DESCRIPTION
The Model 257 continuously monitors 3-phase power
lines for abnormal conditions. When properly
adjusted, the Model 257 monitor will detect phase
loss on a loaded motor even when regenerated
voltage is present.
This device consists of a solid-state voltage and
phase-angle sensing circuit, driving an electro-
mechanical relay. When correct voltage and phase
rotation are applied, the internal relay will energize.
A fault condition will de-energize the relay. When the
fault is corrected, the monitor will automatically reset
(a manual reset version is also available).
The Model 257 does not require a neutral connection
and can be used with Wye or Delta systems. Voltage
ranges are sufficiently wide to allow for proper
adjustment to existing conditions. Both “TRIP” and
“NORM” condition indicators are provided to aid in
adjustment and system trouble-shooting.
SPECIFICATIONS
AUTO Reset
MANUAL Reset
B257B
B257BM
257B
257BM
A257B
A257BM
EX257B
EX257BM
B257B-400
B257BM-
400
257B-400
257BM-400
Nominal AC voltage
(phase to phase)
120 vac 208/240 vac 480 vac 380 vac 120 vac 208/240 vac
Case Color Gray Red Yellow Yellow Gray Red
Adjustment range 85-120vac 160-240vac 380-480vac 300-400vac 85-120vac 160-240vac
Frequency 60 Hz 60 Hz 60 Hz 50 Hz 400 Hz 400 Hz
Power consumption
0.75W 1.5W 4.5W 3.75W 0.75W 1.5W
Transient protection 2500 VAC for 10msec
Repeat accuracy
± 0.1% of set point (fixed conditions)
Response time 50 msec (set or reset)
Dead band Approximately 2%
Output contacts SPDT 10 amps at 240 VAC resistive
Expected relay life Mechanical: 10 million operations
Electrical: 100,000 operations at rated load
Operating temp -40° to +131° F
Humidity tolerance 0 - 97% w/o condensation
Enclosure material Dust cover: ABS plastic
Mounting 8-pin socket ( **sold separately)
Weight 5 ounces
Agency approvals UL Recognized* and CSA Certified
*condition of acceptability: the 380V and 480V versions
must be used with a UL Recognized 600 VAC socket
** Order 8-pin socket number 51X120
DIMENSIONS
TYPICAL APPLICATION
ll Detects phase loss, low voltage, phase reversal
ll 50 Hz, 60 Hz and 400 Hz models
ll Automatic or manual reset
ll Five year unconditional warranty
MODEL 257
3-Phase Monitor
TIME MARK is a division of
Telephone: Main - (918) 438-1220
Sales - (800) 862-2875
Fax: (918) 437-7584
E-mail: sales@time-mark.com
Internet: http://www.time-mark.com
Doc No. 87A189 12/00
© 2000 TIME MARK CORPORATION
11440 East Pine Street
Tulsa, Oklahoma 74116
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