for direct bury cable, but again they are best left to an electrician familiar with their installation.
Finally, I need to issue a disclaimer here to cover my behind...as long as you use the circuit strictly for small loads only you'll probably be OK, but if you can I'd strongly recommend upsizing the wire now to prevent problems in the future. Someday, someone may plug in a big air compressor or something out there, and I don't want any angry emails when the motor burns up. ;-)
Stuart,Thanks for giving such an comprehensible answer. Your response gave clarity to what had become quite confusing. I'm sure AlbionWood will take note of your disclaimer.
Anytime you have a sub feed panel it is a code requirement to feed it with a four wire circuit. This circuit consists of two 120 volt legs, one neutral wire and an equipment ground. By the way, it's a code violation to drive a seperate ground rod at the shop
Really? That's news to me.
In truth, every detached building needs its own ground electrode system, unless it is serviced by only one branch circuit. See NEC section 250-32(a).
A three-wire subpanel feed is OK in a detached building if the ground and neutrals are bonded in the outbuilding's panel, and there is no other metallic path between the two buildings. See NEC section 250-32(b)(2).
You use 2 distances in your first post, 80' and 800'. They make b big difference.
I think that at 800' you will have problems in tripping the 20amp breaker even with a dead short.
I suggest you ask a professionl for advice.
BTW, have checked with the utility to see what it would take to put in a second service? 800 ft. is a long way to run 120V/240V. But it's nothing for a 10KV "Medium Voltage" utility distribution feeder.
The utility around here can barely keep the lines they have up and running. Getting a new panel takes weeks to get permits and then more weeks to get the utility out. And getting a new POLE, I'm told, can take a year. And they charge up the wazoo for that. So for the time being, I must make the best I can with what I have, which is why I posted the questions in the first place..."Everything should be made as simple as possible, but no simpler." A. Einstein
http://www.albionworks.net
With everything else that has been postted, I would suggest that you get a price on spools of #2 or #4 wire from a electrical supply house(not home depot). This might be a soultion.
If I understand correctly, your house is at least 800 feet away from your meter? Is the shop still 80 farther from your home (about 880' from the meter)?. If the shop is being fed from the house's sub panel(or main panel), then the run is from there is only 80' How far is the house from the new shop?. Your house should have the proper wire size going from the powerpole(meter) to you home and it probably is at least a 100amp service, right? Why not use the subpanel (or main panel) in your home to feed the new panel in the shop.
Or am I really missing something?
Let me try again:The old shop was about 700 feet from the main panel. I moved to a larger building (formerly my residence, a cabin we built 5 years ago) about 80 feet further along. So the new shop is about 800 feet from the main panel. My new house is off in a different direction, farther from the shop than the main panel, so that's no help.The new shop already has one feed of #10 3-wire with ground, supplying lights and plugs. Yesterday I added a second #10 feed by extending the feed from the old shop; this is temporarily powering my saws, but will eventually be dedicated to the DC. I'll pull a third #10 feed to power the saws. (Got a bunch of #10 real cheap a few years ago)I'd love to run #2 out there but it would cost several thousand dollars. (Have to buy (3) 1000 foot spools.) I'm saving up to get a new pole and panel brought to the shop, maybe in a year or so."Everything should be made as simple as possible, but no simpler." A. Einstein
http://www.albionworks.net
So if I have this right, you will have 700 + 80 ft of 10 gauge copper cable. At 1.25 ohms per 1000 ft, and 1560 ft total (out and back), that's 1.95 ohms. The table saw load is 12.5A (at full load), which means about 24V dropped across this line. Depending on what the no-load voltage is (assume 240 for now), that would be 240V - 24V = 216V at the motor terminals. US made motors are rated for 230V, which means your supply would be about 6% under rated voltage. Most Asian imports, if seems, are rated 220V, which means they would be operating at about 2% under rated voltage. Motors typically can operate satisfactorily at +/-10% rated voltage (what's actually shown on the nameplate).
Neither of which are terrible, but you should be careful about not overloading the saw. At rated load it's already going to be pulling more than the nameplate amperage, and the heat generated increases as the square of the current. If your no-load system voltage is less than 240V, then you can adjust the math to see what the percent undervoltage would be, but of course it will be worse.
If you have a clamp-on ammeter (less than $20 at Radio Shack), have someone watch it while you cut to see how close to, or how far over, the motor nameplate amperage you go. You'll be able to get a feel for how hard you can push the saw. There's nothing wrong with working it harder than the nameplate amperage for short durations followed by some cool-down time (running). Folks with contractor saws running on 120V work them past the nameplate current all the time, even if they don't realize it.
As far as the dust collector goes, if the current through the motor doesn't exceed the nameplate value, you can run it like that all day long without harm, regardless of what the voltage is supposed to be. In fact, that's true of all motors. If the voltage under load is low, just keep the load light enough that the nameplate current rating isn't exceeded, and it'll run forever.
Those 120V tools, though, only have 1/2 the voltage to start with, so for the same current they'll be suffering twice the voltage drop in the lines, and will therefore be pulling even more current over the rated current (for the same load). Be careful with them, so you don't burn them out.
HTHBe seeing you...
Tom, thanks very much - that is by far the best answer I have received yet.The BS is actually the largest motor I have, and it is substantially overpowered for the work I normally do. I've never even come close to bogging it down. If I start resawing wide pieces, then I'll have to be careful. The TS gets worked a little harder sometimes, but its motor is rated for only 7.5 amps. I'll check both later today and see what the rated voltage is; I didn't know that US and foreign-made motors were different in that way. The BS is a Laguna (Meber)Italian-made 2.5 HP; the TS is a DeWalt 1.5 HP. Both motors undoubtedly foreign, the Meber probably Italian and the DeWalt probably Asian.I've been thinking that it would be a good idea to get one of those clamp-on ammeters so I could know what was really going on. Next time I'm in town I'll see if RS has one.Thanks again, your information was very helpful."Everything should be made as simple as possible, but no simpler." A. Einstein
http://www.albionworks.net
Radio Shack does carry the clamp on style of ammeter but, in case you don't know this, the clamp doesn't work if it is placed around the entire power cord. To use one you have to open the junction box on the motor or at the switch and place the clamp around just one of the hot wires. An alternative is to make up a short extension cord with the conductors separated so you can again hook the meter clamp around just one of the wires.
John W.
No problem, I made the cord for the saw from three strands of that same #10 wire, so all I have to do is unwind a little of the tape holding them together. Thanks for the tip."Everything should be made as simple as possible, but no simpler." A. Einstein
http://www.albionworks.net
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