Phase Loss Relays | McMaster-Carr

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16 Products

About Motor Switches and Starters

Remotely control these relays through an app on your smartphone—they simultaneously monitor phase, voltage, and frequency. The downloadable app lets you change the tripping range, modify settings, and save programs to apply to multiple relays. Tap your smartphone or tablet to the relays to connect to them. They use NFC (near field communication), so you don’t need to manually pair them like Bluetooth devices.

You’ll often see these relays used to protect motors, generators, and other three-phase circuits from burning out or overheating. They'll switch the circuit off if they detect voltage or frequencies outside of the set range or phase loss, imbalance, or reversal. You can see that they're wired correctly and when they're actuated based on the LED indicators. Rated IP20, they have recessed terminals that keep fingers and other objects from touching live circuits. Mount them on a 35 mm DIN rail (also known as DIN 3 rail) for fast installation.

		Trip Voltage			Trip Frequency
Number of Terminals	Input Voltage	Min.	Max.	Input Frequency, Hz	Min., Hz	Max., Hz	Trip Time, sec.	Reset Type	Switching Current @ Voltage	Max. Switching Voltage	Ht.	Wd.	Dp.	Operating System Compatibility		Each
2 Circuits Controlled with 2 Off (Normally Open) or 2 On (Normally Closed)—DPDT
With Screw Terminals
12	208V AC, 240V AC, 300V AC, 480V AC	208V AC	480V AC	50, 60	45	66	0.1-60	Automatic	8 A @ 240 V AC	250V AC	3.5"	0.9"	3.9"	Android 7.0 or Later, iOS 14.5 or Later	0000000	0000000

Multifunction Monitoring Relays

Monitor phase, voltage, and frequency at the same time to protect motors, generators, and other three-phase circuits from burning out or overheating. They'll switch the circuit off if they detect voltage or frequencies outside of the set range or phase loss, imbalance, or reversal. Rated IP20, they have recessed terminals that keep fingers and other objects from touching live circuits. Mount them on a 35 mm DIN (also known as DIN 3 rail) for fast installation.

These relays use IO Link, so they can be programmed, monitored, and reset remotely by connecting them to a programmable logic controller (PLC), human-machine interface (HMI), or computer. If you want to program them locally, they have a keypad.

Relays with spring-clamp terminals connect and disconnect to wire without screws. Because there’s no screw, these connections are less likely to loosen over time, even in high-vibration environments.

		Trip Voltage			Trip Frequency
Number of Terminals	Input Voltage	Min.	Max.	Input Frequency, Hz	Min., Hz	Max., Hz	Trip Time, sec.	Reset Type	Switching Current @ Voltage	Max. Switching Voltage	Adjustment Style	Ht.	Wd.	Dp.		Each
1 Circuit Controlled with 1 Off (Normally Open) or 1 On (Normally Closed)—SPDT
With Screw Terminals and IO Link
12	24V DC	90V AC	760V AC	50, 60	15	70	0.1-30	Automatic	3 A @ 240 V AC 1 A @ 24 V DC	400V AC 250V DC	Keypad, External Controller	3.9"	0.9"	3.6"	0000000	0000000
With Spring-Clamp Terminals and IO Link
12	24V DC	90V AC	760V AC	50, 60	15	70	0.1-30	Automatic	3 A @ 240 V AC 1 A @ 24 V DC	400V AC 250V DC	Keypad, External Controller	3.9"	0.9"	3.6"	0000000	000000

Surface-Mount Motor Voltage Monitors

Protect electric motors from phase loss, phase reversal, overvoltage, undervoltage, and voltage imbalance. Also known as voltage-monitoring relays, these monitors cut power to a motor when a fault occurs.

				Trip Time, sec.		Switching
Input Voltage Range	No. of Terminals	Control Power, W	Voltage Imbalance Adjustment	Automatic Reset	Delayed Automatic Reset	Current, A	Voltage	Ht.	Wd.	Specifications Met		Each
1 Circuit Controlled with 1 Off (Normally Open) or 1 On (Normally Closed)—SPDT
Three Phase
190-480V AC	7	6	2%-8%	1-30	1-500	10	240V AC	3.5"	2.08"	UL Listed	0000000	0000000
475-600V AC	7	6	2%-8%	1-30	1-500	10	240V AC	3.5"	2.08"	UL Listed	0000000	000000

DIN-Rail Mount Motor Voltage Monitors

Mount these monitors to 35 mm DIN rail. They protect electric motors from phase loss, phase reversal, overvoltage, undervoltage, and voltage imbalance. Also known as voltage-monitoring relays, they cut power to a motor when a fault occurs.

						Switching
Input Voltage Range	No. of Terminals	Control Power, W	Voltage Imbalance Adjustment	Trip Time, sec.	Reset Type	Current, A	Voltage	Horsepower @ Voltage	Ht.	Wd.	Specifications Met		Each
1 Circuit Controlled with 1 Off (Normally Open) or 1 On (Normally Closed)—SPDT
Three Phase
200-480V AC	9	5	2%-10%	1-30	Automatic	10	240V AC	1/3 hp @ 240 V AC	3"	2"	UL Listed, C-UL Listed	0000000	0000000

Socket-Mount Motor Voltage Monitors

Plug these monitors into relay sockets for fast installation and replacement. They protect electric motors from phase loss, phase reversal, overvoltage, undervoltage, and voltage imbalance. Also known as voltage-monitoring relays, they cut power to a motor when a fault occurs.

Relay sockets (sold separately) mount to 35 mm DIN rail or flat surfaces.

Voltage Monitors
						Switching							Relay Sockets
Input Voltage Range	No. of Terminals	Control Power, W	Voltage Imbalance Adjustment	Trip Time, sec.	Reset Type	Current, A	Voltage	Ht.	Wd.	Specifications Met		Each		Each
1 Circuit Controlled with 1 Off (Normally Open) or 1 On (Normally Closed)—SPDT
Three Phase
200-480V AC	8	5	2%-10%	0.25-30	Automatic	10	240V AC	2.4"	1.8"	UL Recognized Component, CSA Certified	0000000	0000000	0000000	00000

Overload Protectors for Motor Starters

Upgrade motor starters that use thermal overload protection with these solid-state overloads—they don't use heating elements, so enclosure ventilation and cooling is not required. All have a full-load amp adjustment dial to accommodate circuits with different full-load amp ratings.

If the full-load amp rating is not shown on your motor’s faceplate, estimate the current rating (given the motor’s horsepower and voltage).

2 Auxilliary Contacts with 1 Off (Normally Open), 1 On (Normally Closed)
Overload Current, A	Trip Time, sec.	Overload Protection Class	Motor Protection	Ht.	Wd.	Dp.	Wire Connection Type	Specifications Met		Each
Single Phase
3-12	5, 10, 20, 30	5, 10, 20, 30	Overvoltage, Phase Loss	2.2"	3.5"	3.2"	Screw Terminals	UL Listed, CSA Certified	0000000	0000000
5.5-22	5, 10, 20, 30	5, 10, 20, 30	Overvoltage, Phase Loss	2.2"	3.5"	3.2"	Screw Terminals	UL Listed, CSA Certified	0000000	000000
Three Phase
0.75-3.4	5, 10, 20, 30	5, 10, 20, 30	Overvoltage, Phase Loss	3.2"	3.5"	3.2"	Screw Terminals	UL Listed, CSA Certified	0000000	000000
3-12	5, 10, 20, 30	5, 10, 20, 30	Overvoltage, Phase Loss	2.2"	3.5"	3.2"	Screw Terminals	UL Listed, CSA Certified	0000000	000000
5.5-22	5, 10, 20, 30	5, 10, 20, 30	Overvoltage, Phase Loss	2.2"	3.5"	3.2"	Screw Terminals	UL Listed, CSA Certified	0000000	000000
10-40	5, 10, 20, 30	5, 10, 20, 30	Overvoltage, Phase Loss	2.2"	3.5"	3.2"	Screw Terminals	UL Listed, CSA Certified	0000000	000000
13-52	5, 10, 20, 30	5, 10, 20, 30	Overvoltage, Phase Loss	2.3"	4.5"	4"	Screw Terminals	UL Listed, CSA Certified	0000000	000000
25-100	5, 10, 20, 30	5, 10, 20, 30	Overvoltage, Phase Loss	2.3"	4.5"	4"	Screw Terminals	UL Listed, CSA Certified	0000000	000000