Siemens 480V manual LV Power Circuit Breaker Trip Unit, Static Trip III Trip Unit

480V Metal-Enclosed Switchgear

LV Power Circuit Breaker Trip Unit

General

Static Trip® III Trip Unit

Static overcurrent tripping devices have been standard on Siemens circuit break- ers for over thirty years. The Static Trip Ill trip unit features microprocessor-con- trolled tripping, while providing RMS sensing for standard overcurrent protec- tion, and optional metering and communi- cations functions. Located in the lower right side of the breaker, the trip unit is readily accessible for simple reading and adjustment of all settings and indicators. Static Trip III trip units are interchange- able on all ratings of low voltage circuit breakers.

The time / current characteristics of the Static Trip III trip unit are shown on page 62.

All communicating Static Trip III trip units include a local communication port that supports the breaker-mounted display unit or BDU. The BDU features a high-visibility

Static Trip® Ill Trip Unit (right) and Breaker Display Unit (left)

4

480V Metal-Enclosed Switchgear

alpha-numeric display. Real-time metered values, min/max values, event log data and setpoint data can be read on the BDU in straightforward engineering units. Alarm and relay setpoint can be config- ured using the BDU keypad.

This data can also be communicated to other devices or computers for control monitoring via Siemens’ ACCESS sys- tem. See Section 1 of this guide for a thorough description of ACCESS.

Siemens RMS sensing samples the entire current wave shape and calculates the effective heating value of the current. Static Trip Ill trip units provide accurate protection and avoid unnecessary trips.

Table 4.2 Static Trip III Settings

T: Long Time

Setting a	Delay
(X Sensor Rating)	(Seconds @ 6X Setting)
.5, .55, .6, .65, .7, .75,	3.5, 6, 10
.8, .85, .9, .95, 1.0	17, 30
S: Short Time
Pickup	Delay
(X LT Setting)	(Seconds)
2, 3, 4, 5,	0.8, .15, .22
6, 7, 8, 12	.30, .40
I: Instantaneous
Pickup	Delay
(X Sensor Rating)	(Seconds)
2, 4, 6, 8,	No Intentional
12, 15	Delay
G: Ground Fault
Pickup	Delay
(% Ground Sensor)	(Seconds)
20, 30, 40, 50, 60	.10, .25, .40

aPickup is fixed at 1.1 times long time setting.

Harmonics distort the current wave shape and can increase its peak value. Normal peak-sensing units may trip, causing nui- sance shutdowns.

56	Siemens Electrical Products and Systems	CSI Section 16470
	Specification Guide