In this Digikey search for 47uH toroid inductors, the shielding column shows that some are considered shielded, and others are considered unshielded. And even from the same manufacturer (Bourns).

A similar search at Mouser returns likewise mixed-shielding results.

What's going on?

  • \$\begingroup\$ It may have something to do with the core material? Something with a low μ will have more leakage than a high-μ core. \$\endgroup\$
    – Hearth
    Jun 14 at 2:56
  • \$\begingroup\$ @Hearth -- Thank you, Hearth. In the Digikey search, both shielded and unshielded are a variety of materials. I'm not saying that contradicts what you said, but I have to look more closely. \$\endgroup\$ Jun 14 at 13:43
  • \$\begingroup\$ There's also no real definition for what counts as shielded, as far as I'm aware. \$\endgroup\$
    – Hearth
    Jun 14 at 15:04
  • \$\begingroup\$ @Hearth -- Yes, but there is a continuum, and Shielded and Unshielded are at the extremes, so if you have both extremes, then why aren't there ANY "Semi-Shielded" ? \$\endgroup\$ Jun 14 at 15:24
  • \$\begingroup\$ Mouser has a category for semi-shielded: mouser.com/c/passive-components/inductors-chokes-coils/… \$\endgroup\$
    – Wesley Lee
    Jun 20 at 22:23

1 Answer 1


What a distributor puts in their catalog, is their prerogative. Perhaps subject to marketing agreements with their suppliers, or merchantability laws in respective countries (but that's probably a long shot?).

Notice the datasheets don't say anything about shielding specifically. Compare Bourns 2100 and 2300 series: both claim "low [magnetic] radiation". Which is true enough for many toroids, but it's not shielding, nor are they equipped with any kind of shielding. Probably, whoever entered these parts just chose randomly on this property.

A life lesson: in general, distributor data is only loosely related to the items they represent. Sometimes they're outright broken (data entered from a completely different part? database error?), sometimes they're factually incorrect ("mA" instead of "µA" or vice versa?), sometimes they're extremely lacking (misclassified / item in wrong category, fields empty, etc.). Some simply don't provide any data at all and assume you already know what you're shopping for (MFG+PN and that's about it).

And even then -- you're not guaranteed to get the part number you ordered, as there may rarely be confusion over the part number (there are a few parts having similar or identical numbers, from different manufacturers, and the parts being very different indeed); or you thought you ordered one variant of a part/family but it turned out to be another; or there was a warehouse/pick/delivery error and the package says one thing but it contains something completely different. Your recompense at such point is down to customer service, return policy, etc. Which, if these are nonexistent (say from unreputable foreign sources), may ultimately come down to "Buyer Beware".

The manufacturer may also misrepresent things in their favor. For example, the "540A" power transistor whose pins burn up at a mere 140A. Or that dissipates 500W...in a bath of freon, like anyone is going to actually build a real product that way. They are at least generally okay, as long as you read the datasheet cautiously.


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