Ship current transformers CT which steps down the monitored current to a secondary (output) range of 0 to 5 amps (AC) to power the protective relay.
If the monitored current becomes excessive, the relay triggers a contact-switching auxiliary control circuitry to the breaker’s trip coil.

By using the selected time delay between 0.05 and 30s, short current peaks can be bridged.

Connecting the ship current transformer CT to the current monitoring relay terminals is depicted on the relay diagram’s symbol Terminals coded with the letter B represent connections to the current transformer.

Terminals B1 to B3 connect ship current transformer CTs with different step-down current ratios.

C shows another connection terminal, common for any CT ratio.

Example of a current monitoring relay and a related electrical diagram

The power is applied across A1/A2, and the current signal being monitored is applied across B1 and C. Depending on the measurement of the current ratio, the following connections are allowed:
B1/C: 3-30 mA, B2/C: 10-100 mA, B3/C: 0.1-1 A.
The relay operates with changeover contacts, the motor starter control circuits use NO (normally open) contacts in series with stop button contacts. The result Is that an occasional break in the power supply will stop the motor.

The relay can operate both contact groups, either with or without a time delay, depending on the rotary selector switch (Tv) position.
Whatever mode of operation is adjusted for the relay (either instant or delayed), only one relevant reference number will be used throughout a diagram.
Relay set for overcurrent detection (/>)
If the current Is greater than the set threshold, the output relay is energised, with or without a time delay. When the current returns to a value below the threshold, depending on the hysteresis setting, the relay Is Instantly de-energized.

How to set ship relay set for undercurrent detection

If the current is less than the setting threshold IS1, the output relay Is energized, with or without a time delay.

When the current returns to a value IS2 above the threshold, depending on the hysteresis setting, the relay is instantly de-energized.

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The itemized overview of contactor accessories should help while sending routine ship technical inspections or ship spare orders and when ordering relays or contactors in an emergency.

Check basic ship contactor accessory

1. Basic unit
2. Side-mounted (lateral) auxiliary contact module
3. Pneumatic time module (On- and Off-delay), top-mounted
4. Two pole top-mounted auxiliary contact module
5. Four pole top-mounted auxiliary contact module
6. Mechanical latching module
7. Surge protector

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This addition provides the ordinary relay with time-delay actuation. Time-delay modules are constructed to delay armature motion on coil energisation, de-energisation or both.

A relay with such an accessory becomes a timer and is illustrated with a timer symbol.

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The resulting devices are called mechanically held relays.
Once the closing impulse has been given to the coil (A1-A2), the mechanical latch holds the contactor or the control relay in the closed position without the coil being continually energised.

Interruption of the contactor takes place through a further impulse, which releases the latch, NO (normally open) trip.

The latch reset coil terminals are assigned with the letter’E'(E1-E2).

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Even with a mechanical force against the magnetic system, the contacts of both contactors cannot close simultaneously.

An electrical interlock consists of two interlinked auxiliary NC contacts. While one contractor (eg 1KM1) is energizing, its interlocking contact (1KM1/21- 22) opens, preventing current flow. During this time current flows through the coil of the second contactor (1KM2).

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To reduce the disturbance on ship switchinng elements, coils can be connected to suppressor modules, also called surge protectors, which are connected across the coils and dissipate the energy from the collapsing magnetic field when switched off.

Suppressor modules for relays and contactor coils
include the following:

1. RC links – a resistor in series with a capacitor used with AC operated coils a)
2. diode elements – provide excellent voltage limitation and are used for DC operated coils b)
3. varistor elements – used for AC and DC operated contactors c) and achieve virtually unchanged switching times.

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Relays are used to controlling and regulate circuits for the indirect control of electric motors, valves and clutches.
A modular system is formed around functional basic units, consisting of an AC or DC operated drive (coil with armature) and auxiliary contacts.

The control relay’s basic unit consists of four contact blocks (poles) marked with reference numbers:
• 13-14 (NO contact)
• 21-22 (NC contact)
• 33-34 (NO contact)
• 43-44 (NO contact).

Reference numbers are also shown as a table in most control diagrams, usually below the relay’s coil symbol.
The manufacturer’s stamp should be marked on the unit and reference letters marked adjacent to the terminals (53NO, 61A/C, 75NC, 87A/0).These manufacturer’s numbers are an important reference for reordering or cross-ordering with other manufacturers components.

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The reeds provide a magnetic operating gap and serve as a contact pair providing NO, NC and CO combinations.
Reed relays on ship electrical systems have the advantage of being hermetically sealed and as a result, are protected from atmospheric contaminants.
To make NC or CO contacts, reed switches will occasionally use permanent magnets for magnetic biasing. The current rating of the reed, normally up to one amp, depends on the size, type and amount of plating.

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A current passes through the coil creating a magnetic field that attracts the armature, causing the contacts to move, either making or breaking a connection. The following contacts are known by how they can be thrown:

Ship Normally open contacts (NO)
When the relay is activated, NO contacts connect the circuit and will disconnect the circuit when it is inactive.
Ship Normally closed contacts (NC)
NC contacts disconnect the circuit when the relay is activated and connect when inactive.

Ship Changeover contacts (CO)
The contacts have a common terminal and control two circuits. One is a NO contact and the other is an NC contact. It is also known as a ‘double throw'(DT),

Single Pole Single-Throw contacts on ship (SPST)
These have two terminals that can be connected or disconnected (11-12 or 13-14) and two terminals for the coil. The terminology ‘SPNO’ and ‘SPNC’is sometimes used to indicate the contacts’ de-energized state (Figure b).
Double Pole Single-Throw contacts on ship (DPST)
The relay has four terminals that can be connected or disconnected. This is equivalent to two SPST switches actuated by a single coil and has two terminals for the coil (Figure c).
Single Pole Double-Throw contacts on ship (SPDT)
With a total of five terminals, two for the coll, a further terminal connects to two others as a CO contact (Figure d).
Double Pole Double-Throw

Single Pole Single-Throw contacts on ship (SPST)
These have two terminals that can be connected or disconnected (11-12 or 13-14) and two terminals for the coil. The terminology ‘SPNO’ and ‘SPNC’is sometimes used to indicate the contacts’ de-energized state (Figure b).
Double Pole Single-Throw contacts on ship (DPST)
The relay has four terminals that can be connected or disconnected. This is equivalent to two SPST switches actuated by a single coil and has two terminals for the coil (Figure c).
Single Pole Double-Throw contacts on ship (SPDT)
With a total of five terminals, two for the coll, a further terminal connects to two others as a CO contact (Figure d).
Double Pole Double-Throw contacts on ship (DPDT)
This has eight terminals with two rows of CO contacts. It is equivalent to two SPDT relays actuated by a single coil (Figure e).

Ship miniature relays are also subdivided by their operation:

Non-Latching (stable type)
A relay that is activated when the coil Is energized and turns off when de-energized. Non-latching relays are used In control applications when the switch must return to a neutral state if power is lost.
Latching type relays on ship system
Latching relays are used when power consumption and dissipation are limited. For example, after the Initial actuation of the relay no further power is needed to maintain the state.

1 One Coil Latching Type
This relay uses a pulse input to a single coil and a latching mechanism to maintain the contact as either on or off. By applying signals of opposite polarities the relay is set and reset.

2 Two Coil Latching Type
This relay uses a latching construction and two coils, one to set and another to reset. Setting and resetting is achieved by applying pulse signals of the same polarity.

Miniature relays are designed so that the casing does not become detached under normal use, as performance could be reduced. Consequently, the DIN rail mounting system allows simple replacement of malfunctioned relays. A PCB (Printed Circuit Board) miniature relay, socket-mounted ‘ice cube miniature relays and their terminal designation.

Miniature relays are assembled into control cabinets with their sockets, which can in general be subdivided into two basic types:

• Screw terminals sockets miniature relays
• Screwless terminals sockets (for fast wiring).

All sockets are either panel- or 35 mm rail-mounted (EN 60715). Socket’s terminals as well as relays’ contacts pins are assigned with reference numbers, which should be used when troubleshooting to verify the condition of the contact in an energized and de-energized state.

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