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UL508A Standard for Safety of Industrial Control Panels
UL508C Standard of Safety for Power Conversion Equipment
For Basic unmarked Mechanical Components SCCR is assumed to be 10,000 amps/200hp/149KW
This includes Terminal Blocks, Fuseholders, Bus Bars, Etc
IHI Mechanical Wire Lugs therefore have a default SCCR of 10,000 amps, or (UL508C) motors up to 200hp/149KW.
Mechanical wire connectors typically have the capability to pass testing for 100,000-200,000 amps. Only if such testing is done may the SCCR rating be higher than 10,000 amps for mechanical components. Please inquire if SCCR is required above 10,000 amps on a specific part.
SCCR testing of most mechanical connectors will typically pass with 200,000 amps as far as the metal mechanical connector itself. However, the weaknesses that most commonly occur are in the mounting and pole separation components, typically made of plastic. The more likely scenario for a low SCCR test results is from the weaker mounting block, undersized mounting screws or fragile pole separation insulators, which are more easily damaged from the electromagnetically whipping cable forces.
There are also possible limitations in the metal connector if unusally thin wire retaining walls or necked down cross section are present. The heat flow in a metal (conducting) member under 200,000 SCCR amps may not be fast enough to avoid a local melt down in less robust connector designs. Low wire retaining cabability may cause a loosening wire contact which can generate local heat or arcing.
Good mechanical lug design includes features to assist with wire retention under SCCR testing. UL486 requires mechanical connectors to demonstrate high pull out forces under both static and whirling wire pull force configurations, which generally perform very well under SCCR. Additional wire secureness performance may be custom designed for a client's particular requirements.
Makers of circuit breaker devices have the additional challenge, when SCCR testing, of dealing with ionized (conducting) gas streams which can compromise the pole to pole or pole to ground safe arcing distance and must therefore be controlled in insulator design to avoid SCCR test failure.
For full information of the SCCR rating system users should consult the appropriate UL, IEC and other standards
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