Hi Ted,
The factor to calculate between mils and mm is 39.37. So 162 mils times 39,37 equals 4,1148 mm.
Best
Jan

Ted,
Given that there is a mathematical relationship between the different gauge sizes on the AWG side (see below), I would think there must be a mathematical relationship with the mm sizing but this is way beyond my pay grade to work out! I’ll bet Jan can figure this out!!
Nigel

Thanks very much Nigel for your comprehensive reply. Makes a lot of sense and is easy to calculate.

Didn’t t think of the inefficiency factor !!

Great work you guys.

John

Here is a reply from Nigel who can’t log in right now:

John,

All busbars in marine applications should be copper, preferably tin plated for corrosion resistance.

The ABYC sizing procedure, which was added as an appendix to the latest draft of E-11, uses the following method to estimate the maximum allowable capacity for copper busbars:

1. Calculate the cross-section of the busbars in mm2. If the busbar has holes in the conducting path, subtract half the value of the hole diameter from the width of the busbar.
2. The temperature rating of the busbar corresponds to the lowest temperature rating of conductor insulation, of all conductors attached to the bar; and if the busbar is inside or outside the engine space.
3. The ampacity tables are used to determine the ampacity of a conductor with that cross-sectional area and that insulation temperature rating, in or outside an engine compartment.

Of course, you want to go in the other direction, from amps to CSA! In your case, you can ignore the inrush loads as these are very short term. You need to determine the highest running load and then you can use the BoatHowTo wire size calculator to determine the minimum cross-sectional area (CSA) in mm2 and work backwards from there (e.g., put in a busbar depth, and from this derive the width, and then adjust for any holes).

If, for example, we assume your 3,000W inverter is running at full load on a 12V system the nominal input amps are 3,000/12 = 250A. We should build in an inefficiency factor for the inverter – let’s say 80% efficiency – which gets us to 250/0.8 = 312.5A. Let’s assume an engine room, and we will be conservative on attached conductor temperature insulation and assume 90C. We assume a single conductor (no bundling). In this case we don’t care about voltage drop (we just want to determine ampacity) so we reduce the circuit length in the BoatHowTo wire sizer until we see that the wire sizing at the bottom of the calculator is determined on ampacity and not voltage drop. The wire size calculator gives us a minimum CSA of 107.21mm2 which will then need to be adjusted for any holes.

Nigel

I am interested in the brief note on busbars.

I am looking to install a 3kw inverter on a 12V system to run 19,000BTU air conditioner plus hot water heater.

What is the best material to use for a marine application, not in the engine room and able to carry something like 150 – 200 amps with a surge draw say 3-4 times that?

There would be 6 fasteners holes in the Busbar.

Many thanks and I really enjoy your stuff!

John