Pushbutton contact burn
Pushbutton contact burn
(OP)
Hi,
I took some nice pictures of an arc burned contact, and would like to get your opinion,
- why the spring head seems to have melted so much and, why it takes a spherical shape?
- why the contact support plate is badly affected or even melted in some positions, and the contact not so much? fusion tª of the contact comparing with plate maybe?
Regards!
I took some nice pictures of an arc burned contact, and would like to get your opinion,
- why the spring head seems to have melted so much and, why it takes a spherical shape?
- why the contact support plate is badly affected or even melted in some positions, and the contact not so much? fusion tª of the contact comparing with plate maybe?
Regards!





RE: Pushbutton contact burn
That's easy. Even molten metals have surface tension.
RE: Pushbutton contact burn
so seems that material fusion Tª guess to explain why the support & spring are more affected than the contact itself don´t work..
RE: Pushbutton contact burn
RE: Pushbutton contact burn
The construction of the contactor seems to allow for the possibility of current flow through the spring, which has high resistance, and a very tiny contact area with the actual contactor flange.
So this looks like a gigantic overvoltage that caused arcing that resulted in current flow through the spring, before the two contactor halves made their normal contact with the their two flange tongues in the middle of the switch.
TTFN
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RE: Pushbutton contact burn
Keith Cress
kcress - http://www.flaminsystems.com
RE: Pushbutton contact burn
My theory is that the spring head was melted and the arc continued from the contact support to the partially melted spring, melting the left contact support and forming the metal drop from that material (see that the spring has not lose too much material).
As liquid iron surface tension is really big as VEIBLL notes (i don´t find it now, but about 1,8N/m against i.e. 0,072N/m of water) the spheric drop forms and gravity is not strong enogh to "make it fall" before it cools down.
Regards!
RE: Pushbutton contact burn
RE: Pushbutton contact burn
ice
RE: Pushbutton contact burn
I got to thinking my response may have been short on information. Even small inductive loads, even as small as relay coils, will cause a a pretty healthy arc when the control contacts open. The coil magnetic field collapses, and the energy goes into the contact arc.
One normally installs a reverse diode across the coil to disapate the energy.
ice
RE: Pushbutton contact burn