Circuit breaker symbol and fuse blocks for CAD

The download covers the circuit breaker symbol and the other protective and isolating devices of a control panel: circuit breaker, motor protective circuit breaker, fuse, disconnector, switch-disconnector, thermal overload relay, earth and protective earth. They are drawn after IEC 60617 as named blocks in DWG and DXF, with the same names as the full schematic library, and a PDF sheet shows the eight symbols with their names.

Circuit breaker symbol: the cross on the fixed contact

In the IEC forms, most switching devices start from the same make contact. What tells them apart is a small mark, the qualifier, drawn at the fixed contact:

• a cross for a circuit breaker, which can make, carry and break fault currents
• a short bar for a disconnector, which gives an isolating gap
• a bar with a small circle for a switch-disconnector, which also switches under load
• a semicircle for the main contact of a contactor

The other groups of the schematic library are on the electrical schematic symbols page.

Fuse symbol and when a drawing uses it

The fuse symbol is a narrow rectangle with the conductor running straight through it. A fuse opens by melting, so it has to be replaced after it blows, while a circuit breaker trips and can be reset. Both protect against overcurrent and both take the letter F in the reference designation when that is their task. Control circuits often use small fuses or miniature circuit breakers on the secondary of the control transformer.

Motor protective circuit breaker and overload relay

The motor protective circuit breaker block shows a breaker contact linked to two releases, a magnetic one for short circuits and a thermal one for overload. It is the usual single-pole view of a motor protection switch; for a three-phase feeder, draw it three times and join the poles with a dashed link. The thermal overload relay is a different device. It senses overload with its heating element in the power circuit, but it does not break the motor current itself: its auxiliary contact opens the contactor coil. A feeder with a motor protective circuit breaker often needs no separate overload relay, since the thermal release is already inside. A full feeder is laid out on the motor symbol page.

Disconnector symbols beside the circuit breaker

A disconnector is opened with no load, to leave a safe, visible gap before maintenance. A switch-disconnector can also open under load, which is why it is the usual main switch of a machine. The protective earth symbol adds a circle around the earth mark and stands for the PE conductor that keeps exposed metal at earth potential. The plain earth symbol is for a connection with no protective role to show.

Inserting the circuit breaker blocks

The in-line devices have their base point on the lower terminal and the upper terminal 12.5 mm above it, on a 2.5 mm grid with the current path vertical. Earth and protective earth have their base point at the top end of their lead, so they hang from the end of a wire.

The protective device symbols take their forms from IEC 60617, which the IEC offers as a paid online database. Check the official entries there if a specification quotes a symbol number.