Busbar Riser Design Calculator

Busbar riser design calculator for high-rise buildings

This free interactive lab sizes busbar trunking risers for GCC, Asia, Australia and New Zealand projects. It covers rated current and derating, voltage drop for point and distributed tap-off loads, fault levels along the riser, protection coordination, harmonics and 200% neutral, expansion units, IP rating, fire barriers, slab loading, seismic restraint and a priced BOQ, with a live 3D riser shaft.

What you can check

• Beginner guide to busbar types (sandwich, ventilated, cast resin, plug-in, feeder, lighting track) and insulation materials (epoxy, polyester film, polyimide, PVC, cast resin) with IEC 60085 thermal classes
• Earth fault loop (Zs) check, magnetic field (EMF) estimate, arc flash screening, motor starting dip and a trainee knowledge check
• Busbar sizing with IEC 61439-6 and AS/NZS 61439.6 regional derating (GCC 50°C, ANZ 40°C, IEC 35°C basis)
• Voltage drop ΔV = √3 · I · L · (R cosφ + X sinφ) for point load and distributed tap-offs
• Fault level at the MDB, riser connection and each floor, with Icw and Ipk pass/fail
• Feed breaker LSI settings, selectivity with tap-off MCCBs and end-of-riser sensitivity
• Third harmonic and 200% neutral (2N) sizing, phase transposition and voltage unbalance
• Expansion fitting units, IP54 to IP68 selection, 2 to 4 hour fire barriers and seismic restraint
• Side-by-side comparison of ABB / Vertiv, Schneider, Siemens, Eaton, Legrand Zucchini, EAE, LS, Wilmar, Federal and GERSAN datasets

Frequently asked questions

How is busbar voltage drop calculated in a riser?

Use ΔV = √3 · I · L · (R cosφ + X sinφ) with the manufacturer's R and X at operating temperature. For tap-offs spread up the riser, calculate section by section, because each section carries only the load above it. The result is roughly half of the point-load value.

When does a busbar riser need a 200% neutral?

When the third harmonic current exceeds about 15% of the fundamental, neutral current rises sharply. Above 33% the neutral current governs sizing, so a 200% neutral (2N) busbar or a larger rating is needed.

How many expansion units does a vertical busbar riser need?

Calculate free expansion as α · H · ΔT and divide by the movement each unit can take, then apply the manufacturer's maximum straight-run rule and add one unit at each building expansion joint. Some manufacturers advise a vertical expansion unit on every floor.

Is busbar Icw checked at the switchboard or at the riser?

The busbar must withstand the fault where it connects. The lab checks Icw and Ipk at the riser connection point and, conservatively, at the switchboard.

Developed by Eng. Mannan Maqsood. Results are indicative. Verify every output against the approved manufacturer data, the project specification and the authority requirements.