Download SEMI STEP: Introduction to SEMI S2-0706

SEMI STEP:
Introduction to SEMI S2-0706
Short Circuit Current Rating
Edward Karl
Program Manager
Corporate Product EHS
Applied Materials
Introduction to SEMI S2-0706
Short Circuit Current Rating
• NFPA 79-2005, NFPA 70-2005 (NEC), UL 508A, and IEC 60204-1 are
turning their focus from interrupting capacity of the equipment's
main overcurrent protective device, to short circuit current rating
of the equipment (machine) industrial control panel.
• In an effort to harmonize with changes in these standards, the
nameplate criteria of SEMI S2 and SEMI S22 will be updated in July
to include the short circuit current rating of the equipment or its
industrial control panel.
• SEMI S2 and SEMI S22 will also require that this information be in
the equipment installation instructions.
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SEMI STEP: Introduction to SEMI S2-0706
Introduction to SEMI S2-0706
NEC Compliance Map
Source Reference: SquareD website
http://us.squared.com/us/products/motor_control.nsf/unid/BEABDD3D2C1FB03C85256EBE0047F560/$file/ul508aFrameset.htm
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SEMI STEP: Introduction to SEMI S2-0706
Introduction to SEMI S2-0706
Definitions
• “Short circuit current rating” is defined in UL 508A as "The
prospective symmetrical fault current at a nominal voltage to
which an apparatus or system is able to be connected without
sustaining damage exceeding the defined acceptance criteria."
• “Short circuit current rating” is defined in SEMI S2-0706 and
SEMI S22-0706 as "The maximum available current to which
an equipment supply circuit is intended to be connected."
Speaker’s Note: The intent of the short circuit current rating is to provide end-users and AHJs with
some idea of the maximum fault current the equipment is suitable of being connected.
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SEMI STEP: Introduction to SEMI S2-0706
Introduction to SEMI S2-0706
Impact To Semiconductor Industry
• Per SEMI S2 and SEMI S22 (as well as the NEC, NFPA 79), every
semiconductor manufacturing equipment will need to include the short
circuit current rating of the equipment or its industrial control panel on
the equipment nameplate.
• As a result of NFPA 79E regarding Arc Flash/Arc Blast requirements,
some end-users are now discovering that their facilities may have
available fault current that are greater than 10 KA.
• NEC prohibits the installation of a system with industrial control panel
with a lower short circuit current rating than the available fault current
from the facility.
• There is no standard or code specifying the maximum limit for
available fault current at a facility.
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SEMI STEP: Introduction to SEMI S2-0706
Introduction to SEMI S2-0706
Challenges to Semiconductor Industry
• Since the available fault current at user facilities may vary
significantly, equipment suppliers are faced with the
challenge of designing a reasonable SCCR for their
products:
 If the SCCR is too high, the cost and footprint of their
products may increase.
 If the SCCR is too low, their products may not be
permitted to be connected to the users’ facilities (if the
available fault current is higher).
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SEMI STEP: Introduction to SEMI S2-0706
Introduction to SEMI S2-0706
Methods of Determining Short Circuit Current Rating
of an Industrial Control Panel
I. Use a Listed UL 508A Control Panel
For a Listed UL 508A Control Panel, the Short Circuit Current
Rating would already be included in its nameplate.
II. Conduct Short Circuit Testing
Take a sample of the control panel and subject it to short
circuit testing.
III. Use UL 508A Supplement SB
Follow the method outlined in UL 508A Supplement SB
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SEMI STEP: Introduction to SEMI S2-0706
Introduction to SEMI S2-0706
UL 508A, Supplement SB Method
SB4.1.1 The short circuit current rating of the overall industrial control panel shall
be determined based upon:
a) First, establishing the short circuit current ratings of individual power circuit
components as specified in SB4.2.
Exception: Power transformer, reactors, current transformers, dry-type
capacitors, resistors, varistors, voltmeters, “S” contactor of a wye-delta motor
controller and fire protection equipment are not required to have a SCCR
(SB4.2.1)
b) Second, modify the available short circuit current within a portion of a circuit
due to the presence of current limiting components as specified in SB 4.3,
when applicable; and
c) Third, determining the overall panel short circuit current rating as specified in
SB4.4.
Note: Schneider Electric/SquareD has flowcharts on their website to assist manufacturers in determining
Short Circuit Current of industrial control panel.
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SEMI STEP: Introduction to SEMI S2-0706
Introduction to SEMI S2-0706
Common Methods of Increasing SCCR
Increasing Short Circuit Current Rating (SCCR) of an Industrial Control
Panel can be achieved through:
 Replacing or removing the lowest SCCR components with ones of
higher SCCR.
 Utilizing a Listed combination tested components that has an overall
SCCR that is higher than that of the individual components.
 Utilizing current limiting devices (e.g., transformer, current limiting
fuses, current limiting circuit breakers)
 Empirically test the components or the entire industrial control panel to
determine actual SCCR instead of using calculations.
 Offer current limiting devices as user facility options to lower the
available fault current to the equipment.
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SEMI STEP: Introduction to SEMI S2-0706
Introduction to SEMI S2-0706
Increasing SCCR of Industrial
Control Panel
Note: Information partly based on UL/SquareD presentation
Listed SCCR Branch
Circuit
Combinations
-SCCR listed with UL
-Stand alone rating
without feeder
protection required
- Branch Protection
with Starters,
contactors, Drives,
Motor controllers
- Has High Fault level
Terminal block has
generic SCCR of 10 kA
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SEMI STEP: Introduction to SEMI S2-0706
Example:
Branch circuit
Combination with
SCCR of 22 kA
Removing the weakest link
may increase the SCCR of
the panel (to 22 kA)
Introduction to SEMI S2-0706
Use of Isolation Power Transformers
Note: Information partly based on UL/SquareD presentation
per UL 508A, SB4.3.1
Circuit Breaker
SCCR 10 kA
Isolation
Transformer
Circuit Breaker
20 kA
Contactor
5 kA
Overload Relay
5 kA
Terminal Block
10 kA
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< 10 kVA
5 kA
Note:
• To be considered in the feeder circuit, must have
secondary overcurrent protection
• For a transformer rated 10 kVA or less, the
transformer secondary is assigned an available
current of 5 kA and all secondary side component in
the power circuit must have a SCCR of 5 kA or
greater; on the primary side, only the SCCR of the
primary overcurrent protection is considered relative
to overall panel SCCR (ref. SB4.3.1(a))
• No benefit for power transformer larger than 10 kVA
(ref SB4.3.1(c) – the lowest short circuit current rating
of the components in the secondary circuit is assigned
to the line side of the power transformer circuit)
Example:
• 10 kVA transformer with 10 kA SCCR CB yields 10 kA
SCCR for this power circuit if all components on secondary
side of transformer is at or above 5 kA SCCR.
SEMI STEP: Introduction to SEMI S2-0706
Introduction to SEMI S2-0706
Use of Current Limiting Feeder Circuit Breaker
per UL 508A, SB4.3.2
Note: Information partly based on UL/SquareD presentation
Feeder “CurrentLimiting” Circuit
Breaker
Ip
Circuit Breaker
Contactor
5kA
Note:
• Max. let-through are not standardized for all
Listed CBs; therefore, need to consult
manufacturer’s let-through limits for specific CB.
• SCCR on the line side of current limiting circuit
breaker cannot exceed SCCR of any branch circuit
protection
• Peak current let-through of the current limiting CB
cannot exceed the SCCR determined for any
branch circuit on the load side.
Example:
• 5 kA from Mfg’s Published let through (I peak only)
Overload Relay
Terminal Block
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• If the let through is less than the determined branch rating of
the overall Short Circuit rating, it will be capable of connecting
to available current per mfg’s let through chart or with fuses
per table SB4.2.
SEMI STEP: Introduction to SEMI S2-0706
Introduction to SEMI S2-0706
Use of Current Limiting Feeder Circuit Breaker
Per UL 508A, SB4.3.3
Note: Information based on UL/SquareD presentation
• Class CC, G, J, RK1, RK5, and T fuses are marked “Current Limiting”
• Fuses must be in the feeder circuit
• Peak current is found from Table SB4.2 based on fuse class and
ampere rating. For fuses with ampere rating not in the table, use next
higher ampere rating (for a 10 A Class CC fuse, use peak current for 15
A CC fuse)
• SCCR on the line side of the current limiting fuses cannot exceed
SCCR of any branch circuit protection
• Peak current let-through of current limiting fuses cannot exceed the
SCCR determined for any branch circuit on the load side.
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SEMI STEP: Introduction to SEMI S2-0706
Introduction to SEMI S2-0706
UL 508A, Supplement SBNote: Information partly based on UL/SquareD presentation
SCCR of a control circuit is based on
its overcurrent protection, not the
SCCR of the control circuit
components
Circuit Breaker
Contactor
Fuse
Overload
Relay
Control
Transformer
Terminal
Block
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SEMI STEP: Introduction to SEMI S2-0706
Control Circuit is a circuit that
carries the electric signals
directing the performance of a
controller, and which does not
carry the main power circuit. A
control circuit is, in most cases,
limited to 15 amperes, typically
anything other than power circuit
(e.g., motor, heater, lights or
appliance).
Introduction to SEMI S2-0706
Short Circuit Current Rating
Questions?
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SEMI STEP: Introduction to SEMI S2-0706
Introduction to SEMI S2-0706
Excerpts from References
Edward Karl
Corporate Product EHS
Introduction to SEMI S2-0706
Excerpts from Referenced Documents
17
•
NFPA 70-2005, Article 670.3(A) - Permanent Nameplate. The nameplate shall
include the following information:
(4) Short circuit current rating of the machine industrial control panel
based on one of the following:
a. Short circuit current rating of a listed and labeled machine control
enclosure or assembly
b. Short circuit current rating established utilizing an approved method.
•
NFPA 70-2005, Article 409.110 - Marking. An industrial control panel shall
be marked with the following information that is plainly visible after installation:
(3) Short-circuit current rating of the industrial control panel based on
one of the following:
a. Short-circuit current rating of a listed or labeled assembly
b. Short-circuit current rating established utilizing an approved method
(FPN: UL 508A-2001, Supplement SB, is an example of an approved
method).
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SEMI STEP: Introduction to SEMI S2-0706
Introduction to SEMI S2-0706
Excerpts from Referenced Documents
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•
NFPA 79-2005 (Accepted Proposal), Section 16.4.1 (currently 17.4.1) Machine Nameplate Data. A nameplate giving the following information shall
be attached to the enclosure:
(6) Short-circuit current rating of the control panel.
•
SEMI S2-0706, Section 13.4.12 – A permanent nameplate listing the
manufacturer’s name, machine serial number, supply voltage, phase
frequency, short circuit current rating of the equipment or its industrial
control panel and…
•
SEMI S22-0706, Section 20.4 i) – Equipment Nameplate – A permanent
nameplate should be attached to the main electrical enclosure or equipment
where it is plainly visible after installation. This nameplate should include the
following information: i) short-circuit current rating of the equipment or its
industrial control panel…
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SEMI STEP: Introduction to SEMI S2-0706
Introduction to SEMI S2-0706
Excerpts from Referenced Documents
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•
UL 508A, First Edition, April 25, 2001 (revised through May 1, 2003)
– 52.1 An industrial control panel shall be provided with a nameplate
that includes the following:
b) Complete electrical rating of each source of supply as specified
in 49.1
– 49.5 The input terminals in 49.1 shall have a short circuit current
rating. The short circuit rating shall be based on the requirements in
Supplement SB. (Effective April 25, 2006).
•
IEC 60204-1 (2005), Clause 16.4 - Marking of equipment. Equipment (for
example control gear assemblies) shall be legibly and durably marked in a way
that is plainly visible after the equipment is installed. A nameplate giving the
following information shall be attached to the enclosure adjacent to each
incoming supply: …
- short-circuit rating of the equipment; …
12 July 2006
SEMI STEP: Introduction to SEMI S2-0706