UL Question Corner: Generator Enclosures

I have a typical UL 2200 Listed generator installation set on a concrete pad. The generator has an overall enclosure, and inside that enclosure the bottom of the circuit breaker enclosure is about 24 inches above the concrete pad. The generator enclosure sits on the concrete pad, has sides and a top, but no bottom to attach a raceway. The installer stubbed PVC conduit just above the pad and free aired the load side conductors without a raceway for about 18 inches exiting the bottom of the breaker enclosure to enter the PVC conduit stubs.  Are Listed generator enclosures evaluated as electrical enclosures so that a raceway from the conduit stubs to the circuit breaker enclosure is unnecessary? Or, are they Listed as weather enclosures to protect the generator installation from the elements?


UL certified generator enclosures are evaluated as weather enclosures for generator installations. They are not evaluated as electrical enclosures when open insulated conductors are intended to be installed outside of raceways.  In this case, the conduit stubs would need to extend up to a circuit breaker enclosure to totally enclose those conductors in a suitable raceway.

There are two options for certifying engine generator enclosures. In the first option, the generator enclosure or weather housing alone is Classified/Certified. In the second option, a generator and enclosure are Listed/Certified together as a stationary engine generator assembly.

When the generator enclosure is Classified/Certified alone, it is certified under the product category Engine Generator Enclosures, Construction Only, (FTPP).  The UL Guide Information and certifications for FTPP can be viewed on UL Product Spec at www.ul.com/productspec (enter FTPP at the category code search) or on page 205 of the 2015-16 UL White Book PDF at www.ul.com/whitebook.

This category covers engine generator enclosures (also known as weather housings) investigated for electrical and mechanical construction only. These enclosures are intended to be installed on Listed/Certified stationary engine generators in the field or in a factory. The enclosure assemblies may include components such as mufflers, lights, heaters, fans, battery chargers, alarms and other accessories certified to component standards. Because component investigations vary in the type and level of testing, additional testing may be needed as part of an overall engine generator investigation to address the performance of components as part of an entire system.

In most cases, the combination of a Classified/Certified engine generator enclosure and a Listed/Certified engine generator will require additional investigation and testing and may require a UL Field Evaluation to establish the compliance of a specific combination. The FTTP category also covers enclosures that have been investigated with particular generators. In this case, the combination of the specific generator and specific enclosure is identified as part of the enclosure Classification/Certification.  If an enclosure has not been identified for use with specific generators as part of the Classification/Certification, then the effect of the enclosure on generator operation has not been investigated. These effects include resistance to the elements and impact of an enclosure on generator operating temperatures.

Complete assemblies that have been investigated are identified by the Listing/Certification Mark for Engine Generators (FTSR) on the outside of the engine generator enclosure or weather housing.  The UL Guide Information and certifications for FTSR can be viewed on UL Product Spec at www.ul.com/productspec (enter FTSR at the category code search) or on page 204 of the 2015-16 UL White Book PDF at www.ul.com/whitebook.

The final assembled combination of a generator enclosure with an engine generator and other system components is intended to be installed and investigated for compliance with local requirements to applicable product standards and installation codes, including ANSI/NFPA 70, National Electrical Code.

For generator and generator enclosures that have not been Classified/Certified as a combination, a UL field evaluation can be requested by contacting UL’s Customer Service team at 877-854-3577 (877-ULHELPS) then prompt number 2 or online at www.ul.com/field.



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