# How to calculate temperature of busbar when current flowing through it is 600A for atleast 10mins?

I am new to the bus bar concept. Can anyone please guide me how to calculate the temperature of copper bus bar when current flowing through it is 600A for 10mins.

Should it be this way: Power, P = IlIlR ; R = p*l/A Can you guide me for the rest???

• You also need to know how much heat will be transferred away from the bus bar, as a function of its temperature. – The Photon Jul 2 '17 at 15:47

There is no simple "first principles" formula for this. You can make a fairly good calculation of power input (I^2*R) but that is only half the equation. The power dissipated to the environment depends a many factors including the shape and orientation of the bus bar, what it is connected to, how the vents on your enclosure are oriented, and whether or not you have a cooling fan.

Electrical codes and engineering texts will have "rules of thumb" for different operating conditions. These are designed to be conservative and safe under most conditions, and therefore do not need to capture the full range of effects.

If those guidelines or other rough estimates aren't good enough you basically have two choices: build the system and measure it or do a simulation with something like COMSOL.

Copper has a thermal time constant of 9,600 seconds for a cubic meter. For 0.1meter, ThermalTC is 100X faster. For 0.01 meter, ThermalTC is another 100X faster, thus 0.96 seconds. With 1cm being a sizable bussbar thickness, we now know the BB will temperature-stabilize within some few seconds.

The volume of the bussbar is needed, so you know the heat-storage ability of the copper.

You already have the other equations.

Assume one milliohm resistance, at 600 amps. That is 3,600 watts.

In 1 meter long bussbar of width 10cm and thickness 1cm, I'd expect one degree per second temperature rise.

• Also, it would be a good idea to factor in the increase in resistance with temperature - does "positive feedback" ring a bell? – WhatRoughBeast Jul 2 '17 at 18:18
• Yeap ---- copper has 0.4%/degree Centigrade positive temperature coefficient. Causes trouble for gain-stability of non-inverting opamp circuits, with Ground (and the spreading resistance) used in series with the Rg resistor. – analogsystemsrf Jul 2 '17 at 20:20