[{"data":1,"prerenderedAt":95},["ShallowReactive",2],{"example-busbar-en":3,"faq-busbar-en":58,"sources-busbar-en":91},{"input":4,"output":14},{"widthMm":5,"thicknessMm":6,"lengthM":7,"currentA":8,"material":9,"operatingTempC":10,"ambientTempC":11,"boltedJointCount":12,"jointResistanceOhm":13},30,5,0.5,200,"cu",65,35,2,0.00005,{"crossSectionMm2":15,"currentDensityAmm2":16,"barResistanceOhm":17,"jointResistanceTotalOhm":18,"barLossW":19,"jointLossW":20,"totalLossW":21,"jointShareOfLossPercent":22,"jointEquivalentBarLengthM":23,"steps":24,"warnings":42},150,1.3333333333333333,0.0000676335695,0.0001,2.7053427799999996,4,6.70534278,59.6539227186235,0.3696389261252876,[25,30,34,38],{"label":26,"expression":27,"value":15,"unit":28,"provenance":29},"crossSection","w * t","mm^2","exact",{"label":31,"expression":32,"value":16,"unit":33,"provenance":29},"currentDensity","I \u002F A","A\u002Fmm^2",{"label":35,"expression":36,"value":17,"unit":37,"provenance":29},"barResistance","rho(T) * L \u002F A","Ohm",{"label":39,"expression":40,"value":21,"unit":41,"provenance":29},"totalLoss","I^2 * (R_bar + R_joints)","W",[43,49],{"level":44,"code":45,"params":46,"anchors":47},"critical","BUSBAR_TYPE_TEST_REQUIRED",{},[48],"currentA",{"level":50,"code":51,"params":52,"anchors":55},"warning","JOINT_RESISTANCE_DOMINATES",{"share":53,"equivalent":54},60,0.37,[56,57],"boltedJointCount","jointResistanceOhm",[59,62,65,68,71,74,77,80,83,86,89],{"q":60,"a":61},"How do I estimate the resistance and losses of a copper busbar?","The cross-section is width times thickness, the resistance R = ρ(T) · L \u002F A with temperature-corrected resistivity, and the loss P = I² · (R_bar + R_joints). Current density in A\u002Fmm² serves as a first plausibility measure, not as a limit. Operating temperature is deliberately an input rather than a result — a closed-form thermal formula would be false precision.",{"q":63,"a":64},"Why do the bolted joints matter more than the bar itself?","In busbar systems the critical heating almost never occurs in the bar but at the bolted joints: a single contact resistance of 50 microohms at 200 A produces the same loss as half a metre of bar. Joint resistance depends on torque, surface condition and ageing, so it is an input from a datasheet or measurement — the calculator does not assume it.",{"q":66,"a":67},"Can this calculator tell me the permissible continuous current of a busbar?","No — this is a plausibility estimate, not a design. The permissible continuous rating of a busbar is established by type testing to IEC 61439, not by calculation. Also not modelled are the thermal balance, skin and proximity effects, short-circuit withstand and the electrodynamic forces involved; rating tables are deliberately not stored.",{"q":69,"a":70},"Why do the joints matter more than the bar cross-section?","Because every contact point has its own resistance producing quadratic losses at full current: even 15 µΩ per joint equals centimetres to metres of extra bar length at common bar sizes — the tile computes it for your case. And unlike the copper, joints age: they loosen, corrode and become hotspots. The loss split shows the joint share regularly dominating.",{"q":72,"a":73},"What current density is acceptable for copper bars?","As rough plausibility: 1.5 to 2.5 A\u002Fmm² for continuous load on bare copper bars in indoor air — the same guide value the result card states. The reference case sits below it at 1.33 A\u002Fmm², i.e. conservative. In enclosed, densely packed assemblies the practical value drops; the binding answer always comes from the type test.",{"q":75,"a":76},"How do I keep contact resistances low permanently?","Contact faces bright and flat (with aluminium, add contact grease against oxide), defined torque with a torque wrench, serrated or disc springs against settling — and retorque once after the first month under load. In operation a thermal image is the fastest test: a warm joint under load is an early warning long before anything chars.",{"q":78,"a":79},"Why is this only a plausibility estimate?","Because a busbar's permissible continuous load is established in practice by type testing per IEC 61439 — on the tested assembly, not on a calculator. This page checks whether current density and losses sit in a plausible band, and says so in every output. A calculation posing as a design would be false precision.",{"q":81,"a":82},"Why do the bolted joints matter more than the bar?","In the reference case (30 × 5 mm, 0.5 m, 200 A) the bar itself loses 2.7 W — the two bolted joints at 50 µΩ each lose 4 W, more than the entire bar. Critical heating almost never arises in the copper but at the junction. Exactly why this page includes the joints, which table calculators do not.",{"q":84,"a":85},"Where do I get a joint's contact resistance?","From the joint system's datasheet or — better — from a micro-ohmmeter measurement on the finished joint. It depends on torque, surface treatment and ageing; 20 to 200 µΩ is the usual span. The 50 µΩ default is marked as an assumption; ageing is why switchboard maintenance includes re-torquing and thermography.",{"q":87,"a":88},"What does aluminium change versus copper?","About 60 % higher resistivity — the same bar loses correspondingly more, and the current-density rules of thumb drop. On top, the joint issue sharpens: aluminium creeps under pressure and oxidises; its bolted joints need special treatment. The material is selectable since 5 August 2026; the joint problem remains professional territory.",{"q":90,"a":73},"What current density is usual for copper bars?",[92],{"name":93,"url":-1,"retrievedAt":94,"version":-1},"Official publications of the standards bodies and state authorities (NFPA, IEC, DKE\u002FVDE, CEN)","2026-07-15",1786101727057]