3-Phase Monitor

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 electromechanical 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.

Specs

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)

120VAC 

208/240VAC 

480VAC 

380VAC 

120VAC 

208/240VAC 

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

 2500VRMS for 10 msec

Repeat Accuracy

 ± 0.1% of set point
(fixed conditions)

Response Time

 50 msec (set or reset)

Dead Band

Approximately 2% 

Output Contacts

 SPDT 10A at 240 VAC resistive

Expected Relay Life

        Mech:     10 million operations
        Elec:       100,000 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 oz. 

Agency Approval

UL Recognized* and CSA Certified
*condition of acceptability: the 380V and 480V versions
must be used with a UL Recognized 600 VAC socket

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