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
Die Gotterspammerung - Junkmail of the Gods
Sure, if you like being nibbled by the 'lectricity.
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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.
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.
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
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.
horizontal mill, static converter
single phase 220V
single phase 110V
wood/metal band saw
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.
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
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
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.
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
he table saw has a pop out in the frame of the saw, The Makita has a button on
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
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.
OT, long boring code dissertation
OK I did some looking.
The first thing you need to define is "Continuous duty motor"
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.
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
OK that's a slam dunk
Now how about a non-continuous duty motor
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
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
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.
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),
(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 ;-)
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
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.
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,
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