Checks whether a proposed instrument/HART cable run stays within the host system's maximum permitted loop capacitance, recommends a minimum conductor size for the run length, and gives general-practice EMI separation-distance guidance for routing signal cable near power/VFD cable.
Standards followed
HART/4-20mA cable capacitance practice (host-specific — no single universal IEC constant)General practice consistent with IEEE 518 EMI separation-distance guidance
What it can do
- Total cable capacitance from cable length and the cable's per-length capacitance rating, checked against the host/multiplexer's maximum system capacitance.
- Maximum cable length the host's capacitance budget allows, for the entered cable type.
- Minimum conductor size (AWG) recommendation by run length.
- General EMI separation-distance guidance for instrument cable routed near VFD/power cable.
Example problem
800m of HART cable at 150pF/m, host maximum system capacitance 200nF.
- Total cable capacitance = 150 pF/m × 800m = 120,000 pF = 120nF.
- 120nF ≤ 200nF → within the host's capacitance budget, pass.
- Maximum length for this cable/host combination = 200,000nF-equivalent pF ÷ 150 pF/m = 1,333m.
120nF at 800m, well within the 200nF host limit, with headroom to roughly 1,333m before hitting the capacitance ceiling.
Want the full step-by-step version?
HART maximum system capacitance is genuinely host/multiplexer-specific — there is no single universal IEC number, so it must be entered from the host's own datasheet, not assumed. The EMI separation distances shown are commonly-cited general practice figures, not a verified official IEEE 518 numeric matrix — always confirm against your project's actual IEEE 518 edition or site EMI standard for design-critical spacing. Minimum conductor size guidance is general industry practice, not a single hard standard requirement.