Relays

Contact types

Symbol

Configuration

EU

USA

Make contact (Normally Open)

NO

SPST-NO

DPST-NO

nPST-NO (1)

Break contact (Normally Closed)

NC

SPST-NC

DPST-NC

nPST-NC (1)

Changeover contact

CO

SPDT

DPDT

nPDT(1)

Utilization categories

Category

Type of current

Applications

AC-1

a 1-phase
a 3-phase

Resistive or slightly inductive loads

AC-3

a 3-phase

Starting and braking of squirrel cage motors; reversing direction of rotation only after stopping of motor

AC-4

a 3-phase

Starting of squirrel cage motors, inching, plugging, reversing direction of rotation

DC-1

c

Resistive or slightly inductive loads (2)

AC-14

a 1-phase

Control of electromagnetic loads (< 72 VA), auxiliary control relays, power contactors, electromagnetic solenoid valves, and electromagnets

AC-15

a 1-phase

Control of electromagnetic loads (> 72 VA), auxiliary control relays, power contactors, electromagnetic solenoid valves, and electromagnets

DC-13

c

Control of electromagnetic loads, auxiliary control relays, power contactors, magnetic solenoid valves, and electromagnets

Protection categories

Category

Explanation

Condition

RT 0

Unenclosed relay

Relay is not provided with a protective case

RT I

Dust-protected relay

Relay is provided with a case that helps to protect its mechanism from dust

RT II

Flux-proof relay

Relay capable of being automatically soldered without allowing the migration of solder flux beyond the intended areas

RT III

Wash-tight relay

Relay capable of being automatically soldered and then washed to remove flux residues and minimize the possibility of ingress of flux or washing solvents

RT IV

Sealed relay

Relay provided with a case that has no venting to the outside atmosphere

RT V

Hermetically sealed relay

Sealed relay with an enhanced level of sealing

(1) n = number of contacts.

(2) The switchable voltage can be doubled, for an equal current, by connecting 2 contacts in series.