# 5a or 13a power cable

Posted 16th Apr 2010
I have two power cables 13a and 5a, which should I use for a 400w desktop?
5A should be enough.
5A will be fine.
use whichever you have most of. makes no odds as its the fuse that counts isnt it?
csiman;8379363

use whichever you have most of. makes no odds as its the fuse that counts … use whichever you have most of. makes no odds as its the fuse that counts isnt it?

True. Therefore use whatever you have the least of.

I cannot explain why this makes sense.
thanks for the replies, the 13a power cable on the plug has a engraved mark saying 13a/250v, does it matter if i put a 5a in it?
lilraul;8380414

thanks for the replies, the 13a power cable on the plug has a engraved … thanks for the replies, the 13a power cable on the plug has a engraved mark saying 13a/250v, does it matter if i put a 5a in it?

No :thumbsup:
DEALWARRIOR;8380718

No :thumbsup:

Except when you next use it for that electric fire and the fuse pops.
13A, 5A is borderline and the fuse could blow.
Power (W)= Current (A) x Voltage (V)

Therfore current (A) = power (W) / voltage (V)

From the OP firts post:- 400W divided by 240V = 1.66 recuring (A)

So the 5Amp fuse is 2 of those power supplys without any cause for alarm.

Regards,

John
i won't be using it for anything except for the desktop.

Reason is i got a 1m power cable with a 5a but i brought from ebay a 3m which came with a 13a, so thats why i wanted to swap the 5a and 13a fuse.
heinkeljb;8380891

Power (W)= Current (A) x Voltage (V)Therfore current (A) = power (W) / … Power (W)= Current (A) x Voltage (V)Therfore current (A) = power (W) / voltage (V)From the OP firts post:- 400W divided by 240V = 1.66 recuring (A)So the 5Amp fuse is 2 of those power supplys without any cause for alarm.Regards,John

Not as simple as that. 400W is the rated output load - the PSU will not be 100% efficient and will draw significantly more current when first turned on as the capacitors fill. It is the peak current that will blow the fuse, not the average current, and the peak will be significantly greater than 1.66...
jah128;8381034

Not as simple as that. 400W is the rated output load - the PSU will not … Not as simple as that. 400W is the rated output load - the PSU will not be 100% efficient and will draw significantly more current when first turned on as the capacitors fill. It is the peak current that will blow the fuse, not the average current, and the peak will be significantly greater than 1.66...

Not as simple as that.
just because the psu is rated at 400W it doesn't mean that the demand on it will be 400W, it's likely to be a lot less unless the OP has modded his pc significantly. The 5A fuse will be ok up to 1.2KW.
Does the cable also power the monitor?
the monitor has its own power cable plug.
doberman;8381329

Not as simple as that.just because the psu is rated at 400W it doesn't … Not as simple as that.just because the psu is rated at 400W it doesn't mean that the demand on it will be 400W, it's likely to be a lot less unless the OP has modded his pc significantly. The 5A fuse will be ok up to 1.2KW.Does the cable also power the monitor?

The output rating tells very little about what the onrush current will be... Also, the RMS voltage of mains in the UK is typically on the low side of 230V, not 240V, so your 5A is nearer 1.1KW; the 5 amp fuse will likely suffice, but you would find most similar power supplies will typically be provided with 13A fuses in the mains cable (if one is supplied).
jah128;8383429

The output rating tells very little about what the onrush current will … The output rating tells very little about what the onrush current will be... Also, the RMS voltage of mains in the UK is typically on the low side of 230V, not 240V, so your 5A is nearer 1.1KW; the 5 amp fuse will likely suffice, but you would find most similar power supplies will typically be provided with 13A fuses in the mains cable (if one is supplied).

All of the above is correct but my point was that the rating of the psu only indicates what power it is capable of supplying the actual load on it should be less.
On my pc with a 350W psu the power drawn as measured with a power meter is 110W during normal operation and yes it is greater at startup but only 145W so well under the 1.1kW capability of a 5A fuse. So the 5A is fine.