Bolt, Nut Type Material Selection For Fixing Cable Lug To Busbar Entry Switchgear

Brass?

Copper? Or, copper plated steel.

Copper is the best material to connect any electric conductors. alluminium is second choice for economy and any thirdthing is just adjustment.

These aren't my words but, perhaps they might help...

"Galvanised steel bolts are normally used but brass or bronze bolts have been used because their coefficients of expansion closely match the copper conductor and hence the contact pressure does not vary widely with operating temperature. Copper alloy bolts also have the advantage that the possibility of dissimilar metal corrosion is avoided. Because these alloys do not have an easily discernible yield stress, however, care has to be taken not to exceed the correct tightening torque.

Because of their non-magnetic properties, copper alloys may also be preferred to mild or high-tensile steel where high magnetic fields are expected. Alternatively, a non-magnetic stainless steel may be used. In most cases however, high-tensile steel is used for its very high yield stress."

The most important thing to keep in mind is the reliability of the joint. By this, I refer to the fastener's "tightness". Too many people make the mistake of referring to this as "torque" (including the author of the above excerpt!). There is great danger in this wide-spread misunderstanding: Torque is only the measurement of resistance felt during the tightening process. This means that a "properly torqued" fastener might be too loose if more (physical) resistance was encountered than assumed. This can be due to thread damage, dirt, bar deformation, load transfer, inconsistent lubrication and a host of other things. Those who "torque" to set and check the clamp load of bus bar fasteners are basing the integrity of their connections on engineered guesses and assumptions.

Here's an example of bolts used in bus bars. These are quite interesting because they provide a clear visual indication of their clamp load...

If the fastener is tight enough , the colour in the head is black. If it's too loose, the head is red and must be tightened until it returns to black. Quick, simple and most importantly: No assuming! A number of OEMs now incorporate this technology in their switchgear.

Thanks pwslack,lyn,pravindhameliya and special thanks also to bolt integrity for nice sharing informations Warm regards

In our shop we generally use stainless steel bolts. The decision as to whether to use locking hardware (lock-washers) depends on the length of the bolts. Long bolts require no lock washers because the bolt stretch provides that function, but we always use locking hardware on short bolts. Our bus bars are rated for 500,000 amps.

The ideal fastener material is the same as the lug and busbar. In the case of copper to copper, that would typically be silicon-bronze. Aluminum to aluminum, 2024-T4 aluminum. Stainless steel can also be used but should include belleville (conical spring washers) to maintain a tight, low resistance joint. The appropriate belleville spring arrangement (single or multiple springs installed in series or parallel) should be selected so that the bellevilles do not flatten completely under the required bolt torque (tensile bolt force). The reason fasteners of the same material are best is they will match the thermal expansion coefficient of the materials being joined.