Schneider Electric CA2KN31B7 TeSys K Relay 3NO+1NC 24 V AC

CA2KN31B7: control relay with 3 NO and 1 NC contact and a 24 V AC coil

The CA2KN31B7 is a Schneider Electric TeSys K control relay listed in the datasheet as: TeSys K control relay – 3 NO + 1 NC – <= 690 V – 24 V AC coil. A 3 NO + 1 NC set suits circuits where most functions are ‘make on energise’ but one signal must be the opposite, for example a seal-in contact, two output contacts and one fault or feedback contact that is closed when the relay is off. Seven Star LLC supplies the CA2KN31B7 in Oman and the GCC as an independent supplier based in Muscat.

The datasheet gives the device short name CA2K and the application as control circuit. The contact set is three normally open and one normally closed contact, the coil is 24 V AC 50/60 Hz, and the utilisation categories are AC-15 and DC-13, the standard categories for control-circuit loads such as contactor coils and signal lamps.

Technical specifications of the CA2KN31B7

Contact set and operation of the CA2KN31B7

Three NO contacts can carry the seal-in, the output command and a feedback signal at the same time, while the single NC contact gives an ‘off’ indication or a permissive that falls away when the coil pulls in. The datasheet lists a non-overlap distance between NO and NC contacts, which matters when the NC contact feeds a logic input that must not see both states together.

Operating times in the datasheet: 10 to 20 ms coil de-energisation and NO opening; 10 to 20 ms coil energisation and NO closing; 15 to 25 ms coil de-energisation and NC closing; 5 to 15 ms coil energisation and NC opening. Non-overlap distance between NO and NC contacts: 0.5 mm. Mechanical durability: 10 Mcycles. Maximum operating rate: 10000 cyc/h.

Coil supply, contact ratings and low-level switching of the CA2KN31B7

The 24 V AC coil is intended for control panels fed from a control transformer, which is the usual extra-low-voltage control supply in machine and plant panels. A low-voltage coil keeps hand-held test equipment and push-buttons at a safe level, and the same 24 V supply can feed indicator lamps and PLC input cards.

The datasheet lists the coil voltage as 24 V AC 50/60 Hz. Operating limits: Drop-out: 0.2 to 0.75 Uc (at <50 °C); Operational: 0.8 to 1.15 Uc (at <50 °C). Inrush consumption: 30 VA (at 20 °C). Hold-in consumption: 4.5 VA (at 20 °C). Heat dissipation of the CA2KN31B7: 1.3 W. Immunity to micro-breaks: 2 ms.

A 24 V coil also avoids mains voltage at pushbutton stations and field wiring, which is valuable where operators or maintenance staff work close to the panel.

Conventional free-air thermal current: 10 A (at 50 °C). Rated making capacity: 110 A conforming to IEC 60947. Associated short-circuit protection: 10 A gG conforming to IEC 60947; 10 A gG conforming to VDE 0660. Minimum switching voltage: 17 V. Minimum switching current: 5 mA. Insulation resistance: > 10 MOhm. Rated operational voltage: <= 690 V <= 400 Hz.

The minimum switching figures matter when the relay is used to feed a PLC input or an electronic circuit at 24 V: contacts that normally carry amps can lose reliability at very low voltage and current, so the datasheet minimum should be respected or a different contact technology considered.

Family comparison for the CA2KN31B7

The CA2KN22U7 differs in contacts 2 NO + 2 NC against 3 NO + 1 NC here; coil 230 to 240 V AC 50/60 Hz against 24 V AC 50/60 Hz here. The CA2KN31M7 differs in coil 220 to 230 V AC 50/60 Hz against 24 V AC 50/60 Hz here.

The table lists the CA2K references of this group; contact set and coil are the only things that change, and the body, size and ratings are shared.

Selection checklist for the CA2KN31B7

Selection tip for the CA2KN31B7: the B7 version is the 24 V AC member of the 3 NO + 1 NC pair and needs a control transformer or a 24 V AC supply in the panel. It will not work on 24 V DC, because the datasheet lists an AC coil at 50/60 Hz. Check the transformer rating before adding relays, since the 30 VA inrush of each coil appears at the moment of switching and several relays energised together can drag the secondary voltage down and delay the pull-in of the whole group.

• Check that one NC contact is enough; otherwise use the 2 NO + 2 NC reference.
• Verify which terminal is the NC contact on the front; the terminal numbers are printed beside each screw.
• Coil voltage: 24 V AC 50/60 Hz; operating limits 0.8 to 1.15 times the rated voltage.
• Mounting: rail or plate, body 45 mm wide x 58 mm high x 57 mm deep.
• Short-circuit protection: use the associated 10 A gG fuse noted in the datasheet.

Mounting, wiring and environment for the CA2KN31B7

The relay mounts on a rail or on a plate, measures 45 mm wide x 58 mm high x 57 mm deep and weighs 0.18 kg. Terminals are screw clamps; the datasheet gives 1.3 N.m – on screw clamp terminals – with screwdriver flat Ø 6 mm, and accepted conductors from 0.34 to 4 mm squared depending on type and number. Fit a marker beside each screw group so that the NO and NC terminals are not confused during later maintenance.

The environment is stated as -25 to 50 °C in operation and -50 to 80 °C in storage, an altitude of 2000 m without derating, protection IP2X and a flame retardance of V1 to UL 94. The mechanical robustness data in the datasheet give vibration and shock withstand figures for both the open and closed state, which is useful for relays on moving or shaking machines.

Where the CA2KN31B7 is used in Oman and the GCC

On machine panels with a 24 V AC control transformer, this relay serves as an interposing element between PLC outputs or safety logic and loads at other voltages. The single NC contact is typically used as a feedback signal to a PLC input that confirms the relay has dropped out.

With 24 V AC, the coil inrush of 30 VA and hold-in of 4.5 VA must be added to the transformer budget. In a panel with many relays the sum can be significant, and a transformer sized only for PLC and lamps may run hot.

Information to send with an RFQ for the CA2KN31B7

• Full reference (CA2KN31B7) and quantity required
• Supply and control voltage at site, with the frequency
• Existing panel, rail and neighbouring devices it must fit beside
• Delivery location and timing
• Whether it is a spare, a like-for-like replacement or a new installation
• Contact set needed: number of NO and NC contacts

Documents and quotation

A datasheet for the CA2KN31B7 is attached on this page. It lists the electrical, mechanical and environmental data summarised above, and it should be read together with the manufacturer’s installation instructions for the final design.

Send us the part number, quantity and application and we will confirm availability and a quotation. Seven Star LLC is an independent supplier in Muscat and is not affiliated with the manufacturer.