SCCR Calculator

An SCCR comparison uses an entered component short-circuit current rating and an entered available fault current to produce the difference in kA. The result is the SCCR margin:

\(\displaystyle \text{SCCR Margin} = \text{Entered Component SCCR} - \text{Entered Available Fault Current}\)

The comparison also reports available fault current as a percentage of the entered SCCR. It provides a documented comparison of two reviewed values; it does not establish the short-circuit current rating of an assembly or determine whether equipment is acceptable for installation.

Short-Circuit Rating Comparison

Electrical equipment can be exposed to high fault current during a line-to-line or line-to-ground fault. The available fault current at the equipment location is commonly expressed in kiloamperes, or kA. A component SCCR is also expressed in kA.

For the entered values to show a positive margin, the entered component SCCR must be greater than the entered available fault current.

Result condition	Arithmetic result	Meaning of the entered-value comparison
Positive SCCR margin	SCCR exceeds available fault current	The entered component rating is numerically above the entered fault-current value
Zero SCCR margin	SCCR equals available fault current	The entered values are numerically equal
Negative SCCR margin	Available fault current exceeds SCCR	The entered fault-current value is numerically above the entered component rating

A positive result is not an equipment determination. Actual equipment evaluation can depend on the listed and marked rating of the complete assembly, component combinations, overcurrent protective devices, manufacturer instructions, and the fault-current value at the specific installation location.

Entered Values

The comparison uses three fields:

Field	Entry purpose
Entered component SCCR	Enter the component rating from the reviewed source, in kA
Entered available fault current	Enter the available fault current from the reviewed source, in kA
Source reference	Record the reviewed source for both entered values

The entered component SCCR may come from a reviewed marking, product documentation, listing information, schedule, engineering record, or other controlled source. The entered available fault current may come from a fault-current study, service calculation record, utility information, transformer-based calculation, engineering documentation, or other reviewed record.

The Source reference field creates a traceable link between the numerical comparison and the source used for the entered values. A record note of Source recorded indicates that a reference was entered; it does not validate the rating, the fault-current calculation, the equipment configuration, or the source’s applicability to the installation.

Calculation Results

The result panel emphasizes two numeric comparison values plus traceability notes:

• SCCR margin — The entered component SCCR minus the entered available fault current.
• Available fault current as percent of SCCR — The entered available fault current divided by the entered component SCCR, expressed as a percentage.
• Record note — Indicates whether a source reference was entered.
• Calculation basis and boundary — Keeps the arithmetic separate from equipment approval.

The percentage result is calculated as:

\(\displaystyle \text{Available Fault Current as Percent of SCCR} = \left( \frac{\text{Entered Available Fault Current}} {\text{Entered Component SCCR}} \right) \times 100\)

A lower percentage means the entered available fault current consumes less of the entered component SCCR. The percentage is a comparison value, not a protective-device coordination result and not a measure of equipment withstand capability beyond the entered rating.

Calculation Example

Enter the following reviewed values:

Calculator field	Entered value
Entered component SCCR	35 kA
Entered available fault current	22 kA
Source reference	sccr-record-a

The SCCR margin is:

\(\displaystyle 35\text{ kA} - 22\text{ kA} = 13\text{ kA}\)

The available fault current as a percentage of SCCR is:

\(\displaystyle \left( \frac{22\text{ kA}}{35\text{ kA}} \right) \times 100 = 62.8571\%\)

The entered available fault current is 62.8571% of the entered SCCR.

The result is therefore:

Result	Value
Entered component SCCR	35 kA
Entered available fault current	22 kA
SCCR margin	13 kA
Available fault current as percent of SCCR	62.8571%
Record note	Source recorded

The arithmetic shows that the entered component SCCR is 13 kA above the entered available fault current. It does not confirm the SCCR of a panelboard, industrial control panel, disconnect assembly, motor control assembly, feeder equipment, or other complete piece of utilization equipment.

Field Verification

Apply this comparison after the source values have been reviewed, not as a substitute for obtaining them. The available fault current must correspond to the actual electrical location being evaluated. It can change with transformer size and impedance, conductor length and impedance, service configuration, utility contribution, parallel conductors, on-site generation, and modifications to the distribution system.

A component’s marked or documented SCCR also cannot automatically be treated as the SCCR of the assembled equipment. Field evaluation may require verification of:

• The complete equipment assembly’s marking, listing, documentation, and configuration.
• The relationship between installed components and any applicable overcurrent protective device.
• The actual feeder or branch-circuit source and fault-current conditions at the equipment line terminals.
• Manufacturer instructions and engineered assembly documentation.
• Applicable NEC requirements and the interpretation of the AHJ.

The calculator boundary is specific: it subtracts Entered available fault current from Entered component SCCR and records the entered values. It makes no assembly value, equipment listing, protection relationship, or final system determination.