February 6, 2020
Each component in an industrial control panel must be properly applied for safe and reliable operation. However, the application requirements for each component are complex, unique and often misapplied, resulting in erroneous interpretation that can lead to improper use of the component. To help increase industrial control panel safety, UL’s and Eaton’s Bussmann division experts teamed up to provide answers to frequently asked questions from the webinar, “Common Misapplications in Industrial Control Panels.”
- What is the difference between a motor starter and a motor controller?
A motor controller is a mechanism for switching the motor on and off. A motor starter is a combination of two products, a motor controller, and a motor overload protective device that protects the motor against damage due to overload conditions where the worst-case scenario would be a motor in a locked-rotor condition.
- Why is a branch-circuit protective device and disconnecting means required on the line side of a manual motor controller when it is being used as a motor disconnect or for tap conductor protection?
Manual motor controllers that can be used as a motor disconnect or for tap conductor protection have not been evaluated for these capabilities using the standards for a branch circuit disconnecting means or a branch circuit protective device. To qualify a manual motor controller as a branch circuit disconnect it would need to be evaluated to and meet the requirements of UL 98, the Standard for Enclosed and Dead-Front Switches. To qualify a manual motor controller as a branch circuit protective device for tap conductor protection it would need to be evaluated to and meet the requirements of UL 489, the Standard for Molded-Case Circuit Breakers, Molded-Case Switches, and Circuit-Breaker Enclosures.
Manual motor controllers that are able to be used as a motor disconnect or for tap conductor protection are evaluated to UL 508, the Standard for Industrial Control Equipment. The scope of this Standard covers products primarily intended for use wholly within a branch circuit. This is evident by the creepage and clearance requirements in UL 508 which are less stringent than creepage and clearance requirements in UL 98 and UL 489. The separation between a branch and feeder circuit is provided by a branch circuit protective device. Thus, components in the branch circuit would have a branch circuit protective device connected to their line side. The manual motor controllers in question are examples of such components.
- Why are type E/F combination motor controllers not suitable for the protection of group motor applications or lighting loads?
Type E/F combination motor controllers have been evaluated for use in a single motor branch circuit using the requirements in UL 508. These requirements do not cover this device for the protection of motor group applications or lighting loads. Currently, UL has no published requirements to evaluate these combination motor controllers for the protection of group motor applications or lighting loads.
- I have been told there are terminal blocks that are suitable for use in feeder circuits. What Standard applies to this product and what is the UL product category where they are covered?
Terminal blocks that are suitable for use in feeder circuits have been evaluated to UL 1059, the Standard for Terminal Blocks. The UL product category is XCFR2. Keep in mind that unlike power distribution blocks these terminal blocks are not Listed. They are Component Recognized and only intended for factory installation in end-use equipment. These products have conditions of acceptability or limitations in their end use. Terminal blocks that are suitable for use in feeder circuits are categorized as use Group A, meaning they are suitable for use in service equipment applications including panelboards, switchboards and the like. This application must be confirmed by checking the conditions of use for the terminal block which are provided in the manufacturer’s Component Recognition information stored in the UL Product iQ® online database.
- What kind of components are typically slash rated?
Many components that are primarily designed for use in Europe have slash ratings. By International Electrotechnical Commission (IEC) standards, these components often have a 400 volt (V) straight rating. However, when applied at U.S. voltages and subjected to UL testing requirements, they can only achieve slash voltage ratings. Combination motor controllers and manual motor protectors are typically slash-rated when applied as branch circuit protection. When applied in group motor applications, they can achieve a straight rating provided the upstream overcurrent protective device is straight rated. Additionally, some circuit breakers may have slash-voltages ratings, particularly miniature IEC-style circuit breakers. Fuses are all straight-rated.
- If my panel controls only a single motor load, can I use a UL 508 disconnect as my main switch?
No. A UL 508 disconnect, while acceptable for motor control (on/off), is not suitable as a means of isolation. For isolation of this circuit, you should use a UL 98 disconnect or UL 489 circuit breaker. Additionally, UL 508 disconnects must be installed on the load side of a branch circuit overcurrent protective device, a requirement that makes it incompatible for use as the main disconnect switch.
- Can manual motor protectors be used as branch protection? Is there any application in which this is true?
A manual motor protector, alone, is not suitable for branch protection. To become suitable for motor branch protection, the manual motor protector must be part of a type E/F combination motor controller. This requires the manual motor protector to have “feeder circuit” creepage and clearance distances at the line side terminals, usually achieved by using a line-side adaptor. When this requirement is met, it is suitable for the protection of a single motor load only. It is not suitable as a feeder circuit disconnect, or as protection for group motors as it has not been evaluated for these applications. In fact, no requirement currently exists for evaluating a type E/F combination motor controller for these applications.
- Are UL Listed fuses certified for use as overcurrent protection on 690 volts alternating current (VAC) branch circuits?
No, there aren’t any Listed fuses suitable for branch circuit protection at 690 VAC.
Watch our on-demand webinar and listen in as UL and Eaton's Bussmann division experts delve further into some of the most common misapplications of components within the panel.