cause for busbar overheating in LT panels

prima facie -

30 x 10 is a poor aspect ratio. 60 x 5 gives 62.5% higher surface for heat dissipation. also better conduction at frequencies where the skin effect will be pronounced.

further, a higher aspect ratio leaves more conductor intact at connection points by removal of less mass by drilling for fastening.

50 x 6 is an option where mechanical strength consideration leaves 60 x 5 questionable.

any temperature rise on a conductor has to be looked at with the correct perspective. answering questions asked below will help you to reach a reasonable conclusion.

do you have a photograph of your enclosure with door open? and a correctly dimensioned drawing of the internal arrangement of components with conductor routing?

is 42 deg C the ambient 1 meter away from the control panel enclosure? or nearer? or inside the enclosure in closed condition?

is 100 deg C the peak temperature observed? or the steady state final temperature? and at what location is it measured? how close is the point of measurement to a bend? a joint/connection? a neighboring component (switchgear/device) at a higher temperature?

the heating any conductor is a result of the (I*I*r) heat and any additional heat received from any neighboring component by radiation or conduction.

the rise in temperature due to heating is governed by (a) the ability of the conductor to conduct heat away to neighboring components in contact and at lower temperatures, (b) the ability of the conductor to radiate heat from its surface through air to enclosure walls at lower temperatures and (c) the heat removed by the conductor by air at a lower temperature acting as a cooling medium either by convection or by a forced draft.

100 deg C as a final steady state temperature may not be alarming if the insulation system is coordinated to handle the temperature. however a cooler temperature does nopt necessarily exclude abnormal and unwarranted energy losses.

have you checked that the 271 amps you are drawing is a true RMS measurement? and the current is free from harmonics? if harmonics are present then the heat generated will be high though the current may not appear high on an ordinary moving iron meter.

current harmonics (if present in high proportion) add to the heat due to the pronounced current density on account of the skin effect and the proximity effect.

are you paralleling conducting paths at aly point? with unequal (resistance) conductors?

have you checked for physical flaws in your conductor? like cracks at bending points? and corrosion or contact resistance at connections?

have you checked in your internal layout that the conductor is not receiving convection/draft heat generated elsewhere and reducing the efficacy of cooling? eg - if your conductor is passing horizontally above the fins of a heat sink then expect poor heat extraction from the surface of that conductor.

ooooo have you checked if your line voltages are balanced (equal)?

try generalized fundas for future panel design . . . .

do try painting the inner walls of your enclosure with a dull (matt) black shade to absorb and conduct away more of the radiated heat falling in inner surfaces. if your esthetics permit then paint outer surfaces black too. this will help whenever the ambient temperature outside is lower than the in panel temperature (usually always when powered). if possible remove any restricting baffles above the conductor or make them of perforated aluminum sheet. increase the clearances between conductors to allow better air flow. increase the aspect ratio of the conductor.