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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Introduction to SEMI S2-0706 NEC Compliance Map

3 Source Reference: SquareD website http://us.squared.com/us/products/motor_control.nsf/unid/BEABDD3D2C1FB03C85256EBE0047F560/$file/ul508aFrameset.htm

12 July 2006 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.

" 4 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.

12 July 2006 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.

SEMI STEP: Introduction to SEMI S2-0706 5 12 July 2006

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).

SEMI STEP: Introduction to SEMI S2-0706 6 12 July 2006

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 7 12 July 2006 SEMI STEP: Introduction to SEMI S2-0706

Introduction to SEMI S2-0706

UL 508A, Supplement SB Method

8

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 Short Circuit Current of industrial control panel.

to assist manufacturers in determining

12 July 2006 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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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 Example: Branch circuit Combination with SCCR of 22 kA Removing the weakest link may increase the SCCR of the panel (to 22 kA) 10 12 July 2006 SEMI STEP: Introduction to SEMI S2-0706

Introduction to SEMI S2-0706

Use of Isolation Power Transformers per UL 508A, SB4.3.1

Note: Information partly based on UL/SquareD presentation Circuit Breaker

SCCR 10 kA

Isolation Transformer Circuit Breaker 20 kA Contactor 5 kA Overload Relay 5 kA 11 Terminal Block 10 kA 12 July 2006

< 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

12

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 “Current Limiting” Circuit Breaker Ip Circuit Breaker 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.

Contactor Overload Relay

Example:

• 5 kA from Mfg’s Published let through (I peak only) • 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.

Terminal Block 12 July 2006 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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Introduction to SEMI S2-0706

UL 508A, Supplement SB

Note: Information partly based on UL/SquareD presentation Circuit Breaker Contactor Overload Relay Terminal Block

SCCR of a control circuit is based on its overcurrent protection, not the SCCR of the control circuit components

Fuse Control Transformer 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).

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Introduction to SEMI S2-0706 Short Circuit Current Rating

Questions?

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Introduction to SEMI S2-0706

Excerpts from References Edward Karl Corporate Product EHS

Introduction to SEMI S2-0706 Excerpts from Referenced Documents

•

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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Introduction to SEMI S2-0706 Excerpts from Referenced Documents

•

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 control panel and…

– 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

•

SEMI S22-0706, Section 20.4 i) industrial control panel…

– 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

18 12 July 2006 SEMI STEP: Introduction to SEMI S2-0706

Introduction to SEMI S2-0706 Excerpts from Referenced Documents

•

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; …

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