what fuse to fit to a seasonic 750W prime gold PSU

[boing]

I've just bought a Seasonic SSR-750GD PRIME 750 80 PLUS Gold psu but it only came with a two pin plug and I need a 3 pin to replace it.

The 2 pin end of the included plug states 16A 250V but the socket says 10A 250V.

My current 3 pin spare says 5A 250V on the 3 pin plug and 10A 250V on the socket.

The PSU states an input of 9.5A - 4.5A

I was going to replace my spare with a 16A fuse to match what was shipped but should it be 10A to match the PSU input or does it need a bit of headroom?

 

[Mr Evil]

Fuses in plugs are there to prevent the cable from catching fire in the event of a fault, so fit a fuse appropriate to the cable's current rating. The PSU will have it's own protection, while the house wiring is protected by circuit breakers in the distribution board.

Although 5A is probably enough for a PC, I would want the fuse (and cable) to equal or exceed what the PSU states it can draw.

 

[boing]

Yeah I might go with a 13A that should cover the input range, I guess the worst that can happen going too low is it'll just blow.

 

[boing]

Trying to remember A-level physics classes from the 80's but if the power supply is 750W and the house is 240V wouldn't that mean the peak current the system can draw will be 750/240=3.1A? The systems being used for 3D rendering so it'll be sitting at 100% CPU useage and maybe GPU useage so maybe a 5A is the way to go after all.

 

[Mr Evil]

For a purely resistive load, yes. Power supplies will draw a bit more though, because they have a power factor of less than one. Old ones could be as bad as 0.5, but new ones are very close to 1.0.

Also, 750W is the DC power output. The AC power input will be greater due to losses in the power supply, e.g. if it's 90% efficient at 750W, then it will be drawing 750/0.9 = 833W.

Then there's the mains voltage, which can vary by maybe +/-10%.

Inrush current is more of a problem for fuses though. A lot of electronic devices will draw a much larger current than normal for just a fraction of a second when turned on. The fuses in plugs are "slow blow", so they can take a short overload, but if it's more than they can handle then they will eventually blow when you turn the device on.

 

[boing]

OK, so I think even with efficiency losses 5A should cover it then, thanks for the feedback!