Electrical Safety
Internal Arc Integrity for Cable Transits
Giving network operators the evidence that a cable transit system holds up when switchgear suffers an internal arc fault.
An internal arc fault turns a switchgear enclosure into a pressure vessel in milliseconds. Threepwood’s white paper assessed how a Roxtec cable transit system maintains that enclosure’s tested arc classification, giving operators an evidence base to specify it with confidence.
The challenge
When an internal arc fault occurs inside metal-enclosed switchgear, the arc energy vaporises material and drives enclosure pressure up in a matter of milliseconds. Switchgear is type-tested to an internal arc classification, but that classification assumes the enclosure stays intact.
Cable entries are a potential weak point. Operators specifying a cable transit system need assurance that it contains the pressure transient and preserves the arc performance the switchgear was tested to, not just that it seals against water and dust.
The enclosure is only as arc-proof as its weakest penetration. A cable transit has to survive the same pressure transient the switchgear was certified against.
Our approach
Threepwood examined the internal arc duty a cable transit must withstand, the rate of pressure rise, the peak overpressure and the mechanical loading during the arc, and assessed the Roxtec transit system against it.
The findings were set out in a white paper: a clear, referenceable evidence base linking the transit’s performance to the switchgear’s internal arc classification, so specifiers and asset managers can justify the selection.
The outcome
The results
Evidence to specify
A referenceable basis for selecting the transit without compromising the arc case.
Preserves the classification
Confidence that the tested internal arc performance is maintained at the cable entry.
Supports the safety case
Strengthens operator and designer safety justifications for populated switchgear.
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