Specifications are subject to change without notice 1
Current and Voltage Controls
Product Description
3-phase and neutral moni-
toring plug-in relay for sepa-
rate upper and lower voltage
control. Often used to control
all 3 phases and neutral where
the supplied electrical power
Ordering Key
Housing
Type
Output
Power supply
• Monitoring relay for 3-phase upper/lower
phase-phase neutral voltage control
• Measures if all 3 phase-neutral voltages are
within set limits
• Measures on own power supply
• Operates irrespective of phase sequence
• Upper and lower limits separately adjustable
• Built-in adjustable timer function
• Output: 10 A SPDT relay
• Plug-in type module
• S-housing
• LED-indication for power supply and output ON
• Power supply is the 3-phase + N measuring voltage
is unstable or varies in value
in order to monitor that the
attached motors are perfor-
ming as required. The S 1721
features built-in time delay.
Input Specifications
Input
Pins 5, 6 & 7 Arbitrary phase sequence
Pin 11 Neutral
Measuring ranges (VAC)
Power supply (phase-phase)
3x220 +N 3x380 +N 3x400+N
± 18% ± 18% ± 18%
Range (phase-neutral) 104-150 180-260 188-271
Upper level 130-150 225-260 235-271
Scale
102-118% 102-118%
102-118%
Lower level 104-124 180-215 188-225
Scale 82-98% 82-98% 82-98%
Power supply (phase-phase) 3x415+N
± 18%
Range (phase-neutral) 204-276
Upper level 252-276
Scale 102-118%
Lower level 204-228
Scale 82-98%
measures value of own
supply. Range equals rms
value of a sinusoidal voltage
Output SPDT relay
Rated insulation voltage 250 VAC (rms)
(cont./elect.)
Contact ratings (AgCdO) µ (micro gap)
Resistive loads AC 1 10 A/250 VAC (2500 VA)
DC 1 1 A/250 VDC (250 W)
or 10 A/25 VDC (250 W)
Small inductive loads AC 15 2.5 A/230 VAC
DC 13 5 A/24 VDC
Mechanical life ≥30 x 106operations
Electrical life AC 1 ≥2.5 x 105operations
(at max. load)
Operating frequency ≤7200 operations/h
Dielectric strength
Dielectric voltage ≥2 kVAC (rms) (cont./elect.)
Rated impulse withstand volt. 4 kV (1.2/50 µs) (cont./elect.)
(IEC 60664)
Type Selection
Plug Output Timer Supply: 220 VAC Supply: 380 VAC Supply: 400 VAC Supply: 415 VAC
Circular SPDT Yes S 1721 156 220 S 1721 156 380 S 1721 156 400 S 1721 156 415
Circular SPDT No SYY 155 220 SYY 155 380 SYY 155 415
3 Phase-neutral Max. and Min. Voltage Control
Types S 1721, SYY 155
Output Specifications
S 1721 156 220
2Specifications are subject to change without notice
Sockets◊S 411
Hold down spring◊HF
Mounting rack SM 13
Socket covers BB 4
Front mounting bezel FRS 2
Potentiometer lock PL 2
For further information refer to "Accessories".
AccessoriesTime/Range Setting
Range setting
Upper potentiometer:
Adjustment of upper limit in
percent.
Middle potentiometer:
Adjustment of lower limit in
percent.
Hysteresis
1-3% of rms-value
Time setting
Bottom potentiometer:
Time setting on relative scale
(not SYY 155).
Time
Adjustable delay on release:
0.2 to 10 s
S 1721, SYY 155
Reaction time τ= 2 s, worst case reaction
time may be up to 5 x τ
Adjustable delay on release
built-in (0.2s - 10s)
Note:
Reaction time + set time =
real delay on release time
Accuracy
OFF delay 10s, -1/+3 s on max.
< 0.1 s on min.
Time function
Delay on release 0.2-10 s. adj.
Indication for
Power supply ON LED, green
Output ON LED, red
Environment (IEC 60947-1)
Degree of protection IP 20 B (IEC 60529)
Pollution degree (IEC 60664)
1: S 1721 380/400/415
SYY 155 380/415
2: S 1721 220, SYY 155 220
Operating temperature -20° to +50°C (-4° to +122°F)
Storage temperature -50° to +85°C (-58° to +185°F)
Weight 200 g
Approvals UL, CSA
Power supply AC types Overvoltage cat. III (IEC 60664)
Rated operational voltage (IEC 60038)
Through pins 5, 6, 7 & 11 220 3 x 220 VAC ± 18%,
(neutral) 45 to 65 Hz
380 3 x 380 VAC ± 18%,
45 to 65 Hz
400 3 x 400 VAC ± 18%,
45 to 65 Hz
415 3 x 415 VAC ± 18%,
45 to 65 Hz
Voltage interruption ≤40 ms
Dielectric voltage None (supply/elect.)
Rated impulse withstand volt. 4 kV (1.2/50 µs) (line/neutral,
line/line), direct connection
to electronics
Internal measuring circuit is
connected to pins 5 & 11
Rated operational power 3.5 VA
Mode of Operation
Connected to 3 phases and
neutral, the S 1721 and SYY
155 measure sinusoidal vol-
tages. The phase sequence is
arbitrary.
The relay operates as long as
all 3 phase-neutral voltages
are within the set upper and a
lower limit. The two limits are
set separately.
For S 1721 applies that if one
or more of the phase-neutral
voltages rises above the up-
per limit or drops below the
lower limit, the relay releases
after the set time period
whereas SYY 155 releases
immediately.
The relay operates again
when all 3 phase-neutral vol-
tages are within set limits.
Hysteresis on operate is 2%.
Example 1
Mains monitoring
The relay measures if the 3
phase-neutral voltages are
within the upper and lower
limits. The limits are adjusted
on the two built-in potentio-
meters.
Example 2
Monitoring load supply
The relay can protect loads,
such as heating elements,
against overvoltage and
thereby against increase in
current, which could otherwise
destroy the heating elements.
Undervoltage to ohmic loads
causes insufficient heating
capacity, and this can also be
monitored.
The relay cannot be used for
load monitoring if the load is a
motor, as the regenerated
phase voltage at e.g. fuse
blowing is indefinable and
dependent on the mechani-
cal performance when the
failure occurs.
Supply Specifications General Specifications
Specifications are subject to change without notice 3
Operation Diagrams
S 1721
Upper limit
Hysteresis
Lower limit Hysteresis
Relay ON Phase L1, L2 and L3
SYY 155
Upper limit
Hysteresis
Lower limit Hysteresis
Relay ON Phase L1, L2 and L3
S 1721, SYY 155
Wiring Diagrams
S 1721, SYY 155 S 1721, SYY 155
Example 1 Example 2
