Bus Bar

This has to be a homework or take home exam question. I hope all of these lazy bums fail their class.

E = IR (for DC or single phase). I think it is E = √3IR/2 for 3-phase, but I haven't done this for a while. For bus bars of short length, R is almost zero, so I am surprised that anyone bothers to calculate it (as opposed to long conductors with small cross-section).

Voltage drop at bus bars are neglegible because it is the point wherein close to supplied loads. What you need to calculate is the feeder cables from the power source where your MDB busbars is getting its power. Allowable Voltage drop from point "0" or power source to the farthest circuits not in the MDB or busbar point but to the farthest supplied circuits- shall not be more than 5% of supply voltage.

Voltage drop formula:(English system)

Vd = (2xKx I x L)/CM - SINGLE PHASE 2 or 3wire

Vd = (1.732 x K x I x L)/CM - three phase

where:

K = resistivity of cable per 1000feet, value changes with temperature and size of cable.

L= Length of cable/conductor in feet

CM = Circular mil area of the conductor

I = Load current in amperes

http://cr4.globalspec.com/search/sitesearch?do=show&sort=textmatchrank&srch=busbar&order=asc