How do I size it for 120V?
I'd put a fuse . Also EMI filter of lowest current rating possible as those have bigger inductance and, presumably, filter better. They also come at least in two flavors: normal and medical. I don't remember the difference, but you can google it.
10W it approx 80ma at full load, so fuse would be 0.15A ?
there are some good filter, you can make some similar drop some details like thermistor,
I bought common chokes , for low power filters ...
https://www.aliexpress.com/item/-/32703970119.html
I'd put a fuse . Also EMI filter of lowest current rating possible as those have bigger inductance and, presumably, filter better. They also come at least in two flavors: normal and medical. I don't remember the difference, but you can google it.
Don't use glass fuses , instead use either resettable fuse or HRC fuse , which ever you can get cheaper , the minimum voltage rating of a fuse needs to be 300V.
In case of HV surge , easily blows up , sending glass everywhere and damaging nearby components
Fuses protect not upstream, but downstream wiring.
But it comes down to the definition of direction: Downstream means from the supply, to the load. So, your breaker panel protects the downstream wiring to the wall socket. And your small glass fuse does in fact protect against fire of the load - i.e. your small 10VA transformer, that could otherwise catch fire when severely overloaded.
The glass fuse in your appliance have nothing in common of protecting the wiring from the socket to it. That is the job of the breaker panel.*
*Some freaked out countries even put another fuse in their crazy looking plugs, to compensate for the simple and dangerous design of their plugs.
cheapest HRC fuse £0.142 each, breaking capacity 1.5kA. One third more expensive, 43 times the breaking capacity.
cheapest HRC fuse £0.142 each, breaking capacity 1.5kA. One third more expensive, 43 times the breaking capacity.
Concerning the price, it seems I was wrong. I took the price for fuses in DMM, but they have higher voltage rating. Indeed, ceramic fuses are not much more expensive than glass ones. I didn't knew they are also HRC. Do they have sand inside?
*Some freaked out countries even put another fuse in their crazy looking plugs, to compensate for the simple and dangerous design of their plugs.
Oh, and breaker panel fusing usually 15-30A in 220V countries, typical IEC cable rating 6-10A. So the breaker will open when the cable from the wall is overstretched will it?
Oh, and breaker panel fusing usually 15-30A in 220V countries, typical IEC cable rating 6-10A. So the breaker will open when the cable from the wall is overstretched will it?The main purpose of a breaker or fuse is to prevent fire.
So how hot will your typical IEC cable rating 6-10A get with a breaker panel fusing usually 15-30A.
Heat of cable = time + power.
What is the temperature rating of the insulation?
To have possibility to start a fire you have up to when insulation fails.
And NO the fuse or breaker is not there to protect the source of power in a properly designed power system. The power source has a fuse or breaker that serves this function.
Simple electricity rules apply.
I actually think the UK plugs are the safest design out there.
I actually think the UK plugs are the safest design out there.
Until you stand on one while barefoot. Then they become the most painful plug design out there.
The earlier example was of a 1A load capacity fuse with a 1.6kA breaking capacity versus a 1A fuse with a 35A breaking capacity. If the current flowing in a fault exceeds the breaking capacity of a fuse, that fuse will fail to open the circuit and can even induce a higher current fault itself, tripping the next bit of protection upstream. So, an example for the latter case would be that 1A glass fuse with a breaking capacity of only 35A. It's very easy to generate a fault current of >35A with a simple accidental dead short - loose wire, loose screw, that kind of thing. The 1A HRC fuse would break that fault current, the 1A glass fuse wouldn't and might even become a lower impedance than the fault it was trying to isolate.
Cerebus
I understand what you stated in your post.
As the fault current becomes a greater % of supply you have a chance to have this kind of need.
But looking at total system changes things..
To get from 35A to a 1.6kA state you would need a very fast change. You would need a fast change just to get to 35A point.
The connecting wire inductance will reduce fast changes a lot. Each stage of breakers or fuses is separated by more inductance.
Short of a lighting strike, I see little chance. And here it becomes a race against time for what gets blown.
The rare case of the glass exploding just shows a need for an enclosed fuse holder or use of fancy fuse that does not explode. That is selecting one of two options..
But there is a point where you are just selling numbers with little purpose.
You could make the same clam for breaking voltage. Above a point nothing or very little is gained.
This chain of posts started with a power supply that would have a cable that connects to an outlet. This is part of the facts.
One thing that puzzles me is how this is possible. I shorted glass fuses several times, they blew instantly. Not even a spark was visible. The only way I see fuse don't open is when somehow evaporating wire inside the fuse turns into plasma or something. But I thought it's more danger for DC, not for AC as plasma disappears at zero crossing.
So, how can a glass fuse conduct under overcurrent condition?