In the picture below, there are 4 green components. Does anybody know what kind of component they are?

Some information:

  • When the circuit is live, I measure no voltage drop.
  • My multi-meter measures 0 ohms in either direction.
  • The context is the power input stage of the whole pcb.

enter image description here


I actually found a visually identical part:

enter image description here

It is a PTC Resettable fuse, by Bel Fuse, PN 0ZCJ0100FF2E. So there you go.

  • \$\begingroup\$ Have you measured across them? Could they be surface mount fuses? \$\endgroup\$
    – scld
    Sep 12, 2013 at 3:51
  • \$\begingroup\$ @Chris My first thought was that they were fuses (and they may very well be), but I'm intrigued by their appearance of having polarity, the fact they look as in anti-parallel configuration, and that they have both pairs in series. \$\endgroup\$ Sep 12, 2013 at 3:53
  • \$\begingroup\$ What makes you think they have polarity? They could be surface mount capacitors or resistors for that matter. How can anyone give more than just a guess at this? \$\endgroup\$ Sep 12, 2013 at 3:57
  • \$\begingroup\$ @trav1s They just kind of look like they do, but it is probably due to how they are built, and are probably fuses. I just thought I would check in case anybody has seen them before. \$\endgroup\$ Sep 12, 2013 at 4:01
  • \$\begingroup\$ What kind of device are they in? And are they connected directly to ground or vcc? parallel or series? \$\endgroup\$
    – Passerby
    Sep 12, 2013 at 4:56

2 Answers 2


Three possibles in order

  1. Ferrite Inductors, used sometimes to reduce conducted noise on power supplies. DC Resistance is zero, but 10-1000 ohms at high frequency.
  2. 'Poly Fuses' 'PTC Resistors' 'Resetable Fuse' Often have low resistance. When they heat up the resistance goes up which limits the current due to a fault.
  3. Sense Resistors, used to sense current. Often these have very low resistance (much less than an ohm)
  4. Zero Ohm resistors, sometimes these end up on power supply rails so that engineers can measure current.
  • 6
    \$\begingroup\$ That's four possibilities. ;) \$\endgroup\$ Sep 12, 2013 at 7:24
  • \$\begingroup\$ @Li-aung One of them must be impossible... \$\endgroup\$ May 14, 2015 at 22:36

It all points to them being fuses. The polarity appearance is probably an artifact of their construction, and they don't really have any polarity.

The two bottom ones are in parallel, doubling up the current capacity.

The two top ones are not really in parallel, it looks like they branch out to different parts of the circuit, so they are simply independent fuses for independent branches.

  • 5
    \$\begingroup\$ It's worth noting that putting fuses in parallel is a bad practice. They will likely not share current equally, and as such may go open-circuit at a lower current then intended. \$\endgroup\$ Sep 12, 2013 at 5:02

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