The future of DC Circuit protection

On the secondary side, switched-mode power supplies provide DC voltage to control circuit loads (e.g., controllers, operating panels, displays and auxiliary relays). These control circuits also call for wiring protection and if the load has no protective unit of its own, device protection as well. Furthermore, Machinery Directive EN 60204 requires the detection of hazardous ground faults in control circuits and switching off within five seconds.

The overcurrent protection in primary switched-mode power supplies reacts very quickly to overcurrents on the output side. Selective protection of individual current paths in the secondary circuit via fuses or conventional circuit breakers is often ineffective if the power supply cannot deliver a brief overcurrent.

Possible applications:

• Low-voltage, high-power and DP fuses

• High overcurrents required for fast tripping

Explanation:

• In the example: ten-fold overcurrent (related to fuse nominal current): tripping within the range 30 ms (best case) or 200 ms (worst case)

• Only two-fold overcurrent: tripping within the range 2 s (best case) or >100 s (worst case)

Possible applications:

• Found in circuit breakers or motor protection switches

• High overcurrents required for fast tripping

Explanation:

• In the example: three- to five-fold overcurrent for B-characteristic and AC operation, additional safety factor 1.2 or 1.5

• Thus, in the worst case scenario, a tripping current of 7.5 times the nominal current is necessary.

Functions of a WAGO ECBs:

• Ensure precision settings

• Reaction within a short time – even at low overcurrents

• Protection of long cable runs and small cross sections possible

Explanation:
WAGO ECBs ensure reliable protection, even at low overcurrents and with long cable lengths.

The ECB verifies that the output current is greater than the nominal current. As soon as the output current exceeds the nominal current, the output is electronically switched off by a semiconductor switch. The trip time depends on the magnitude of the overcurrent. The measurement of the output current, processing and calculation of the tripping time, as well as actuation of the semiconductor switch are performed by a microprocessor that monitors one or more output channels. The corresponding tripping times can be taken from the graph on the right.

• Switch off secondary-side overcurrents and short circuits – even with long cable runs and small conductor cross-sections – precisely, quickly and repeatedly

• Selectivity

• Remote operation via digital input and output

• Readout functions (communication) through serial data transfer via digital input and output

• Advantageous installation size and width, for example, eight output channels in just 32 mm that saves almost 80% of installation space compared to miniature circuit breakers

• Adjustable current assignable for each channel

• Satisfy EN 60204-1 requirements for dependably switching off ground faults after five seconds

• Remote digital input resets all tripped channels

• Digital output transmits a simple group message indicating whether one of the channels was tripped by an overcurrent