Zts series automatic transfer switches – GE Zenith ZTS Series User Manual

Page 2

background image

Electrical Ratings

Ratings 40 to 4000 amperes

2, 3 or 4 Poles

Open type, NEMA 1,

3R, 4, 4X and 12

Available to 600 VAC,

50 or 60 Hz

Suitable for emergency and

standby applications on

all classes of load, 100%

tungsten rated through

400 amps

UL 1008 listed at 480 VAC

CSA C22.2 No. 178

certified at 600 VAC

IEC 947-6-1 listed at 480 VAC

Performance Features

Contact transfer speed

less than 100 milliseconds

High close-in and

withstand capability

Temperature rise test per

UL 1008 conducted after

overload and endurance

tests - exceeds UL


Available in ZTS (utility-

generator), ZTSU (utility-

utility), ZTSG (generator-

generator) and ZTSM

(manual) configurations

Design and

Construction Features

Double throw,

interlocked operation

Electrically operated,

mechanically held by a

simple, over-center


Segmented silver tungsten

alloy contacts with

separate arcing contacts

on 225 amp and above

Arc quenching grids,

enclosed arc chambers,

and wide contact air gap

for superior source-to-

source isolation on all units

Control circuit disconnect

plug and drive inhibit

switch for safe maintenance

Components accessible

for inspection and

maintenance without

removal of the switch

or power conductors

Mechanical indicator and

contact chamber cover

designed for inspection,

safety and position





is the building block

of our transfer switch product line.
This ruggedly built power contactor
family of switches has been specifically
designed for transfer switch duty with
dependability, versatility and user
friendliness of prime concern.


switches are available in open type construction

for switchboard installation or


enclosed to

the customer’s specifications. The power panel
components, consisting of power switching contacts,
drive mechanism and terminal lugs, are mounted
on a specially formed panel. Logic devices including
microprocessor control auxiliary time delays and
special accessory equipment are assembled on the
door for ease of maintenance and separation from the
power section. They are connected with a numbered
wiring harness equipped with a disconnect plug that
allows isolation of the control panel for maintenance.

ZTS Series Method of Operation
When the normal source voltage fails or drops to a
predetermined point (usually 80% of nominal), if
required, a circuit is closed to start the engine
generator set. When the emergency source reaches
90% of rated voltage and 95% of rated frequency, the
drive solenoid is energized through the emergency
coil control relay, causing the main contacts to
disconnect the load from the normal source and
connect it to the emergency source. After the drive
solenoid has completed its electrical stroke and is
seated, the emergency coil control relay opens to
disconnect it. The transfer switch is now mechanically
locked in the emergency position.

When normal voltage is restored to a predetermined
point (usually 90% of nominal), the control voltage
sensing energizes. The normal side coil relay closes,
and after the drive solenoid has completed its electrical
stroke and is seated, the coil control relay opens to
disconnect it. The transfer switch is now mechanically
locked in the normal position.

Drive Mechanism




switches employ the simple “over-

center” principle to achieve a mechanically locked
position in either normal or emergency and



high speed drive assures contact transfer in 100 ms
or less. High contact pressure and positive mechanical
lock allow for high withstand and closing ratings, far


requirements. All


units are listed with


umbrella breaker, severe breaker and current

limiting fuse ratings.

ZTS Series

Automatic Transfer Switches

Neutral Switching


Zenith ZTS Series is available in true four pole

designs for multi-source power systems that require
neutral switching. The neutral contact is on the same
shaft as the associated main contacts. This ensures
positive operation, and avoids any possibility that
the neutral contact will fail to open or close, as is
possible when the neutral pole is an add-on accessory.
The neutral contacts are identical to the main contacts,
having the same current carrying and high withstand/
closing ratings as the mains. They are designed to
break last and make first to reduce the possibility of
transients while switching the neutral.

Safe Manual Operation


manual operator consists of a large, easy-to-use

handle that fits securely for manual operation during
installation and maintenance or in an emergency.



may be provided with an operator inhibit

switch to disconnect the electrical drive prior to
maintenance. Fully enclosed wrap-around arc covers
shield the main contacts and mechanical components,
preventing operator exposure during manual operation.

Transferring Large Motor

or Highly Inductive Loads
Some loads, especially large motors, receive severe
mechanical stress if power is trans-ferred out of phase
while the motor is still rotating. Also, back



ated by a motor may result in excess currents that
can blow fuses or trip circuit breakers.



offers four solutions to these problems:



age 2

1. Universal Motor

Disconnect (UMD): This load

control disconnects a large

motor via its control circuit

for an adjustable period of

time prior to transfer in either

direction. For switching multiple



Zenith Accessory A62

disconnects the motors prior to

transfer and brings them back

on line sequentially.
2. Accessory R50: This is an

in-phase monitor that compares

the phase angle between both

sources of power and prevents

transfer until the two are approxi-

mately in phase (within a self

adjusting range).



high speed transfer action

coupled with the



microprocessor control logic

ensure closures at or near

zero degree phase difference.

3. Series





offers delayed transition

switching on transfer switches

rated 40 amperes and above –





Series. This

programmed center-off position

allows for the full decay of

rotating motors or transformer

fields. It can also be used for

load shedding of selected

circuits or other appli-cations

which require a means to

disconnect the load from either

source. Major


system manu-

facturers recommend delayed

transition switches for proper

restart sequencing of their systems.
4. Series





series of closed transition switches



operation during

a source failure with a highly

engineered control system that

allows momentary paralleling

(100 ms) of two acceptable

sources, thereby limiting the

impact of transfer on the load.