Below you will find answers to our most frequently asked questions.

How do I determine what size generator set is required for my site?

By providing a summary of the sites different horsepower or amperage loads and the voltages they require, we can use a sizing program to determine your power requirements.  It may be necessary to use a licensed electrician to perform this site survey.

Based on this data we can recommend a generator set that will provide the power your site requires.

To use our power calculator, click here.

To view electrical formulas used to determine power consumption, click here.

What is the difference between a emergency and non-emergency generator set?

Emergency generators are exempt from the Tier 4 rules because these engines run infrequently and thus would not be among the major contributors to total NOX and PM emissions. Emergency engines built after January 1, 2011, can be sold meeting Tier 2 limits and do not—by EPA definition—require exhaust after-treatment (Table 1).

Courtesy: MIRATECH Inc.

But the EPA definition of emergency is strict. To qualify for the exemption, an emergency generator set engine may run only when the normal power source such as the local utility fails, except for tightly limited maintenance and testing.  Generators used in peak-shaving, revenue generation, and similar applications do not qualify for the EPA’s emergency genset exemption. There is no Tier 4 limit on the number of hours an emergency generators can run in an actual emergency. However, non-emergency run time is limited to a maximum of 100 hours per year for maintenance and testing. Therefore, many applications running low-use hours—for example, 101-200 hours per year—fall into the non-emergency category and must meet the newly enacted Tier 4 standards.

The current challenge that owners are facing is that factory-certified solutions available for the >560 kW range of generators is extremely limited. This situation leaves them to seek aftermarket systems that will satisfy emissions requirements and allow for field compliance.

For additional questions or to contact a WPP sales representative, click here.

What are U.S. EPA Tier 4 regulations?

In 2004 the EPA published the final rule introducing Tier 4 emission standards, which are to be phased-in over the period of 2008-2015 The Tier 4 standards require that emissions of particulate matter (PM) and oxides of nitrogen (NOx) be further reduced by about 90%.   NOx are known to contribute to the formation of ground-level ozone, and particulate matter exposure has been shown to have adverse health effects on the respiratory system.  Tier 4 emissions levels are similar to those required by the 2007-2010 standards for on-highway engines.

Tier 4 refers to the latest emission milestone established by the U.S. Environmental Protection Agency and the California Air Resources Board applicable to new engines found in off-road equipment including construction, mining and agricultural equipment, marine vessels and workboats, locomotives and stationary engines found in industrial and power generation applications. As of January 1, 2014, these emissions standards apply to new engines that power equipment commonly found in most construction and agricultural applications while new engines manufactured for much larger applications including marine, locomotives must have met the standard by January 1, 2015. These emissions standards apply to new and remanufactured engines and do not apply to older engines.

The Tier 4 emission standards—phased-in from 2008 through 2015—introduce substantial reductions of NOx (for engines above 56 kW) and PM (above 19 kW), as well as more stringent HC limits. CO emission limits remain unchanged from the Tier 2-3 stage.

Engines up to 560 kW. Tier 4 emission standards for engines up to 560 kW are listed in Table 3.

Table 3
Tier 4 emission standards—Engines up to 560 kW, g/kWh (g/bhp-hr)
Engine Power Year CO NMHC NMHC+NOx NOx PM
kW < 8 (hp < 11) 2008 8.0 (6.0) 7.5 (5.6) 0.4a (0.3)
8 ≤ kW < 19 (11 ≤ hp < 25) 2008 6.6 (4.9) 7.5 (5.6) 0.4 (0.3)
19 ≤ kW < 37 (25 ≤ hp < 50) 2008 5.5 (4.1) 7.5 (5.6) 0.3 (0.22)
2013 5.5 (4.1) 4.7 (3.5) 0.03 (0.022)
37 ≤ kW < 56 (50 ≤ hp < 75) 2008 5.0 (3.7) 4.7 (3.5) 0.3b (0.22)
2013 5.0 (3.7) 4.7 (3.5) 0.03 (0.022)
56 ≤ kW < 130 (75 ≤ hp < 175) 2012-2014c 5.0 (3.7) 0.19 (0.14) 0.40 (0.30) 0.02 (0.015)
130 ≤ kW ≤ 560
(175 ≤ hp ≤ 750)
2011-2014d 3.5 (2.6) 0.19 (0.14) 0.40 (0.30) 0.02 (0.015)
a – hand-startable, air-cooled, DI engines may be certified to Tier 2 standards through 2009 and to an optional PM standard of 0.6 g/kWh starting in 2010
b – 0.4 g/kWh (Tier 2) if manufacturer complies with the 0.03 g/kWh standard from 2012
c – PM/CO: full compliance from 2012; NOx/HC: Option 1 (if banked Tier 2 credits used)—50% engines must comply in 2012-2013; Option 2 (if no Tier 2 credits claimed)—25% engines must comply in 2012-2014, with full compliance from 2014.12.31
d – PM/CO: full compliance from 2011; NOx/HC: 50% engines must comply in 2011-2013

In engines of 56-560 kW rated power, the NOx and HC standards are phased-in over a few year period, as indicated in the notes to Table 3. The initial standards (PM compliance) are sometimes referred to as the ‘interim Tier 4’ (or ‘Tier 4i’), ‘transitional Tier 4’ or ‘Tier 4 A’, while the final standards (NOx/HC compliance) are sometimes referred to as ‘Tier 4 B’.

As an alternative to introducing the required percentage of Tier 4 compliant engines, manufacturers may certify all their engines to an alternative NOx limit in each model year during the phase-in period. These alternative NOx standards are:

  • Engines 56-130 kW:
    • Option 1: NOx = 2.3 g/kWh = 1.7 g/bhp-hr (Tier 2 credits used to comply, MY 2012-2013)
    • Option 2: NOx = 3.4 g/kWh = 2.5 g/bhp-hr (no Tier 2 credits claimed, MY 2012-2014)
  • Engines 130-560 kW: NOx = 2.0 g/kWh = 1.5 g/bhp-hr (MY 2011-2013)

Engines Above 560 kW. Tier 4 emission standards for engines above 560 kW are listed in Table 4. The 2011 standards are sometimes referred to as ‘transitional Tier 4’, while the 2015 limits represent final Tier 4 standards.

Table 4
Tier 4 emission standards—Engines above 560 kW, g/kWh (g/bhp-hr)
Year Category CO NMHC NOx PM
2011 Generator sets > 900 kW 3.5 (2.6) 0.40 (0.30) 0.67 (0.50) 0.10 (0.075)
All engines except gensets > 900 kW 3.5 (2.6) 0.40 (0.30) 3.5 (2.6) 0.10 (0.075)
2015 Generator sets 3.5 (2.6) 0.19 (0.14) 0.67 (0.50) 0.03 (0.022)
All engines except gensets 3.5 (2.6) 0.19 (0.14) 3.5 (2.6) 0.04 (0.03)

Other Provisions. The Tier 4 regulation and later amendments include a number of additional provisions:

  • Smoke Opacity—Existing Tier 2-3 smoke opacity standards and procedures continue to apply in some engines. Exempted from smoke emission standards are engines certified to PM emission standards at or below 0.07 g/kWh (because an engine of such low PM level has inherently low smoke emission).
  • Crankcase Ventilation—The Tier 4 regulation does not require closed crankcase ventilation in nonroad engines. However, in engines with open crankcases, crankcase emissions must be measured and added to exhaust emissions in assessing compliance.
  • DEF Refill Interval—For SCR-equipped nonroad diesel engines, a minimum DEF (urea solution) refill interval is defined as at least as long (in engine-hours) as the vehicle’s fuel capacity [3408].
  • Ammonia Emissions—While ammonia emissions are unregulated, the EPA recommends that ammonia slip should be below 10 ppm average over the applicable test cycles [3693].
  • Emergency Operation—To facilitate the use of certain nonroad engines in temporary emergency situations, the engines can be equipped with an AECD to override performance inducements related to the emission control system—for example, to allow engine operation without urea in the SCR system during an emergency [3408]. This flexibility is intended primarily for engines used in construction equipment and portable equipment used for temporary power generation and flood control.
  • ABT Program—Similarly to earlier standards, the Tier 4 regulation includes such provisions as averaging, banking and trading of emission credits and FEL limits for emission averaging.

Do Tier 4 regulations only impact the US?

Similar regulations will impact the European Union and likely Canada and Japan. In the EU the regulations are called Stage IIIB/IV; in Japan they are called Step 4. Neither Japan nor Canada have completed adoption of Tier 4/Step 4, but we expect them to do so in the near future. In the EU the regulations do not apply to engines < 19 kw or engines > 560 kW at this time and we expect Japan to be the same as the EU. The regulation in Canada is expected to be essentially identical to the U.S. regulation.

What is Tier 4 Interim vs. Tier 4 Final (Stage IIIB/Stage IV)?

Tier 4 Interim regulations begin in 2011 for most power categories and Tier 4 Final is phased beginning in 2014. Tier 4 Interim is intended to enable a gradual phase in to final regulations for manufacturers. Tier 4 Final regulations require additional reductions in NOx. Alternative phase-in periods from Interim to Final are intended to provide time to transfer technology from highway engines to non-road engines.

How do I meet or exceed Tier 4 diesel engine emission standards?

Through advancements in engine design, modern diesel engines have been transformed into one of the cleanest prime movers available today. Some of these engine improvements include high-pressure common rail fuel injection systems, electronically controlled injector solenoids, and advanced turbocharging. While these improvements enabled engine manufacturers to meet Tier 2, and Tier 3 standards, in order to meet the more stringent Tier 4 interim and Tier 4 final regulations, exhaust after-treatment was required.

There are three major technologies used for exhaust after-treatment.

  • Selective Catalytic Reduction (SCR) – This works by combining the exhaust gases with ammonia (urea or DEF, diesel emissions fluid) and passing this mixture over a catalyst. Roughly 1 gallon of DEF is required to treat 20 gallons of diesel fuel.
  • Diesel Particulate Filter (DPF) – This works by using a mechanical filter to trap soot particles after they have been partially oxidized by a catalyst. At certain intervals during operation, the trapped particles are incinerated.
  • Exhaust Gas Recirculation (EGR) – This works by recirculating a small amount of cooled exhaust gas back into the combustion chamber. This reduces the combustion temperature and effectively reduces the production of NOx. However, EGR increases particulate emissions, so a DPF will be needed to meet Tier 4 final regulations.


The US EPA issued a number of rules to control emissions of toxic air pollutants from existing stationary reciprocating internal combustion engines (RICE).

The rules, entitled National Emission Standards for Hazardous Air Pollutants (NESHAP) for Reciprocating Internal Combustion Engines, are intended to reduce emissions of toxic air pollutants—such as formaldehyde (HCHO), acetaldehyde, acrolein, methanol and other air toxics—from several categories of previously unregulated stationary engines. The EPA has determined that carbon monoxide (CO) can be often used as an appropriate surrogate for formaldehyde. Since testing for CO emissions has many advantages over testing for emissions of hazardous air pollutants (HAP), many of the emission standards have been finalized in terms of CO as the only regulated pollutant.

The NESHAP regulations for stationary engines are published in Title 40, Part 63, Subpart ZZZZ (63.6580) of the Code of Federal Regulations (CFR). Regulatory documents as well as fact sheets and related information can be also found in the US EPA stationary engine pages [3115].

Where does the NESHAP rules apply?

The NESHAP rules are applicable to “existing” diesel and SI engines, as well as to certain categories of “new” and “reconstructed” engines, as determined by their date of construction or reconstruction. “Existing” engines are defined as follows:

  • “Area sources” of air toxics emissions: Engines constructed or reconstructed before June 12, 2006.
  • “Major sources” of air toxics emissions:
    • Engines ≤ 500 hp constructed or reconstructed before June 12, 2006.
    • Engines > 500 hp constructed or reconstructed before December 19, 2002.

“New” engines or “reconstructed” engines are those constructed or reconstructed, respectively, after the above dates. Engines required to meet NSPS requirements are considered to be compliant with NESHAP requirements and no further requirements apply under the NESHAP rules.

Emergency Engines. The NESHAP requirements apply to engines used for non-emergency purposes. The following operational requirements must be met by emergency engines:

  • There is no time limit on the use in emergency situations (e.g., power outage, fire, flood).
  • The engine may be used for up to 100 hours per calendar year for maintenance checks, testing, and for emergency demand response (i.e., blackout and brownout prevention).
  • The engine may be used for up to 50 hours per year for certain non-emergency uses such as local reliability (the operation counts toward the above 100 hour limit).

What are the types of NESHAP emission standards?

The NESHAP regulations include three types of emission standards:

  1. Emission Limits—Limits for lean-burn engines are expressed as volumetric, dry CO concentrations (ppm) at 15% O2. Limits for rich-burn SI engines are expressed as volumetric, dry concentrations of HCHO (ppm or ppb) at 15% O2. The standards must be met during any operating conditions, except during periods of start-up (of maximum 30 minutes). Emissions are tested at 100% load.
  2. Percentage CO/HCHO Reductions—Alternative compliance options are available in certain engine categories, expressed as percentage CO or HCHO/THC emission reductions. These reductions can be achieved by retrofitting engines with emission controls, such as oxidation catalysts (OC) on lean-burn engines or non-selective catalytic reduction (NSCR, three-way catalysts) on rich-burn engines.
  3. Equipment Standards—Engines must be retrofitted with emission controls: oxidation catalysts on lean-burn engines and NSCR catalysts on rich-burn engines.

Can I operate a generator set on propane instead of natural gas?

Most natural gas powered generator sets can be converted to run on propane in vapor state. LPG Vapor conversions are the simplest. On the Ford ESG642 (4.2L) engine used by many manufacturers, addition of a Link Module and reconnection of one wire to the module is required. The natural gas regulator would need to be reset and an adjustment would need to be made to the fuel mixer and speed control.

Can a generator set’s output voltage be changed?

Many generator sets have twelve line leads (cables). Depending on the connections that are made between the load and the generator line leads, single-phase and/or three phase voltages are possible. When making changes to a generator sets output voltage, consideration needs to be given to the resulting output current. Replacement of the main circuit breaker is usually required. Other necessary changes would involve replacing analog type meters in a mechanical control panel, or programming changes to an electronic control panel.

Do you offer dual-fuel or bi-fuel generators?

Most of the diesel-powered generator sets we offer can be converted to bi fuel operation using one of several after-market add-ons that we can install quickly and inexpensively, without making any mechanical or physical alterations to the engine itself. With a bi-fuel add-on, generators can burn up to 70% natural gas, resulting in significant reductions in fuel costs and certain types of emissions. Dual fuel is a different type of engine from bi-fuel. To learn more about bi-fuel technology, click here.

Please contact us for specific detail or for a quote.

What are the maintenance requirements of my generator set?

The operation and maintenance manual for your generator set gives the periodic maintenance required and how frequently it should be performed. Many customers rely on Worldwide Power Products to perform those services through an annual maintenance agreement.

Please contact us for specific detail or for a quote.

When do the new emission regulations begin to apply?

Tier 4 Interim emissions regulations will be phased in by engine power category, followed by Tier 4 Final standards. The Tier 4 engine power categories are expressed in kilowatts (kW). Tier 4 began in 2008 for all engines under (<) 19 kW, and for those greater than or equal to 19 but less than 56 kW (19 ≤ kW < 56). For engines in the 130 ≤ kW ≤ 560 category, and those in the category for above 560 kW, Tier 4 Interim applies in 2011. Finally, for the 56 to 130 kW (56 ≤ kW < 130) category, Tier 4 Interim applies in 2012. Tier 4 Final standards generally are applicable three years after the Tier 4 Interim start date. [/av_toggle] [av_toggle title='What is next for diesel engine emission standards?' tags=''] New, more strict European Stage V regulations began to be implemented in Europe in 2019, and continue in to 2020. Since the engine business is global, these European standards will very likely be adopted here in the US, and be referred to as “Tier 5”. There is still some debate over this as the EPA has not committed to adopting these standards. These new regulations will be relatively easy to meet with the technology that is available today. What regulators want to more stringently control is the ultra-fine particles of soot in diesel exhaust, the sub-micron level particles. These particles are considered to pose the greatest threat to lung health because they can lodge deep inside lungs and stay there. These particles can be removed by using a DPF (diesel particulate filter) on every diesel engine. For the future, if Stage V/Tier 5 is implemented as anticipated, a DPF will likely be included on every diesel engine, large or small, stationary or mobile. It appears that this will include diesel engines less than 24 horsepower that are currently exempt from Tier 4 requirements. [/av_toggle] [av_toggle title='What is tier 1-3 emission standards?' tags=''] The 1998 nonroad engine regulations were structured as a 3-tiered progression. Each tier involved a phase-in (by horsepower rating) over several years. Tier 1 standards were phased-in from 1996 to 2000. The more stringent Tier 2 standards took effect from 2001 to 2006, and yet more stringent Tier 3 standards phased-in from 2006 to 2008 (Tier 3 standards applied only for engines from 37-560 kW). Tier 1-3 emissions standards are listed in Table 1. Nonroad regulations use the metric system of units, with regulatory limits expressed in grams of pollutant per kWh.

Table 1
EPA Tier 1-3 nonroad diesel engine emission standards, g/kWh (g/bhp·hr)
Engine Power Tier Year CO HC NMHC+NOx NOx PM
kW < 8 (hp < 11) Tier 1 2000 8.0 (6.0) 10.5 (7.8) 1.0 (0.75)
Tier 2 2005 8.0 (6.0) 7.5 (5.6) 0.8 (0.6)
8 ≤ kW < 19 (11 ≤ hp < 25) Tier 1 2000 6.6 (4.9) 9.5 (7.1) 0.8 (0.6)
Tier 2 2005 6.6 (4.9) 7.5 (5.6) 0.8 (0.6)
19≤ kW < 37 (25 ≤ hp < 50) Tier 1 1999 5.5 (4.1) 9.5 (7.1) 0.8 (0.6)
Tier 2 2004 5.5 (4.1) 7.5 (5.6) 0.6 (0.45)
37 ≤ kW < 75 (50 ≤ hp < 100) Tier 1 1998 9.2 (6.9)
Tier 2 2004 5.0 (3.7) 7.5 (5.6) 0.4 (0.3)
Tier 3 2008 5.0 (3.7) 4.7 (3.5) -†
75 ≤ kW < 130 (100 ≤ hp < 175) Tier 1 1997 9.2 (6.9)
Tier 2 2003 5.0 (3.7) 6.6 (4.9) 0.3 (0.22)
Tier 3 2007 5.0 (3.7) 4.0 (3.0) -†
130 ≤ kW < 225 (175 ≤ hp < 300) Tier 1 1996 11.4 (8.5) 1.3 (1.0) 9.2 (6.9) 0.54 (0.4)
Tier 2 2003 3.5 (2.6) 6.6 (4.9) 0.2 (0.15)
Tier 3 2006 3.5 (2.6) 4.0 (3.0) -†
225 ≤ kW < 450 (300 ≤ hp < 600) Tier 1 1996 11.4 (8.5) 1.3 (1.0) 9.2 (6.9) 0.54 (0.4)
Tier 2 2001 3.5 (2.6) 6.4 (4.8) 0.2 (0.15)
Tier 3 2006 3.5 (2.6) 4.0 (3.0) -†
450 ≤ kW < 560 (600 ≤ hp < 750) Tier 1 1996 11.4 (8.5) 1.3 (1.0) 9.2 (6.9) 0.54 (0.4)
Tier 2 2002 3.5 (2.6) 6.4 (4.8) 0.2 (0.15)
Tier 3 2006 3.5 (2.6) 4.0 (3.0) -†
kW ≥ 560
(hp ≥ 750)
Tier 1 2000 11.4 (8.5) 1.3 (1.0) 9.2 (6.9) 0.54 (0.4)
Tier 2 2006 3.5 (2.6) 6.4 (4.8) 0.2 (0.15)
† Not adopted, engines must meet Tier 2 PM standard.

Manufacturers who signed the 1998 Consent Decrees with the EPA may have been required to meet the Tier 3 standards one year ahead of schedule (i.e. beginning in 2005).

Voluntary, more stringent emission standards that manufacturers could use to earn a designation of “Blue Sky Series” engines (applicable to Tier 1-3 certifications) are listed in Table 2.

Table 2
EPA voluntary emission standards for nonroad diesel engines, g/kWh (g/bhp·hr)
Rated Power (kW) NMHC+NOx PM
kW < 8 4.6 (3.4) 0.48 (0.36)
8 ≤ kW <19 4.5 (3.4) 0.48 (0.36)
19 ≤ kW <37 4.5 (3.4) 0.36 (0.27)
37 ≤ kW < 75 4.7 (3.5) 0.24 (0.18)
75 ≤ kW <130 4.0 (3.0) 0.18 (0.13)
130 ≤ kW < 560 4.0 (3.0) 0.12 (0.09)
kW ≥ 560 3.8 (2.8) 0.12 (0.09)

Engines of all sizes had to meet smoke standards of 20/15/50% opacity at acceleration/lug/peak modes, respectively.

The regulations included several other provisions, such as averaging, banking and trading of emission credits and maximum “family emission limits” (FEL) for emission averaging.

What is an SCR (selective catalytic reduction) system do?

SCR is an emission control technology and it stands for “Selective Catalytic Reduction”.  An SCR system requires the use of diesel exhaust fluid (DEF or urea).  DEF is stored in a tank and then injected into the exhaust system. The injection causes a catalytic process that reduces NOx.

What Is Selective Catalytic Reduction? -Save

What does an EGR (exhaust gas re-circulation) system do?

EGR is an emission control technology and it stands for “Exhaust Gas Re-circulation”.  An EGR system works in conjunction with variable vane geometry turbo charger (VGT).  The intake air is diluted with exhaust gases.  The dilution reduces NOx formation during combustion.  This minimizes emissions to eliminate the need for particulate filters.  It can be used in conjunction with a DOC (diesel oxidation catalyst).

EGR Systems & ComponentsSave

What technology best addresses Tier 4 Final?

Engine manufacturers have used the following three technologies to address Tier 4 emissions standards:

  1. SCR (Selective Catalytic Reductions)
  2. EGR (Exhaust Gas Re-circulation)
  3. DPF (Diesel Particulate Filters)