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Basics of Safety SwitchesA quickSTEP Online Course

www.usa.siemens.com/step© Siemens industry, Inc.

© Siemens Industry, Inc. 2016

Trademarks

Siemens is a trademark of Siemens AG. Product names mentioned may be trademarks or registered trademarks of their respective companies.

National Electrical Code® and NEC® and NFPA 70® are registered trademarks of the National Fire Protection Association.

NEMA® is a registered trademark and service mark of the National Electrical Manufacturers Association.

UL® is a registered trademark of UL, LLC.

Other trademarks are the property of their respective owners.

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Course Topics

Welcome to Safety Switches. This course covers the following topics:Chapter 1 – Basic Concepts

• Introduction• Circuit Protection• Fuses• Enclosures

Chapter 2 – Siemens Safety Switches• Design and Ratings• Switch Types

Final ExamIf you do not have an understanding of basic electrical concepts, you should complete Basics of Electricity before attempting this course.

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Course Objectives

Upon completion of this course you will be able to…• Explain the difference between fusible and non-fusible safety switches• Explain the need for circuit protection• Identify fuse types and classes• Define common fuse ratings• Identify the types of Siemens safety switches• Explain the basic construction, operation, ratings, and benefits of Siemens safety

switches• Identify Siemens safety switch accessories

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Definition

A safety switch is a common type of enclosed switch. Safety switches are most commonly used as a disconnecting means for an electrical service or as a disconnecting means for an electric motor.

The enclosure provides a degree of protection to personnel against incidental contact with live electrical equipment. It also provides protection to the enclosed equipment against specific environmental conditions.

There are two families of Siemens safety switches, general duty and heavy duty.

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Application

NEC® Article 430.102 requires a disconnecting means for each motor controller and the disconnecting means must be within sight of the controller.

This disconnecting means can also serve as a disconnecting means for the motor if it is in sight of the motor and the machinery to which the motor is connected.

NEC® Article 430.102 includes an number of additional details and exceptions. Refer to the full article for details.

Various types of devices can serve as the disconnecting means for a motor, but safety switches are designed to reliably serve this purpose.

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Poles

The term poles refers to circuits that pass through a switch. The number of poles is the number of circuits that the switch can connect and disconnect.

The accompanying drawing, for example, shows a 3-pole safety switch. The three circuits are mechanically connected so that all three poles connect and disconnect the line and load simultaneously when the switch is operated. In the accompanying illustration, each pole has a fuse for overcurrent protection.

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Symbols

Symbols are used in a diagram to represent components. The symbols commonly used for a disconnect switch are shown in the accompanying graphic. The switch is normally shown in its "off" or "open" state.

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Throw

Throw is the term used to specify the number of circuits to which a conductor can be connected. All the examples shown so far have been for single throw switches. However, Siemens also offers double throw switches in both general duty non-fusible and heavy duty fusible and non-fusible designs.

Double throw switches are used to transfer loads from one power source to another or to connect a single power source to either of two loads. For example, the accompanying illustration shows 3-pole, non-fusible switches. For either of the two applications, no power is applied to a load with the switch in the center (Off) position, and only one set of contacts can be closed at a time.

In the diagram on the left, with the switch in the up position, the upper power source is connected to the load. With the switch in the down position, the lower power source is connected to the load.

In the diagram on the right, with the switch in the up position, the power source is connected to the upper load. With the switch in the down position, the power source is connected to the lower load.

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Fusible and Non-Fusible Safety Switches

As shown in the top illustration, a non-fusible safety switch has no circuit protection capability. It simply provides a convenient means to open and close a circuit. Opening the circuit disconnects the load from its source of electrical power, and closing the circuit connects the load.

Circuit protection must be provided by external overcurrent devices such as a circuit breaker or fuses and a motor protection device. In many cases, circuit protection is provided on both sides of the non-fusible switch. For example, circuit protection can be provided in a panelboard or switchboard that provides power to the switch and an overload relay can be located near the motor.

As shown in the bottom illustration, a safety switch can be combined with fuses in a single enclosure. This is referred to as a fusible safety switch. The switch provides a convenient means to manually open and close the circuit, and the fuses provides overcurrent protection.

Even when a fusible safety switch is used, additional circuit protection may be required to protect the load because the primary function of the safety switch’s internal fuses is to protect the wiring from damage due to overcurrent.

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Chapter 1 – Basic Concepts

This chapter covers the following topics:

• Introduction

• Circuit Protection

• Fuses

• Enclosures

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Overcurrent

Current flow in a conductor always generates heat. The greater the current flow, the hotter the conductor. Excess heat is damaging to electrical conductors. For that reason, conductors have a rated continuous current carrying capacity or ampacity. Current beyond the rated capability of a conductor is referred to as overcurrent. Overcurrent can result from a short circuit, an overload, or a ground fault. The first two types of overcurrent conditions are described in the following paragraphs.

A short circuit occurs when two bare conductors touch causing the resistance between the conductors to drop significantly. This reduction in resistance causes an immediate and destructive increase in current.

An overload is a typically a much lower current than a short circuit. An overload occurs when too many devices or the wrong type of devices are connected to a circuit or when electrical equipment is made to work beyond its rated capabilities.

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Short Circuits

When exposed conductors touch, a short circuit occurs, and the circuit resistance drops to nearly zero. Because of this very low resistance, short circuit current can be thousands of times higher than normal operating current.

Ohm’s Law shows the relationship of current, voltage, and resistance. For example, a 240 volt motor with 24 ohms of resistance would normally draw 10 amperes of current.

When a short circuit occurs, resistance drops dramatically. For example, if the above resistance dropped to 24 milliohms due to a short circuit, the current would increase to 10,000 amperes.

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Instantaneous Overcurrent Protection

When a short circuit occurs in an unprotected circuit, current continues to flow until the circuit is damaged or the power is removed manually. The peak short-circuit current of the first cycle is the greatest and is referred to as peak let-through current. The electromagnetic force associated with this current can cause mechanical damage to electrical components.

The maximum destructive energy let-through is a measure of the energy associated with this current. It is capable of producing enough heat to melt conductors.

A properly applied overcurrent protection device will instantaneously open the circuit, limiting peak let-through current (IP) and energy.

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Motor Overloads

In general, the greater the amount of overcurrent, the more quickly a circuit must be disconnected from its power source. Therefore, instantaneous overcurrent protection is essential when a short circuit occurs. Overloads, however, require a delayed response. To understand this better, consider the operation of a typical AC induction motor.

When most motors start, they draw current in excess of their full-load current rating. For example, a NEMA design B motor typically has a starting current of about six times its full-load current. For some high-efficiency motors, the starting current is even higher. Motors are designed to tolerate a high starting current for a short time. As a motor accelerates to operating speed, its current drops off quickly.

In the accompanying example, the motor’s starting current rises to 600% of full load current, but after eight seconds, current has dropped to the rated value. Depending on the size of the motor, the time required for the current to drop to the full load level or below may be shorter or longer. Whatever this time is, it is critical for the motor’s power circuit to be designed to handle this short-duration overload.

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NEC® Articles

Various NEC® articles discuss overcurrent protection. Some of the relevant articles are listed below.

• Article 210 covers branch circuits• Article 215 covers feeders supplying branch circuit loads• Article 230 covers service conductors and their control

and protection• Article 240 covers general requirements for overcurrent

protection and overcurrent protection devices (up to 600 volts)

• Article 430 covers motors, motor circuits, and controllers

It is beyond the scope of this course to cover this content, but it is useful to consider the intent of this information. In general, these articles are designed to ensure that conductors and overcurrent protection devices are properly sized for their loads and that overcurrent protection devices provide the appropriate level of protection for conductors in the event of an overcurrent.

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• Introduction


• Fuses

• Enclosures

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Fuses

Most fuses are one-shot devices. When a fault occurs, the fuse element melts and opens the path for current, interrupting the fault. The time it takes for a fuse to interrupt the fault is called the clearing time, which includes the time it takes for the fuse element to melt plus the time it takes to extinguish the arc of current across the melting element.

The clearing time for a fuse is inversely related to the level of fault current over a fuse’s designed range. This means that the fuse clearing time is less for a higher level of fault current than for a lower level of fault current.

Many fuses used in power distribution systems are current limiting. There are various factors required to classify a circuit protection device as current limiting, but essentially it means that, as shown in the accompanying graphic, a current limiting fuse significantly reduces the peak let-thru current when a fault occurs. The intent is prevent damage to conductors and protected equipment by reducing the electrical energy applied to the conductors and load.

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Fuse Types

There are various types of fuses used in power distribution systems. Three common types are shown in the accompanying list.

Fast-acting fuses open quickly when an overcurrent occurs. For this reason, they are used to provide short circuit protection for non-inductive loads. As such, they are not suitable for use with motors and other inductive loads.

Time-delay fuses provide a delayed response to allow temporary overloads to clear. Because the amount of delay required varies with the load characteristics, fuses are available to fit the full range of load requirements. Because time-delay fuses provide both short circuit and overload protection, they are used in a wide range of applications.

Dual-element fuses may have time-delay designation because these fuses have two fuse elements. One element provides overload protection with time delay. (UL states that time delay means having a 10-second operating delay at 500% of the fuse label rating.) The second element provides short circuit protection similar to a single-element fuse. Dual-element fuses are most frequently used on motor loads.

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Fast-Acting Fuse

Time-Delay Fuse

Dual Element Fuse


Fuse Ratings

Because application requirement vary, fuses are available with a wide range of characteristics. In addition to size, mechanical design, and element type, the ratings shown in the accompanying list must be considered when choosing a fuse for an application.

The voltage rating of a fuse must be at least equal to the circuit voltage. The voltage rating of a fuse can be higher than the circuit voltage, but never lower. A 600 volt fuse, for example, could be used in a 480 volt circuit, but a 240 volt fuse should not be used in a 480 volt circuit.

The current rating, also called ampere rating, of a fuse is its continuous current-carrying capacity. The current rating of fuse must match the requirements of the load and associated conductors.

The interrupting rating of a fuse is the maximum current that the fuse can safety interrupt. The interrupting rating required must be at least equal to the the level of fault current available for the circuit.

For additional information on fuse selection, refer to the previously listed articles in the NEC®.

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Voltage Rating

Current Rating

Interrupting Rating


Low Voltage Fuse Classes

Underwriters Laboratories (UL) establishes and standardizes basic performance and physical specifications for products that undergo its safety test procedures. Among the standards developed by UL are standards for classes of low voltage fuses (fuses with voltage ratings of 600 volts or less).

Fuses are grouped into classes based on their operating and construction characteristics and ratings. When selecting fuses, it is a good idea to refer to the fuse manufacturer’s application data to make sure that a specific fuse is appropriate for the fault characteristics and types of loads involved.

The accompanying graphic shows the most commonly used low voltage fuse classes for safety switches. Siemens general duty switches use fuses in classes H,K, R, and T. Siemens heavy duty switches use fuses in classes H, J, K, L, R, and T.

The accompanying graphic also shows fuse kits required for class R fuses. A class R fuse kit prevents the use of lower rated H and K fuses.

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• Introduction


• Fuses

• Enclosures

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Enclosures

For the purpose of this course, an enclosure is the case that houses the components of an electrical device. The function of the enclosure is to prevent someone from accidentally touching an internal component that may have voltage applied and to protect internal components from damage.

Various standards describe enclosure types. One of the more frequently cited standards is NEMA standard 250. In addition to NEMA standard 250, published by National Electrical Manufacturers Association, UL 50 and UL 508, published by Underwriters Laboratories Inc., are also important standards for electrical equipment enclosures. These standards provide enclosure descriptions, features, and test criteria for hazardous and nonhazardous locations.

The following brief descriptions cover enclosures available for Siemens safety switches. Within the industry, it is common to refer to the enclosure type numbers as NEMA types, but these type numbers also apply to UL 50 and UL 508.

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Type 1 Enclosures

Type 1 enclosures are intended for indoor use primarily to provide protection against limited amounts of falling dirt and contact with the enclosed equipment in locations where unusual service conditions do not exist.

Siemens type 1 safety switch enclosures have the following features:

• Tangential knockouts in all box surfaces (30-600A heavy duty and 60-600A general duty)

• Two- and three-point mounting with top keyhole• Formed flange enclosure edges• 180º plus side opening door• Drawn cover design for increased durability and

resistance to damage (30-600A)• Rugged metal handle with a red insulating grip• Front operable cover interlock release with positive

rotating• release action (30-1200A heavy duty and 60-600A

general duty)• Metal nameplates on all heavy duty switches

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Type 3R Enclosures

Type 3R enclosures are intended for outdoor use primarily to provide a degree of protection against falling rain and sleet. They are not intended to provide protection against conditions such as dust, internal condensation, or internal icing.

Siemens type 3R safety switch enclosures have the following features:

• Tangential knockouts in all box surfaces below lowest live parts (30-600A)

• Two- and three-point mounting with top keyhole• Formed flange enclosure edges• 180º plus side opening door• Double overlap enclosure door top to provide superior protection

against entry of rain• Type HA hub provision 30A general duty• Type HS hub provision (30-200A switches)• Galvanized steel construction • Drawn cover design for increased durability and resistance to

damage (30-200A)• Rugged metal handle with a red insulating grip• Front operable cover interlock release with positive rotating release

action (30-1200A heavy duty and 60-600A general duty)• Metal nameplates on all heavy duty switches

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Type 4/4X Enclosures

Type 4/4X enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against windblown dust, rain, splashing water and hose-directed water. They are not intended to provide protection against conditions such as internal condensation or internal icing. This enclosure type meets the 4X definition by providing a high degree of protection against corrosion.

Siemens type 4/4X safety switch enclosures have the following features:

• Ground lugs installed as standard• External mounting feet with two-, three- and four-point mounting• Formed front gasket flange with continuously welded seams• Heavy duty, front-opening, low-profile stainless steel latches• Stainless steel enclosure• Stainless steel interior parts on 30-200A switches• Formed-out enclosure flanges that prevent liquid entry when door is

open• Rugged hinge design• 180º-plus opening door• Rugged metal handle with a red insulating grip• Front operable cover interlock release with positive rotating release

action (30-1200A heavy duty)• Stainless steel nameplate

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Non-metallic 4X Enclosures

A non-metallic 4X enclosure made of fiberglass-reinforced polyester and has no external metal parts.

Siemens non-metallic 4X safety switch enclosures have the following features:

• External mounting• Ground lug installed as standard• Fiberglass reinforced polyester enclosure• No external metal parts• Removable door for easy wiring• Front operable cover interlock release with positive

rotating release action

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Type 3R/12 Enclosures

Type 3R/3S enclosures are intended to provide a degree of protection against windblown dust and to allow operation when ice-laden. They are not intended to provide protection against conditions such as condensation or internal icing.

Type 12 enclosures provide a degree of protection against dust, falling dirt, and dripping water in indoor locations, but are not intended to protect against conditions such as internal condensation.

Siemens type 3R/12 safety switch enclosures have the following features:• External mounting feet with two, three and four-point mounting• Formed front gasket flange• Unique heavy duty, front-opening, low-profile latches• Galvanized steel enclosure• Formed out enclosure flanges that provide an added degree of

protection against entry of dust• Rugged hinge design• 180º-plus opening door• 3R/3S/12 rating as standard allows outdoor use• Rugged metal handle with a red insulating grip• Front operable cover interlock release with positive rotating release

action (30-1200A heavy duty)• Metal nameplates on Type 3S/12 enclosures

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Type 7 and 9 Enclosures

Type 7 enclosures are intended for indoor use in locations classified as Class I, Groups A, B, C, or D, as defined in the NEC.

Type 9 enclosures are intended for indoor use in locations classified as Class II, Groups E, F, or G, as defined in the NEC.

Siemens type 7 and 9 safety switch enclosures have the following features:

• Molded case switch available in 30-600A ratings• Cast aluminum enclosure• External door clamps• External mounting feet• Metal nameplate

Articles 500 through 504 of the NEC® cover the use of electrical equipment in locations where fire or explosions due to gas, flammable liquids, combustible dust, or ignitable fibers may be possible. The accompanying graphic summarizes the materials that are found in Class I and II locations. Refer to the NEC® for additional information.

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Chapter 2 – Siemens Safety Switches


• Design and Ratings

• Switch Types

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Switch Design

A Siemens VBII safety switch enclosure houses the switch mechanism, wire connectors, and an operating mechanism.

A handle, connected to the operating mechanism, opens and closes the visible blade contacts.

If the switch is fusible, the enclosure also houses the fuse clips.

Provisions for locking the door and/or switch handle are also provided.

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Knife Blade Switch Principle

Switches use contacts to break the circuit and stop the flowof current. A typical switch assembly consists of a stationary contact, a hinged movable contact, and an operating handle. The hinged movable contact may also be referred to as a knife blade. If the movable contact is not touching the stationary contact, no current flows.

Moving the handle to the "on" position closes the contacts and provides a complete path for current to flow from the power supply to the load.

Moving the handle to the "off" position opens the contacts, interrupting the flow of electricity. As the contacts start to open, current continues to flow across the air gap between the two contacts in the form of an arc. Current continues to flow until the physical distance between the contacts is great enough to interrupt the flow of current.

The point at which the arc is extinguished is called the break distance.

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VBII Safety Switch Design

Unlike the knife-blade switch, the switching action of Siemens 30 to 200 amp VBII safety switches breaks the arc in two places, creating two smaller arcs and reducing the heat generated. Switching speed is also increased because the breaking distance is effectively doubled. The overall result is enhanced performance and increased longevity.

Also, in contrast to the knife blade switch, VBII safety switch blades are self-aligning, ensuring positive contact. Furthermore, the electrical hinge, a wear and friction point, has been eliminated resulting in fast, positive, and reliable switching action.

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Over-center-toggle Switch Action

Another feature which enhances the speed of switching is the over-center-toggle design. During operation of the switch, as the handle is moved past the midpoint, the switch suddenly and rapidly snaps from off to on or from on to off, depending upon the direction of movement of the handle. Besides enhancing the switching speed, this also gives a positive feel to the switch operation.

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Defeatable Cover Interlock

The VBII safety switch cover interlock prevents someone from opening the door while the switch is in the "on" position. Normally, the interlock also prevents someone from turning the switch on with the door open. However, for the purposes of testing or servicing, the door interlock is defeatable. As shown in the accompanying illustration, this can be done with an ordinary screwdriver.

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VBII Safety Switch Types

The following types of Siemens VBII safety switches are available:

• General duty switches• Heavy duty switches• Double throw switches

General duty switches are intended for applications where reliable performance and continuity of service are needed, but where duty requirements are not severe and no usualservice conditions are present.

Heavy duty switches have a rugged construction that enables reliable performance and continuity of service in a broad range of single throw applications.

Double throw switches are intended to transfer a load from one power source to another or to connect one power source to either of two loads.

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Switch Ratings

All Siemens safety switches have voltage, ampere, and short circuit withstand ratings and are load break and, where appropriate, horsepower rated. Siemens fusible safety switches, when used with designated fuses, also have an interrupting rating.

The voltage rating is the maximum voltage that a switch is designed for. The applied voltage can be less than the voltage rating, but not more. Switches have both AC and DC voltage ratings.

The ampere rating is the maximum continuous current that a switch is designed to carry.

The short circuit withstand rating is maximum short-circuit current that a safety switch can carry for a short time.

The interrupting rating is the maximum current that a fusible switch can safely interrupt with the fuses designated for that that switch.

Load break and horsepower ratings are assigned based on successful completion of the UL testing sequences shown in the accompanying tables.

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Chapter 2 – Siemens Safety Switches


• Design and Ratings

• Switch Types

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VBII General Duty Safety Switches

VBII general duty safety switches are intended for use primarily on power supplies rated at 240 VAC or less, where the available fault current is 100 kA max. (with Class J, R, or T fuses) or 10 kA max. (with Class H fuses). They can be supplied in a Type 1 (indoor) or Type 3R (outdoor) enclosure.

Fusible general-duty safety switches are available with two or three poles (both with solid neutral). Non-fusible general duty safety switches are available with two or three poles. All general duty switches have both cover and handle padlocking capabilities.

General duty plug fuse type switches (not shown) are available for 120/240 or 240 volt applications. 1-pole and 2-pole versions are available are rated at 30 A. A separately supplied, 30 A Type S plug fuse is required. A 2-pole non-fusible version is also available and is rated at 60 A.

Ampere ratings: 30, 60, 100, 200, 400, 600 AVoltage ratings: 240 VAC/250 VDCFusible switches will accept the following UL class fuses:• 30A “LF” - 30A max plug fuses• 30-600A “GF” Class H or K standard• 30-600A “GF” Class R with kit• 100-600A “GF” Class J - move base• 100-200A “GF” Class T with kit• 400-600A “GF” Class T - move bases

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VBII Heavy Duty Safety Switches

Heavy duty safety switches are intended for use in applications where one or more of the following conditions apply:1. Rugged construction, reliable performance, continuity of service and ease

of maintenance are emphasized.2. Available fault currents higher than 10,000 A are likely to be encountered,

such as in manufacturing plants, mass production industries, and commercial, institutional and other large buildings served by network systems or transformers of higher capacities.

3. System voltage is 600V AC or DC max.4. Type 12 or 4/4X enclosure is required.

Ampere ratings: 30, 60, 100, 200, 400, 600, 800, 1200 AVoltage ratings: 240, 480, 600 VAC; 250, 600 VDCFusible switches will accept the following UL class fuses:• 30-600 A “HF” Class H or K Standard• 30-600 A “HF” Class R with kit• 30-200 A “HF” Class J - move base• 100-200 A “HF” Class T with kit• 400 A and 600 A “HF” Class R with kit• 400 A and 600 A “HF” Class T with kit• 400A (new design) “HF” Class J - move base (no kit required)• 600 A, 240 V “HF” , Class J - move base to 600 V position and install kit• 600 A, 600 V , Class J with kit• 800-1200 A “HF” Class L or Class T with kit

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VBII Heavy Duty Safety Switch Enclosures

Siemens offers a broad selection of heavy duty safety switches with Type 1 or 3R enclosures. Selected heavy duty safety switches are also available with other enclosure types such as Types 4/4X stainless steel with viewing window, Type 4X non-metallic, and Type 12 with viewing window.

Siemens safety switches with a window for viewing visible blade position and Type 4/4X stainless steel or Type 12 enclosures are available with 30 to 400 A ratings. The window also allows viewing of indicating fuses for 30 to 200 A fusible switches.

Siemens heavy duty safety switches are also available in 30 to 200 A ratings with 316 grade stainless steel Type 4/4X enclosures with or without a viewing window. These enclosures are more corrosion resistant than the standard 304 grade stainless steel enclosures. Type 316 stainless steel enclosures are especially suited for environments containing a high level of chlorine or other chemicals commonly encountered in marine, waste management, food and beverage, petrochemical, and mining applications.

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Interlock Receptacle Safety Switches

Interlock receptacle safety switches provide a receptacle for powering heavy-duty portable equipment such as refrigerated trucks, welders, and other portable electric tools.

These switches are fitted with a Pyle National or similar receptacle which is interlocked to prevent insertion or removal of the plug when the switch is in the "on" position. The receptacleprevents operation of switch if an incorrect plug is inserted.

Interlock receptacle safety switches are rated for 30, 60, and 100 amperes. These switches are available with Type 12 or 4/4X enclosures.

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VBII 4-Pole and 6-Pole Safety Switches

VBII 4-pole and 6-pole heavy-duty fusible and non-fusible safety switches are available with current ratings of 30 to 200 amperes. 4-pole switches are available with either a Type 1 or Type 12/3R enclosure. 6-pole switches are available with either a Type 12/3R or Type 4X stainless steel enclosure.

These switches are commonly used as a disconnecting means for 2-speed, 2-winding motors. A 4-pole switch is also used in 3-phase, 4-wire circuits when a switching neutral is required.

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Enclosed Photovoltaic Disconnect Switches

Solar disconnect switches are designed for use in DC photovoltaic power generation circuits. These circuits are defined by article 690 of the NEC® which requires the grounded conductor to be at ground potential at all times, preventing it from being switched.

Siemens solar disconnect switches incorporate powerful magnets that assist the double break switching action that quickly dissipates the very hot arcs generated when a 600 VDC circuit is opened under load.

30-200 A, 600 VDC fusible and non–fusible switches are available in Type 1 and 3R enclosures. They are provided with an additional door-mounted warning label as required by the NEC and are supplied with a factory-installed equipment ground bar. They are built to UL98 requirements but are UL listed in file number E335018 as UL1741 photovoltaic disconnect switches. These 3-pole switches are approved to switch three separate 600 VDC circuits. The design incorporates many of the standard VBII switch features.

400-600 A, 600 VDC fusible and non–fusible switches are available in a Type 3R enclosure and are UL98B listed.

200 A, 1000 VDC fusible switches are available Type 1 and 3R enclosures and are UL98B listed.

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Double Throw Switches

Heavy duty, double throw, non-fusible switches are available with current ratings of 30 to 1200 amps. General duty, double throw, non-fusible switches are available with current ratings of 100 or 200 amps. Most products are available with a Type 1 or Type 3R enclosure. A few versions are available with a Type 12/3R or Type 4X enclosure.

Double throw switches are used to connect a single power source to either of two loads or to transfer loads from one power source to another.

For example, a critical piece of equipment often needs a back-up power supply in case the main power supply fails or needs maintenance.

In the accompanying example, a motor can be connected through a double throw switch to power supply A or power supply B. When the handle is in the center position the switch is off and no power flows to the motor. Moving the handle to the up position connects the motor to power supply A. Moving the handle to the down position connects the motor to power supply B.

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Safety Switch Accessories

Some of the accessories available for Siemens VBII safety switches are shown in the accompanying illustration.

Heavy duty switches are UL approved to accept copper lug kits. Equipment ground kits are available for general duty and heavy duty switches. Isolated ground kits are also available for 30 to 600 A heavy duty switches. Some circuits with a high degree of computer or other electronic loading require an isolated ground to prevent interference from the building ground and neutral lines.

Auxiliary contacts are available only for heavy duty switches. They come with one normally open and one normally closed or two normally open and two normally closed contacts. A PLC auxiliary switch for 30 to 200 A switches is also available. It has very low contact resistance, which is compatible with PLC circuits.

Fuse puller kits are field installable in 30 to 100 A heavy duty switches.

Class R fuse clips are used to prevent the installation of noncurrent-limiting Class H or Class K fuses. All general and 30 to 600 A heavy duty switches are field convertible to accept Class R fuse clip kits. Page 2-18


VBII Safety Switch Catalog Numbers

Each VBII safety switch has a catalog number. The catalog number provides a description of the safety switch. There are nine parts to the catalog number for a Siemens VBII safety switch.

For example, as the accompanying chart shows, a switch with the catalog number HF364NRCUA has the following characteristics:

• Switch Type: Heavy Duty• Fused or Non-fused: Fused• Number of Poles: 3• Voltage Rating: 600V• Ampere Rating: 200A• Neutral: With Neutral• Enclosure Type: 3R• Special Application with: Factory-installed

Copper Lugs• Series Type: 400A, 600A

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VBII Safety Switch Accessories Catalog Numbers

Each type of safety switch accessory has a catalog number. The catalog number provides a description of the accessory. There are five parts to the catalog number for a Siemens VBII safety switch.

For example, as the accompanying chart shows, an accessory with the catalog number HR64NA has the following characteristics:

• Switch Type: Heavy Duty• Accessory Type: Class R – Fuse Clip Kit• Voltage Rating: 600V• Ampere Rating: 200A• Series Type: 400A, 600A

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Simulators

Engineered to provide a real-world experience, Siemens simulators are fully functional, ready-to-use systemsavailable in a variety of configurations.

System-level design makes the simulators an invaluable tool for program testing and debugging, reinforcing learning, shop floor troubleshooting, and more. With portable construction and hard-shell cases, they can be easily transported. Custom-built systems are also available.


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SITRAIN® Training for Industry

Online Self-paced Learning – Programs with maximum flexibility so students can easily fit courses into their busy schedules

Virtual Instructor-led Learning - Classroom lectures delivered in the convenience of your home or office

Classroom Learning - Expert and professional instructors, proven courseware, and quality workstations combine for the most effective classroom experience possible at your facility or ours

How-to Video Library - Quick, affordable, task-based learning options for a broad range of automation topics for training or purchase

Simulators - World-class simulation systems available for training or purchase


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SITRAIN World

From the basics to advanced specialist skills, Siemens SITRAIN courses deliver extensive expertise directly from the manufacturer and encompass the entire spectrum of Siemens Industry products and systems.

Worldwide, SITRAIN courses are available in over 200 locations in over 60 countries.

For additional information including a SITRAIN world map and SITRAIN contacts worldwide: http://sitrain.automation.siemens.com/sitrainworld/Default.aspx

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Course Completion

This course covered the following topics:

Chapter 1 – Basic Concepts• Introduction• Circuit Protection• Fuses• Enclosures

Chapter 2 – Siemens Safety Switches• Design and Ratings• Switch Types

This course has covered the topics shown on the left. Thank you for your efforts. You can complete this course by taking the final exam and scoring at least 70%.

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