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I've encountered this resistor R12 while trying to understand how a board is working. It seems to be much bigger than the other SMT components and basically just looks like a flat metal tile without symbols.

Do these kind of resistors have a specific name, or present a certain best practice for appliances?

My assumption is that this might be a dedicated shunt for a higher current, but the lack of any symbols got me confused.

enter image description here

Update to provide more context

The device being examined is a socket extension that can measure the current going through the mains. Besides this resistor, the component I wasn't able to identify was this little guy:

enter image description here

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  • \$\begingroup\$ Check if it has a "current through" path and two smaller measurement traces, then its for sure a shunt. \$\endgroup\$ – PlasmaHH Dec 13 '16 at 16:20
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    \$\begingroup\$ Maybe it's installed upside-down? \$\endgroup\$ – pjc50 Dec 13 '16 at 16:31
  • \$\begingroup\$ It's a medium-long shot, but some laser trimmed resistors looks similar and have no markings on them. Is it a high end product of some sort? Ah! Just saw your edit. I vote for precision laser trimmed resistor! \$\endgroup\$ – winny Dec 13 '16 at 16:33
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It could also be a "poly-fuse". There are many helpful clues to be gathered from the context. That comparatively gigantic thing next to R12 suggests it may be an input or output port of some kind. Perhaps a power input where a poly-fuse would be appropriate. Even a simple resistance measurement across the mystery device would be most helpful.

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    \$\begingroup\$ Maybe it was a poly-fuse, then someone installed a no-blow fuse. \$\endgroup\$ – Olin Lathrop Dec 13 '16 at 16:29
  • \$\begingroup\$ Like putting a penny behind the Edison-socket screw-in fuse? :-) \$\endgroup\$ – Richard Crowley Dec 13 '16 at 16:30
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Hard to tell without a bit more context, but it could be a "zero ohm resistor" aka "link" or "jumper". Basically not acting as a resistor, but given a R designation nonetheless. These can be used where the designer isn't sure if a resistor is needed, and wants to try different options, where one board is used to make two slightly different products, or just to connect two traces where it was too hard to route without it.

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