Protection of ELV circuits
Protection of ELV circuits
(OP)
Hi Everyone
I am new to the forums and would like some advice for circuit design. 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.
I am new to the forums and would like some advice for circuit design. 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.





RE: Protection of ELV circuits
The above is probably a false assumption. Any laptop charger (perhaps excluding the worst of the knock-offs) would have current limiting on the output side.
RE: Protection of ELV circuits
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.
RE: Protection of ELV circuits
RE: Protection of ELV circuits
Best to you,
Goober Dave
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RE: Protection of ELV circuits
The spec for the PSU:
http://www.meanwell.com/search/DR-75/DR-75-spec.pd...
RE: Protection of ELV circuits
Probably not - when the PSU is first energised there is probably an inrush current to charge the capacitors. The 2A fuse might be sized to accommodate this so anything less might lead to nuisance tripping.
RE: Protection of ELV circuits
It is a bit trickier on the AC side, at least here in the USA, as UL says you have to use 18 AWG or larger on the AC side, even after fuses. UL trumps logic around here.
Z