Dangerous Devices - ASTRA BT311 Multi Way Extension Lead

A hideous device which is dangerous in just about every way possible.

This item was obtained on eBay from a seller based in the UK, the item was also shipped from the UK.
Without even opening the packaging, several major problems are evident. The illegal 3 pin plug is a poor copy of a BS1363 type, and does not have a fuse. None of the socket outlets have shutters of any kind.

The packaging does not have any manufacturer's name, address, barcode or any other identification.

The Video

View this video on Youtube.

Initial Testing

A basic test for electrical items such as extension leads is to confirm earth continuity from the plug pin to the earth holes of the sockets, and to any exposed metal parts. This device fails the test, there is apparently no continuity at all.


The three pin plug is blatantly non-compliant - pins are the wrong length and incorrectly spaced. There is no fuse.

The three pin sockets are of the type where a whole range of different plugs can be inserted, resulting in the holes being far larger than on sockets designed for a single type of plug. There are no shutters of any kind.

The blue item above the voltmeter is a switch.


Internally, connections are all poorly soldered together. Wire ends have not been trimmed properly, leaving excess wire on some terminals.

The power indicator is a standard LED and small resistor, with bare wires connecting it directly across the supply.

All of the socket terminals are loose, only being held in place by small pegs on the rear plastic casing.

Line is switched, neutral and earth are directly connected. The earth wire is solid green - it should be green/yellow stripe.

Wire Testing

The flex is a very strange type - the inner insulated conductors are loose within the white outer covering. The individual conductors have an inconsistent appearance, with the colour varying considerably.
The surface of the insulation is textured and irregular. The inner conductors appear to be copper plated aluminium - certainly not solid copper.

The section of flex tested is 86cm long. Resistance values in ohms are Brown:0.540, Blue:0.568, Green:1.996
The flex as supplied is 1.2m long, which using those resistance figures equates to Brown 0.753 and Blue 0.792, a total resistance of 1.545 ohms.

If the device was used at it's alleged maximum rating of 10 amps, volt drop in the flex would be 15.45 volts, or about 6.5% if used on a 240V supply.

Power dissipated in the flex would be 154 watts - a substantial amount of power which would result in the temperature of the flex rising significantly.

Earth Wire

The earth is not connected, but even if it was, it would be useless. The section tested had a resistance of nearly 2 ohms, equivalent to 2.785 ohms for the whole 1.2m length. A fault between line and earth inside the adaptor would have a resistance of 3.583 ohms.
Assuming an impedance for a typical socket outlet of around 0.5 ohms - (0.35 ohms for the supply and 0.15 ohms for the circuit wiring) - gives a total of just over 4 ohms, or a fault current of 60A at 240V. As there is no fuse in the plug, the next protective device would probably be a 32A circuit breaker or 30A fuse. A current of 60A there will not trip the breaker or blow the fuse for well over a minute.

If the circuit included an RCD it would trip very quickly. If not, 60 amps would flow through the adaptor and flex causing it to heat up and burst into flames.

Ebay listing for this item (July 2014)

eBay listing for Astra BT311 Multway Adaptor, July 2014 This image is the ebay listing captured in July 2014, shortly after purchasing the adaptor.

The listing describes the item accurately, as the description is taken fron the product packaging. The seller despatched the item quickly and used decent packaging.

It is likely that the seller was unaware of the dangerous nature of this product.

The listing has since ended and the item is no longer for sale.