Cummins/Onan OT3-UG-3 — Due to the serious shock hazard from high voltages

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Procedure

1. 1. Move the operation selector switch on the gen­ erator set or Stop/ Auto/Handcrank switch on the automatic transfer switch (whichever ap­ plies) to Stop.
2. 2. Disconnect the starting batteries of the gen­ erator set (remove the ground [ -] lead first).
3. 3. Remove AC power to the automatic transfer switch. If the instructions require otherwise, shock hazard. Place rubber insulative mats on dry wood platforms over metal or concrete floors when working on any electrical equipment. Do not wear damp clothing (particularly wet shoes) or allow skin surfaces to be damp when handling any electrical equipment. Jewelry is a good conductor of electricity and should be removed when working on the electrical equipment. Do not work on this equipment when mentally or physically fatigued, or after consuming alcohol or any drug that makes the operation of equipment unsafe. OT3-UG-3 www . ElectricalPartManuals . com www . ElectricalPartManuals . com
4. 1. Introduction ABOUT THIS MANUAL This manual contains service procedures for an OT transfer switch. Sections 1 , 2, 3, and 4 cover the utility-to-generator set automatic transfer switch. Although much of the information on theory of op­ eration, Power Sentry® calibration, and trouble­ shooting in sections 1 , 2, and 3 is applicable to gen­ erator set-to-generator set, utility-to-utility, and several significant differences. set-to-generator set transfer switch. utility transfer switch. automatic/remote transfer switch. that was shipped with the transfer switch for spe­ Section 4 of this manual covers transfer switch as­ fore starting any service procedures. Identify all printed inside the front cover and observe all warn­ troubleshooting, remember that the generator set, transfer switch, and utility power source are all in­ terdependent. TRANSFER SWITCH APPLICATION Transfer switches are an essential part of a build­ ing's standby or emergency power system. The Normal power source, commonly the utility line, is backed up by an Emergency power source, often a generator set. The transfer switch supplies the electrical load with power from one of these two power sources. The load is connected to the common of the trans­ the load is supplied with power from the Normal source (as illustrated). If the Normal power source is interrupted, the load is transferred to the Emer­ gency power source. When Normal power returns, the load is retransferred to the Normal power source. The transfer and retransfer of the load are the two most basic functions of a transfer switch. Power Sentry is a registered trademark of Onan Corporation.
5. 1. 1 NORMAL 1 .---ʙ I ʘ I I I I I I I I I L- r EMERGENCY LOAD 9C1101 (TYPICAL FUNCTION) www . ElectricalPartManuals . com AUTOMATIC TRANSFER SV\nTCHES Automatic transfer switches, capable of automatic operation without operator involvement, perform the following basic functions: 1 . Sense the interruption of the Nor mal power source.
6. 2. Send a start signal to the generator set (Emer­ gency power source).
7. 3. Transfer the load to the Emer!}ency power source.
8. 4. Sense the return of the Normal power source.
9. 5. Retransfer the load to the Normal power source.
10. 6. Send a stop signal to the generator set. MODEL IDENTIFICATION Identify your model by referring to the Model and Electrical characteristics are shown ˷on the lower portion of the nameplate, which is located on the for a list of feature/option codes. If it is necessary to contact a dealer or the factory regarding the transfer switch, always խJive the com­ listed on the nameplate. This information is neces­ sary to properly identify your unit among the many types manufactured. CABINET The standard cabinet meets the requirements of the National Electrical Manufacturers Association (NEMA) for a UL Type 1 cabinet. This 1ype is desig­ nated as a general-purpose, indoor cabinet. The door of a typical utility-to-generator set cabinet is Indicator Lamps There are four indicator lamps on the cabinet door. The Normal Available and Emergency Available lamps are lit whenever their corresponding power sources (utility or generator set) arծe producing power. These two lamps can be lit simultaneously. The Normal Connected and Emer9ency Con­ nected lamps indicate which power source is con- 1 -2 nected to the load. Only one of these two lamps can be lit. Test/Normai/Retransfer Switch This switch has three positions. In the Normal posi­ tion, the transfer switch is set for automatic opera­ tion. Moving the switch to Test sends a start signal to the generator set. After the transfer time delay, the generator set will assume the load-provided is in the With Load position. Moving the switch to Normal causes the load to transfer to the Normal power source after the retransfertime delay. To avoid the delay and cause a fast retransfer of load to the Normal power source, move the switch to the Retransfer position. Optional Meter Package The optional meter package includes an AC amme­ ter, an AC voltmeter, a frequency meter, and a phase selector switch. AC Voltmeter: The voltmeter measures line-to-line voltage of the selected power source. AC Ammeter. The ammeter measures the line cur­ rents of the load. Frequency Meter: This meter measures the out­ put frequency of the selected power source in hertz. Phase Selector Switch: This switch is used to se­ lect the source and phase to be measured. On transfer switches with an AC ammeter, the load wires must each pass through a current trans­ former. Optional Auto/Manual Switch (Utility-to-Generator Set) The Auto/Manual switch is used to enable or dis­ able the automatic retransfer function. This switch has two positions. In the Auto position, normal auto­ matic retransfer is enabled. In the Manual position, automatic retransfer (from a functioning generator set back to utility power) is disabled; only manual retransfer (using the Test/Normai/Retransfer switch) is possible. In the event of generator set failure, however, the Power Sentry control logic will ignore the Auto/Manual switch and initiate retrans­ fer to utility power. Auto/Manual switch on utility-to-utility transfer switches. www . ElectricalPartManuals . com NORMAL CONNECTED LAMP NORMAL AVAILABLE LAMP PHASE SELECTOR SWITCH (FOR OPTIONAL METERS) OPTIONAL AUTO/MANUAL SWITCH #,-------@ 0 EMERGENCY CONNECTED LAMP EMERGENCY AVAILABLE LAMP OPTIONALAC VOLTMETER OPTIONAL AC AMMETER OPTIONAL FREQUENCY METER TEST/NORMAL/ RETRANSFER SWITCH M1694-48 CABINET EXTERIOR
11. 1. 3 www . ElectricalPartManuals . com TRANSFER SWITCH ASSI::MBL Y the contacts that transfer the load between Normal and Emergency power. The transfer switch is me­ chanically interlocked to prevent simultaneous closing to both power sources. The main parts of the transfer switch discussed here are the contact assemblies, linear actuator, capac:itor(s), Motor Disconnect switch, auxiliary switches, and auxiliary contacts. Transfer switch assembly' maintenance procedures are described in Section 4. Contact Assemblies The transfer switch either has three or four poles. Three pole transfer switches are provided with a neutral bar. The contact assemblies make and break the current flow. When closed to either the Normal or the Emergency power source, the con­ tacts are mechanically held. A mechanical inter­ lock prevents them from closing to both power sources at the same time. Linear Actuator The linear actuator is a linear inducti on motor that moves the contact assemblies between the Normal power source and the Emergency power source. Unear actuator operation is initiated automatically with automatic transfer switches. Manual operation Manual Operation. Capacitor(s) vide the phase shift necessary to d1rive the linear motor. If the capacitor is faulty, thH linear motor does not operate. Motor Disconnect Switch The Motor Disconnect toggle switch, on the acces­ sory control panel, enables and disables the linear actuator circuit. Place the switch in the Auto posi­ tion to enable the linear actuator. Place the switch in the Off position to disable the linear actuator. Auxiliary Switches to the position of the transfer switch. When the transfer switch is in the Normal position, switches S2, S3, S4, and S5 are actuated. WhEm the transfer switch is in the Emergency position, switches S6,
12. 1. 4 and to the schematic and wiring diagram package for more information on the functions of the individ­ ual switches. The schematic and wmng diagram package is shipped with the transfer switch. Contact your dis­ tributor if you do not have a set of drawings. Refer to Section 4 for a description of auxiliary switch maintenance procedures. Auxiliary Contacts Auxiliary contacts are provided on the Normal (switch S2) and Emergency (switch S6) sides of the transfer switch. They are actuated by operation of the transfer switch during transfer and retransfer. The Normal side auxiliary contact switch is actu­ ated when the transfer switch is in the Normal posi­ tion. The Emergency side auxiliary contact switch is actuated when the transfer switch is in the Emer­ gency position. The auxiliary contacts have current ratings of 1 0 amperes at 250 VAC. ELECTRONIC C ONTROL ity-to-generator set transfer switch. Due to differ­ ences in cabinet sizes, the location of some of the optional modules in your transfer switch may not be the same as shown here. control system is the Power Sentry Control. The Power Sentry includes voltage sensing circuits, time delay circuits and control relays. There are also several adjustment potentiometers and indica­ tor lamps on the Power Sentry. The adjustments must be performed only by qualified service per­ sonnel. Power Sentry Time Delays 1 5 or (optionally) 0 to 90 seconds. This brief time delay prevents generator set starting during power interruptions of short duration. Timing starts the moment of Normal (utility) power interruption. If the duration of the interruption exceeds the delay time, the control system signals the generator set to start. www . ElectricalPartManuals . com 1 0 minutes. It begins timing when the load is retransferred to the Normal power source. At the end of the delay, the stop signal is sent to the gen­ erator set. This time delay allows the generator set to cool down at no load before stopping. Transfer Time Delay: This delay begins when generator voltage and frequency reach the settings of the control. After the delay, the transfer switch transfers the load to the Emergency power source. OPTIONAL SIGNAL MODULE INDICATOR LAMPS OPTIONAL METERS OPTIONAL
13. 3. WIRE START ACCESSORY CONTROL PANEL OPTIONAL PROGRAMMED TRANSillON MOTOR DISCONNECT SWITCH This brief time delay allows the generator set to sta­ bilize before the load is applied. It has an adjust­ able range of 0 to 120 seconds. Retransfer Time Delay: This delay begins the mo­ ment Normal line voltage and frequency return. Af­ ter the delay, the transfer switch can retransfer the load to the Normal source. The delay allows the Normal source to stabilize before retransfer. It has TEST & EXEROSE WITH/WITHOUT LOAD SWITCHES 0 0 i I 0 POWER SENTRY CONTROL 0 0 AUTOMATIC TRANSFER SWITCH SC1581 RGURE 1·3. UTIUTY· TO-GENERATOR SET TRANSFER SWITCH INTERIOR COMPONENTS
14. 1. 5 www . ElectricalPartManuals . com Undervoltage Sensing Two voltage sensors, one for the Normal side and one for the Emergency side, monitor source volt­ ages for an undervoltage condition and generate signals, which are sent to the time delay module. If, for example, an undervoltage condition is sensed on the Normal source, the voltage se1nsor module sends a signal to the time delay module that initi­ ates and controls the timing for generator set start and the transfer of load. The standard transfer switch has undervoltage sensing for all phases of the Normal and Emer­ gency power sources. Overvoltage and Frequency Sensing Option Overvoltage and frequency sensing are available as a single option. Overvoltage Sensing: With optional overvoltage sensing, the Normal and Emergency sources are monitored for an overvoltage conditio1n. As with the standard undervoltage sensing, the voltage sensors signal the time dEŰIay module, which controls the transfer or retransfer sequence. overshoots in voltage. Frequency Sensing: With optional frequency sensing, the Normal and Emergency sources are monitored for variations in frequency. The sensors detect whether or not the source is within an adjust­ able bandwidth. As with the standard undervoltage sensing, the fre­ quency sensors signal the time dEŰIay module, which controls the transfer or retransfer sequence. nore momentary dips or rises in frequency. Two-Wire Starting The starting circuit is a basic supervisory function of the electronic control. Water-cooled generator sets use a two-wire start control. Although the logic is more involved, the two-wire starting circuit can be thought of as a single-pole, single-throw switch. A closed switch signals the generator set to start. An open switch signals the electric generator set to stop. Three-Wire Starting Option The optional three-wire starting control (available only on 40- to 125-ampere units) enables the trans- 1 -6 fer switch to start and stop a three-wire start gen­ erator set. Three-wire starting logic is similar to a single-pole, double-throw switch. A common is closed to one side to send a start signal, and to the opposite side to send a stop signal. In addition to start and stop functions, the control has an over­ crank relay, a preheat relay, two Timing lamps, a Lockout lamp, a Reset switch, a preheat delay On/ Off switch, and an Auto/Stop/Handcrank switch. Programmed Transition Option The optional Program Transition module is used to introduce a pause during transition. Programmed transition allows the transfer switch to assume a time. In this position, the load is not connected to either power source (Normal or Emergency). This feature allows residual voltage from inductive loads completed. Signal Module Option The main function of the optional Signal Module is to delay transfer (or retransfer) for a preset time a transfer (or retransfer) is about to occur. This op­ tion is typically used in elevator applications. Float Battery Charger Option The optional float-charge battery charger regulates its charge voltage to continuously charge without damage to the battery. As the battery approaches full charge, the charging current automatically ta­ pers to zero amperes or to steady-state load on the battery. The battery charger has an am meter for i n­ dication of charging current and has a fuse for pro­ tection of the battery charger circuit. Auxiliary Relays Option Optional auxiliary relays provide contacts for ener­ gizing external alarms, remote indicators, and con­ trol equipment such as louver motors and water pumps. Exerciser Clock Option The optional exerciser clock initiates generator set start/run cycles at programmable intervals and for programmable durations. It is a 7-day, 24-hour clock that can store and execute up to ten start/stop programs (exercise cycles). www . ElectricalPartManuals . com Load Shed Option The optional Load Shed function is used to discon­ nect the load from an available Emergency source in order to reduce the power consumed from that source. The Load Shed function (when activated by a customer-supplied signal) moves the transfer switch from the Emergency position to the neutral position. Alarm Module Option The optional alarm module provides an audible in­ dication that the transfer switch has transferred to the emergency power source. Phase Sequence/Balance Monitor Option The optional phase sequence/balance monitor senses A, B, and C phases of utility power. If there is an over- or undervoltage, a phase reversal, a loss of one phase, or an unbalanced voltage condition; a normally energized relay drops out, initiating the generator set start/transfer of load sequence. Standby Set Start Sequencer Option The optional standby set start sequencer is avail­ able only on a generator set-to-generator set trans­ fer switch. The standby set start sequencer re­ sponds to a remote start signal from the utility-to­ generator set transfer switch by directing a start sig­ nal from the generator set-to-generator set transfer switch to the RMT start input of the generator set that is selected as the preferred source. Area Protection/ Remote Test Transfer The transfer switch can be wired with a remote test transfer switch. Closure of a set of contacts across the remote test transfer inputs (terminals 7 and 8 of TB2) causes the transfer switch to sense a (simu­ lated) utility power failure and send a start/run sig­ nal to the generator set. The load is transferred to the generator set when generator set power be­ comes available. On 300.3090 mother boards, the Wlth/WHhout Load swHch must be In the With Load position. On
15. 300. 3953 mother boards, this Input Is NOT depend­

Source: manual:962-0512 Onan OT III series (spec G) 40 to 1000 Amp Transfer Switch Service manual (11-1992).pdf. Figures and steps are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.