Siemens Circuit Breaker Expands Design Possibilities

Siemens 3VA Molded Case Circuit Breakers

A circuit breaker such as the Siemens new 3VA molded case circuit breaker line is an essential piece of safety equipment that protects critical infrastructure from the harmful effects of short circuits and overloads.

MCCBs rank among the most important safety components in low voltage power distribution.  An estimated 30 million MCCBs are installed each year around the globe.

Siemens 3VA5 molded case circuit breaker.

The new UL-certified series of 3VA molded case circuit breakers from Siemens was designed for low-voltage power distribution in buildings, infrastructure, and industrial applications. But the line was not just designed to protect devices today, but to grow as applications demand and needs change.

Siemens 3va electrical circuit breaker line is built around a modular concept with a variety of models and accessories.

Steiner Electric has placed in inventory Siemens 3VA products that meets the needs of Chicago-area contractors, electricians, MROs, OEM personnel and more.

The 3VA Family

This wide-ranging list of devices include multiple circuit breaker types, auxiliary switches and alarms, a variety of trip options, and the lugs and wire connectors that keep it all together.

 

Siemens 3VA5 circuit breakers are available in 125 A and 250 A
Siemens 3VA5 circuit breakers are available in 125 A and 250 A frames with a variety of options for each.

Steiner offers these breaker boxes based on two Siemens 3VA5 frame families.

  • The 125 A frame is a 3-pole breaker box with 25 kA @ 480 V interruption rating that come in models that trip at 15 A, 20 A, 50 A, 100 A, and 125 A.
  • The 250 A frame has a 35kA @480 V interruption rating, and trip circuits are rated at 150 A, 200 A, 225 A, and 250 A.

Both devices require minimum space because of their compact design. The footprint for the 3VA5 125 A frame model is 3 in. by 3.8 x 5.5 in. and the footprint for the 250 A frame is 4.13 in. x 4.21 x 7.28 in.

Safe Tripping

For safe operation, the 3VA5 Siemens circuit breakers are based on the concept of thermal magnetic trip units (TMTUs). These TMTUs are two separate tripping mechanisms – thermal and magnetic—that are built into the same device.

In a thermal-magnetic circuit breaker, the trip unit includes elements designed to sense the heat resulting from an overload condition and the high current resulting from a short circuit.

The thermal safety component works on thermal inverse-time, meaning the higher the current, the faster the breaker trips. The thermal element is a bimetallic strip, which means it has two different metals bonded together that have different thermal expansion characteristics. As that strip warms up, the thermal differences cause the metals to twist and bend and eventually contact a trip bar causing the contacts to spring open.

The second safety component is the magnetic trip. The circuit breaker has a trip unit that senses a magnetic field generated by current to detect a short circuit. This type of circuit breaker trips immediately when a short circuit occurs, but delays an appropriate amount of time before tripping in the event of an overload.

Array of Design Options

Steiner offers a wide range of Siemens’ internal accessories that can fit in any of the 3VA products. They can be adapted flexibly, quickly and easily to individual specifications. Color coded for simple installation process, they are designed to always be installed at the correct position in the circuit breaker.

A door mounted rotary operator. Just one of the many options available from Steiner.
A door mounted rotary operator. Just one of the many options available from Steiner.

Accessories include multiple operator options, including door mounted rotary operators that come either with illumination, which provides a clear indication of the switching position, and without an illuminating kit.

Also available is the Max Flex flange mount operating system that allows the user to locate the circuit breaker almost anywhere within an enclosure. It uses a flexible cable that connects to a breaker operator mechanism and a handle located on the enclosure’s flange.

Also available are auxiliary and alarm switches that can be integrated with all sizes of Siemens breakers. The switches snap for easy installation and to swap out as needs change.

3VA9, UL, UVR undervoltage release
The Siemens 3VA9, undervoltage release switch.

Auxiliary switches can be used to operate indicator lights, relays or other accessories to provide the breaker’s status. Alarm switches indicate that the circuit breaker has tripped due to an overload, short circuit or ground fault. A shunt trip will trip a breaker remotely, and an under voltage trip release will activate when voltage shuts off or dips.

So, when looking to install new or replacement breakers, consider the 3VA5 products that offer myriad design possibilities.

Applications of Switchgear and Switchboards

switchgear vs switchboard

The terms “switchboard” and “switchgear” are interchangeable to engineers and architects. While they are in fact, interchangeable, they do both have distinct differences that are worth noting. These differences include configurations, components, reliability, standards and applications.

One of the major differences between switchboards and switchgear is the type of breakers that are used. The basic types are sealed, semi-open and open types. Specifically, these are called molded case, insulated case and power circuit breakers.

Molded case circuit breakers (MCCBs) are often used in all types of low-voltage switchboards and panelboards. These breakers can be found in ratings from 15 amps to 3,000 amps.

SQD JDL36200
Molded Case Circuit Breaker – MCCB

The breaker mechanism is sealed inside of the external molded case. If the breaker has a failure then it is to be replaced. These breakers are typically bolted onto the bus, or may have plug-in designs. The removal or addition of MCCBs to a switchboard must ONLY occur when the switchboard is turned off.

Power circuit breakers have ratings that range from 800 amps to 5,000 amps. PCBs are tested with different standards from MCCBs or ICCBs. They are attached to the bus in a drawout design, which allows the breakers to be withdrawn partially or fully while the entire switchgear is powered on. They have various components that are inspected and replaced. These components include arc chutes, contacts and pole assemblies.

To understand the differences between Switchboards and Switchgear, we will need to look at several variable considerations – Maintainability, Economics, System Coordination, Size and Project Application.

(Note: this article will cover circuit breaker type switchboards as compared to switchgear, and though some engineers may have a preference for fusible switchboards, this would get into fuses vs. circuit breakers, a topic for another discussion)

MAINTAINABILITY

Switchgear has the type of maintainable steel frame breakers which you are able to draw out. Switchgear also has mechanisms that draw out or rack out on racking arms. The main reason to use switchgear over switchboards is due to the ease of maintenance. Switchgear is more maintainable – this is due to the breakers that are used. Air circuit breakers are used in switchgear and insulated or molded case breakers are used in switchboards.

Switchgear incorporates low voltage power circuit breakers – abbreviated to LVPCB. Steel framed LVPCB’s have heavy-duty metal frames that are designed for ease of maintenance.

On the other hand, plastic-enclosed breakers must be disassembled to access the operating mechanisms, which makes it more complicated to maintain. In addition to this, plastic-enclosed breakers – if not requiring disassembling, would need to be unsealed to get to the internal components.

ECONOMICS

As in other applications, the economics are an important area to focus on. In many instances the initial factor that a potential customer or buyer reviews is the installed cost.

Group mounted switchboards tend to be less costly, while the individually mounted switchboards are about 15 to 50% more than group mounted switchboards. This all depends on the number and type of devices that are required. Typically, you will find that switchgear is more expensive than individually mounted switchboards.

SYSTEM COORDINATION

LVPCB’s don’t need an instantaneous trip function to be built in. Main and feeder breakers, likewise can be built without the instantaneous trip function.

Without it, main, feeders and other downstream devices are able to be more freely coordinated. Switchgear is more sophisticated in its trip functionality than switchboard breakers. This allows for a higher degree of coordination.

Circuit Breaker Maintenance
Circuit Breaker Basics

 SIZE

Another important consideration is the size. Switchgear is larger because of the rear access that is necessary for cable terminations, while switchboard construction is smaller and usually requires front access because of the group mounted circuit breaker arrangement.

Some applications are restricted in space, thus, a group-mounted switchboard is the only option. If the equipment needs to be against the wall, thereby eliminating the option for rear access, then the only alternative is group-mounted switchboards that allow for front-accessible terminations.

Group mounted switchboards require the use of molded case breakers as feeders. Because of this, the density can be greater and the overall width would be less. Applications that require higher levels of reliability, maintainability or remote operation need to be designed to allow for rear access of that gear.

PROJECT APPLICATION

Some projects require the use of switchgear, while other projects would be better suited with switchboards. An example of this is schools and the healthcare industry. Power to a school would not be as critical as that to a hospital.

The ability to precisely coordinate breakers allows for enhanced power integrity, thus preventing nuisance trips, resulting in reduced outages. For instance, hospitals require more reliable and dependable power due to the urgency of the industry, since lives are involved and operating tables are used.

operating tables
Power is essential for Hospitals

A switchboard that has a size and cost advantage is suited well for a school, while the switchgear may be better for the hospital. In either case, it would be beneficial to look at the location or project and determine what would be the best option on a case-by-case basis.

 

The Circuit Breaker

A circuit breaker is one of the most important safety devices in your home, but most people don’t give them much thought until their lights go off or they can’t watch TV because the breaker has tripped.  When the electrical wiring in a building has too much current flowing through it, the breaker cuts the power.

But do you know how old the circuit breaker is?

Circuit Breaker Steiner Electric Continue reading “The Circuit Breaker”