Murphy A20 Series Magnetic Switch, Pre-Alarm Using A20/A25TABS, Typical Internal Wiring Diagrams

Magnetic Switch

INDUCTIVE AND HIGH CURRENT LOADS REQUIRE THE USE OF A MAGNETIC SWITCH. The SWICHGAGE® contacts are for light-duty elec- trical switching to operate alarms or control devices. Murphy manufactures the Magnetic Switch for protection of the pilot-duty SWICHGAGE® limit contacts.

TATTLETALE® Magnetic Switches show the cause of shutdown for applica- tions that include: capacitor discharge or magneto ignitions, battery systems and electric motor driven equipment. Typical wiring diagrams are shown below.

A20T Temperature		117 Magnetic Switch
SWICHGAGE®
	HIGH	C	S	B
C	N. O.

Energized To Run Devices
_	+
Battery

A20P Pressure		A20T Temperature			518PH TATTLETALE®
	SWICHGAGE®		SWICHGAGE®
					R
LOW				HIGH	G NC SW1 SW2 B
	N.O. SWICHGAGE®
N. C.	C	instruments	C	N. O.

	_	+
Energized To Run Devices	Battery
N.C. switches option

Pre-Alarm Using A20/A25TABS

The A20TABS and A25TABS features a standard limit contact for equipment shutdown on high temperature. It also has an internal SPDT snap-switch to sig- nal an alarm before shutting down. When the snap-switch trips (preset point), on rising temperature, the switch completes a circuit to activate an alarm. If the temperature continues to increase, the face-adjustable pointer contact will make

and the shutdown circuit will be completed (see the typical diagram below for reference). The front contact shutdown limit setting (which is adjustable) and the snap-switch are preset at the factory. Refer to “Temperature Ranges and Factory Settings” table on opposite page for settings. For alternative alarm before shutdown, see Magnetic Switch model 760A or 761APH.

Alarm Before		A20TABS
Shutdown			®
		SWICHGAGE
MINI-SIREN®
			G
ABS		HIGH
N. C.	C	N. O.
Shutdown Device		Opens circuit to
or Ignition Circuit		shutdown engine.

518PH

TATTLETALE®

R

NC SW1 SW2 B

_	+
	Battery

Typical Internal Wiring Diagrams

Pointer shown in the shelf position. Pointer type contact rating: pilot-duty 2 A @ 30 VAC/VDC resistive.

Snap-acting switch rating: 3 A @ 30 VDC inductive. 4 A @ 125 VAC inductive.

A20T A20T-HL A20TABS A20TE

HIGH LOW HIGH ABS

HIGHRESET

SET

N. C. C N. O.	N. C. C	N. O.	N. C. C N. O.	N. C. C N. O.
A25T	A25T-HL	A25TABS	A25TABS-HL	A25TE

N. C. C N. O. N. C. C N. O. N. C. C

RESET

N. O.	N. C.
SET	RESET

C	N. O.	N. C. C	N. O.
	SET	RESET	SET

HIGH

LOW

HIGH

HIGH

LOW

HIGH

L

P

H

L

P

H

L

P

H

L

P

H

L

P

H

Bulletin AT-95026B page 3 of 4