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Frequently Asked Questions
What actually sets the current rating?
Temperature rise, not current per square millimetre.
Cross-section and surface finish both count.
So does how many bars sit together.
And how much air the enclosure moves.
The same bar is rated differently in different boards.
Why do the supports matter more than the bar?
Because a fault is a mechanical event.
Currents in opposite directions repel each other.
The force rises with the square of the current.
Peak current arrives, not the RMS value.
Insulator spacing is what has to survive it.
Copper or aluminium?
Copper for conductivity and for forgiveness.
Aluminium for weight and for cost.
Aluminium needs more section for the same current.
It creeps under bolt pressure and it oxidises.
Which makes its joints the part to get right.
What is the plating for?
Stable contact resistance at the joint.
Tin is usual, silver where duty is hard.
It resists oxide through thermal cycling.
Bare copper works if it is prepared properly.
But it will not tolerate a humid, dirty room.
What makes a bolted joint last?
Contact pressure that holds over time.
Correct torque, recorded at assembly.
Disc springs keep load as the metal creeps.
Clean, flat, properly prepared faces.
And a re-check after the first thermal cycles.
Does the shape of the bar matter?
Yes, once the bar becomes large.
Current crowds toward the surface at mains frequency.
A very thick bar wastes its middle.
Several thinner laminations carry more.
The gaps between them matter as much as the count.
How are the earth and neutral bars sized?
By what they may actually have to carry.
The earth bar on fault current and its duration.
The neutral on unbalance, not on a rule of thumb.
Harmonic-rich loads push triplen currents into the neutral.
Which can make a full-size or oversized neutral correct.