Understanding How to Apply UL 489 and UL 1077 Devices
Do you know the differences between UL 489 and UL 1077? The key to understanding UL 1077 supplementary protection and UL 489 branch protection requirements is to first understand how to identify the products, the applications they can be used for and importance of selecting the correct device in compliance with UL standards.
While both types of protection are useful and have similar purposes, each should only be used to fit specific applications in order to optimize your control panel. If they are not applied correctly, safety hazards such as electric fire or shock can occur.
A UL 489 device can be used as branch circuit protection and for supplementary protection. However, UL 1077 devices are only acceptable for providing supplementary protection where there is branch circuit protection ahead of it. The UL1077 device is a cost-effective way to replace small fuses that protect sensitive equipment. Lakeland has compiled the must-know information regarding UL 489 and UL 1077 with help from suppliers Schneider Electric and Eaton/Bussmann.
UL 489 Circuit Breakers and Branch-Circuit Overcurrent Devices
The NEC defines a branch circuit as the circuit conductors between the final overcurrent device protecting the circuit and the outlets. UL 489 opens automatically on overload and short circuit. In addition, it protects wire and cable against overload and short circuit.
A branch-circuit overcurrent device is capable of providing protection for service, feeder, and branch circuits and equipment over the full range of overcurrents between its rated current and its interrupting rating.
UL 489 Branch Protection Applications
UL 489 can be used within a variety of applications including:
- Control panels
- Motor control centers
UL 1077 Supplementary Protectors and Supplementary Overcurrent Protective Devices
A supplementary protector is a manually re-settable device designed to open the circuit automatically on a predetermined value of time versus current or voltage within an appliance or other electrical equipment.
A supplementary protective device is intended to provide limited overcurrent protection for specific applications and utilization equipment such as luminaires and appliances. This limited protection is in addition to the protection provided in the required branch circuit by the branch circuit overcurrent protective device. Per NEC, they cannot be used as feeder or branch circuit protective devices.
UL 1077 Supplementary Protection Applications
A good rule of thumb to follow is to only use UL 1077 to protect circuits inside the equipment that do not feed circuits that exit the equipment. Applications that UL 1077 can be used for include:
- Electrical equipment
- Control circuits
- Control power transformers
UL 489 versus UL 1077 Testing Requirements
UL 489 undergoes more rigorous testing than UL 1077. According to UL, branch circuit overcurrent protective devices are rated for at least 5,000 amperes interrupting rating and are often rated at a much higher level. In contrast, supplementary protectors typically have only been tested at 5,000 amperes or less, unless a manufacturer requests evaluation at a higher value. A circuit breaker’s trip current rating is required to be calibrated at 135% whereas manufacturers can select the trip current rating on a supplementary current protector. Overall, the branch-circuit protectors are more regulated versus manufacturer-specified.
Need Application Assistance?
UL states that their requirements are often based on their published and nationally recognized Standards for Safety. With safety being one of Lakeland Engineering Equipment Company’s core commitments, our team is dedicated to staying on top of industrial code requirements and standards to best serve our customers. For application assistance regarding UL 489 and UL 1077, contact us today.