Roto-Phase Questions and Answers
What is the Roto-Phase?
In brief, the Roto-Phase is often termed a phase converter, but it is more
accurately defined as a phase generator. It generates one voltage which when
paralleled with the two voltages generated from a single phase line produces
three phase power. Induction as well as resistance three phase loads can be
operated from the Roto-Phase with performances favorably comparable to those
applied to a solid three phase line.
Is a Roto-Phase required for each motor?
No. Generally, only one Roto-Phase is needed to operate the variety of motors
found on larger farms, machine shops (except CNC equipment), quarries, sewage
plants. etc. The motors may be operated in any sequence or duty cycle as
normally required, simultaneously or individually.
Is it necessary for the Roto-Phase to start first?
Yes. It must be up to speed (two to three seconds) before any three phase load
How does the Roto-Phase differ from static phase converters?
Most converters in the past have been static types, designed to operate
only one motor of equal horsepower. They are not true multi-motor converters.
Roto-Phase, being a rotary type, is a three phase distribution system in which a
variety of motors can be operated individually or simultaneously, just as though
connected to a three phase line. As Roto-Phase is rotating, a phase shift is
accomplished through a rotor spinning within an electrical field. The result is
a true three phase. Static converters do not revolve, only manufacturing a
voltage whereby the motor "thinks" it sees three phase.
How does performance compare with static phase converters?
Performance substantially exceeds that of all static phase converters—a
comparison is almost unrealistic. Most static phase converters are poorly
designed—some do little more than cause a three phase motor to start, but then
"single phase" the motor on run—a dangerous condition. Some static types can
give a reasonable performance, but even they are limited in comparison.
Why is the Roto-Phase substantially better than a static phase converter?
The reasons are manyfold. Motors are operated at their 100% load rating whether
Wye or Delta, any RPM, variable loads, single speed or two speed, 50 or 60 Hz,
any type of load application, resistance and induction loads. No static
converter can make all of the above claims. Plus, a number of motors are
operated while the static types are generally confined to one motor.
How does Roto-Phase compare with a solid three phase line?
Roto-Phase is a manufactured device that comes closest to a solid three phase
line. Compared with an Open Delta three phase system, the Roto-Phase is equal and
every bit as good. Against other solid three phase systems the Roto-Phase is
merely the best substitute. Never-the-less, solid three phase is often not
economically feasible nor readily available. For short seasonal loads or small
loads, it is generally impractical. The Roto-Phase cost is often just a fraction
of the cost of extending a three phase line, whether a few hundred feet or many
miles. Cost of operation on a single phase line is invariably less than on solid
three phase. Rate costs are less, with no demand or power factor penalties. In
recent years ARCO has seen a number of examples where a user has had solid three
phase removed and replaced with a Roto-Phase.
Are all rotary phase converters the same?
Definitely not! The best example is using our smallest and Light Duty Roto-Phase
III. It will not only equal, but in some ratings actually exceed most
competition brands. Strangely, the Light Duty Roto-Phase III costs less than the
competition "top of the line". ARCO makes a variety of rotary converters:
Standard Duty, Heavy Duty, Light Duty, Automatic Start, Manual Start,
Submersible pump, CNC, etc. Roto-Phase is the oldest of its type - with over 20
years successful application. The Roto-Phase reputation has made it the largest
selling rotary in the world. We set the standards others strive to meet.
How does Roto-Phase compare with single phase motors?
Single phase motors are practical to about 5 hp, above that they are only
marginal. Inherently, there is high maintenance with single phase motors,
relative short life, less efficiency than three phase types, and the cost is
much more. Savings can often be affected by using a Roto-Phase and three phase
What about the so-called "soft-start" motors?
They are basically nothing more than a two or three phase motor coupled to a
static phase converter, with variations. They still only operate one piece of
equipment and are often restricted to easy start loads only. Generally, one
Roto-Phase (that can handle a number of motors) is about the same cost as the
How is the correct Roto-Phase model determined?
All models are rated in horsepower and the nameplate shows the largest motor
that can be used as well as the total horsepower capacity of all motors that it
can handle the largest motor hp capacity is true hp and is not intended to
operate mis-rated motors or motor loads. If the largest matched motor has a
continuous overload, or is a brand with poor power factor, the next larger
Roto-Phase may be required. Generally, one motor equal to the largest motor
rating can be handled plus smaller motors to the unit total capacity. Where
there are several larger motors, a larger Roto-Phase is often needed.
Are resistance loads operated?
Yes. Resistance loads such as battery chargers, welders, transmitters, EDM, etc.
are readily handled. All of a resistance load goes through the Roto-Phase stator
windings which is not true with induction loads. Sizing, however, is very
important and the factory should be consulted for recommendation.
Will a three phase motor operate at full rated load?
Yes - and at nameplate rating of the motor. There have been several private and
university tests where it has been established that motor windings, at full
load, attain the same degree of heat when connected through the Roto-Phase as
the motor windings do when connected to solid three phase. Motors operated
through the Roto-Phase should not be operated continuously above 110% load. and
preferably "T"-frame motors should not exceed 100% load.
What is the efficiency?
The efficiency of the system and motors is comparable to that on a three phase
line. Furthermore, efficiency is better than single phase motors and equals or
exceeds motors operated with static converters.
How about phase "balancing" and ampere readings?
No phase balancing of motors is required. With static converters phase balancing
is a "must", often impossible to do. With the Roto-Phase, motor leads T1 and T2
are fed from the single phase source and should equal the motor rating when
operating at full load. T3 is the "manufactured" phase and is difficult to
properly read and interpret with an ammeter. The typical reading is lower than
the other two phases. From years of experience it has been learned that if T,
and T2 are at the nameplate rating, T3 should be ignored when lower than the
other two. This condition will not harm the motor where voltages are reasonably
Will the Roto-Phase operate both "Delta" and "Wye" connected motors?
How about inrush current of the motors on start?
A unique condition exists in the Roto-Phase which is favorable to the power
supplier and is one reason why so many utilities have permitted 50, 75 and 100
hp motors on their single phase lines, starting across-the-line. The starting
KVA of a three phase motor connected to the Roto-Phase is about 30% less than
the same motor operating on solid three phase. It has been observed on numerous
occasions that a 30, 40 or 50 hp motor on a medium loaded single phase 7200 volt
line creates virtually no objectionable line disturbance. Further, there are
instances of 75 hp motors operating with the Roto-Phase with across-the-line
start over 50 miles from the substation.
What KVA transformer is required?
The rule of thumb—one KVA per hp of total load expected to be operated
simultaneously, plus other load and auxiliary lighting.
Where should the motor magnetic starter be located?
Always on the three phase side and it should be a three phase magnetic starter.
It should be noted that the manufactured phase (T3) must not go through a heater
coil on two-heater coil starters, and T3 should not be connected to the holding
Can a reduced voltage starter be used?
Yes. but applications should be carefully selected. Consult factory for
What voltages are available?
208, 230, 460, 575 - 50 and 60 Hz is available
Is there a limitation as to the number of motor starts per hour?
No. Motors may be started as often as required.
Can long starting cycles be operated?
Yes. Motors with six minute starts, for example, impose no problems when
Can motors be reversed?
Yes. With the same action and degree of efficiency as connected to a solid three
What about two or four-speed motors?
Only the Roto-Phase can handle different speed motors. Static converters are
confined to single speed motors.
What are some of the jobs Roto-Phase can handle?
CNC equipment - Augers - Compressors - Elevators - Fire sirens - Paper balers -
Saw Mills - Cream separators - Computers - Silo unloaders - Machine tools -
Hammermills - Pumps - Fans - Submersible pumps - Hoists
Years of experience show the list to be endless.
Can the Roto-Phase be installed remote?
Yes. Distance is not a factor, providing sufficient size wire is used, and
allowing for voltage drop. Your utility or electrician can calculate voltage
Is it difficult to install?
No. It is the easiest of all types to install, comparable to installing any
electric motor. A disconnect switch or magnetic starter is needed to start the
converter and the single phase wiring must be adequate to handle the current of
all of the motors to be operated. It must be emphasized that our wiring
recommendations should be carefully followed.
What is the life expectancy of the Roto-Phase?
The Roto-Phase can last longer than the motors and equipment being used. It is
never more than lightly loaded and very cool running under load. Temperature
rise is greatest under no-load condition.
What is the cost of operation?
We make no claims on savings on electric bills because kilowatts used will be
the same whether motors be single phase, three phase, or three phase motors
operated through the Roto-Phase. However, an Indiana power company's three year
study revealed that corn was dried at less than 1/2˘ per bushel electrical cost.
Their study also revealed that no single phase motor or three phase drying
installation had a per bushel electric cost as low as this. The high efficiency
of the Roto-Phase distribution system largely accounts for this.
How does cost compare with other methods?
The Roto-Phase has about the same list price as some static converters. But
remember—Roto-Phase will operate 5, 10, 20 motors while the static converter
operates but one. Against the medium size single phase motors the price is very
competitive, again, the single phase motor does only a single job.
Many users will weigh the cost of bringing in solid three phase versus the cost
of the Roto-Phase. More often than not, seasonal farm loads where monthly demand
or minimum charges prevail may indicate that the Roto-Phase is the least costly
Is there a warranty?
Yes, unmatched in the industry. To obtain a detailed copy, contact ARCO
Who is ARCO?
In 1964, ARCO acquired the electric motor manufacturing assets and facilities of
Shelby Electric, makers of special purpose motors since World War II. ARCO
continued to manufacture special purpose motors for OEMs and cryogenic types for
NASA—some of which are still in outer space.
We have changed the concept of phase conversion by being able to provide
balanced 3 phase lines when needed. We really do set the standards others strive
What is ARCO'S experience in phase conversion?
As founders of the Roto-Phase (the original multi-motor three phase converter)
our Roto-Phase is time tested and unchanged since 1963. That, coupled with
experienced application engineering, places ARCO #1 in the phase conversion
Many Roto-Phase models are CSA approved.