Schneider Electric 2.0A Short-Time Protection Switches, English, I2t off Isd at 10 Ir seconds

48049-136-05	Micrologic™ 2.0A, 3.0A, 5.0A, and 6.0A Electronic Trip Units
Rev. 01, 07/2012	Section 1—General Information

Short-Time Protection

Figure 8: Short-Time Protection Switches

Short-time protection protects equipment

Micrologic 5.0A Trip Unit

Micrologic 6.0A Trip Unit

against short circuits.

• Short-time protection is standard on 2.0A,

5.0A and 6.0A trip units. It is not available on

3.0A trip units.

• Short-time protection is based on the long-

time pickup (Ir).

• The short-time pickup (Isd) (A) sets current

level (below instantaneous trip level) at

which circuit breaker will trip after the preset

time delay.

• The short-time delay (tsd) (B) sets the length

of time that the circuit breaker will carry an

A

B

06133204

		long time
	Ir		.8 .9			tr		8
	.7					(s)	4		12
	.6			.95	2				16
	.5			.98	1				20
	.4 x In 1						.5 @ 6 Ir24
		short time
	Isd		4			tsd		.4	.3
3				5		(s)	.4
					.3				.2
2.5				6
2				8	.2				.1
1.5				10			.1	2	0
			x Ir			on		I t	off

delay

alarm

instantaneous

I i

8

6 10

4 12

315

2off

x In

A

B

06133351

		long time
	Ir		.8		tr		8
	.7			.9	(s) 4			12
	.6			.95	2			16
	.5			.98	1			20
	.4 x In 1				.5 @ 6 Ir24
		short time
	Isd		4		tsd	.4	.4 .3
3				5	(s)
					.3			.2
2.5				6
2				8	.2			.1
	1.5 x Ir			10	.1			0
					on I2t off
						delay
			E		tg	.4	.4 .3
	D			F	(s)
					.3			.2
	C			G
	B			H	.2			.1
	A			J	.1		I2t	0
					on			off

ground fault

alarm

instantaneous

I i

8

5 10

4 12

315

2off

x In

test

ENGLISH

overcurrent above the short-time pickup

current level before tripping. It is adjustable

on the 5.0A and 6.0A trip unit and factory set

to zero on the 2.0A trip unit.

• The I2t on/I2t off option provides improved

selectivity with downstream protective

devices:

— With I2t off selected, fixed time delay is

provided.

— With I2t on selected, inverse time I2t

protection is provided up to 10 x Ir.

Above 10 x Ir, fixed time delay is

provided.

• Intermittent currents in the short-time tripping

range which do not last sufficiently long to

trigger a trip are accumulated and shorten

the trip delay appropriately.

• Short-time protection can be zone-selective

interlocked (ZSI) with upstream or

downstream circuit breakers.

• Setting tsd to the 0 setting turns off zone-

selective interlocking.

• Short-time protection uses true RMS

measurement.

• Short-time pickup and delay can be adjusted

to provide selectivity with upstream or

downstream circuit breakers.

Table 2:	Micrologic Trip Unit Short-Time Delay Values
Setting		Short-Time Delay
I2t off (Isd at 10 Ir) (seconds)		0	0.1	0.2	0.3	0.4
I2t on (Isd at 10 Ir) (seconds)			0.1	0.2	0.3	0.4
tsd (min. trip) (milliseconds)		20	80	140	230	350
tsd (max. trip) (milliseconds)		80	140	200	320	500

NOTE: Use I2t off with ZSI for proper coordination. Using I2t on with ZSI is not recommended as the delay in the upstream device receiving a restraint signal could result in the trip unit tripping in a time shorter than the published trip curve.

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