Relay symbol: coil, contact and timer blocks for CAD

This download holds the relay symbol set for control schematics: the plain coil, the on-delay and off-delay timer coils, normally open, normally closed and changeover contacts, the contactor main contact, the two time delay contacts and the thermal overload relay. Each is a named block in the DWG and DXF, with the names of the full schematic library, plus a PDF chart.

Relay symbol: one coil, contacts drawn elsewhere

On an IEC schematic the coil, a rectangle, sits in the control circuit where it is switched, and each of its contacts appears in the circuit it switches. They belong together because they share the same reference designation, such as K1, and a cross-reference table under the coil lists where each contact is used. When the coil and a contact are drawn next to each other, a dashed mechanical link joins them. The rest-position rule is on the electrical schematic symbols page.

The terminals follow a fixed marking scheme. The coil is A1 and A2. Auxiliary contacts take two digits: the first counts the contact, the second gives its function, 1 and 2 for a normally closed contact, 3 and 4 for a normally open one. So 13-14 is the first make contact and 21-22 the second, a break contact. A changeover contact is numbered 11, 12 and 14 around its common terminal.

Contactor symbol and main contacts

A contactor is a relay built to switch power. Its coil is drawn with the same rectangle, but its main contacts carry a small semicircle at the fixed contact, and they are numbered 1-2, 3-4 and 5-6 for the three poles. In the reference designation scheme a contactor takes the letter Q, while a relay that only handles signals takes K.

Time delay relay symbol: on-delay and off-delay

The on-delay coil has a crossed box beside it and the off-delay coil a filled box. The contacts carry an arc, often called the parachute, that slows the blade in one direction: the movement is delayed in the direction that goes from the arc towards its centre. So the on-delay make contact closes late and opens at once, and the off-delay make contact closes at once and opens late.

Overload relay next to the contactor

The thermal overload relay block is the heating element that sits in the power circuit between the contactor and the motor. Its auxiliary contacts, usually 95-96 normally closed and 97-98 normally open, are drawn in the control circuit with the plain contact symbols. The 95-96 contact goes in series with the contactor coil.

Drawing relay circuits with these blocks

All blocks sit on a 2.5 mm grid with the current path vertical. The base point is the lower terminal and the upper terminal sits 12.5 mm above it, so coils and contacts drop onto vertical wires without adjusting. The changeover contact has its common terminal at the base point, the make terminal 12.5 mm above and the break terminal 5 mm to the left. For the start and stop buttons that drive the coil, see the push button symbol page.

Coils and contacts are drawn after IEC 60617. IEC sells access to that symbol database by subscription, and its official sheets are not reproduced here.