Compact impact

Compact impact

The DS301C single-phase and neutral, voltage-independent, residual-current circuit breaker with overcurrent protection (RCBO), protects against short-circuits, overloads and earth faults. This single-module device eases congestion and simplifies installation in low-voltage panel boards →01.

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Jorge Bonilla, Carlos Amado Najera, David Ichaso Iñigo ABB Electrification, Smart Buildings, Madrid, Spain, jorgejuan.bonillahernandez@es.abb.com, carlos.amadonajera@es.abb.com, david.ichaso@es.abb.com;  
Massimiliano Amato, Luca Ghezzi ABB Electrification, Smart Buildings, Milan, Italy, massimiliano.amato@it.abb.com, luca.ghezzi@it.abb.com; 
Jean-Philippe Garzon ABB Electrification, Smart Buildings, Bagnères-de-Bigorre, France, jean-philippe.garzon@fr.abb.com

Driven by the desire for more capillary control and increased safety, the number of branches in low-voltage electrical installations – and the quantity and type of circuit breaker found there – is undergoing profound change. This rapid evolution means more electrical devices must be accommodated into electrical panelboards. This poses a major miniaturization challenge to circuit-breaker manufacturers like ABB. The trend mostly concerns final distribution lines, usually hosting loads supplied by one phase and the neutral conductor.

01 The DS301C, ABB’s new single-module, voltage-independent RCBO.
01 The DS301C, ABB’s new single-module, voltage-independent RCBO.
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This context explains the remarkable market acclaim for ABB’s newly released DS301C. The DS301C is an extremely compact, one-phase and neutral RCBO that combines protection against short-circuit, overload and earth fault – all in a single circuit breaker just one module wide, as opposed to the two-module width of current approaches. Crucially, the breaker is voltage-independent – ie, it works without an external power source.

Space savings through targeted specification
To allow space optimization, the electrical ratings of the DS301C have been precisely matched to the targeted applications – for example, residential, commercial, marine and railway installations. The DS301C is characterized by a rated current of up to 20 A, a more-than-respectable short-circuit capacity of 6 kA, and – for earth faults – the classic maximum residual current of 30 mA. The DS301C not only detects current leakages with sinusoidal waveforms but also the truncated or distorted waveforms associated with electronic appliances, such as LED lights, computers, etc. A compact product like the DS301C allows panels to be more compact, too – a benefit greatly appreciated when extending or retrofitting electrical installations in hospitals, boats, trains, etc.

The inside story
One side of the DS301C accommodates the phase and the other, the neutral conductor →02. Overcurrent protection – ie, short-circuit and overload – is arranged on the phase side. Short-circuits are detected by a trip coil, where the strong magnetic field produced by the several kA of the short-circuit current moves a ferromagnet to trigger the trip quickly. A bimetallic strip bends due to the overheating induced by overloads (which are less sudden than short circuits), thus triggering the trip.

02 The DS301C interior. All components have been miniaturized and thoughtfully located in the small available space. 02a Neutral side with earth-fault sensor and actuator. 02b Phase side with short-circuit and overload sensors and actuation, along with current switching means and the circuit devoted to earth-fault processing.
02 The DS301C interior. All components have been miniaturized and thoughtfully located in the small available space. 02a Neutral side with earth-fault sensor and actuator. 02b Phase side with short-circuit and overload sensors and actuation, along with current switching means and the circuit devoted to earth-fault processing.
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On the neutral side of the device, if an earth fault occurs, the current leakage to ground induces an imbalance between phase and neutral currents. A differential transformer detects this disparity and feeds a small circuit board where the signal is filtered to prevent unwanted trips due to surges, for example. A sensitive relay collects the output and triggers the trip.

To meet the demanding size requirements, earth-fault protection and the bulkiest components are accommodated across the two halves of the breaker.

A toggle-operated mechanism controls the position of moving contacts that are tripped under the action of the actuators. The patent-pending structure of the mechanism relies on two connected and interacting subparts: Arc extinguishment in an arc chamber finishes the current switch-off process on the phase conductor to complete the disconnection of the faulty branch from the upstream mains, while the neutral conductor is interrupted without the help of an arc chamber.

Earth-fault protection
Earth-fault protection is a particularly important aspect of the device’s performance as just a few milliamperes leaking to ground through a person can be lethal.

Remarkably, for the compactness achieved, earth faults are addressed with so-called voltage-independent (VI) technology. In VI devices, the earth-fault sensing and subsequent actuation use only the (very small) energy of the earth fault; no external supply is required. Despite the challenges of miniaturizing VI RCBOs, the DS301C is as compact as an electronic RCBO, which depends on the availability of a voltage difference between phase and neutral for power. This dependency means electronic RCBOs are not operational if the neutral conductor is interrupted upstream and someone is touching the phase downstream. In contrast, this type of potentially lethal earth fault is protected against by the DS301C.

High-resolution selectivity
A reference installation with 18 branches serves to highlight the DS301C’s advantages →03.

03 A reference installation with 18 branches. 03a Traditional solution with three DIN rails, each hosting one RCCB and six MCBs. 03b Three DIN rails hosting six RCBOs each. 03c The compact DS310C solution.
03 A reference installation with 18 branches. 03a Traditional solution with three DIN rails, each hosting one RCCB and six MCBs. 03b Three DIN rails hosting six RCBOs each. 03c The compact DS310C solution.
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A traditional solution has the 18 branches grouped into three sets of six. In each set, the six branches are protected against earth faults by a single residual current circuit breaker (RCCB), which is at least two modules wide, and against short-circuits and overloads by six miniature circuit breakers (MCBs), each a module wide →03a. Not infrequently with this approach, earth-fault protection is addressed by a three-phase RCCB that takes up four modules, as in →03a, and only then do the three phases separate into a maximum of six branches (two per phase, as allowed by the relevant standards) that are individually protected by single-phase MCBs. Three DIN rails are required to mount this equipment. In this arrangement, an earth fault in one branch trips the associated RCCB, taking out the five healthy branches in the set, too.

Fault protection selectivity is highly important in any electrical installation, especially when service continuity is essential. An alternative conventional approach would be to use 18 two-module RCBOs, each protecting a single branch →03b. Here, earth-fault, short-circuit and overload protection is selective for each branch, but three DIN rails are still needed.

Due to the half-width size of the DS301C solution, 18 RCBOs now occupy only one-and-a-half DIN rails while still delivering selective earth-fault, short-circuit and overload protection to each branch →03c.

Fast and easy installation
Speedy and straightforward installation was a cornerstone of the DS301C design philosophy in order to shorten installation time and make the process error-proof.

Either flexible cables or rigid busbars may be used to wire the circuit breaker. Additionally, the DS301C comes in versions compatible with ABB’s newly released fast wiring system, which allows product mixing on the same DIN rail. This system has the added advantage that the electrical feed-in connections that bring power from one DIN rail to the next in the vertical direction can be accomplished by the first circuit breaker in the line, requiring neither dedicated products nor specially shaped busbars that constrain the type and number of products that can be mounted.

04 With a height of just 85 mm, the DS301C is easier to install.
04 With a height of just 85 mm, the DS301C is easier to install.
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Fail-safe terminals prevent the insertion of the electrical conductor into the wrong aperture and the DS301C clipping system allows easy product mounting onto the DIN rail without removing busbars from neighboring breakers.

05 Shown is an example of breaker technology today, with single-pole MCB on single branches. With the DS301C, ABB can now offer, in the same space, also earth-fault protection at single branch level.
05 Shown is an example of breaker technology today, with single-pole MCB on single branches. With the DS301C, ABB can now offer, in the same space, also earth-fault protection at single branch level.
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With a height of only 85 mm, the DS301C is less tall than competing devices, making wiring easier, particularly in panelboards, where DIN rail separation can be as little as 125 mm →04-05.

Small size but high-end features
Compactness does not prevent the DS301C from providing customers with high-end features. For example, there is a visual indication of the cause of a trip: For earth faults, a mechanical flag (the blue rectangle in →01) informs the user. This feature is not available in competing compact breakers. Should the contact become welded during a trip, the toggle remains midway between the open and closed position. Hence, the “on” and “off” labels are hidden, indicating the contact’s situation.

As per applicable standards, a button allows users to periodically test the earth-fault sensing and actuation drivetrain by injecting an artificial residual current and producing a differential trip.

ABB’s comprehensive portfolio of DIN-rail accessories (the System Pro M series), which encompasses, for example, signal and auxiliary contacts, trip coils and a motor recloser, supplements the DS301C and caters to all levels of panelboard sophistication.

All inscriptions on the housing, including electrical markings, are laser-printed for precision, readability and durability. With a smartphone, the user can easily access datasheets and technical information from ABB via a QR code on the front of the DS301C.

Green light for sustainability
Sustainability was a major driver during the development of the DS301C (the product is part of the ABB Ecosolutions™ portfolio). For example, all polymeric parts in this lightweight product are made of recyclable thermoplastic. Furthermore, the “all-in-one” circuit breaker design means power losses are lower when compared to the duplicated resistive elements, such as contacts and electrical terminals, in alternative setups with MCBs and RCDs. Cooling requirements are also reduced. These environmental benefits are significant as power flows continuously through the device over its multi-decade service life and power losses form a large part of its ecological footprint.

Innovating the familiar
The DS301C development is a prime example of how innovation can impact even long-familiar products and technologies. The key here is to adopt a comprehensive approach that addresses the market needs and matches the user’s desired experience while considering sustainability throughout the product life cycle. With the compact DS301C, panel builders can now deliver safety and control to even the furthest or busiest branches of the low-voltage distribution network. 

Photo fig. 01: ©Stillfix/stock.adobe.com; BillionPhotos/stock.adobe.com

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