Electrical advice please

isofa

yangptangkipperbang wrote: »

Many extension leads are of very basic manufacture and do not offer good quality connections or cable at the best of times

Some comments from one of the MANY websites that cover this topic:-

<snip>

and many websites that offer contrary advice, to be found everywhere...

Scaremongering nonsense.

In stark contrast to this excellent post from securityguy:

securityguy wrote: »

0.75mm copper wire has a resistance of about 20 ohms per KILOMETER. You're seriously claiming that an additional ten meters of that in circuit (ie, a 5m extension lead), which would have a resistance of 0.2 ohms, thus causing a voltage drop of 2.6V at 13A, is going to alter the triggering of an over-current device? How? They're current-sensitive devices, anyway. And if by "protective devices" you mean RCDs, then they're measuring the current difference between the two legs, which is unaffected by the length of the circuit.

The reason appliances have tiddly short leads is that copper is expensive, and if you're mass producing high-current appliances, saving two meters of three-core 13A flex is a worthwhile saving. And flexes which are too long tend to be coiled up and cable-tied, which is bad for the insulation and bad for the heat dissipation in the cable. 13A through 0.2 ohms will dissipate 40W, which if the cable is tightly wound is a serious risk (I'm always careful to completely uncoil the extension lead that I use for my lawn mower).

Perhaps some others can now put away their tin-foil hats?

battleborn

Be careful buying electrical accessories off ebay, they may be cheap, but more than likely they have no certification and have not been tested to British and European standards.

vaio

securityguy wrote: »

0.75mm copper wire has a resistance of about 20 ohms per KILOMETER. You're seriously claiming that an additional ten meters of that in circuit (ie, a 5m extension lead), which would have a resistance of 0.2 ohms, thus causing a voltage drop of 2.6V at 13A, is going to alter the triggering of an over-current device? How? They're current-sensitive devices, anyway. And if by "protective devices" you mean RCDs, then they're measuring the current difference between the two legs, which is unaffected by the length of the circuit.

The reason appliances have tiddly short leads is that copper is expensive, and if you're mass producing high-current appliances, saving two meters of three-core 13A flex is a worthwhile saving. And flexes which are too long tend to be coiled up and cable-tied, which is bad for the insulation and bad for the heat dissipation in the cable. 13A through 0.2 ohms will dissipate 40W, which if the cable is tightly wound is a serious risk (I'm always careful to completely uncoil the extension lead that I use for my lawn mower).

good post and that's before you take into account the loads the OP is talking about which I'd have thought would only be a couple of hundred watts in total

personally I'd still go for http://www.ebay.co.uk/itm/GOOD-QUALI...item51accf0ebd

yangptangkipperbang

securityguy wrote: »

And this differs from every other 13A connection in your house because...?

..............by asking that you have shown your ignorance of the subject..............

yangptangkipperbang

isofa wrote: »

Scaremongering nonsense.

.......in your case "ignorant" nonsense.............

Fifer

yangptangkipperbang wrote: »

..............by asking that you have shown your ignorance of the subject..............

Would you care to explain why a CE marked, good quality 13A plug is more likely to become loose from a CE marked good quality 13A trailing socket carefully laid away from foot traffic, than from a good quality, CE marked 13A wall socket?

(There is an argument that the trailing socket may be more secure as the loose cable will allow it to travel with the plug if tugged, where a socket attached to a wall cannot.)

Owain_Moneysaver

Ratboy wrote: »

My Victorian house has a distinct lack of power sockets; , so 4-way sockets are plugged into 4 way sockets, and when unplugging various devices, there is an enormous spark when unplugging....YIKES!

But has a modern fusebox...Seems like the power companies must address the issue?

You should avoid plugging/unplugging items on load. This is difficult with things like laptop power supplies which have no mains on/off switch but have a high inrush current.

Owain_Moneysaver

securityguy wrote: »

0.75mm copper wire has a resistance of about 20 ohms per KILOMETER. You're seriously claiming that an additional ten meters of that in circuit (ie, a 5m extension lead), which would have a resistance of 0.2 ohms, thus causing a voltage drop of 2.6V at 13A, is going to alter the triggering of an over-current device? How? They're current-sensitive devices, anyway.

Yes.

The maximum earth fault loop impedance for a circuit protected by a Type B 32A MCB to give a 0.4 second disconnection time is 1.50 ohm.

The maximum impedance of circuit protective conductors to allow 5 second disconnection time for socket outlets is 0.31 ohm.

The severity of the electric shock received when there is a phase to earth fault (indirect contact) depends entirely on the impedance of the circuit protective conductor. The volt drop across the protective conductor is applied to the person receiving the shock. Since this volt drop is equal to fault current times protective conductor impedance, if the protective conductor has a lower impedance the shock voltage will be less. Thus it can be sustained for a longer period without extreme danger.

This limitation on the impedance of the circuit protective conductor is of particular importance in TT systems where it is likely that the resistance of the earth electrode to the general mass of earth will be high. (Extracted from The Electricians Guide Fifth Edition
by John Whitfield)

securityguy

Owain_Moneysaver wrote: »

Yes.

The maximum earth fault loop impedance for a circuit protected by a Type B 32A MCB to give a 0.4 second disconnection time is 1.50 ohm.

240V over 1.5 ohm is a current of about 160 amps. That's because MCBs don't trip on instantaneous current, rather there's a time/current product required to trip them. These are the breakers protecting your ring mains. A breaker which will pass 32A continuously need about 140A to guarantee opening in 0.5s.

You are attempting to claim that an extension lead is somehow affected by this. An extension lead that is contributing perhaps 0.2 ohms.

Let's assume that there's a straight fault to earth at the far end of a long extension lead (10m? 20m?). What's going to trip first: the 3 or 5A fuse on the appliance plug (or possibly, as we're talking about computer equipment, the 3A fuse internal to the PSU), the 13A fuse on the extension block, the 13A fuse on the plug, the 32A MCB on the ring main or (assuming that we aren't all living in the Thatcher years) the 300mA RCD on the consumer unit if someone touches the fault? My money's on the RCD winning that race if you're unlucky enough to touch the conductors the very moment the fault arises, but in the more common situation, the fuses blew ages ago.

One reason why British electrics are safer (some would argue over kill, but they're wrong) is that supply flexes are protected by fuses suitable for their own capacity, rather than the overall capacity back to the consumer unit. Scenarios in which 100A currents are passing through extension leads without anything tripping are just scaremongering. Nasty if you're American. Not nasty in the UK.

Ratboy

Owain_Moneysaver wrote: »

You should avoid plugging/unplugging items on load. This is difficult with things like laptop power supplies which have no mains on/off switch but have a high inrush current.

I understand that, and try to prevent it at all times; but certain high voltage items connected via an adaptor cause a green type scum (egris???); that causes a higher resistance on the plug, and also things plugged in over time, also cause this, due to vibration of the frequencies (I know! :rotfl:), NOT!, but many washing machines vibrate the live terminals out of the plug, causing a fail. Extensions, especially 2/3 way suffer from this a lot. But my 4 ways bad fitting presumably due to the build up of this green goo?

I presume; I'm no scientist; that this green is a reaction between incompatible metals being used? Isn't it copper that goes green? Silver goes black?