Round pin era electrics are back

[Andrew Gabriel]

Early installations were lighting only, and charged by the number of lights.

[John Rumm]

You are missing the important point...

What is *required* is fault protection, not overload protection. (A lamp is unlikely to generate an overload anyway).

A BS3036 rewireable fuse with 15A wire in it will need something like

180A to open in 0.1 sec, and 90A to open in 0.4

So say you have a small appliance with a skimpy 0.5mm^2 CSA conductor flex (e.g. so called 3A flex), and PVC insulation (no idea what the k factor for fabric would be!) you can show:

s = sqrt( 180^2 x 0.1 ) / 115 = 0.49mm

So your flex is still (just about) protected by the main circuit fuse, even though it has no overload protection.

A flex of that nature connected to a 30A rewireable or 32A MCB however would have no fault protection.

[Gefreiter Krueger]

Depends how severe the short is. I've had 1A wire sizzle with a 5A fuse when it slightly shorted where it was stapled to the wall.

[spuorgelgoog]

Me too.

All up = off.

Have to get round to changing the lounge light switches; at the moment the left switch is up for off and the right switch is up for on.

Owain

[Andy Wade]

For an appliance needing more than 5 A you just use an unfused plug. The flex of such an appliance will be large enough to be protected by the upstream fuse or MCB - 20 A max. Fused plugs are used for low current appliances which tend to have smaller flexes, requiring local protection.

The little (3/4 x 3/16 in.) BS 646 fuses used in round pin plugs are only available up to 5 A rating in any case.

[Stephen]

I pointed that out earlier in the thread....

[Andrew Gabriel]

The power generated at a fault site means it will never stay stable passing a current inbetween the overload and the fault current. That tiny site generating in excess of 4kW will wither blow itself open circuit, or generate a full-on arc shorting out the supply and generating a fault current to blow the fuse. You simply can't have a cable fault which generates only an overload current.

[ARW]

Same as Andrew Gabriel. "All switches in the off position means the light is off. (That rule works for triple and more switching too.)"

[Gefreiter Krueger]

It's a lot simpler to just have everything downstream of the fuse capable of taking that much current.

[dennis]

That would be normal for industrial stuff, but for some reason doesn't apply to where people live.

The cost savings must be massive (or not!).

[Gefreiter Krueger]

Well if I have 2 amp wire on a lamp I fit a 2 amp fuse in the plug.

[John Rumm]

Which is fine and good practice. With old electrical items it may even be required to maintain adequate fault protection. With modern appliances, they are usually designed for sale in all markets, and hence in most cases the flex will be selected to be adequately fault protected by a 16A MCB.

(hence the number of devices you buy with flexes that are too short!)

[Gefreiter Krueger]

(I thought that was just to save money).

[John Rumm]

Partly...

If you made it longer, you would need a thicker flex. On some appliances that may be considered a hindrance.

[Gefreiter Krueger]

Best to fit the correct fuse in the plug for the cable, then there can be no problem. Since appliances all come with plugs nowadays, the manufacturer can ensure it does.

[SteveW]

I have actually wired ours that way, but whether my wife would remember to check if she needed to change the bulb while I was out is another matter.

Pull switches can also leave people in the dark (pun intended) about whther the light is switched on or not.

SteveW

[Gefreiter Krueger]

The bulb blows when you turn it on, so you know it's on.

[SteveW]

Plenty of MR16 230V lamps for sale out there. I wonder if that is correct or is it that the connection is the same, but they should be referred to as something else?

SteveW

[SteveW]

Of course, but if it blows when the kids use it, in all likelihood they'll switch it back and forth a few times to see if it suddenly comes on.

SteveW

[Gefreiter Krueger]

I just don't stick my finger in the socket to test it. Simply insert the new bulb by holding the glass/plastic. Or in the case of mine, the live LEDs :-)