¬ Frequently Asked Questions
Q. How do I determine the fuel consumption or emissions data for my gen-set?

A. Gen-Set is the combination of a synchronous AC generator (alternator) with a prime-mover (usually a diesel or gaseous engine), a fuel system, exhaust system, and gen-set control systems.

Marathon Generators manufactures only the electrical generator (alternator) and supplies them as an OEM to the Gen-Set packager. We have no knowledge of the engine / prime mover or any of the other components other than the alternator.

Questions about fuel consumption, emissions data or any other engine related question should be directed to the gen set packager or the engine manufacturer.

Q.  My Gen-Set runs, but the generator will not build voltage or produce power.  How do I troubleshoot?

A.  Marathon produces a number of different types of generators – for different applications.  To download a guide on how to troubleshoot your generator click on the appropriate link below:

Light Tower, Capacitor Pancake Generators  -  Capacitor Regulated Pancake Trouble Shooting Guide  

General Purpose AVR Pancake Generators  -  Pancake Generator Trouble Shooting Guide

MagnaPLUS / MARINER / HARSH DUTY Generators  -  MagnaPLUS Generator Trouble Shooting Guide

LimaMAC and Lima MAC Irrigator Generators  -  Lima MAC Service Shop Notes - All Frames

Q. How do I connect / reconnect my Marathon generator for a different voltage?

A. Click on Connection Diagrams for a link to the wiring diagrams for 3 phase and single phase generators.

12 lead, 3 phase generators may be connected for single phase application.

10 lead, 3 phase generators are limited to HIGH WYE (SERIES STAR) and LOW WYE (PARALLEL STAR) connections and cannot be connected for single phase application.

MagnaPLUS / MARINER / HARSH DUTY generators are equipped with linkboards to ease generator reconnection. Click Link Board Connection Diagrams for detailed instructions.

Q.  I have a replacement DVR2000E+.  Does it need to be set up / How do I set it up?

A.  Yes, every replacement DVR2000E+ must be set up for the intended generator installation.  For a typical, single, stand-alone generator installation click on DVR2000E+ Quick Start Guide. For the complete DVR2000E+ User Manual, click on Voltage Regulator Operations Manual ."

Q. How do I determine the proper engine adaption requirements for a replacement generator?

A. If the generator is either a Lima Electric Co type LIMA®MAC or Type SER, or a Marathon Electric type MAGNAPLUS, check the generator nameplate for an engine adaption kit (ADPT KIT) part number and/or generator serial number. If a Marathon Electric type MAGNAMAX check the nameplate for a model number and/or serial number. Contact the factory with these numbers for information as to what engine adaption was installed when the unit shipped from the factory.

If none of the above information is available, or if the generator is of another make or model, click on generator adaption for information regarding taking measurements to determine the existing generator's SAE drive disc size, and SAE flywheel housing size.

Q.  What are the Cap Screw Torque Specifications?

A.  Click on Torque Specs for more information.

Q. How do I identify a Marathon Electric generator from the generator Model Number?

A. Click on generatormodelcodes for a matrix of generator model codes to determine the generator type, frame size, number of bearings, voltage range, and special engine adaptions.

Q.  What is the estimated thermal life of a generator, and how can I increase the life through proper selection?

A.  Click on Thermal Life for more information.

Q.  How do I properly select a generator when my application includes non-linear loads such as VFDs, battery chargers, welders, or UPS Systems?

A.  Harmonics are created anytime diodes and/or thyristors (SCRs) are used to convert AC to DC as they switch on and off, creating a non-linear load. These harmonics can have a significant impact on a limited power source, such as a generator set. Click on Generator Selection and Non-Linear Loads for more information.

Q. What are the advantages of adding a PMG to a synchronous AC generator?

A. Click on PMG for an article discussing the advantages of a PMG Excitation Support System.

Q. What are the operating parameters/specifications of Marathon's Add-On PMG excitation support system?

A. Click on Add-On PMG Specs for these specifications.

Q. How do I reduce a Marathon Electric generator's nameplate rating to compensate for an installation site having an ambient temperature above 40°C, and/or an altitude greater than 3,300 feet (1,000 meters) above sea level?

A. Click on Rating Adjustment Nomograph. Reduce the generator's nameplate kVA rating by the de-rating factor determined by applying the site altitude and ambient temperature to the nomograph. (See the example outlined in blue.)

Q. Are Marathon Electric generators suitable for installation in Class 1, Division 2 Hazardous locations?

A. Yes with certain limitations. Click on Hazardous Locations for an article discussing the suitability of Marathon Electric generators for installation in Hazardous Locations.

Q. What is a synchronous generator?

A. A synchronous AC generator (alternator) is an alternating current generator whose rotating speed is directly proportional to the frequency of the AC voltage wave it produces. All Marathon MAGNAPOWER®, MAGNAMAXDVR®, MAGNAPLUS®, PANCAKE®, and LIMA®MAC generators are synchronous generators.

Q. What is an induction generator?

A. An Induction (asynchronous) generator is an AC generator (alternator) whose rotating speed is not directly proportional to the system frequency. An induction generator is basically an induction motor tied to, operating in parallel with, another source of electrical power - usually the public utility - whose shaft is caused to turn faster than the synchronous speed (frequency) of this other power source. Under this condition, the induction generator delivers power back onto the power source. Marathon's PRIMELINE® generators are induction (asynchronous) AC generators.

Q. What does the term Time Constant mean?

A. The term time constant refers to the length of time required to change from one condition to another. Usually considered to be the time required to complete 63.3% of the total rise or decay of voltage and/or current flow following the addition or rejection of electrical load.

Q. What is a generator's Transient Reactance (X'd)?

A. This value determines the current flowing during the period when the subtransient reactance is the controlling value.

Q. What is a generator's Sub-Transient Reactance (X"d)?

A. The apparent reactance of the stator (main armature) winding at the instant a short circuit (fault) occurs. This reactance is used for the calculation if the initial maximum symmetrical and asymmetrical fault current.

Q. What are the storage and operating temperature limits of Marathon generators?

A. Storage and operating temperature ranges of Marathon generators will vary depending upon the model of automatic voltage regulator being used. The storage and operating temperature ranges for the standard AVRs used with Marathon generators are:

1. Marathon Electric Model SE350 automatic voltage regulator storage temperatures, are (-) 65°C to (+) 85°C, and operating temperatures are (-) 40°C to (+) 60°C.
2. Marathon Electric Model PM300 automatic voltage regulator storage temperatures, are (-) 65°C to (+) 85°C, and operating temperatures are (-) 40°C to (+) 60°C.
3. Marathon Electric Model DVR2000E/EC automatic voltage regulator storage temperatures are (-) 40°C to (+) 80°C, and operating temperatures are (-) 40°C to (+) 70°C.
4. Basler Electric Model AVC63-12B2 automatic voltage regulator (used with our 400 Hertz generators) storage temperatures are (-) 40°C to (+) 80°C, and operating temperatures are (-) 40°C to (+) 70°C.

Should the voltage regulator being used be other that those listed above, please consult with the factory for these temperature ranges.

Q. What is meant by the terms a bearing B10, or L10 life?

A. Bearing life us usually expressed as the number of hours an individual bearing will operate before the first evidence of metal fatigue develops. B10, or L10 are terms used when referring to bearing life. Click on Bearing Life for a discussion of these terms.

Q.  Is there a specific direction of generator shaft rotation, clockwise or counter clockwise, that needs to be adhered to for Marathon generators to operate properly?


A. All standard Marathon synchronous generators products including LIMA®MAC, MAGNAPLUS, MAGNAMAXDVR, MAGNAPOWER, and Pancake are fitted with bi-directional fans, and are designed to operate properly without harm, with the shaft rotating in either a clockwise or counter clockwise direction. However, for three phase operation, all standard three phase Marathon generators have an A - B - C phase sequence when the generator shaft is rotating counter clockwise as viewed from opposite the generator drive end (viewed from the exciter end) unless otherwise required by a customer's generator specification, or purchase order. For this reason, it is always a good and safe electrical practice to check the generator's phase sequence to assure phase sequence compatibility with any electrical distribution system prior to initial closure onto the electrical load.
If the generator’s phase sequence is opposite to the desired system phase sequence, the generator phase sequence can be changed (ie. From A – B – C, to C – B – A) by swapping L1 and L3 at the master circuit breaker, or transfer switch (if a transfer switch is included in the installation). To do this, disconnect L1 from pole 1 and L3 from pole 3 of the master circuit breaker or transfer switch, and install L1 on pole 3, and L3 on pole 1 of the master circuit breaker or transfer switch. L2 must remain on pole 2 of the master breaker or transfer switch.
If the generator is connected for total single phase performance, there is no phase sequence, and therefore, this check is not needed.