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IL01906001E
Instructional Literature
Page
2
Effective: May 2005
Arcflash Reduction Maintenance Switch
Application and Installation
1. Arcflash Reduction Maintenance Switch
Applications
1.1 The Arcflash Reduction Maintenance Switch Is Used
to Reduce Incident Energy
When the Arcflash Reduction Maintenance Switch is enabled and
fault current causes its operation, the fault clearing time of the
associated circuit breaker is very fast. Table 1 shows how inci-
dent energy varies with fault duration time for a work location
where the bolted fault level is 40 kA.
Table 1. Incident Energy vs. Fault Duration Time.
Table Notes:
Incident energy values shown in the table were calculated using the IEEE
1584 method for a 480 V system with a working distance of 24 in.
(609.6 mm). Other parameters are:
Grounding Type = Solid Grounded, and
Equipment Type = Switchgear
* Typical fault clearing time using the Arcflash Reduction Maintenance
Switch will be 0.05 seconds. Note that this time will vary slightly
depending on the circuit breaker manufacturer and type.
1.2 Choosing the Reduction Setting
The Arcflash Reduction Maintenance Switch has five (5) reduction
settings (RS) (see Figure 1) that are based on multiples of the per
unit secondary current monitored by the trip unit of its associated
circuit breaker:
(2.5 ×, 4.0 ×, 5.9 ×, 7.6 × or 9.8 × sensor rating).
Figure 1. Arcflash Reduction Maintenance Switch RS.
One of these RSs must be determined and selected by a person
who is experienced in power system analysis. Each application of
an Arcflash Reduction Maintenance Switch will require power sys-
tem analysis to determine the fault currents that flow through the
circuit breaker associated with the Arcflash Reduction Mainte-
nance Switch.
This setting choice normally does not change unless there are
future system modifications that could increase or decrease fault
levels at the circuit breaker location.
The RS is determined using the following steps:
1. Calculate the arcing fault current flowing through the circuit
breaker associated with the Arcflash Reduction Maintenance
Switch.
Note:
Table 1 shows that arcing fault current can be much lower than of the
bolted fault current for system voltages less than 1000 V. Formulas from NFPA
70E-2004, Annex D
©
NFPA
, and IEEE Std. 1584
TM
-2002 can be used to calcu-
late the arcing current.
2. Determine the total transient load current that can flow to
loads fed by the circuit breaker equipped with the Arcflash
Reduction Maintenance Switch. These can include motor in-
rush and transformer in-rush.
3. Choose a RS for the Arcflash Reduction Maintenance Switch
that is below the minimum arcing current (85% of calculated
arcing current) and above the total transient load current (see
Figure 1). Include the tolerance of the Arcflash Reduction
Maintenance Switch pickup in the setting choice.
BOLTED FAULT
kA
ARCING FAULT
kA
FAULT DURATION
sec
INCIDENT ENERGY
cal/cm
2
40.0
20.0
2.00
89.0
40.0
20.0
0.50
22.2
40.0
20.0
0.40
17.8
40.0
20.0
0.30
13.3
40.0
20.0
0.20
8.9
40.0*
20.0*
0.05*
2.2*
WARNING
ONLY QUALIFIED PERSONS, AS DEFINED IN THE NATIONAL ELEC-
TRIC CODE, WHO ARE FAMILIAR WITH THE INSTALLATION AND
MAINTENANCE OF POWER CIRCUIT BREAKERS AND THEIR ASSOCI-
ATED SWITCHGEAR ASSEMBLIES SHOULD PERFORM ANY WORK
ASSOCIATED WITH THESE BREAKERS.
PICK UP
SETTINGS
REDUCTION SETTING
SWITCH POSITION
9.8
R1
7.6
R2
5.9
R3
4.0
R4
2.5
R5
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