Bus Bar Size Calculator

Why accurate busbar sizing is required?

While selecting busbar one should keep in mind the application, current carrying capacity and budget as under size busbar can cause heating and damage in bus bar while over size busbar can affect the cost of project.

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Types of busbar?

On the basis of material, busbar is of five types:

Material Current carrying capacity per mm2 Application Copper 1.2 Amp/mm2 Panels and board Aluminum 0.8 Amp/mm2 Panels and board Galvanized steel 0.6 Amp/mm2 Electrical earthing Iron steel 0.6 Amp/mm2 Trolleys, unloader & traction Silver steel 1.6 Amp/mm2 Rarely used due to high cost

AC & DC busbar:

There is no difference in a DC and AC busbar. For example: a busbar with 200 Amp current carrying capacity be either used for carrying AC or DC 200 Amp current.

What is safety factor (S.F)?

It is a common practice to size a busbar with the consideration of future load expansion. For this reason, we consider some safety factor while busbar sizing. Normally, safety factor is taken as 25% of the load.

Standard bus bar size:

S.Nos. Standard bus bar size 1 20*6 mm 2 20*10 mm 3 30*10 mm 4 40*10 mm 5 63*10 mm 6 80*10 mm 7 100*10 mm

Busbar sizing calculator parameter:

• Choose the method: provide load (in kVA) and busbar size
• If load selected: rated current of equipment and required safety factor (S.F) to be entered
• For option: option for DC, 1-phase AC and 3-phase AC.
• For DC circuits: voltage (in volts), power (in kW) and safety factor (S.F) (in percentage) are required
• For AC circuits: voltage (in volts), power (in kVA), and safety factor (S.F) are required.
• If busbar size selected: width and thickness of busbar to be provided in mm.

Steps for busbar sizing calculator:

When busbar size is given:

The formula for current carrying capacity of a busbar, when busbar size is given:

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For copper busbar:

For silver steel busbar:

For aluminum busbar:

For iron busbar:

For galvanized steel busbar:

When load is given:

For DC circuit:

The formula for DC circuits is given below.

For 1 phase AC circuit:

The formula for single phase AC circuit is same as DC with an addition of power factor (p.f) which is given as:

For 3 phase AC circuits:

The formula for three phase AC circuit is same as two phase AC circuit but instead of 2 we use square root 3 (~1.73) when voltage is expressed in terms of line to line (Vll) which is given as:

When voltage is expressed in terms of line to neutral then we use 3 instead of 1.73.

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I ordered two different types of flexible busbars in order to compare them. Flexibility comparison is done without measurements. Just by the feeling I got while flexing them. The two types of busbars that I've tested are on the image below. The first is the laminated one from Weber Power Tech. The second is the braided one from the Minerals Official Store.

And here are the results:

1. Axial flexibility - the braided busbar is the winner. The laminated one requires a lot more force to change its length.
2. Radial flexibility seems equal.
3. Contact area - the braided one wins. The laminated one has an oval hole while the braided one has a round hole.
4. Price - the braided one is cheaper.

The most important aspect is axial flexibility. This is what the busbar should mitigate while cells are expanding and contracting. For me the winner is clear.

Docan also offers braided busbars. The price is even lower, but the middle part is not tinned according to the pictures. I'll be using these for my build due to the price difference.

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I see different options for that. Soldier the wires directly or use the cell stud to connect them. I'm likely going for soldered balancing leads.

The laminated one is a kind of monolith at the ends. And it should be straightforward to drill and tap it. I'll probably try this on the braided sample I have, but my expectation is that it won't be reliable.

Looking forward for your experiences in the braided busbars!
What is the max amperage they handle?

Some have reported the braided busbars will not hold torque as they tend to 'squish' after some time requiring constant retorqueing.

The one that was given as an example back then was just plain braided wire (no crimped copper tube at the end). I have serious doubts that the one that I've pictured will have that issue.

But I can test that with the sample I have. I'll torque it down to 8Nm. The same will be done with the laminated one. In a week I'll check to see if there is a difference.

The one that was given as an example back then was just plain braided wire (no crimped copper tube at the end). I have serious doubts that the one that I've pictured will have that issue.

But I can test that with the sample I have. I'll torque it down to 8Nm. The same will be done with the laminated one. In a week I'll check to see if there is a difference.

Mine are 1” four ply, they were soldered in fixture and squeezed while hot. Then embossed in the terminal/nut contact area to cold work and make parallel the metal with a force of 10,000 lbs. After all that I still had to re torque it ten times before it wouldn’t give anymore. Finally after six months they don’t move. Apparently the metal cold flowed. This would have been a disaster if it was in an enclosure where you wouldn’t check it. For all my work, I rate that as a fail.

Mine are 1” four ply, they were soldered in fixture and squeezed while hot. Then embossed in the terminal/nut contact area to cold work and make parallel the metal with a force of 10,000 lbs. After all that I still had to re torque it ten times before it wouldn’t give anymore. Finally after six months they don’t move. Apparently the metal cold flowed. This would have been a disaster if it was in an enclosure where you wouldn’t check it. For all my work, I rate that as a fail.

Not to derail the thread, but how do you like the active balancer? They worked fine, but they need a voltage switch to turn them on above 3.42 volts per cell and they need time above that voltage to do the job. That’s an old picture. I went to a Neey smart active balancer and that has many times the balancing power but then the Daly bms got weird. So the smart simple move is I got two 200amp JK bms’s and get new buss bars/jumpers. So the Heltec is retired and the Neey/Daly will be retiring. What I made is diagonal 2/0 cables jumpers because I didn’t like the 7mm wide slot in the laminated buss. I thought it would greatly reduce the contact area and current capacity versus 1/4” of a lug. Found out that the Ancor cable/Selterm lugs with a small bow in it for flexibility had .08/.07 M ohms versus the stock buss .06 which isn’t bad. Brum noted the laminated has .09 M ohms and that’s still excellent. The problem I just realized is with cable jumpers is when the ends are free, it’s quite flexible but once you lock down the lug angle (torque the terminals) it’s as stiff as a rod! So my thinking is despite the overly large slot and no reports of frequent re torquing, the laminated buss may be the way to go if they can handle the current with small terminals. My problem is I already made 31 jumpers so I’m going with them. They may be pivoting at the terminals because my antioxidant is “green grease” and they are torqued only to 4Nm with a Bellevue washer. I’ll checking torque. Hey, life is learning.