Hey Everyone
If a transformer is used in a design is it safer to enclose it in a metal box or a plastic box? Most lab equipment (power supplies, scopes etc) use a metal case. Wouldn't plastic be safer? Is metal only used for strength?
Depends. If the metal case is properly grounded, it is at least as safe. If it is not grounded, plastic is safer. Because if it is grounded, and a failure happends, current will pass to gnd, and the ground relay will sense that, turning off power. So, if you intend to use it in an *dry* envirorment without earthed wall outlets, pick plastic. Otherwise, I'd stick to metal. Also reffer to faradays cage...It won't hurt you to touch the metal case when it is powered, as long as no current is passing trough you, but rather trough gnd connection which will likely have less resistance than humans. In norway, the voltage upon touch to an earthed part *shall* never be above 50V, so then you must adjust ground resistance according to the maximum current which can pass in a single-phase short (short to earth). This was slightly offtopic, but hope it explains a bit:)
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That helps, thanks.
The secondary output of the transformer is rectified to produce DC. Should the ground of the DC be connected to the case, which is also connected to the ground (earth) in the plug?
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