Q6013 Class 3 Derating Rules

---
name: q6013-class-3-derating-rules
description: "Use when a Class 3 build has to show a commercial part runs inside its derated envelope. Verify that every electrical and thermal stress on a selected commercial EEE part sits inside the lowest assurance derating limits of ECSS-Q-ST-60-13C clause 6.2.2.5: look up the part family's voltage, current and power ratios and its junction step-down, uplift an applied value that came from nominal analysis alone, turn each maker rating into the largest applied value the rule leaves, derive a junction temperature from a measured case temperature, grade every stress, carry one past its limit only inside the approved relaxation band, and name the tightest margin. Trigger: ecss, q-st-60-13c-clause-6-2-2-5, class-three-eee-derating-limits, commercial-part-voltage-derating, commercial-part-power-dissipation-derating, junction-temperature-step-down, nominal-analysis-stress-uplift, approved-derating-relaxation-band."
license: Apache-2.0
compliance: STANDARDS-REF
standards:
  - id: ecss
    reference-only: true
gated: false
domain: space-systems
pack: space-systems
compatibility: "agentskills.io SKILL.md; any SKILL.md host (Claude Code, Hermes, OpenClaw)"
metadata:
  domain: space-systems
  subdomain: ecss
  tags: [ecss, q-st-60-13-commercial-eee-component-scope, q-st-60-13c, q6013-class-3-derating-rules, class-three-eee-derating-limits, commercial-part-voltage-derating, commercial-part-current-derating, commercial-part-power-dissipation-derating, junction-temperature-step-down, nominal-analysis-stress-uplift, approved-derating-relaxation-band]
  version: 0.1.0
  author: Aero Agent Skills
---

# ECSS Commercial EEE Components -- Class 3 Derating Rules (space-systems/ecss/q6013-class-3-derating-rules)

Use when the task is the stress limiting of ECSS-Q-ST-60-13C clause
6.2.2.5 at the lowest assurance class -- turning a commercial part's
maker rating into the smaller envelope the build is allowed to work it
in, and grading the applied electrical and thermal stresses against
that envelope.

## Domain quick reference

- A commercial part is rated by its maker for a commercial life in a
  commercial environment. The rating is never used directly: a derating
  factor is applied to every electrical stress and a step down to the
  temperature ceiling, so the part spends its life inside the envelope
  the datasheet draws.
- Electrical stress is kept as a ratio of applied to rated: the steady
  working voltage against the rated voltage, the steady working current
  against the rated current, and the dissipated power against the rated
  dissipation. Thermal stress is kept as an absolute ceiling, expressed
  as a step down from the rated maximum junction or hot-spot
  temperature.
- Each part family carries its own row, because the mechanism the
  derating protects against differs -- dielectric wear-out on a ceramic
  capacitor, electromigration on a die interconnect, contact erosion on
  a relay. One blanket factor across a board is not a derating rule, it
  is an average of unrelated mechanisms.
- The table at this class is the loosest of the three. More of the
  maker's rating is left available, because the class carries the
  lowest assurance target and pays for it with the least margin against
  the spread a commercial line can move by.
- What this class adds is an uplift on the input rather than a relief
  on the limit. A worst-case circuit analysis is often not run at this
  class, so an applied value declared from nominal analysis alone is
  uplifted by a fixed factor before it is graded. The uplift stands in
  for the spread the analysis would have found, and it can turn a
  nominal pass into a breach -- which is the point of it.
- The bounded relaxation the middle class opens is available here too:
  a single electrical stress may be carried past its table limit by no
  more than a fixed band where a derating relaxation record has been
  raised and approved for that stress on that part. Past the band the
  record buys nothing.
- The thermal ceiling takes no relaxation and no uplift relief at any
  class. The step down is the whole of the margin against a wear-out
  mechanism, so a record that moves it is moving the mechanism, not the
  paperwork.
- A junction temperature that was never predicted directly can still be
  had: the measured case temperature, the junction-to-case thermal
  resistance and the dissipated power give it. A result with no
  junction figure at all is half a result and is reported as not
  demonstrated rather than quietly passed.
- The useful output is not the pass or fail. It is the allowable
  applied value each rule leaves, the headroom against it, and which
  single stress is closest to its limit -- that is the one a thermal
  excursion or a rating change will break first.

## Workflow

1. Declare the part family, each applied stress with the maker rating
   it works against and the analysis it came from, any approved
   relaxation record per stress, and either a predicted junction
   temperature or the case temperature, thermal resistance and
   dissipation to derive one. Reject an uncategorized family rather
   than defaulting it; the row is chosen by family.
2. Look up the family's voltage, current and power ratios and its
   junction step-down. Reject a stress kind the table does not cover.
3. Uplift every applied value that came from nominal analysis alone,
   then turn each rating into the largest applied value the rule
   leaves, so the answer a designer needs is a number rather than a
   verdict.
4. Grade each stress on its uplifted value. A stress sitting exactly on
   its limit is on-limit and compliant. A stress past the limit is a
   breach unless an approved record covers that stress and the
   overshoot stays inside the band.
5. Resolve the junction temperature, derive it from the case where it
   was not predicted, and grade it against the derated ceiling with no
   relaxation available.
6. Name the tightest margin across the graded stresses; that is where
   the design has the least room and where the next change will land.
7. Close with one verdict, separating a clean pass from one that leans
   on an approved relaxation and from one left open by a junction that
   was never demonstrated, and carry every finding with it.

## Pitfalls

- Grading a nominal applied value as if it were a worst case. The
  uplift is what this class substitutes for the analysis that was not
  run, and skipping it passes parts on numbers nobody bounded.
- Applying one blanket factor to every part on the board. The families
  fail by different mechanisms, so a ceramic capacitor and a digital
  integrated circuit do not share a voltage rule, and averaging them
  overstresses whichever is tighter.
- Reading the loosest table as the whole of the class difference. The
  uplift and the relaxation band are the other two halves, and the band
  only opens where a record names the stress and the part; an
  unrecorded overshoot is a breach at this class exactly as above.
- Letting an approved record carry a stress any distance. The band is
  bounded, and a record covering an overshoot past it is a waiver
  against a mechanism rather than a derating decision.
- Relaxing the junction ceiling. The step down is the margin, and the
  record that would move it is moving the wear-out life of the part.
- Passing a part on its electrical stresses alone. Every ratio can sit
  low while the junction runs hot, so a missing temperature that cannot
  be derived is an open item, not a silent pass.
- Comparing a ratio with its limit by bare arithmetic. The ratio is a
  quotient and the allowable is a product, so a stress built to sit
  exactly on its limit or on the band edge can land a few units in the
  last place above it; the comparison absorbs that representation error
  while the limit stays untouched.

## Behavior contract (gate 3)

The family row validation, limit lookup, nominal-analysis uplift,
allowable applied value, stress ratio, relaxation band, junction
derivation from case temperature, thermal ceiling, per-stress grading,
tightest-margin selection and overall verdict are exercised by the gate
3 contract test: scripts/test_q6013_class_3_derating_rules.py against
scripts/q6013_class_3_derating_rules_logic.py (stdlib unittest,
offline). Run:
python3 scripts/test_q6013_class_3_derating_rules.py

## Compliance

- ECSS standards are freely downloadable (ESA); cite the source and
  paraphrase per standards-map.yaml.
- compliance: STANDARDS-REF, gated: false.