Schneider Electric CA2SK20B7 TeSys SK Relay 2 NO, 24 V AC

CA2SK20B7: a compact TeSys SK 2 NO relay on a 24 V AC coil

The CA2SK20B7 is a very compact Schneider Electric control relay: a TeSys SK relay with two normally open contacts and a 24 V AC coil. The datasheet title is: Control relay, TeSys SK, 2NO, up to 690V, 24V AC coil. It is only 27 mm wide, so several fit side by side on a short length of DIN rail. Seven Star LLC supplies the CA2SK20B7 in Oman and the GCC as an independent supplier based in Muscat.

The reference reads as follows: CA2SK is the TeSys SK control relay range, the digits 20 describe two normally open contacts and no normally closed contacts, B stands for 24 V and 7 for an AC coil at 50/60 Hz. Only a complete match of those characters ensures the right coil and the right contact arrangement.

Datasheet table for the CA2SK20B7

Coil and timing of the CA2SK20B7 on a 24 V AC supply

The coil works from 0.85 to 1.1 times 24 V, which is about 20.4 to 26.4 V, below an ambient of 50 °C, and it releases between 20 and 75 % of nominal, about 4.8 to 18 V. The narrower window than the 0.8 to 1.1 Uc of larger relays makes the quality of the 24 V AC supply important: a small transformer with poor regulation can fall below 20.4 V when several loads operate at the same time.

The datasheet gives 16 VA at inrush and 4.2 VA hold-in, equal to roughly 0.67 A and 0.18 A at 24 V (derived figures, for supply sizing only), and a heat dissipation of 1.4 W. Closing takes 7 to 14 ms and opening 6 to 8 ms, so the relay is fast, and the maximum operating rate is 1200 cycles per hour, with a mechanical durability of 10 million cycles. The low operating rate is the main limit: it suits control and interface duty, not fast pulsing.

Contacts and protection of the CA2SK20B7

Both contacts are normally open and rated for a conventional thermal current of 10 A at 55 °C in AC-15 and DC-13 duties, with a rated operational voltage up to 690 V. The recommended protection is a 10 A gL fuse. At 10 A the relay can switch small contactor coils, solenoid valves, indicator lamps and signal circuits, and its two contacts can be used as two separate outputs.

The CA2SK20B7 is not a motor contactor. For a motor, or for a load with a high inrush, a TeSys D contactor from the LC1D family is the right device, and the two-pole TeSys SK relay then acts as the interface that carries the PLC signal to the contactor coil.

Standards and environment of the CA2SK20B7

Certifications listed in the datasheet are CB Scheme, cULus, EAC, CE and UKCA. The standards include EN/IEC 60947-5-1 and UL 60947-5-1, and the datasheet also lists IEC and UL 60335-2-40 Annex JJ, a clause of the standard for heat pumps, air conditioners and dehumidifiers, which suggests that this relay is also used in HVAC equipment. Insulation is rated 690 V in several standards, including UL 508 and CSA C22.2 No 14.

For the environment, operation is listed from -20 to 50 °C and storage from -50 to 70 °C, with an altitude of 2000 m without derating. The housing is rated IP2X and the protective treatment is TC per IEC 60068. The operating range is narrower than that of the TeSys D relays, so a hot cabinet in the region should be checked against the 50 °C limit, in particular close to heaters, drives and power supplies.

Mounting and wiring the CA2SK20B7

With a size of 56 mm x 27 mm x 55.5 mm and a net weight of 0.132 kg, the CA2SK20B7 mounts on a DIN rail or on a plate. Terminals are screw-clamp, accepting up to 6 mm² solid or flexible conductors with specific limits for two cables (1.5 to 4 mm² solid, 0.35 to 2.5 mm² flexible), and the datasheet gives a tightening torque of 0.8 N.m with a Pozidriv No 1 screwdriver. This is lower than on larger relays, so use the correct screwdriver to avoid damage to the screw head.

In a spare-parts context the CA2SK20B7 is easy to hold because the relay is small and the coil voltage is the only variable. Mark it clearly as 24 V AC, because 24 V DC relays of other families look similar and a DC supply will not hold an AC coil properly. After installation, check the coil voltage at the terminals under load and verify the operation of each contact before the load is connected.

Where the CA2SK20B7 is used in Oman and the GCC

The 24 V AC control voltage is typical of HVAC and building services, where a small transformer supplies thermostats, damper actuators and relays. In the region these are chillers, fan coil units, air-handling units and cooling towers at hotels, hospitals, malls and industrial sites, and also pump panels in desalination and water-treatment plants that use 24 V AC for the control circuit.

Because the CA2SK20B7 is only 27 mm wide, it is also popular in small interface panels where one controller output has to drive several loads. The principal risk in the Gulf is heat in rooftop and plant-room enclosures. Keep the relay within the -20 to 50 °C operating limit by allowing ventilation, and avoid mounting it near the transformer that supplies its coil.

Information to send with an RFQ for the CA2SK20B7

• Full reference CA2SK20B7 and the quantity
• Confirmation that the coil is 24 V AC 50/60 Hz and not 24 V DC
• What each of the two contacts will switch (voltage, current, signal level)
• The equipment or panel it belongs to, and whether it is a spare, a replacement or a new installation
• Delivery location in Oman or the GCC and date required

Documents and quotation

A datasheet for this product is attached on this page. It lists the electrical, mechanical and environmental data summarised above, and it is worth reading beside the panel drawing before you order.

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.