Verifies that an associated apparatus (safety barrier / galvanic isolator) and an intrinsically safe field device — plus the field cable connecting them — can be combined without a dedicated system certification, using the IEC 60079-11 'entity concept'. All five entity parameters (voltage, current, power, capacitance, inductance) must satisfy the required inequalities, with cable capacitance/inductance added to the field device's own values.
Standards followed
IEC 60079-11 (intrinsic safety 'i')IEC 60079-14 (electrical installations design, selection, erection)
What it can do
- Voltage, current and power checks: Uo≤Ui, Io≤Ii, Po≤Pi.
- Field cable capacitance/inductance calculated from length and per-length cable data (or the standard 'unknown cable' defaults).
- Capacitance and inductance checks against the barrier's Co/Lo, including the IEC 60079-14 '1% rule' (use full Co/Lo, or halve both, depending on the field-side Ci/Li relative to Co/Lo).
- Overall pass/fail summary across all five entity parameters.
Example problem
P+F-style barrier: Uo=28V, Io=93mA, Po=650mW, Co=0.083µF, Lo=4.2mH. Field device: Ui=30V, Ii=130mA, Pi=1000mW, Ci=5nF, Li=0µH. 500m of cable at the standard 60pF/ft, 0.2µH/ft defaults.
- Voltage/current/power: 28≤30 ✓, 93≤130 ✓, 650≤1000 ✓.
- Cable capacitance = 197 pF/m × 500m = 98.5 nF; total Ci = 5 + 98.5 = 103.5 nF.
- Li/Lo = 0/4.2mH = 0% < 1%, so the 1% rule applies → use the full Co = 0.083µF (83nF), not halved.
- Capacitance check: 103.5nF > 83nF → FAILS — the cable run is too long / too capacitive for this barrier at this length.
Voltage, current and power all pass; capacitance fails at 500m with these defaults — a shorter run or a barrier with higher Co would be needed (the default deliberately includes a failing condition).
Want the full step-by-step version?
Cable capacitance/inductance defaults (60pF/ft, 0.2µH/ft) match common 'unknown cable' assumptions used industry-wide (e.g. manufacturer control drawings) — always use the actual cable's datasheet values when known. The absolute practical ceiling some guidance places on reduced (halved) capacitance (~1µF for IIB, ~600nF for IIC) is not hard-coded here; enter your barrier's own certified Co/Lo values directly. This is an entity-concept screening check, not a substitute for a full IS system/loop certification or a hazardous-area classification study.