
Data sheet
Liquid Level Alarms, Safety Control, Liquid Level Regulator
RT 280A, RT 281A
RT 280A and RT 281A are primarily used as liquid
level alarms and safety switches to prevent too
high a liquid level in liquid separators.
Secondarily, RT 280A and RT 281A can be used
as liquid level regulators where a liquid level
dierential of up to ±40 mm can be permitted.
When used as safety switches, RT 280A and RT
281A ensure that the max. permissible refrigerant
level in ooded evaporators, pump tanks or
liquid separators is not exceeded.
As liquid level regulators, RT 280A and RT 281A
maintain a constant average refrigerant level
in ooded evaporators, pump tanks or liquid
separators.
Features
Approvals
• Waterproof versions, enclosure IP66
• Single pole changeover switch (SPDT) suitable
for AC / DC loads
CE-approved according to
EN 60947-4, -1 EN 60947-5, -1
• Interchangeable contact system
Meets the requirements of VDE 0660 (VDE:
Verband Deutscher Elektrotechniker)
© Danfoss | DCS (jmn) |2016.07
DKRCC.PD.GF0.A4.02 | 520H11306 | 1

Data sheet | Liquid Level Alarms, Safety Control, Liquid Level Regulator, types RT280A, RT281A
Technical data
Refrigerants
R717 (NH3), R22 and R502
"For other refrigerants, please contact Danfoss."
R12 -50 – 10 °C
Operating ranges for RT 280A
R22 and R717 (NH
) -50 – 0 °C
3
R502 -65 – -5 °C
Operating ranges for RT 281A R22 and R717 (NH
) -30 – 20 °C
3
Ambient temperature -50 – 70 °C
Switch Single pole changeover switch (SPDT), code no. 017- 4030 66
AC1: 10 A, 400 V
Alternating current
AC3: 4 A, 400 V
1
)
Contact load
AC15: 3 A, 400 V
Direct current DC13: 12 W, 220 V
Weight 2.0 kg
Enclosure IP66 to IEC 529.
Pressure connection G
3
⁄8 A with ø 6.5 / ø 10 mm weld nipple
Max. working pressure PB = 22 bar
Max. test pressure Pe = 25 bar
Materials
Ordering
Adsorption charge
Thermostatic element
3 m capillary tube
Max. permissible bulb temperature: 80 °C
Bulb with electric heater
1)
Max. short-time AC3 current: 28 A
10 W heater for 24 V DC or AC The heater must be constantly
energised whilst the system is in operation. 1.5 m connection cable.
Liquid level dierential
With a steady liquid level and a liquid level
variation rate of max. 15 mm/min, the dierential
will be approx. 10 mm on a rise in level and
approx. 20 mm on a fall in level. In unfavourable
operating conditions, dierentials of approx.
20 mm on a rise in level and approx. 60 mm on a
fall in level must be expected.
Gaskets are non-asbestos.
RT 280A code no. 017D004066
RT 281A code no. 017D004666
© Danfoss | DCS (jmn) |2016.07
DKRCC.PD.GF0.A4.02 | 520H11306 | 2

Data sheet | Liquid Level Alarms, Safety Control, Liquid Level Regulator, types RT280A, RT281A
Design / Function
3. Pressure connection
4. Bellows element
5. Setting disc
9. Scale
10. Loop terminal
11. Pg 13.5 screwed cable
entry
12. Spring
14. Terminals
15. Spindle
16. Switch (17-4030)
17. Upper guide bush
18. Contact arm
20. Lower guide bush
38. Earth terminal
RT 280A and RT 281A units are based on RT 260A.
The lower element is thermal and has an
electrically heated bulb.
As stated, the units are primarily for use as liquid
level alarms and safety switches. In designing the
units, emphasis was placed on the failsafe function
In the event of a defect in the thermal element,
the compressor is stopped and liquid injection
cut o. Restart is only possible after the defect
has been rectied.
Note:
If the evaporating temperature, and with it the
reference pressure, is higher than the max.
regulation range temperature, the unit will react
as though the liquid level in the liquid container
was too high.
This also applies in the case of loss of charge, for
example if the capillary tube or heating element
in the bulb is damaged, or if current to the
heating element falls.
The element heating or cooling signal is
compared to the reference pressure and then
.
converted to an electric on / o impulse.
The regulating principle is based on the heat
conduction dierence between the liquid and
vapour phases of the refrigerant.
© Danfoss | DCS (jmn) |2016.07
DKRCC.PD.GF0.A4.02 | 520H11306 | 3

Dimensions [mm] and
weights [kg]
Net weight 2.0 kg
© Danfoss | DCS (jmn) | 2016.07
DKRCC.PD.GF0.A4.02 | 520H11306 | 4