UL 489 or UL 1077 in Control Panels and Equipment - A Quick Guide
A common question that comes up with OEM machine builders and control panel builders is “How do I know when to use UL 1077 or UL 489 breakers in panels or equipment?” The answer is seemingly simple, but like most simple questions, there is usually some confusion. No one wants to be the only person in the room who puts up their hand and asks a question to which they believe “everyone else” knows the answer.
By contrast, “Recognized” devices under UL 1077, Supplementary Protectors for Use in Electrical Equipment, are evaluated only for use as components in “Listed” products.
In contrast to “Listed” circuit breakers, UL 1077 supplementary protectors are “Recognized” components. This means that they are investigated for factory installation in “Listed” products, such as a UL 508a panel.
Both UL 489 and UL 1077 devices must pass a series of calibration, overload, endurance and short-circuit tests.
The UL 489 and UL 1077 Standards testing are similar, but the UL 489 testing is more rigorous. Unlike UL 489, a UL 1077 circuit protection device does not necessarily need to survive the test. See Figure 1, below, for a comparison of the testing.
- UL 489 - 1 inch through the air, 2 inches over surface.
- UL 1077 - 3/8 inch through the air, 1/2 inch over surface.
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