UL 50 is the UL standard that specifies the design requirements for enclosures for electrical equipment and how they are to be tested.
Relation to UL
To demonstrate a control cabinet’s compliance, it is certified with an appropriate UL label. To do so, it must meet all the requirements described in the relevant standard. UL 50 is the UL standard that specifies requirements for enclosures for electrical equipment and must therefore be taken into account when certifying a switchgear assembly.
What is UL 50?
The UL 50 standard specifies the requirements for enclosures used in electrical equipment. For an enclosure to receive UL 50 certification, it must meet a whole series of requirements. A key requirement is that the enclosure protects people from accidental contact with the enclosed device, but protecting the components from environmental influences also plays a role.
What is the difference between the UL 50 and the UL 50 E?
UL 50 E supplements UL 50 with environmental design requirements. These include, among other things, requirements for protection against water, oil, dust, and other contaminants. This UL standard therefore focuses on protecting the device from environmental influences. The standard distinguishes between six types of enclosures for indoor applications (Types 1, 2, 5, 12, 12K, and 13) and seven for indoor and outdoor use (Types 3, 3R, 3S, 4, 4X, 6, and 6P).
The specific requirements that must be met vary depending on the enclosure’s intended use. For example, for outdoor enclosures, a rain test, a corrosion protection test, or even an immersion test may be required to ensure that the electrical components inside are adequately protected from water.
What requirements does UL 50 specify for the enclosures of electrical devices?
The requirements of UL 50 vary depending on the enclosure type. What they all have in common, however, is that protection is always required only to “a certain degree” (“a degree of protection”). For example, a Type 3 enclosure provides a certain degree of protection against dust ingress but is not completely dusttight. Similarly, no UL 50-certified enclosure offers complete protection against injury to persons. The standard specifies in detail the degree of protection that each enclosure type must provide and the tests required to verify this.
To which enclosures does UL 50 not apply?
UL 50 generally applies to all enclosures for electrical equipment. However, there are a few significant exceptions to this rule. As a general rule, specific provisions in product-specific standards take precedence over UL 50. This means that if a product-specific UL standard imposes different or more stringent requirements on the enclosure of a particular device—such as a control cabinet—those requirements take precedence.
UL 508 A and UL 50
The requirements that control cabinets must meet in order to obtain UL certification are specified in UL 508 A. That standard also defines the standard requirements for the construction of the enclosures. Consequently, the protective function of the enclosure is also tested for cabinets certified according to UL Standard 508 A. An additional test according to UL 50 is therefore not necessary for control cabinet enclosures.
Does UL 50 also apply to areas at risk of explosion?
Control cabinets used in potentially explosive atmospheres are subject to very specific requirements, depending on the level of risk. For example, it may be necessary for the enclosure to withstand an explosion inside it or to be completely sealed against the ingress of the explosive ambient atmosphere. However, these requirements are not defined by UL 50, but rather by UL 1203. Therefore, UL 50 does not apply to control cabinets in potentially explosive atmospheres.
Other Significant Exceptions to UL 50
Although the Canadian CSA recognizes UL standards, special rules apply in Canada for certain types of enclosures. Further details can be found in Appendix B of UL 50. Furthermore, junction boxes, such as those used in swimming pools, and all outlet boxes larger than 100 in³ (1,640 cm²) are exempt from UL 50 in both countries. The requirements for these are specified in UL 1241 and UL 514, respectively.
Zusammenfassung
The UL 50 standard defines the requirements for the enclosures of electrical devices. UL 50 E supplements the standard with environmental design requirements. The requirements of UL 50 vary depending on the type of enclosure. There are six enclosure types for indoor use and another seven for both indoor and outdoor use. However, there are also exceptions where UL 50 does not apply, namely whenever the provisions of specific product standards take precedence, such as UL 508A or UL 1203.
