How are copper busbars connected to each other?

Question

How are busbars connected to each other? A quick google image search makes it obvious that it is bolts.

https://i.ibb.co/8D05Sk5/power-dist-jpg.jpeg

The specifics of the bolts is what I am most interested in:

1. What material are the bolts made of? It looks to be stainless which is odd since stainless has higher resistance. This makes me conclude that bolts are not meant to carry current, and are really only for holding the two busbars together. Copper would be the best case as it would expand allong with the buss bars but copper is soft so it might loosen faster. Do you know of a code requirement for what material busbar bolts should be?
2. Stack layout? - What would be the stacking look like? BOLT-> WASHER (what kind?) -> Copper1 -> Copper2 -> Washer(what kind?) - Nut (what kind?) -> Double nut?. I’m reading to use a Belleville washer. Again is there a code requirement in your country for this?
3. Torque specifications? - I believe that torque specification should be at the recommended rating depending on the material of bolt. I also believe that bolt size will depend on the busbar size, but there could be code requirement of how much force copper be squished together. (Do you know of any in your country?)

A bit of disclaimer I’m not trying to build anything. I am really just curious to how it is done.

Answer 1

Here are some example excerpts from Siemens product data for switchboards and circuit breakers.

I didn't check other manufacturers, but I recall Belleville washers to be standard in bolted joints. I suspect there is some variation in the fastener dimensions and torque, depending on ratings and application, but this gives an idea.

Siemens uses a Belleville washer on each side of the joint and 1/2" SAE Grade 5 Carbon Steel Bolts, with a torque of 50 ft-lbs:

All splice plates can be accessed, bolted and unbolted from the front of the switchboard to make connections of adjacent sections easy. Each splice plate is attached with a 1/2 inch bolt and a 2-inch or 3-inch belville washer on each end. This reduces installation time while increasing contact pressure at the joint. To make installation and servicing of the splice plates easier, all phase and neutral through-busses are stacked one above the other.

Securing line and load-side busbars
Use grade 5 bolts 1/2" and Belleville washers. Tighten to a torque of 70 Nm / 50 lb-ft.

In the US, these details of manufacture aren't generally covered by the Electrical Code (Usually NEC or some variation). Instead, the Codes require equipment to be listed, and the listing agency (e.g. UL) will apply a standard (e.g. UL 891).

Answer 2

(1)

For bolt-material, i found this table. However, it seems to be incomplete.

Table 20, Page 96

(2)

Regarding bolting, i found these explanations:

Figure 60/61, Page 90

Figure 70/71, Page 98

(3)

Regarding torque, i found this information:

Table 22, Page 99

You can derive your torque from this graph:

Figure 69, Page 95

Answer 3

When bolting bars together is not an option or not preferred (for example, when combining busbars in a corner), flexibar can be used. Yes, you can bend anything up to 10x100mm. No, you don't want to if you don't have to.

Examples (no affiliation) are Eriflex advanced using tinned copper and Cu-flex using woven copper.

This allows you to put the connections in all kind of shapes:

Multiple types of clamps exist, usually from the same manufacturer as the rest of the flexibar. As for technical details as torque, to make sure you're using rated material you'd have to follow the manufacturer's specification.