Monday, 19 November 2012

Further surgery.....Updated

Thanks to the outstanding support from the life savers at RepRap Pro this week, the house hasn't burnt down!

Poor molding on a BS 1363 13A mains plug
Why? It would appear that unfortunately Huxley #710 may have had a faulty mains plug supplied. I should have paid more attention to the molding of the plug its self. As you can see it's not a good quality molding and clearly now I dig deeper there are defects in the plug molding that I should have paid attention too. I was just too excited to get Huxley #710 working and start having fun!

In the UK we use a square pin 13A design and whilst I am a little biased, think its the best design in the world. However there are out there, cheap and or counterfeit molded plugs which can be lethal! Check out the link here (http://www.esc.org.uk) to see the potential effects of counterfeit and sub standard products. The problem shown in the video is because the fuse in the plug is not operating to specification. But I suspect there is more to the story than just this.

If you take a close look at the picture of my plug you can see a line running from the hole in the center of the plug to the top right. You can also see the line actually runs back to meet the left side of the textured circle. This is an excellent example of  poor molding.

BS 1363 plugs include a fuse and I stripped the fuse out, here you see another interesting issue. A blue 13A fuse! Normally this should be brown, the printing on the fuse is usually much clearer. There should also be an ASTA logo at least and I suspect opening the fuse might yield even more issues. Of course the logo alone is no protection but if we add up all the oddities, its clear the product might not be of the standard we should be receiving.

A blue 13 Amp cartridge fuse, probably not to standard
Checking the rating on the power supply I suspect it should have been supplied with a maximum of a 3 A (Amp) fuse and probably a 1A fuse would have been better. The rating on the power supply is 100 to 240 V, 2 A. It looks like its a 118 watt device (19V at 6.23 A) so even a 3A fuse would be a little over specified, given that UK mains voltages are generally very stable. ( Power = Amps * Volts ). If the socket on the end is to be believed, remembering we can't really trust anything on this lead, the socket is rated at 2.5A  The cable is marked as having conductors with a cross sectional area of 0.75 mm. The outer diameter of the cable flex seems consistent with the markings but would need stripping down to confirm the cable implementation. Either way, even a good 13A fuse with a 0.75 mm cable is not a good idea!

I will confirm the power consumption (and thus the current) when I get the replacement lead (yes, I have a clip on ammeter for A.C. mains cables like these).

Finally, easy recognition. The earth pin should be solid metal unlike the one shown here where there is a plastic section on it. The earth pin is the thicker pin at the top of the image, the lower two pins are now specified with plastic sections to prevent fingers accidentally touching Line (Live) and Neutral pins when inserting or removing plugs from sockets.

Click on the image for higher resolution views.

If you have a RepRap Pro device you can contact them  through their web site. If you have any other appliance with one of these leads with the characteristics shown. Stop using it immediately. In the UK, return the product to the shop for a refund or replacement. If in doubt, ask a qualified electrician.
Incorrect BS 1363 plug having partially insulated earth pin.


29 November 2012- Update -
Received a replacement mains lead from RepRap Pro today, shown in the image with the black printing on the 5A (5 Amp) fuse. I shall be fitting a 3 Amp fuse to mine as I measured the continuous current at just under 500 mA. A 3 Amp fuse is readily available in the UK for 240 mains plugs, whilst the 1 Amp variants are less common. The inrush current might be high leading to occasional failure of a 1 Amp fuse at worst. However I would have to insert (clamp-on or series connect) my multimeter in the connection further up the supply to measure the inrush current, as my clamp-on mains cable current meter does not record peak inrush currents. At the moment I am working on installing the next release of the Marlin software and would like to check out the physical movement of Huxley #710 for which the mains 240v power supply is required.

Replacement BS 1363 plug with supplied Bussmann 5A fuse

The fuse on this holder is hard to get out of the plastic clip and the strain relief on the 13 Amp plug seems a little stiff. But I would expect it to with stand a cable pull test. Of the order of 40N, 100 times 1 second duration. The cable is straining at the end of what should be the strain relief section. i.e the strain relief is not really moving distributing the strain. If you look at the strain relief in the photograph you can see the difference between the connector end strain relief and the mains plug strain relief.

On the faulty lead I did a tear down and discovered the cable conductors were in fact not the correct diameter being 0.1 mm diameter with 28 strand rather than 0.2 mm diameter with 24 strands. The 0.1 mm diameter strands gave an outside diameter of 0.75mm for a twisted conductor, but I am stretching the bounds of possibility here (it's  not the correct way to determine cross sectional area for multi strand conductors, I am just guessing what they might try to use as an excuse). The specification is cross sectional area not diameter! A subtle but important difference. So I get around 0.45 mm² cross sectional area as opposed to 0.75 mm² required by the standard. This means the cable can not carry the rated current, never mind the resultant over current due to the fitted 13 Amp fuse, that no doubt is anything other than a 13 Amp rating!  The earth conductor was yellow with no green stripe, this probably indicates the insulation is not properly formulated as well. So coupled with an incorrect fuse, the incorrect cross sectional area was a serious issue if a fault developed in the power supply. Check here for more information on other counterfeit and poorly manufactured BS1363 mains plugs. If you think this is only an issue with UK cables, don't sit there and be smug! The cable was marked CE KEMA-KEUR and a number of other pseudo approval marks. Other marking was H03VV-F 3CX0.75mm². Be on the look out for it, where ever you are!

Looking forward to receiving the second replacement lead for the other power supply soon. Seems strange to send two packages, but perhaps they are in 'short' (pun intended) supply at the moment ;-) .

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