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So for my electrical engineering classes, we were tasked to make an operational amplifier.

However, on the day of testing the instructor showed me that the bottom of my breadboard (which he had given me) was one big conductive plate, and that some of my wires were pushed far enough into the breadboard to make contact with it, creating a connection between any wires touching it, as well as a capacitive connection to the entire rest of my circuit.

He said that this broke the design specifications of the circuit, and I got a much worse grade than I first expected.

Can someone please explain to me why anyone would design a breadboard like that?

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    \$\begingroup\$ Photo? Manufacturer? Also, your professor is mean for deducting points for that instead of letting you just adjust it. \$\endgroup\$ – Passerby Feb 15 '13 at 6:29
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Especially when more than one is used, the plastic modules are often mounted on a metal plate for structural integrity.

Normally the double-sided foam tape which comes on the back of the modules would provide some insulation. However, it is possible for wire to get pushed out between the plastic of the module and the metal contract strip forming a given row, pierce the foam, and short to the carrier.

This is particularly true if you have an old or worn module, and smaller 24 gauge wire, for example stripped from old telecom cable.

If you have a single module, you can peel up the foam backing in a corner and see the individual contact strips underneath - hopefully there ins't (yet) a gap between them and the plastic.

With school-issued lab equipment, you are likely to have both well-worn modules, and either the classic multiple modules on a metal plate with binding posts, or an attache case "nerd kit" which functions as a carrier plate - either way, you are more likely to see these accidental shorts than someone using a single new module on its own.

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It can be used as a ground-plane (Wikipedia) to reduce cross-talk and noise due to switching transients and/or RF.

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