Kitchen mains sockets - 2 way to 4 way?

[Bob Eager]

Exactly my point - so the earth loop impedance is relevant, and your mention of fuses rather less so.

[David Hansen]

On Tue, 30 Jan 2007 19:16:19 +0000 someone who may be Dave Fawthrop wrote this:-

Incorrect. One of the functions of fuses is to protect against electrocution caused by indirect contact. They are, however, unlikely to protect against electrocution caused by direct contact.

[Derek Geldard]

What's that ?

[Dave Fawthrop]

|Huge wrote: | |> Which is what I actually have - 3 "proper" mains sockets, 3 x 12 way |> Olson strips, plus 3 x 4 way strips on the UPS and 1 x 6 way under |> my desk, for a total of 54 sockets. | |I was about to say "is that all", but then I counted mine, and only came |to 50... so I will not bother mentioning it! ;-)

Just think of 54 ordinary 13 amp sockets 54 * 60mm = 3.25 *meters*, there is no way anyone in their right mind would fit a 3 meter line of 13 amp sockets in *any* room.

[David Hansen]

On Tue, 30 Jan 2007 20:53:11 +0000 someone who may be Derek Geldard wrote this:-

Indirect contact is where a conductive part which is not normally energised becomes energised because of a fault. If the conductive part is the metal casing of something then this is not good for health. However, if the conductive part is equipotentialy bonded and automatic disconnection of the supply by a fuse is in use then the dangers to health are reduced. Anyone touching the conductive part when the fault happens will still get a shock, but it will usually not be fatal. Anyone not touching the conductive part when the fault happens but who touches it later will not get a shock, because the supply will have been disconnected.

Direct contact is contact with a conductive part that is normally energised, in other words part of the electrical system. Although normally a wire, in some circumstances this can be something else, like a busbar or conductor rail.

[John Rumm]

Not been in many electronics or avionics labs then I guess...

Mine are not all in a line needless to say. There are five doubles on the wall - part of the house wiring, the rest are mostly spread around the 10 outputs from my two 1kVA UPSs. (plus one or two 4 way extensions directly from the mains for appropriate loads). Typically they are neatest when fixed to an equipment shelf or in a rack.

[Dave Fawthrop]

|On Tue, 30 Jan 2007 19:16:19 UTC, Dave Fawthrop | wrote: | |> On 30 Jan 2007 16:59:39 GMT, "Bob Eager" wrote: |> |> |On Tue, 30 Jan 2007 15:42:17 UTC, Dave Fawthrop |> | wrote: |> | |> |> On Tue, 30 Jan 2007 14:30:17 +0000, John Rumm |> |> wrote: |> |> |> |> |Dave Fawthrop wrote: |> |> | |> |> |> the office I have one 13 amp socket -> 4 way -> 4 way -> 12 way, perfectly |> |> |> safely because the actual current used is only a few amps. |> |> | |> |> |and what is the earth loop impedance (and hence disconnect time in the |> |> |event of a fault) at the end of that lot? ;-) |> |> |> |> It has no less than 3 fuses in the extensions which I try to keep at a |> |> reasonable value, so the wire fuses of the ring main are unlikely to blow. |> |> Come to think of it I can not remember replacing those ever in 40 years. |> | |> |Fair enough. The main fuse won't blow fast, so it's irrelevant that the |> |extension fuses won't blow fast, as you'd be dead anyway.. |> |> Fuses do *not* protect against electrocution, never did. | |Exactly my point - so the earth loop impedance is relevant, and your |mention of fuses rather less so.

10-30ma say 100ma to be certain, kills fairly reliably. Do you use a 100ma fuse on mains?

Fuses only protect wiring and appliances.

[Bob Eager]

That's what I was saying. If you only have fuses, it doesn't matter about the earth loop impedance, as you're not protected and will be dead anyway.

[John Rumm]

of course they do!

They won't help in the case of direct contact, however they will in the case of indirect contact - primarily by ensuring that the power is disconnected before you get a chance to come into contact with the live surface, and/or by limiting the duration of contact to under 0.4 secs for portable appliances.

[<me9]

This is a succinct precis of the downside of prat P

[David Hansen]

On Tue, 30 Jan 2007 22:06:27 +0000 someone who may be Dave Fawthrop wrote this:-

Incorrect. Read up the basics of earthed equipotential bonding and automatic disconnection of supply.

[nog]

No doubt I should have said "every socket is capable of ...", which is what I really meant.