Why does nut bolts of an elect. connection carrying high current get loose by heating and cooling cycles.?

Answer 1

The tightness of a nut-bolt connection is dependent on the interference between the thread of the bolt and the corresponding thread surface of the nut.

Different materials have different coefficients of thermal expansion.

Since bolt and nut material are often different (and different still from the connection itself, usually!), everything moves relative to everything else. If the nut "grows" faster than the bolt - as is often the case - a certain amount of looseness in introduced, because the friction forces maintaining torque are lessened, allowing the nut to "back off". Additionally, having current flow through the bolt (don't kid yourself, some will!) will create a localized heating effect within the bolt itself, possibly leading to a change in physical properties such as tensile strength and/or yield strength.

Once that happens, the joint is now "loose ... increasing local heating and causing more trouble during the next cycle.

A corrseponding issue is the use of different materials where electrical current is present; due to galvanic action, some material may be deposited from one point to another. This property of dissimilar material is well known and documented; it can also cause a lot of grief at a bolted connection.

These two points are the main reasons that plated copper and plated (or stainless) hardware is chosen ... and the amount of current through the joint cross-section is considerably lower than what might be present in the conductor itself.

Answer 2

The term high current may mean different levels to people in different parts of the electrical industry from electronics to consumer electronics to industrial electronics / electrical tools to power generation industry.

Selection of proper material for the current carrying conductors as well the nuts and bolts is very important to reduce the impact of heating and cooling cycle due to the on-off or continuous use of the device. There are also other feature to keep the components secure like serrated or other non-rotating washers, spring loaded washers, locknuts, locking pins etc. There are also alternate ways like crimp connections, soldered connections, spring loaded connections etc.

Answer 3

There are articles with the aid of human beings that would want to have an time table except absolutely the reality. technological information marches forwards and we parent out stuff that we did not understand previously. There are different aspects. did you understand that NASA got here upon that the Ice Caps on Mars are melting? Mankind might want to no longer likely have brought about that, proper? The solar has were given to be dealing with some style of cycle. when we seem at climate history, with evidence got here upon contained in the floor, tree earrings, significant historic activities, it is going to change into quite obtrusive that the planet has had numerous cycles of international warming and international cooling, lengthy before human technologies change into taking section in a lot of a function. i do no longer have self belief that anybody element is responsible. that is a blend. That makes it puzzling to study that is "extra" or "a lot less" responsible.

Answer 4

keep weathering introduce corrosion=resistance=impedance=heat=expansion=low current=cooling= n the cycle shall go on and on =looser a connection become additional heat n cooling cycle becomes,hence resistance become so immense,that small surface/contact area is no longer able to carry out the current in demand,result therefore is excessive heat to an a applied scenario=stuffed-up thin go ,end of an chapter-oi-greep smiling-cheers

Answer 5

Expansion and contraction. When it heats up, it expands. When it cools, it contracts. To a bolt (threaded) and nut, the lateral movement of the expansion/contraction basically unscrews the nut.