3-Phase Monitor

 

• Detects phase loss, low voltage, phase reversal
• 50Hz, 60Hz and 400Hz models
• Automatic or manual reset
• Five year unconditional warranty

 

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.

 

Specifications

AUTO Reset MANUAL Reset	B257B B257BM	257B 257BM	A257B A257BM	EX257B EX257BM	B257B-400 B257BM-400	257B-400 257BM-400	EX257B-415V EX257BM-415V
Nominal AC (phase to phase)	120VAC	208/240VAC	480VAC	380VAC	120VAC	208/240VAC	415VAC
Case Color	Gray	Red	Yellow	Yellow	Gray	Red	Yellow
Adjustment range	85-120VAC	160-240VAC	380-480VAC	300-400VAC	85-120VAC	160-240VAC	340-440VAC
Frequency	60Hz	60Hz	60Hz	50Hz	400Hz	400Hz	50Hz
Power consumption	1.4W	2.4W	3.7W	3.0W	1.4W	2.4W	3.3W
Transient protection	2500VAC for 10ms
Repeat accuracy	± 0.1% of set point (fixed conditions)
Response time	50ms drop out
Dead band	Approximately 2%
Output contacts	SPDT 10 amps at 240VAC resistive
Expected relay life	Mechanical: 10 million operations Electrical: 100,000 operations at rated load
Operating temp	-20° to +131° F
Humidity tolerance	0 - 97% w/o condensation
Enclosure material	ABS plastic cover
Mounting	8-pin socket ( **sold separately)
Weight	5 ounces
Agency approvals	UL Recognized* and CSA Certified *Conditions of acceptability: (1) the 380V and 480V versions must be used with a UL Recognized 600VAC socket. (2) For use in a Pollution Degree 2 environment (3) To be installed on the load side of branch circuit protection rated 10A.

Downloads

Document	File Type	File Size	Download
Model Model 257 Datasheet	PDF	608 KB

© 2023 Relay Specialties, Inc.
17 Raritan Road, Oakland, NJ 07436 | 800-526-5376
Created By: G.Dezines