Introduction

Transfer switches are used to protect electrical loads against prolonged loss of power. The load (3) is connected to either the emergency (1) or the normal source (2) through the transfer mechanism (4). If power is lost from the normal source (2) the transfer mechanism transfers the load to the emergency (secondary) sources (1). Transfer is automatic (ATS) if the switching is based on intelligence circuitry and accomplished by a transfer motor. Transfer is manual (MTS) if switching is based on operator decision making and physical transferring by use of a handle. With ATS, the load is automatically returned to the normal source (2) when normal power is restored.

ATS INPUT/OUTPUT
1. E1, E2 and E3 input to ATS from emergency source. 2. N1, N2 and N3 input to ATS from normal source. 3. T1, T2 and T3 output from ATS to the load. 4. Transfer mechanism.

Identification

The transfer switch model number is located on the door.

TYPICAL ATS NAMEPLATE

The model number tells eleven things about the Automatic Transfer Switch (ATS).

1. A "T" as the first character of the model number specifies the equipment as a transfer switch.

2. The second character of the model number specifies the type of transfer switch operation and application.

3. The third character of the model number specifies the power switching panel rating, neutral assembly bar, intelligence panel and transfer switch layout drawing.

4. The fourth character of the model number specifies the enclosure size.

5. The fifth character of the model number specifies the system connected voltage.

6. The sixth character of the model number specifies the system frequency.

7. The seventh character of the model number specifies an auxiliary relay with contacts for external use, if required, to indicate transfer switch position on normal source.

8. The eighth character of the model number specifies an automatic plant exercise timer, if required.

9. The ninth character of the model number specifies a two-position selector switch to allow selection of either the normal or emergency power source as the preferred source, if required.

10. The tenth character of the model number specifies an adjustable time delay (0.2-30 min.) for engine cool-off, if required.

11. The eleventh character of the model number specifies the change number to which the transfer switch was built.

Component Description

The ATS consists of a sheet steel enclosure housing five operating assemblies:

1. Breaker Assembly.

2. Transfer Mechanism.

3. Intelligence Panel.

4. Plant Exerciser (optional).

5. Controls and Monitor Panel.

Breaker Assembly

The emergency breaker (EB) and normal breaker (NB) are of three-pole, molded case construction. The Normal Source breaker (NB) is located on the right side of the enclosure. The Emergency Source breaker (EB) is located on the left side. (NB) and (EB) are interlocked mechanically through the transfer mechanism. They are interlocked electrically through relays and switches. As a result of interlocking, only one breaker can be closed at one time.

The breakers cannot be prevented from tripping by holding the manual operating handle (1). The breaker handle (1) moves to a neutral "tripped" position on a fault. After the fault is cleared, the breaker is reset by rotating the ATS manual operating handle counterclockwise to the desired source breaker position.

ATS Breakers (Transfer Mechanism Removed for Illustration) EB Emergency ATS breaker. NB Normal ATS breaker.
1. Trip handles.

BREAKERS AND AUXILIARY SWITCHES

EAS1 Emergency Circuit Breaker Lockout

EAS2 Emergency Bell Alarm Contact (amber trip lamp)

EB Emergency Circuit Breaker

ELS Emergency Limit Switch-Controls Transfer Motor

ES1 Emergency Source Contact-Auxiliary Lamps

ES2 Emergency Source-Controls Red Lamp

NAS1 Normal Circuit Breaker Lockout

NAS2 Normal Bell Alarm Contact (amber trip lamp)

NB Normal Circuit Breaker

NLS Normal Limit Switch-Controls Transfer Motor

NS1 Normal Source Contact-Auxiliary Lamp

NS2 Normal Source-Controls Green Lamp

TM Transfer Motor

Each breaker contains two standard switches and one optional switch. Each switch is operated by breaker contact action. ^*The switches are:

1. Normal and Emergency Limit Switches (NLS and ELS)^*

2. Normal and Emergency Source Auxiliary Switch (NS and ES)

3. Normal and Emergency Auxiliary Switch (NAS and EAS)

Normal and Emergency Limit Switches (NLS and ELS)

225-2000 AMP ATS LIMIT SWITCH (INTERNAL TO BREAKER)
EB Emergency Breaker (ELS Internal). NB Normal Breaker (NLS Internal).

100 AMP ATS LIMIT SWITCH (EXTERNAL TO BREAKER)
2. 100 amp ATS. 3. Lever. 4. External limit switch.

These standard switches are used to start and stop the transfer motor. The NLS and ELS switches are breaker operated in the ATS units rated 225 A and above. On the 100 A unit, the limit switches (4) are mechanically sequenced by a lever (3) operated by the gear box. The transfer mechanism opens one source breaker. The breaker contact of that source closes the switch contact in preparation for return of the load. At the same time, the transfer mechanism closes the other source breaker. That source breaker in closing, opens the switch contact to stop the transfer motor.

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^*In the 100 amp ATS, the limit switches are operated by the transfer mechanism.

Normal Source Switch and Emergency Source Switch (NS and ES)

POWER SOURCE INDICATOR LAMPS
5. Emergency power source lamp - red. 6. Normal power source lamp - green. NT1 Normal Transformer ET1 Emergency Transformer

These standard switches operate power source indicator lamps. The Normal Breaker (NB) and Emergency Breaker (EB) contacts operate the NS and ES switches. The NS and ES switches are located inside the NB and EB.

The NS2 contact controls a green pilot light (6). When lit, the green light (6) indicates that the load is connected to the normal source (power is on the system from the normal system). The ES2 contacts control a red light (5). When lit, the red light (5) indicates that the load is connected to the emergency source. Power is then on the system from the emergency source.

The standard green (6) and red (5) pilot lights cannot indicate the status of the source if there is no power on the system. If the normal source fails, the green light (6) goes out momentarily until either the normal source returns or transfer is made to the emergency source. When emergency power appears on the system, the ATS will transfer to the emergency source. The red light (5) will then light.

The NS switch is tied into the normal transformer (NT1). The ES switch is tied into the emergency transformer (ET1). The ES1 and NS1 contacts can be used to power other 110 volt pilot lights. However, the current draw on such lights cannot exceed .1 amp due to other demands on NT1 and ET1. These switch contacts cannot be used to control other auxiliary equipment other than pilot lights.

Normal Auxiliary Switch and Emergency Auxiliary Switch (NAS and EAS)

These optional switches operate to lockout the transfer motor in problem faults. At the same time, these switches light a lamp which shows which source breaker has tripped. The NB and EB contacts operate NAS and EAS. NAS and EAS are located inside NB and EB. NAS is used only in the dual generator application where the thermal-magnetic trip is used in both EB and NB. The optional EAS is used in both the single and dual generator application.

The NAS contact (NAS1) is also called the normal circuit breaker lockout. The EAS contact (EAS1) is called the Emergency Circuit Breaker Lockout. The term "lockout" refers to the (NAS1 and EAS1) contact opening (when NB or EB trips) and electrically isolating the transfer motor. The normally closed (NC) lockout control (NAS1) and (EAS1) prevent the transfer motor from transferring the alternate source into a problem fault.

The NAS contact (NAS2) is called the normal bell alarm contact. The EAS contact (EAS2) is called the emergency bell alarm contact. When the NB trips, the normally open (NO) contact NAS2 closes. This completes circuitry to a yellow lamp (8). The yellow lamp (8) lights indicating the NB has tripped. When the EB trips, the (NO) contact (EAS2) closes. This completes circuitry to a yellow lamp (7). This yellow lamp (7) lights indicating the EB has tripped.

BREAKER TRIP INDICATOR LAMPS (OPTIONAL)
7. Emergency breaker trip lamp - amber. 8. Normal breaker trip lamp - amber.

Transfer Mechanism

AUTOMATIC TRANSFER SWITCH - TRANSFER MECHANISM
1. Transfer mechanism (225 A to 1000 A). 2. Oscillating beam (not shown - located on back of panel). 3. Intelligence panel. EB Emergency breaker. NB Normal breaker.

There are three types of transfer mechanisms:

1. 100 amp.

2. 225 A to 1000 A.

3. 1200 A and 2000 A.

The transfer mechanism (1) transfers the normal breaker (NB) and emergency breaker (EB) contacts. The intelligence panel (3) signals the transfer mechanism (1) when to transfer.

Once transfer has been made, the transfer mechanism (1) provides mechanical interlocking. The interlock prevents both breakers (EB and NB) from being closed at the same time. The mechanical parts between the handles and the motor keep positive contact between all parts.

OSCILLATING BEAM INTERLOCK
2. Oscillating beam. 4. Pivot 5. Nonconductive plungers.

The mechanical interlock is backed up with an oscillating beam (2) interlock. This interlock is mounted on the panel at the rear of the breakers. When one breaker is closed, a nonconductive plunger (5) extends into the opposite breaker to prevent it from closing. The closed breaker must open before the other breaker can be closed. However, both breakers can be open at the same time.

The transfer mechanism (1) allows the breakers to be trip-free in the closed position. This allows either breaker to trip under fault conditions. The trip-free interlock setup works on the standard high instantaneous breaker and optional thermal-magnetic trip.

100 A Transfer Mechanism

This transfer mechanism consists of a pivoting rocker arm (1) which toggles the circuit breaker handles (2). The rocker arm (1) is moved by a rotating slide pin (4). The slide pin (4) is rotated by a lever (7). The lever is rotated by a transfer motor and gear box. The slide pin (4) engaging the rocker arm (1) converts rotary motion to linear motion. A spring operated brake stops the motor when the motor is shutoff. The brake is released by a solenoid connected in parallel with the motor. The limit switches (5) which stop and start the motor are mechanically sequenced by the lever (7).

100 AMP ATS TRANSFER MECHANISM
1. Rocker arm. 2. Breaker handles. 3. Operating instructions. 4. Slide pin. 5. Limit switches. 6. Interconnect plugs. 7. Lever.

To operate manually, the logic must be disconnected. It is disconnected by disconnecting the panel interconnect plugs (6). The transfer mechanism will restore itself to its previous position if the logic circuit is not disconnected. Next, disconnect the motor by unscrewing the slide pin (4) from the slot in the rocker arm (1). Remove the slide pin. The rocker arm (1) then becomes the manual handle. Instructions on manual operation and switch position are printed (3) on the rocker arm (1).

225 A to 1000 A Transfer Mechanism

The components of this transfer mechanism are a center drive gear (4), transfer motor (3), secondary gears (1), and two cam driven toggles (7). The toggles (7) directly operate the breaker handles. The changing of rotary motion to vertical movement is accomplished by a roller pin mounted on each toggle (7). Each pin rides in a groove (5) in cam (6). The toggle (7) moves up and down on guide rods (2) attached to the metal housing.

A brake operated by a spring stops the motor when the motor is shutoff. The brake is released by a solenoid connected in parallel with the motor. Limit switches which stop and start the transfer motor are mechanically operated by the breaker contacts.

225 AMPS & ABOVE ATS - TRANSFER MECHANISM (REMOVED FROM ATS AND REAR VIEW)
1. Secondary gears (2). 2. Guide rods (2). 3. Transfer motor. 4. Center drive gear. 5. Cam grooves. 6. Cam. 7. Toggles (2).

To operate manually, the logic circuit must be disconnected. This is done by disconnecting the panel interconnect plugs (8). If the handle (9) is operated manually without disconnecting the logic circuit, the transfer mechanism will restore itself to its previous position. On the 225 A to 2000 A ATS, it is constructed to have a free-wheeling, ratchet sprocket drive. During automatic operation of the transfer mechanism, the operating handle (9) remains stationary. This handle (9) is electrically dead to eliminate the possibility of an electrical shock. To operate the ATS manually, turn the handle (9) counterclockwise one-half turn (180°) until one breaker opens and the other closes. Emergency and normal positions are shown by the arrow (10). The red or green source lamps indicate which source the switch is connected.

225 AMPS & ABOVE ATS - TRANSFER MECHANISM (INSTALLED AND FRONT VIEW)
3. Transfer motor. 8. Interconnect plugs. 9. Manual handle. 10. Switch position indicator.

1200 A and 2000 A Transfer Mechanism

The 1200 A and 2000 A transfer mechanism is very similar to the 225 A to 1000 A mechanism. The 1200 A and 2000 A mechanism has an idler gear between each of the secondary gears and the drive gear. This provides greater torque.

Intelligence Panel

INTELLIGENCE PANEL
1. Intelligence panel. 2. Interconnect plugs (2).

The intelligence panel (1) monitors the utility power and load demand. If a loss of power or fault occurs, the intelligence panel signals the transfer mechanism to switch to the alternate source. The intelligence panel (1) is mounted on the lower part of the ATS. It is connected to the transfer mechanism above it by means of cables terminating in two interconnect plugs (2). The plugs (2) are keyed to prevent improper insertion.

INTERCONNECT PLUG

One size intelligence panel is used in all eight sizes of ATS. Each intelligence panel is drilled and tapped for the maximum number of options that can be installed.

The major components of the intelligence panel are:

1. Power Supply Transformers.

2. Logic Package.

3. Logic Relays.

4. Auxiliary Relays.

5. Time Delay Engine Start Relay (TDES).

Power Supply Transformers

The intelligence panel has three transformers:

1. Normal Transformer 120 V output.

2. Emergency Transformer 120 V output.

3. Logic Transformer 24 V output.

The normal transformer (NT1) and emergency transformers (ET1) reduce the line voltage to 120 V for operating the transfer motor and pilot devices. NT1 and ET1 have multiple taps to use the supply voltage that is available. System voltages of 208 V, 220 V, 240 V, 380 V, 415 V, 480 V or 600 V can be adapted to by inserting the voltage selection plug (4) in the proper socket. Other voltages and frequencies can be used. This is done by adjusting the voltage and frequency plug-in cards of the solid-state logic package (5).

POWER SUPPLY TRANSFORMERS
3. Logic transformer. NT1 Normal Transformer. ET1 Emergency Transformer.

VOLTAGE SELECTION PLUG
3. Logic transformer. 4. Voltage plug.

The logic package requires 24 V. This is supplied by the logic transformer (3).

LOGIC PACKAGE
3. Logic transformer. 5. Logic package.

Logic Package

LOGIC PACKAGE - COMPONENT DESCRIPTION
5. Logic package. 6. Printed circuit (PC) cards. 7. Adjustment dial. 8. Adjustment lock. 9. Light emmitting diode (LED). 10. Under-voltage PC cards. 11. Under-frenquency PC card. 12. Time delay cards. 13. Mounting screws (2).

A solid-state logic package (5) is also mounted on the intelligence panel. It contains six printed circuit (PC) cards (6) which provide the intelligence. The PC cards (6) are plug-in, modular and solid-state units. Each PC card has adjustment dials (7) to adjust both dropout and pickup values. The dials (7) can be screwdriver or finger adjusted. Each card also has an adjustment lock (8). This locks in the adjustment setting.

A light emitting diode (LED) (9) is located on the face of each plug-in card. On the two voltage PC cards (10) and the one frequency PC card (11) the LED (9) light appears when the characteristics are within preset limits. On the two time delay PC cards (12), the LED (9) light appears after the preset time has elapsed. These LED's are useful when troubleshooting.

LOGIC PACKAGE - PC CARD IDENTIFICATION
14. Function identification plate. 15. Normal source voltage monitoring (standard). 16. Time delay, emergency to normal (standard) TDEN. 17. Time delay engine cooldown (optional) TDEC. 18. Driver card. 19. Emergency source voltage monitoring (standard). 20. Emergency source frequency monitoring (standard).

The two voltage cards (15) and (19) cannot be switched. Voltage card (15) monitors 3-phase and card (19) monitors 1-phase.

Either of the two timing cards (16) and (17) may be used in any of the three time delay slots of the card cage. However, each card is limited to one type of function. A timing card cannot be used in the voltage or frequency lots or vice-versa. The cards are key interlocked to prevent improper insertion. Each card is held in place by two screws (13).

1. Normal Source Voltage Monitoring Card

NORMAL SOURCE VOLTAGE MONITORING CARD
15. 3-Phase normal source voltage monitoring PC card.

The normal source is monitored by the first card (15). The normal source voltage monitoring card (15) is standard. It senses line voltage in each phase of the normal three-phase power supply. This removes the possibility of running the load on less than three phases. The values for switch transfer are adjustable. They are normally set at 70% dropout and 90% pickup.

2. Time Delay Emergency to Normal Card (TDEN)

TIME DELAY EMERGENCY TO NORMAL CARD (TDEN)
16. TDEN PC card.

The TDEN PC card (16) is the first of three cards in the time delay section (14) of the logic package. It is a standard card. It delays transfer from the emergency source to the normal source to permit the normal source to become stable. It is adjustable from .2 minutes to 30 minutes. It is factory set at 10 minutes.

3. Time Delay Engine Cool-Off Card (TDEC)

TIME DELAY ENGINE COOL-OFF CARD (TDEC)
17. TDEC (optional).

The TDEC card (17) is the second of three cards in the time delay section (14). The TDEC card (17) is optional. It can be interchanged with TDEN card (16). This card functions after the load has been switched back to normal. The TDEC card (17) permits the generator set to run in the no-load condition. This allows the engine to cool gradually, eliminating loss of coolant. It is adjustable .2 minutes to 30 minutes. It is factory set at 10 minutes.

In some applications, this function could be accomplished by the Automatic Start/Stop Control (ASSC). The ASSC is not a part of the ATS. In this situation, a blank cover is supplied as standard equipment in place of TDEC card (17).

4. Driver Card

DRIVER CARD
18. Driver card.

The third card in the time delay section is a driver card (18). It completes the circuitry but does not add time.

5. Emergency Source Voltage Monitoring Card

EMERGENCY SOURCE VOLTAGE MONITORING CARD
19. 1-Phase emergency source voltage monitoring card.

This PC card (19) is one of two standard cards in the emergency source monitoring section. Its job is to prevent transfer from normal to emergency source until proper voltage appears. Transfer occurs when the generator set voltage is at least 90% of normal. This voltage is field adjustable between 70% and 100%. The dropout voltage is set at 70% at the factory.

When operating under the emergency source and the generator voltage drops below the dropout voltage, the PC card (19) starts to initiate action. If the utility is out, the ATS remains in the emergency position. However, if the utility has returned and the TDEN card (16) is timing out, the ATS will override the delay. It will transfer immediately to the utility (normal source).

6. Emergency Source Frequency Monitoring Card

EMERGENCY SOURCE FREQUENCY MONITORING CARD
20. Emergency source frequency monitoring card.

The last PC card (20) prevents transfer from the normal source to the emergency source until the proper frequency appears. The emergency frequency is preset between 40 Hertz (Hz) and 65 Hz. On the 60 Hz system, this frequency pickup value is factory set at 57 Hz. On a 50 Hz system, it is factory set at 47 Hz.

When operating under emergency conditions, if the frequency of the generator decreases to the dropout value, the emergency frequency monitoring card will prepare to initiate action. If the utility is out, the ATS stays in the emergency position. If the utility has returned and the TDEN is being timed out, the ATS will override the delay and go to utility immediately. The factory dropout setting of the frequency card is 55 Hz on the 60 Hz ATS. On the 50 Hz ATS, the dropout value is factory set at 45 Hz. The lower end of the adjustment range is 40 Hz.

Logic Relays

The three plug-in relays to the right of the logic package are made to work by the logic package. They make sure that electrically the breakers will not close on each other. These relays are the cleanable, electromechanical, plug-in type with see through dust covers. The relay contacts are rated at 10 amps.

LOGIC RELAYS
NR Normal source relay. ER Emergency source relay. EC Engine start-stop relay.

The logic relays and their functions are as follows:

1. Normal Source Relay (NR)^* - A standard relay that controls the various contacts (NR1, NR2, NR3 and NR4) in the ATS circuitry which contribute to operation of the transfer motor and in turn, the opening and closing of the breakers. It also contributes to the engine start contact circuitry with one contact (NR5).

2. Emergency Source Relay (ER)^* - A standard relay that is the final relay to close its contact (ER2) when transferring to emergency from normal. It is made to operate by the logic package only when the generator set is up to proper voltage and frequency.

3. Engine Cool-Off Relay (EC)^* - An optional relay that is included only when the optional engine cool-off timer (TDEC) is provided. This relay (EC) controls a contact (EC1) which is part of the engine start contact circuitry. This allows the engine to cool down under no load conditions before being shutoff.

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^*See the ATS Operation section, Page 26, for sequencial operation.

Auxiliary Relays

AUXILIARY RELAYS
1. Mounting holes for normal relay auxiliary (NRA). ERA Emergency relay auxiliary (optional).

The emergency relay auxiliary (ERA) and normal relay auxiliary (NRA) are optional. These two relays are added when current demand will be in excess of that used by pilot lamps (0.1 A). The ratings of each set of contacts is 6 A inductive or 10 A resistive and 120 VAC. The relays are heavy duty industrial relays. They can handle solenoids and motor starter coils. Each relay provides two (NO) and two (NC) contacts. These relay contacts transfer when the normal or emergency source is energized or de-energized.

Location and prime usage is as follows:

1. Normal Relay Auxiliary (NRA) - This optional relay is located above the TDES option and to the right of the ERA on the intelligence panel.

2. Emergency Relay Auxiliary (ERA) - This optional relay is located above the TDES option and to the left of the (NRA) on the intelligence panel. One set of contacts is used with the TDEC option in the "Engine Start Contact" circuitry. The NO contact is closed while the emergency source is present. See section, "Operation of the ATS" for further details.

Time Delay Engine Start Relay (TDES)

TIME DELAY ENGINE START RELAY (TDES)

This relay is also a part of the intelligence panel. So that the generator set is not started on momentary outages, this relay is used for a time delay on start of the engine. The relay is adjustable between 0 and 50 seconds. It is factory set at three seconds. The relay is of the pneumatic bellows-type which is field adjustable.

Plant Exerciser

PLANT EXERCISER LOCATION
1. Plant exerciser (typical unit).

The plant exerciser (1) is a 168 hour clock timer. It provides automatic test operation of the ATS. The exerciser is adjustable 0 to 168 hours in 15 minute stages for at least one time a week. A 60 or 50 Hz exerciser is used depending upon frequency. The plant exerciser can be used to:

Check starting circuit without interrupting the normal supply; or

Simulate power failure and change to the emergency source.

Show/hide table

NOTICE
When changing the line voltage selection plug, be sure to reconnect the plant exerciser to conform to new voltage.

Panel Controls and Monitoring Lights

The monitoring lights and the switches are located on the face of the Nema I enclosure. The wall mounted enclosure covers 100 thru 1000 amps. The floor-standing enclosure covers 1200 thru 2000 amps.

The functions of the exterior switches and lamps are as follows:

1. Four-position selector switch permits four types of switch operation:

Test - The test position simulates power failure. Engine starting is initiated and the switch will transfer when emergency voltage appears.

Auto - The auto position returns the transfer switch to normal operation.

Off - The off position is used during maintenance or manual operation. This position de-energizes the control relays, opens the engine start circuit, and opens the transfer motor circuit. The switch will not operate nor will the engine start on power failure. A white light is also furnished that lights only when the switch is in the off position.

Engine Start - The engine start position keeps the transfer switch on the normal source and initiates the engine start circuit. The switch will transfer if normal source fails during test.

2. White Pilot Light - Lights only when the above switch is in the off position.

3. A Two-Position Selector Switch (Optional) - For use mainly when the normal and emergency source are both generator sets. This option permits selection of either generator set as the preferred source to which the ATS will always transfer if that source is available. The switch is marked Source 1/Source 2.

4. Green Pilot Light - Lights when normal supply is connected to load.

5. Red Pilot Light - Lights when emergency supply is connected to load.

6. Amber Pilot Light (Optional) - Used with the thermal-magnetic breaker in the dual generator setup. Lights when normal breaker trips.

7. Amber Pilot Light (Optional) - Used with thermal-magnetic breaker in the single or dual generator setups. Lights when emergency breaker trips.

8. White Pilot Light (Optional) - Lights when Source 1 breaker is closed.

9. White Pilot Light (Optional) - Lights when Source 2 breaker is closed.

CONTROLS AND MONITORING LAMPS
1. FPSS Four position selector switch. 2. OFF White pilot light - FPSS is "off" position. 3. TPSS Two position selector switch. 4. NL Green pilot light - normal breaker closed. 5. EL Red pilot light - emergency breaker closed. 6. TN Amber pilot light - trip, normal breaker. 7. NE Amber pilot light - trip, emergency breaker. 8. S1 White pilot light - source 1 breaker closed. 9. S2 White pilot light - source 2 breaker closed.

POWER SWITCHING MODULE & INTELLIGENCE PANEL

ATS Operation

Switch De-Energized (Four Position Selector Switch (FPSS) in "OFF" Position)

All contacts are shown with no power applied to the switch or the load (nonenergized state).

Circuit conditions are as follows:

Normally open contacts are open.

Normally closed contacts are closed.

Normal and emergency limit switches (NLS) and ELS) are closed.

FPSS contact (17-18) is in the closed position. (When power is available and the FPSS is in the "OFF" position, the white "OFF" lamp is lit.)

Normal Energized/Emergency De-Energized (FPSS In "Auto" Position)

The following FPSS contacts are closed:

Contact (9-10) - located in the emergency sensing circuit

Contact (11-12) - located in the engine start contact circuit

Contact (4-14) - located in the normal sensing circuit

The following circuit conditions exist:

Normally open normal relay (NR) contacts are closed - NR2 and NR4.

Normally closed NR contacts are open - NR1, NR3 and NR5.

Normally closed time delay engine start (TDES) relay contact (2-6) is open. Contact (2-6) is located in the engine start contact circuit.

Normal limit switch (NLS) contact is open. This occurred when the normal breaker was closed. When the NLS contact opens due to breaker action, the transfer motor is shutoff.

Normal source (NS) breaker auxiliary pilot light switch contact (NS2) closes. This lights the normal source green pilot light (NL).

Normally closed time delay engine cooldown relay (EC) contact (EC1) is open. (Only if this option is part of the ATS.)

Normally open emergency relay (ER) contact (ER2) remains open.

This is the condition with the normal source providing power and no problems.

Normal Energized/Loss Of Normal Source (FPSS In "Auto" Position)

This condition could come about by:

a. A load fault tripping the service entrance breaker, or

b. A voltage or frequency drop.

LOSS OF NORMAL SOURCE (Service Entrance Breaker Tripped)
ATS Automatic transfer switch. ASSC Automatic start-stop control.

The logic package senses the loss of power and initiates the following thru the (NR):

Normally open (NR) contacts open - NR2 and NR4.

Normally closed (NR) contacts close - NR1, NR3 and NR5.

The engine cooldown relay (EC) is deenergized.

Engine cooldown relay contact (EC1) closes

When contact NR4 opens, this opens the TDES circuit. TDES starts timing out. After timing out, TDES contact (2-6) closes. Contact (2-6) closing, completes the engine start contact circuit. The emergency source (generator set) is started and brought up to speed (frequency) and voltage.

Emergency relay auxiliary (ERA) energizes. ERA contact (9-10) closes. (Only if engine cooldown option is part of the ATS.)

When the emergency source is at specified voltage and frequency, the logic package closes ER contact ER2. The transfer motor (TM) then transfers the load to the emergency source through opening of the normal breaker and closing of the emergency breaker.

When the normal breaker opens, it in turn:

a. Opens the breaker switch NS2. This shuts "OFF" the green normal source light (NL).

b. Closes NLS so transfer can come about fast back to the normal source when the normal source returns.

When the emergency breaker closes, it in turn:

a. Closes the breaker switch ES2. This turns on the red emergency source light (EL).

b. Opens ELS which shuts "OFF" the transfer motor [brake solenoid (BS) gives positive stop of the motor].

Normal (Or Emergency) Energized and Normal (Or Emergency) Source Breaker Trips (FPSS In "Auto" Position)

The ATS normal and emergency breakers in a normally recommended installation should not trip before the service entrance (thermal-magnetic) breakers. In cases where the normal breaker trips before the service entrance breaker, the logic package will sense voltage as still being at leads N1, N2 and N3. As a result, the emergency source generator is not started and transfer is not initiated. The same is applicable where the ATS emergency breaker trips.

LOSS OF NORMAL SOURCE (ATS NORMAL SOURCE BREAKER TRIPPED)
ATS Automatic transfer switch. ASSC Automatic start-stop control.

In applications where legal codes allow the service breaker to be replaced by ATS thermal-magnetic trip breaker, the same results would come about as described above.

Normal Energized - Thermal Magnetic Breaker Trips (FPSS In "Auto" Position)

Trip Switch Lockout And Alarm Option Operation

This option is part of the thermal-magnetic trip setup. It is used in the following ATS arrangements:

a. Emergency Source Breaker - Single or dual generator automatic operation.

b. Normal Source Breaker - Dual generator automatic operation.

DUAL GENERATOR AUTOMATIC OPERATION
ASSC Automatic start-stop control. ATS Automatic transfer switch.

This switch option is operated by the TM in the 100 ampere ATS or by the breaker in the 225 amp and above. In the case of the normal breaker tripping (thermal-magnetic trip - dual generator application), the breaker opens switch contact NAS1 (Normal Circuit Breaker Lockout). This locks the TM out until the normal breaker is reset. This prevents emergency source startup.

At the same time that NAS1 contact opens, switch contact NAS2 (Normal Bell Alarm Contact) closes. When NAS2 closes, the circuit for the normal source trip alarm lamp (TN) is complete. The amber lamp (TN) lights.

The emergency source breaker switch EAS1 and 2 operate the same. Upon resetting the breaker, the transfer motor can operate and the amber trip lamp (TN or EN) is turned off.

Emergency Energized - Normal Source Returns (FPSS In "Auto" Position)

Logic package senses through leads (N1, N2 and N3) when the normal source has returned. The logic package initiates a time delay through the time delay emergency to normal (TDEN) card. This allows for utility stabilization. At the end of the delay, the following occurs:

Normally open NR contacts are closed - NR2 and NR4.

Normally closed NR contacts are opened - NR1, NR3 and NR5.

Normally closed ER contact ER2 is opened.

Normally closed TDES contact (2-6) is opened.

The TM operates when NR2 and NR4 close. The TM transfers the load to the normal source through the opening of the emergency breaker and closing of the normal breaker.

When the emergency breaker opens, it in turn:

a. Opens the breaker switch ES2. This shuts "off" the red emergency source light EL.

b. Closes the emergency limit switch ELS. Transfer can then occur to emergency source if the normal source should again fail.

When the normal breaker closes, it in turn:

a. Closes the breaker switch NS2. This turns "ON" the green normal source light (NL).

b. Opens NLS which shuts "OFF" the transfer motor (brake solenoid (BS) gives positive stop of motor).

If the engine cooldown option is included in the ATS logic package, the following relays are used:

a. Time Delay Engine Cooldown (TDEC) Relay EC.

b. Emergency Relay Auxiliary (ERA).

After transfer has been made back to the normal source, the engine cooldown relay (EC) remains closed because of the time delay engine cooldown logic card (TDEC). The TDEC keeps the EC relay contact EC1 in the nonenergized condition for a certain amount of time. When the time delay is complete, EC is energized and EC1 opens. With EC1 open, the engine start contact circuit is open, which shuts down the engine.

While the generator is in operation, the emergency relay auxiliary (ERA) remains energized. After EC1 opens, the engine shuts down. This de-energizes ERA. With ERA de-energized, ERA contact (9-10) opens.

ATS Ratings

The ATS is offered in eight basic ratings (100A, 225A, 400A, 600A, 800A, 1000A, 1200A, and 2000A) for use on three-phase systems of 600V or less. The ATS can be applied to either a three-wire or four-wire system. In the four-wire system, the fourth wire is a solid neutral that is not switched. Application depends on installation and use.

Continuous Rating - High Instantaneous Trip

AUTOMATIC TRANSFER SWITCH (HIGH-INSTANTANEOUS BREAKERS)

The ATS can be applied to any inductive and/or resistive load. When properly installed, the ATS can handle the maximum demand of the load continuously. The continuous ampere rating of the standard ATS (both ATS breakers high instantaneous) at a power factor of .8 and 100% use of capacity is as follows:

Continuous Rating - Thermal-Magnetic Trips

When the ATS serves as both isolation/protective device and automatic transfer switch, the ATS should be derated 10%. This allows for temperature rise (inside the ATS) above the rating of the thermal overload trip. The breaker can then carry system load without nuisance trips. The following table is used to select an ATS with optional thermal-magnetic trips in either or both sources. These thermal-magnetic trips operate along with the standard high instantaneous breakers. The eight basic ratings has been increased to twenty ratings by using different trip ratings in the basic ATS sizes. Trip ratings are matched to KW ranges.

DUAL GENERATOR ATS (ONE OR TWO THERMAL-MAGNETIC TRIPS)