Stray Current Interference Bond Resistor
Sizes the resistor that limits an interference bond to its target current, and the power it must dissipate.
Example
You enter
- Open-circuit potential across bond points (V) 0.45
- Current through a temporary solid bond (A) 8.5
- Target bond current (A) 3
- Interference shift on the foreign line (mV) 250
- Resistor rating margin (x dissipation) 5
You get
- Circuit resistance, solid bond 0.0529412
- Total resistance for the target 0.1500 ohms for 3.0 A
- Resistor to add 0.0970588
- Continuous dissipation 0.87 W, every hour of every year
- Rate the resistor at 4.4 W or more, in a ventilated test station
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeThe number that matters is not the resistor but the retest: a bond that satisfies the arithmetic and leaves the foreign line discharging has moved the problem, not fixed it.
Formula or tablecircuit resistance = open-circuit potential / solid-bond current; resistor = (potential / target current) - circuit resistance; dissipation = current^2 x resistance.
Source and editionNACE SP0169 (now AMPP) and the CP designer govern. The foreign structure's operator and the interference retest govern.
Free accessOhm's law.
What governsEstimate. AHJ and licensed professional govern.
API field namesopen_circuit_v, solid_bond_current_a, target_bond_current_a, interference_shift_mv, rating_margin_factor, circuit_resistance_ohm, required_resistance_ohm, resistor_ohm, dissipation_w, recommended_rating_w
- Rating several times the dissipation, because the resistor runs continuouslyCP practice
- Retest mandatory on both structures; the arithmetic does not certify the bondNACE SP0169