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razorcut 06-08-2011 05:35 PM

Using the correct fuses in appliances?
Hi there

I posted on here a while ago regarding which size (value) of fuse should go into the plugs of which appliances.

I live in the UK and sometimes buy rackmountable audio recording equipment from mainland Europe. Because they assume that most customers come from mainland Europe, they always include the standard Euro-type plug for connecting to the IEC power connector at the rear of the equipment which means I have to find my own IEC (C13) power cable to use in the UK.

Okay...I'm aware that there's a formula for calculating an appliance's current draw from an electrical outlet providing I have that particular appliance's details.

Power(W) = Current(A) x Voltage(V).

Am I correct in assuming that if I use this formula modified to Power(W)/Voltage(V), then this will equal an appliance's Current draw in Amps(A)? If so, do I then go with a fuse in my plug which is slightly higher than this? Basically, the next highest commercially available fuse I can buy? Am I correct so far?

Anyway...I took receipt of a preamplifier unit the other day which has an external Power Supply Unit (PSU) with the following details on the underside of the PSU.

Input: 100-240v~1.6A Max, 50-60Hz
Output: +15v 3.33A
Output Power: 50W Max

The preamplifier's manual states.

Power requirements:
Voltage range: 9 to 18 Volts DC

Current consumption:
@ 9VDC Current is 1000 mA typical: Power = 9W
@ 12VDC Current is 800 mA typical: Power = 9.6 watts
@ 15VDC Current is 610 mA typical: Power = 9.15 watts
@ 18VDC Current is 520 mA typical: Power = 9.36 watts
I'm a bit confused as to which size (value) of fuse to go with in my plug.

Is the current draw 1.6A or 610mA? Which size (value) of fuse would I use in my plug?

Obviously, I will buy the correct rating of cable and plug especially for the unit instead of switching fuses in a 13A cable I already have as I'm aware that was suggested the last time I posted here.

Any advice would be greatly appreciated.

Kindest Regards


AllanJ 06-09-2011 08:28 AM

It's hard to say what size fuses should go into the power plug or into the chassis of a piece of electronic equipment. You really need the instruction manual.

Some equipment has an initial inrush of current that will blow the fuse if the fuse is too small. Sometimes a slow-blow fuse is used to solve this.

Some equipment needs a fast blow fuse to protect the electronic subcomponents inside. The fuse value could be a little more than the current draw rating on a label in back, but again you need the instruction manual.

In your specific case I would try a 1 amp fuse. Equipment that autoselects the voltage (from a range) and draws more or less current depending on the voltage it got generally does not require that you change the fuse depending on the voltage you give it. So the maximum stated current draw of 1000 milliamps (1 amp) is the starting point for choosing a fuse. (What I mentioned earlier would apply to a situation where you might really need a bigger fuse like 1-1/2 amps, but you don't know that yet.)

Where did you get the number 1.6 amps?

razorcut 06-11-2011 09:38 AM

Hi Allan

Thanks for the reply and information. I really appreciate it.

The 1.6A figure came from the Input rating on my preamplifier's external PSU. I thought that this was the maximum current which the PSU would be drawing from the outlet, hence the appropriate fuse in the plug would be based on this? Was this totally the wrong thing to be looking at then?

I think my confusion about the whole "which fuse size" question centres around whether or not the appropriate fuse in the plug is determined by the current draw of the unit itself or the external PSU. Is it the unit then?



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