7DO721.7 B & R Automation
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The B & R Automation 7DO721.7 is a relay output module from the System 2003 Controllers series featuring 4 outputs with relay changeover type. It has a rated output current of 4 Amps, an AC switching capacity of 1000 VA, and supports a maximum switching voltage of 264 VAC or 125 VDC. The module offers a contact-to-contact isolation of 1.4 kV and a contact-to-pcc isolation of 4 kV.
Internal Product Review
The 7DO721.7 is a System 2003 relay/changeover output controller with 4 outputs. Rated for 4 A output current and 240 VAC / 24 VDC operation, the module supports dependable switching in industrial control panels. A 10 ms maximum switching delay makes the module an excellent choice for responsive output control.
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Product Description:
The 7DO721.7 relay output module is produced by B&R Automation and belongs to the System 2003 Controllers series. Designed for discrete control tasks, the card uses electromechanical changeover contacts that let a processor switch external loads such as solenoids, indicator lamps, and small motors. By converting low-level controller signals into field-level switching, it provides galvanic isolation and extends the automation system to both AC and DC power circuits used throughout a machine or process line.
The module draws only 1.4 W from the backplane, so cabinet thermal rise remains low. Each channel can handle up to 1000 VA on resistive 50 Hz or 60 Hz networks, or 120 W on 30 VDC supplies, which allows the module to work with different load types. A rack-mounted T 5 A H / 250 V fuse protects the card, while the board itself is rated for continuous operation at a system supply of 240 VAC or 24 VDC. When higher voltage is required, the contacts can switch up to 264 VAC or 125 VDC at a steady load current of 4 A per channel. Total bus current is limited to 16 A across all outputs, and relay-to-relay insulation of 460 VAC helps prevent crosstalk. Contact resistance is 100 mΩ at 6 VDC and 100 mA, and the relay changeover output provides both normally open and normally closed switching options.
For transient events, the contacts can withstand a surge of 15 A for 200 ms, which covers inrush from inductive loads. Command latency remains bounded by a maximum of 10 ms, so sequence timing stays predictable. Electrical separation is strengthened by 1.4 kV contact-to-contact and 4 kV contact-to-PCC impulse withstand levels measured with a 1.2 × 50 µs waveform. This isolation helps protect control electronics when different voltage domains share the same backplane. The module has four relay outputs, so it can switch mixed AC and DC loads within the stated limits.
