Specification

Motor Control Solutions SCCR Requirement in UL 508 A
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SCCR Requirement in UL 508 A
NEC Article 409, NFPA 79, and UL 508A require that the SCCR be marked on all
control panels.
The final builder or assembler of the equipment inside the panel is responsible for
providing the SCCR for the overall panel, determined by one of the following three
options:
• Testing each panel construction and recording the construction in the follow-up
procedure. With the multitude of possible product combinations within a panel,
this option may require much testing and maintenance. Third party testing and
certification may also be required.
• Purchasing previously tested constructions (combinations) from a major
supplier of equipment that can be tabulated in the control or machine panel
builder's procedure. Once you have all the component ratings, either use an
outside service or UL 508A, Supplement SB.
• Using a method described in UL 508A, Supplement SB.
NOTE: Using the interrupting rating of the main OCPD for the panel is not an
acceptable practice.
Ratings: Tested Combination vs. Component
UL 508A, Supplement SB describes three steps to determine the SCCR of an
industrial control panel. One of those steps is to determine the SCCR of all the
individual power panel components using one of the following methods:
• Use the SCCR value marked on the component.
• Use assumed SCCRs in Table SB4.1 of Supplement SB.
• Use the tested SCCR from component combinations per UL 508.
Method 1 is often called component rating. Component rating involves looking at
each individual component in the circuit and applying the lowest component rating
to the overall system.
Method 2 uses Table SB4.1 (see Table 4) of Supplement SB, which applies a
blanket maximum SCCR for all components. The SCCR for motor controllers is
graduated based on its horsepower rating.
WARNING
INADEQUATE SHORT CIRCUIT INTERRUPTING RATING
Do not use the interrupting rating of the main OCPD as the SCCR rating for the
controller.
Failure to follow these instructions can result in death, serious injury, or
equipment damage.
Table 4 – Extract of Table SB4.1
Component: Motor Controllers (rated in HP
1
)
1
Highest rated horsepower of motor controller.
Short Circuit Current Rating (kA)
a. 0–50 5
a. 51–200 10
b. 201–400 18
c. 401–600 30
d. 601–900 42
e. 901–1600 85