PTC Thermistors
Temperature Sensors for Motor
Protection and Electronics

(temperature-sensitive resistors)

FEATURES

– rapid response protection for electrical machines
– compact size for easy assembly into windings
– silvered copper leads

PTC-Ther

mistors

02-02-02

1000-Y

-180

Microtherm International Cooperation

YD

1

YG

1

YD

3

YG

3

EF

1

YGM 1
YGM 3
TKA 1
TKA 2

DESCRIPTION

PTC thermistors act as thermal protection for electrical machines, and
are well known particularly as motor-protectors. They are available with
or without insulating sleeve and have flexible connecting leads.
PTC thermistors have a non-linear resistance/temperature response,
and at a specified temperature the resistance changes rapidly to a very
high value.

DIMENSIONS

YD 1 
Single thermistor
with shrunk-sleeve

YGM 1 
Mini-version 
with shrunk-sleeve

YD 3 
Triplet version (in series)

YGM 3 
Mini-version

EF 1
Sensor

Standard

mini

threaded

OPERATION

PTC thermistors exhibit very high sensitivity over a
narrow temperature band. For temperature measure-
ment in this range, NTC thermistors are easier to
measure and more accurate.

- PTC’s are classified according to their nominal

response temperature 

q

NAT

but all have similar

resistance characteristics to simplify the choice 
of switching device; the relationship of resistance 
to temperature of all these PTC’s is as follows:

STANDARD RESISTANCE VALUES

Single PTC

Temperature Resistance

measuring 

Voltage

°C

V

V

– 20 to 

q

NAT

– 20

250 max./100 max.

2.5

q

NAT

– 5

550 max.

2.5

q

NAT

1.000 2.5

q

NAT

+ 5

1.330 min.

2.5

q

NAT

+ 15

4.000 min

7.5

PTC thermistors are especially suited as temperature
sensors for monitoring the windings of electric
machines, and also for use in simple fail-safe circuitry.
When a given temperature (nominal response tempe-
rature 

q

NAT

) is exceeded, the circuit can be switched

off through a relay or amplifier, since the PTC-sensor
will have an extremely high ohmic value in the region
of its response temperature. This will have the same
effect as a break in the circuit or a failure of the
thermistor.

TECHNICAL DATA

Nominal response temperature

80 ° to 180 °C in steps 

of 10 °, plus 145 ° and 155 °C

Maximum allowable operating temp.

T

max.

200 °C

Max. allowable operating voltage at + 25 °C

U

max.

25V (per bead)

Max. allowable power dissipation at + 25 °C

690 mW

Insulation strength (between leads and outer insulation)
also for threaded sensor

2.5 kV

Conductors - silvered copper wire with teflon insulation

PTFE

Insulation stripping

approx 10 mm

Conductor cross-section

0.25 mm

2

for single, double 

and triple PTC’s

CONDUCTOR LENGTHS

Single PTC

500 mm 

6

10 mm

Double PTC

500 - 180 - 500 m 

6

10 mm

Triple PTC

500 - 180 - 180 - 500 mm 

6

10 mm

SPECIAL VERSIONS

PTC’s are also available in many special housings
(can be manufactured to customers specifications)

INSTALLATION TIPS

For PTC temperature sensors in electrical windings:
- the thermistors can only be inserted in the windings

before impregnation

- it is advisable to embed one in each phase, if

possible in the centre of the coil generating most
heat, and generally on the outflow side of any air
movement

- air inflow onto the temperature sensor will interfere

with heat transfer

- if using varnish/lacquer which is not chemically

neutral, suitability tests must be undertaken by the
customer

- WARNING! It is very important that the sensor must

be installed parallel with the copper of the winding,
so that the teflon leads can assume the form of the
rest of the winding and thereby retain the high-
voltage resistance rating.

Triple PTC

Temperature Resistance

measuring 

Voltage

°C

V

V

– 20 to 

q

NAT

– 20

750 max./300 max.

7.5

q

NAT

– 5

1.650 max.

7.5

q

NAT

+ 5

4.000 min.

7.5

q

NAT

+ 15

4.000 min.*

7.5

* one PTC might reach 

q

NAT

+ 15 °C, while the second or even both

of the others could still remain at room temperature.

The PTC’s resistance values for motor protection are
specified in DIN 44081/44082. Resistance values
below 

q

NAT

–20 are not specified, and resistance

when cold is no indication of the PTC’s condition. It is
ideally between 40 - 200 ohms but can be anywhere
between 35 - 250 ohms.
The greatest resistance change occurs between 

6

5 °C either side of 

q

NAT

, being at least 15%/K.

Twin/double and triple PTC’s are available with
standard or mini-bead.

QUALITY STANDARD

Random testing is carried out according to DGQ
P90/P10 (DIN 40080). AQL values can be fixed by
arrangement.

ORDERING INFORMATION

Quantity

Type

Temperature

Resistance 

code No.

max.

1.000

YD1

C 510

250 ohms

PTC-Ther

mistors

02-02-02

1000-Y

-180

Single PTC

YD

= standard size bead 4 mm with shrunk-sleeve

YG

= standard size bead 4 mm with shrunk-sleeve and epoxy seal

YGM = mini-bead 3 mm with shrunk-sleeve and epoxy seal

Type

Type Type

Resp.

Std. Colour 

code

YD1

YG1

YGM1

temp.

q

NA

YD1 C508

YG1 C508

YGM1 C508

80 

6

5

white - white

YD1 C509

YG1 C509

YGM1 C509

90 

6

5

green - green

YD1 C510

YG1 C510

YGM1 C510

100 

6

5

red - red

YD1 C511

YG1 C511

YGM1 C511

110 

6

5

brown - brown

YD1 C512

YG1 C512

YGM1 C512

120 

6

5

grey - grey

YD1 C513

YG1 C513

YGM1 C513

130 

6

5

blue - blue

YD1 C514

YG1 C514

YGM1 C514

140 

6

5

white - blue

YD1 C545

YG1 C545

YGM1 C545

145 

6

5

white - black

YD1 C515

YG1 C515

YGM1 C515

150 

6

5

black - black

YD1 C655

YG1 C655

YGM1 C655

155 

6

5

blue - black

YD1 C516

YG1 C516

YGM1 C516

160 

6

5

blue - red

YD1 C517

YG1 C517

YGM1 C517

170 

6

5

white - green

YD1 C518

YG1 C518

YGM1 C518

180 

6

5

red - white

TEMPERATURE-RESISTANCE CURVE

Triple PTC

YD

= standard size bead 4 mm with shrunk-sleeve

YG

= standard size bead 4 mm with shrunk-sleeve and epoxy seal

YGM = mini-bead 3 mm with shrunk-sleeve and epoxy seal

Type

Type Resp.

Std. Colour 

code

YD3

YG3

temp.

q

NA

YD

YG

YD3 C508

YG3 C508

80 

6

5

white - black - black - white

YD3 C509

YG3 C509

90 

6

5

green - black - black - green

YD3 C510

YG3 C510

100 

6

5

red - black - black - red

YD3 C511

YG3 C511

110 

6

5

brown - black - black - brown

YD3 C512

YG3 C512

120 

6

5

grey - black - black - grey

YD3 C513

YG3 C513

130 

6

5

blue - black - black - blue

YD3 C514

YG3 C514

140 

6

5

white - black - black - blue

YD3 C545

YG3 C545

145 

6

5

white - black - black - black

YD3 C515

YG3 C515

150 

6

5

black - black - black - black

YD3 C655

YG3 C655

155 

6

5

blue - black - black - black

YD3 C516

YG3 C516

160 

6

5

blue - black - black - red

YD3 C517

YG3 C517

170 

6

5

white  - black - black - green

YD3 C518

YG3 C518

180 

6

5

red - black - black - white

Mini PTC

YGM = mini-bead 3 mm with shrunk-sleeve and epoxy seal

Type

Resp.

Std. Colour code

YGM3

temp.

q

NA

YGM3

YGM3 C508

80 

6

5

white - yellow - yellow - white

YGM3 C509

90 

6

5

green - yellow - yellow - green

YGM3 C510

100 

6

5

red - yellow - yellow - red

YGM3 C511

110 

6

5

brown - yellow - yellow - brown

YGM3 C512

120 

6

5

grey - yellow - yellow - grey

YGM3 C513

130 

6

5

blue - yellow - yellow - blue

YGM3 C514

140 

6

5

white - yellow - yellow - blue

YGM3 C545

145 

6

5

white - yellow - yellow - black

YGM3 C515

150 

6

5

black - yellow - yellow - black

YGM3 C655

155 

6

5

blue - yellow - yellow - black

YGM3 C516

160 

6

5

blue - yellow - yellow - red

YGM3 C517

170 

6

5

white  - yellow - yellow - green

YGM3 C518

180 

6

5

red - yellow - yellow - white

Threaded housing

YGM mini-bead 3 mm with shrunk-sleeve and epoxy seal

Type

Resp.

Std. Colour code

EF1

temp.

q

NA

EF1 C508

80 

6

5

white - white

EF1 C509

90 

6

5

green - green

EF1 C510

100 

6

5

red - red

EF1 C511

110 

6

5

brown - brown

EF1 C512

120 

6

5

grey - grey

EF1 C513

130 

6

5

blue - blue

EF1 C514

140 

6

5

white - blue

EF1 C545

145 

6

5

white - black

EF1 C515

150 

6

5

black - black

EF1 C655

155 

6

5

blue - black

EF1 C516

160 

6

5

blue - red

EF1 C517

170 

6

5

white  - green

EF1 C518

180 

6

5

red - white

When ordering please specify thread size, otherwise the stock M4 size will
be supplied.

PTC-Ther

mistors

02-02-02

1000-Y

-180

Firmensitz:

Postanschrift:

Telefon 49 (0) 72 31 787-0

Microtherm GmbH

Microtherm GmbH

Telefax 49 (0) 72 31 787-155

Täschenwaldstraße 3

Postfach 1208

Internet: http://www.microtherm.de

D-75181 Pforzheim

D-75112 Pforzheim

e-mail: stammhaus-pforzheim@microtherm.de

ELECTRICAL DATA

POWER SUPPLY:
Voltage:

42 V, 110 V, 230 V, 400 V, 415 V0 ac

Special voltages:

eg dc, please ask

Tolerance:

+ 10 % ... – 15 %

Power consumption:

less than 3VA

Frequency:

40 – 60 Hz

Operating temp.:

– 20 °C to 60 °C

RELAY OUTPUT
1 change-over contact
Switching capacity at 250V
Use category AC 11 3A
Continuous current rating 6A
Max. current rating of overload fuse 6 A

VOLTAGE TESTING
Test voltage between supply, relay contacts and PTC
circuit, 2.5 kV
Test voltage on output contacts, 1.0 kV

PTC CONNECTION
Max. quantity of PTC connectable:

6 pcs

Terminal voltage for PTC’s
Range:

larger 1.6 k

Smaller 3.6 k +/- 10 %

SPECIAL VERSIONS

PTC sensors can be delivered with a warning label/
tag. This has a 4 cm cord, so that the tag can be seen
from the exterior when attached to the motor, equip-
ment or plant, and will warn against applying voltages
higher than 2.5V (surely this should be 2.5 kV).
The ordering code for this label ist K105.

PTC SWITCHING DEVICE 
TYPE TKA1, TKA2
PTC RELAY UNIT 
TYPE TKA1, TKA2

FEATURES

●

sensor and relay unit are both interchangeable

●

fixed sensor response temperature from 
80 - 180 °C

●

safe monitoring of sensing circuit and sensor

●

upto 6 PTC’s can be connected

●

quick installation housing (DIN-EN 50022) or 
screw fixing (M4)

●

also available with push-button test light 
(can be retrofitted)

DESCRIPTION

These PTC relay units have been developed as state
of the art devices. All other commercially available
units can be replaced with ours.
Relay unit and sensors as per DIN 44081 and 44082
give optimum protection against thermal overload.
Together they provide a rapid and reliable motor-pro-
tection system.

Two basic formats are available:
TKA1 for applications where space is at a premium
TKA2 in a DIN housing, eg. for use in control panels

Any PTC thermistors that conform to DIN 44081 or
44082 can be connected to these relay units.

INSTALLATION

Screw or snap-on fixing TKA2
Installed on a 35 mm rail to DIN 46277 B.3 by means
of an integral snap-on housing.

Screw fixing TKA1

We reserve the right to alter specifications without notice.

PTC-Ther

mistors

02-02-02

1000-Y

-180