Why No Continuity Between 85 and 86 on Relay

The relay is an electromagnetically operated switch, where with a low level input current, typically in the range of 100 mA and 150 mA, can be switched high level current up to 80 A, in some cases and more. When the input current flows through the copper coil, the magnetic field is generated and the hinged soft iron plate is fast attracted, which in turn is mechanically connected to the one movable contact of the switch (see figure 1 below).

The other contact of the switch is non-movable (stationary contact), placed at very short distance next to the movable contact. Depending on the relay type, the switch contacts can be normally open or normally closed. The number of poles refers to the number of switches, so a single pole relay has one switch.

Different Types of Single-Pole Relays

On figure 1 is shown a typical single-pole normally open relay, where the contacts are normally open when the relay is not activated (OFF), i.e. coil is not energized. When the relay is activated (ON), i.e. coil is energized, in that case the contacts are closed (contacts 8 and 9 are connected), so the relay switch is switched ON.

Figure 1. Single-pole normally open relay:
1. Housing
2. Pole piece
3. Return spring
4. Copper coil
5. Hinge
6. Flexible copper braid
7. Soft iron core
8. Movable electrical contact
9. Non-movable electrical contact

On figure 2 is shown a typical single-pole normally open tied pin relay. When the relay is not activated (OFF) the contacts are normally open. When the relay is activated (ON), in that case the contacts are closed, i.e. the relay switch is switched ON.

Figure 2. Single-pole normally open tied pin relay:
1. Housing
2. Pole piece
3. Return spring
4. Copper coil
5. Hinge
6. Flexible copper braid
7. Soft iron core
8. Movable electrical contact
9. Non-movable el. contact with two pins

On Figure 3 is shown a typical single-pole normally closed relay. When the relay is not activated (OFF) the contacts are normally closed (connected 8 and 9). When the relay is activated (ON), in that case the contacts are open.

Figure 3. Single-pole normally closed relay:
1. Housing
2. Pole piece
3. Return spring
4. Copper coil
5. Hinge
6. Flexible copper braid
7. Soft iron core
8. Movable electrical contact
9. Non-movable electrical contact

On figure 4 is shown a typical single pole changeover relay. In this case, the contact A is normally open and the contact B is normally closed. When the relay is not activated (OFF) the contact A is open (switched OFF), and the contact B is closed (switched ON). When the relay is activated (ON), the contact A is closed (switched ON), and the contact B is open (switched OFF).

Figure 4. Single-pole changeover relay:
1. Housing
2. Pole piece
3. Return spring
4. Copper coil
5. Hinge
6. Flexible copper braid
7. Soft iron core
8. Non-movable el. contacts (A and B)
9. Movable electrical contact

Specifications, Characteristics, Wiring Symbols and Marking of Relay Pin

The relays are usually supplied with 12 V directly from the vehicle battery. The electrical resistance (impedance) of the coil is vary and is different depending upon the manufacturer of the relay as well as relay's type, but in general a typical value should be expected between 50 ohms and 200 ohms. Input current typically is in the range between 100 mA and 150 mA.

Figure 5 shows the usual marking of pins (terminals) and layout for a single-pole normally open relay. The mainly, marking of pins are with numbers given in wiring symbols below. Sometimes pin numbering (marking) can be different, for example with numbers 1, 2, 3, 4 or similar. In that case, to find out the pins, must follow the relay symbol scheme, which is usually drawn on the top or on the side of the relay housing.

Figure 5. Single-pole normally open relay:
Pin 85 negative electric pole of the coil (mass)
Pin 86 positive electric pole of the coil (command signal)
Pin 30 permanent plus 12V
Pin 87 switched plus

When on pin 86 is brought a command signal the relay is activated (ON). In that case the switching contacts are closed (pin 30 and pin 87 are connected), so the switch is switched ON. Some vehicle/engine management systems require to be used a resistor (R) to limit the current flow through the coil or the use of a diode (D) to dissipate the stored energy in the coil. In both cases the layout of pins are same and are shown on figure 5.

NOTE: The relay types without integrated diode may work even if the coil pins are connected opposite (doesn't matter where is connected positive, i.e. negative pole of the coil pins). But, in the case when is used relay with integrated diode, you must be careful how connecting the relay, pin 85 to negative, and pin 86 to positive pole. If you connect opposite, it may produce a fuse breakdown or some other element breakdown into the related electrical circuit where the relay is connected.

Figure 6 shows the standard marking of pins and layout for a single pole normally open tied pin relay. The construction and pin numbering can vary depending upon the manufacturer.

Figure 6. Single-pole normally open tied pin relay:
Pin 85 negative electric pole of the coil (mass)
Pin 86 positive electric pole of the coil (command signal)
Pin 30 permanent plus 12V
Pin 87 or 87b switched plus (tied pin)

When on pin 86 is brought a command signal the relay is activated (ON). In that case the switching contacts are closed (pin 30 and tied pin 87 are connected), so the switch is switched ON.

Figure 7 shows the standard marking of pins and layout for a single-pole normally closed relay.

Figure 7. Single-pole normally closed relay:
Pin 85 negative electric pole of the coil (mass)
Pin 86 positive electric pole of the coil (command signal)
Pin 30 permanent plus 12V
Pin 87 switched plus

This type of relay works opposite than previous types. In normal position when coil is without command signal (not activated), the switching contacts are closed (pin 30 and pin 87 are connected), i.e. the switch is switched ON. When on pin 86 is brought a command signal the relay is activated. In that case, the switching contacts are open (pin 30 and pin 87 are disconnected), so the switch is switched OFF.

Figure 8 shows the standard marking of pins and layout for a single pole changeover relay. The construction and pin numbering can vary depending upon the manufacturer.

Figure 8. Single-pole changeover relay:
Pin 85 negative electric pole of the coil (mass)
Pin 86 positive electric pole of the coil (command signal)
Pin 30 permanent plus 12V
Pin 87 switched plus (normally open)
Pin 87a switched plus (normally closed)

In this case, at normal position when coil is without command signal (not activated) the pin contact 87 is normally open (switched OFF), and the contact 87a is normally closed (switched ON). When the relay is activated with a command signal, the contact 87 is closed (switched ON), and the contact 87a is open (switched OFF).

Rarely, in some cases can be found a relay type with an integral fuse added for protection. This type is shown below.

Figure 9. Single-pole relay type with an integral fuse:
Pin 85 negative electric pole of the coil (mass)
Pin 86 positive electric pole of the coil (command signal)
Pin 30 permanent plus 12V
Pin 87 switched plus

Diagnostics and Testing Procedures

• Check that there is any "clicking" sound at the moment of the activating the relay.
• Check the condition of the wires and terminals (corrosion, overheating, toughness of terminals, etc.).
• Unplug the relay and check the electrical resistance of the coil (between the pins 85 and 86). The resistance should be roughly between 50 ohms and 200 ohms. If the reading is drastically out from these values, as well as the two extreme values: zero, or infinite, is required replacement.
• Check that there is an open circuit (infinite resistance) between the switch terminals (30 and 87) for a normally open relay when the coil is not energized (relay is not activated/OFF).
• Check that there is continuity between the switch terminals (30 and 87) for a normally open relay when the coil is energized (relay is activated/ON). See figure 10.

Figure 10. Testing procedure:
Connect pin 85 and one pin from light to the negative (minus) pole of the battery, as well as pin 87 to the other pin of light. Then connect pins 30 and 86 to the positive (plus) pole of the car battery. If relay working properly, then the light must be switched ON. If you disconnect 86 or 85, then the light should be switched OFF.

NOTE: The relay types without integrated diode can work and you can test even if the pin 85 and pin 86 are connected opposite, but at the relays with integrated diode, you must be careful how connecting the relay when testing!
Pin 85 must be connected to the negative pole, and pin 86 must be connected to the positive pole of the car battery.

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