QUESTION
I have an AC/DC (240VAC/24VDC) power supply unit supplying one DC circuit. My question is, should I have a circuit breaker on the DC side to protect the DC circuit? And if a circuit breaker is required on the DC side, in what way is it different to a laptop charger, which does not have protection on the DC side? I am interested in best practice from an Australian standards point of view.
REPLIES
Paulusgnome
It really does depend on the power supply in question.
For instance, I use plenty of 240VAC/24VDC switchmode supplies in the machines that we build, and these all have built-in short-circuit and overload protection which operates far more quickly than a circuit breaker. If I were to attempt to protect a 40A switchmode supply with a 40A CB, it would be clear from testing that the CB would never get the chance to trip, beaten every time by the PSU electronics.
However, if I were to attempt to use a cheap-and-nasty PSU without any short-circuit or overload protection, then it would be necessary to provide a CB of fuse to provide that protection, or risk frying both PSU and wiring loom under fault conditions.
SOURCE
https://www.eng-tips.com/viewthread.cfm?qid=374103
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