Why fuse in computer power cables(leads)

up?

CJT wrote:

Short circuiting in a cmputer that is running continuously for years in Datawarehouse should be very rare I believe.

In the environment of Datawarehouse chances of cable getting cut and short circuiting should be highly unlikely.

Can you please explain "ring main GPO ccts"? I am totally nontechnical.

Regards Nagesh

shorts

that probably varies by country to satisfy local laws

it's probably following the law

I think you will find the fuse is also there to protect the cable as well encase its cut through or a short on the cable the fuse does not just protect the computer

Don't look now but US building codes _require_ ground fault interrupters anywhere that there's a significant risk of a short to something other than the neutral.

Hey, we've got all the 240 we want. We just don't waste it on clock radios and electric pencil sharpeners.

Normal residential service in the US is 240. We split it to get two 120V phases, but the 240 is there any time we have a real use for it.

The simple fact is that you Brits are going to defend your quaint way of life to the death, and that's as it should be.

That's why the fuses don't blow very often.

Probably due to India having Fault-current-relays? like rest of Europe, not the deadly dangerous anitique system as in UK. Detects if current is equal in & out of house (live & 0 wires)....if greater than treshold (like if you grap the live wire, mine´s 30 mA) it trips & saves your life.....not needing it to be a true shortcuirt.

Normally dont reply on such a X-poster...but hey why not might save his life :))))))))

Best regards

ChipMIK, expecting some serious shouting from you UK-guys :)

Too true - my personal opinion is that the UK is an awful lot safer than the US. Current imbalance trips are pretty standard around here (south uk); individually fused plugs; plugs that make it diffcult to disconnect by just pulling the cable; man sized 240V instead of the wimpy 110v ... ;))) tee hee Neil

Dont forget the UK has a lot of ring main GPO ccts, so thats why they use the fused plugtops.

-- Regards ..... Rheilly Phoull

Here is some explanation of UK wiring (from

UK wiring is somewhat special case. The UK is unusual in having fused plugs as standard (according BS1363 parts 2 and 4). 13A max in eachplug, and 30A at the panel for each ring. Maximum current at wall outlet in the UK is for 13A. The plugs carry a fuse holder and the fuse should be rated to suit the appliance used (fuse rating from 1A up to 13A exist). The fuse in the plug is for protecting the cable to the appliance, not the appliance itself. For the latter, the appliance would have its own fuse (or other suitable protection means). Neutral is neither switched nor "protected". UK mains plugs are polarized. In the UK, a wiring system known as a ring mains is used. UK standard (for the last 30 years or so) has been the ring -main (domestic and commercial) rated at 30/32A @230V. A single cable runs all the way round part of a house interconnecting all of the wall outlets. This will be protected by one large fuse in the fuse box. A typical house will have three or four such rings. The power rings are normally protected by a 30 amp fuse and the lighting rings by 5 or 10 amp fuses. Those fuses protect the wiring, not the appliances so, every appliance carries its own fuse in the plug.

The design philosophy of e.g. the German system (Schuko) is that a room (or a small number of rooms) has a 10 A or 16A fuse in the consumer unit, and all leads and plugs are designed to withstand any short-circuit current that will not yet blow the fuse (today usually circuit breakers are used, not fuses). If a fault occurs, a circuit breaker is trivial to reset, The fuses are generally in the main distribution panel. The fuse inside equipment will provide the protection agains constant overload. This equipment fuse is rated based on the power the equipment might take, and the wire going to equipment must be thick enough to handle that load current that this fuse can pass before breaking.

That fuse would be in the fuse box on tha wall. 10A for light, 16A for power outlets and e.g. 3*25A for an electric stove.

Actually there is no requirement for a fuse in the equipment itself, depending on what type of equipment it is and what kind of cable it has. If it has 1.5mm^2 cabeling, then the main fuse is enough, since the wires in the wall are also 1.5mm^2 and these are rated for 16A continous current and several thousands for a short duration short-circuit. It is also permissible to use lighter cables (0.75mm^2) for lighter equipment. This type of cable should still be able to stand 16A for some time.

For the british system in equipment without a fuse in the plug you would need something like 1.5mm^2 cables to all types of equipment. A 0.75mm^2 cable would likely have problems at 32A. Remember that power goes with the square of the current in cables, so the 0.75mm^2 cable would actually get heated up four times as trong as it would in germany with current that just about does not blow the fuse.

As a result the british need additional fuses in thinner cables. I would guess that for 2.5mm^2 cables the british can do without the fuse in the plug.

Arno