UL 508A MANUAL MANUAL
UL 508A MANUAL CODE

If investigated for tap conductor protection in group motor installations, they can additionally be marked вЂњSuitable for Tap Conductor Protection in Group Installations.вЂќ The advantage of this marking is that the 1/10 th rule for tap conductor protection per NEC430.53 and UL 508A 31.4 then applies versus the 1/3 rd rule. Devices listed for use in group motor installations will be marked for such use to indicate that the device has undergone the appropriate testing to deem it suitable for such use. In group motor applications, other limitations such as horsepower ratings and tap rule restrictions (per NEC 430.53 or UL 508A 31.4 for Industrial Control Panels) must also be investigated. Some MMPs have been tested and listed for group motor applications so that several of them may be able to be protected by a single motor branch-circuit short-circuit and ground-fault protective device, such as an upstream fuse or circuit breaker sized not to exceed the maximum ampere rating allowed per the device listing.

UL 508A MANUAL MANUAL

Thus, per NEC430.109 and UL 508A 30.3.3, a motor branch-circuit short-circuit and ground-fault protective overcurrent device and branch-circuit disconnect are required on the line side of the MMP.ДЇigure 2: Examples of manual motor controllers (MMPs) Similarly, these devices do not have the creepage and clearance distances to be used as a motor branch-circuit disconnect. This is because their creepage and clearance distances are typically not sufficient as required by branch-circuit overcurrent devices such as UL 489 circuit breakers.

However, MMPs are not listed nor permitted to provide motor branch-circuit short-circuit and ground fault protection per NEC430.52. If marked вЂњSuitable as Motor DisconnectвЂќ MMPs are permitted to serve as an вЂњat the motorвЂќ disconnect per NEC 430.109, provided they are located between the final motor branch-circuit short-circuit and ground-fault protective device per 430.52 and the motor. MMPs may be also be used as a motor controller (ON-OFF Function) to meet NEC Article 430 Part VII. Manual motor controllers, sometimes called manual motor protectors (MMP), are permitted to provide motor overload protection as required per NEC 430.32. Combination motor starters would incorporate a circuit breaker or fused switch ahead of the motor starter to provide motor branch circuit short-circuit and ground fault protection. The objective of this article is to provide guidance to the reader to use the deviceвЂ™s instructions and markings to ensure proper application and marking when used in industrial control panels.ДЇigure 1: Traditional NEMA (left) and IEC (right) Motor Starters. As a field application engineer, the author finds these devices often misunderstood and misapplied.

UL 508A MANUAL CODE

This article covers important safety criteria based on Code and Standard requirements for the proper application of manual motor controllers and self-protected combination motor controllers. Hence, the question that results: is the device being applied as a manual motor controller or a self-protected combination motor controller? The answer is often unclear, which can complicate proper device application and equipment marking requirements for industrial control panel builders. However, if applied as a self-protected combination motor controller, typically the ratings are reduced and additional accessories and marking requirements are needed. On the other side of the device, the listing and ratings are shown when applied as a self-protected combination motor controller. On one side of the device, the listing and ratings are shown when applied as a manual motor controller. The confusion with these devices results from the fact that the same device can be dual-listed as both a manual motor controller and a self-protected combination motor controller. The advantage of these devices is the reduced cost and size when compared to traditional motor controllers and combination motor starters. Some of the most commonly used, but often misunderstood and misapplied devices in industrial control panels are manual motor controllers and self-protected combination motor controllers.

Ul 508a manual