Fuse ratings?!

[V_King]

Hello, sorry if it is a wrong section, not really sure where would this go.
I am wiring up MeanWell TDR240-24 PSUs and need to pickup the input fuses. The manual recommends either slow blow 4A cartridge fuses or C16/D16 miniature circuit breakers. That is a lot of difference in current rating for a 0.69A input current protection. Or am I not understanding something?

Screen dump from the MeanWell manual is in the attachment.

Thanks
 

[Alti]

Suggested fuse and maximum number of the unit that can be connected to a circuit breaker at 400V are shown as below.

[Zero999]

Yes, this is normal. The power supply will draw a large current surge, when initially powered, which would blow a lower rated fuse.

The fuse is only there to protect against fire. If it blows, it's highly likely it's because the power supply has failed and will require replacement.

[Alti]

The manual recommends either slow blow 4A cartridge fuses or C16/D16 miniature circuit breakers.

The circuit breakers are there to protect wiring, not the PSU, and this number of units guarantees nuisance-free operation on power-on. OTOH the fuse is for limiting damages inside of the unit in case of internal mishaps. This is not one or the other.

The D16 might not trip below 320A so additional fusing highly recommended. But C16 is for <80A currents so I am guessing that 19 units won't trip it on startup. That is about 4A per single unit which does not make much sense with T4A fuse as it assumes no inrush - for such inrush-free loads there are IEC60127-2/1 fuses which are 3x faster than what they recommend.

[TheMG]

It's not entirely clear but I don't think it's one or the other. What they are recommending, I think, is a fuse for each individual power supply.

The number of units per circuit breaker is just for your reference, and is a maximum number of power supplies you can feed from each type of breaker in order to avoid nuisance trips from the inrush current on power up. In other words, up to 19 of these power supplies can be powered from a single 16 amp C or D curve breaker.

[V_King]

Thanks for all the advise, both fuses it then. As comprehensive as some manuals are, I found fusing sections are always very brief, leading to some misunderstandings!