Aging and Paranoia?

[John Whitworth]

Yesterday I bought a pack of three remote controlled energy saving adaptors from Asda for a fiver. The principle is great, but I can't help but wonder just how protected I am against a fault in something of this type. I.e. if I switch off all of my computer equipment at the wall, I know it's not going to go wrong and start a fire. But with these devices - how can I be sure?

I guess this is a general point really. If something electronic does go wrong - i.e. one of these devices - what safety features are going to prevent a fire. Immediate thoughts would be that it's all local to the device - i.e. the fuse on it. I guess that the MCB isn't going to stop much, as 32A for an entire circuit is plenty more than it would take to heat something up to burn, surely?

The reason I want these adaptors is not to reduce standby usage - it's just to make it easier to switch the PC etc on, as it's all tucked away in the extremities of 'under the desk'.

Cheers

JW

[Dave Liquorice]

I got a set a month or so ago, good value. I wanted to be able to switch the WiFi on/off without having to find the correct, half hidden, wall wart to unplug. One snag is that they forget their channel programming if they lose mains for any reason. When power comes back they enter learning mode, if you aren't careful they all end up on the same channel.

The power switching is done by a relay. So it's only the electronics in the device you have to worry about, if that fails it is pre any plug top fuse of any connected equipment. I don't remember seeing an internal fuse when I had the cover off but then I wasn't looking for that.

[Harry Bloomfield]

Dave Liquorice formulated the question :

It should all be AFTER the plug top fuse and protected by the fuse. Most often the MCB will trip out before the fuse or as well as the fuse blowing.

[Simon C.]

I use similar [from Lidl] for inaccessible switches. I suppose its an extra electric/electronic device, and the more you have the more chance something will go wrong. No idea what sort of safety devices they have.

After a TV on standby started crackiling and smoking a few years ago just before bedtime I too think about fire more than I used to. My solution so far is better 'switch off' discipline [even if its a remote socket] and smoke detectors in *every* room.

[Mike Clarke]

But if it's a plug-in adaptor type thingy it will be before the plugtop. It may or may not have it's own replaceable fuse, many do not - if its electronic circuitry developed a fault it would probably act as a fuse by releasing its magic smoke long before even a 3A fuse was aware of it.

[brass monkey]

Yes, I use them for that and to reduce standby power. I must be switching something like 15 sockets with 3 of these. Thing is, are these more or less likely to start a fire than the items they control. Not to cause undue worry, but I've actually seen veroboard on fire caused by IC's on a development project.

[Harry Bloomfield]

Simon C. explained on 06/10/2010 :

I've just checked one of our remote sockets and I cannot see any obvious use. I would guess (hope) that there is an in-line fuse mounted on the PCB inside the unit, which would protect the electronics - but not the outlet socket.

[Dave Liquorice]

electronics

It can't be after "plug top fuse of any connected equipment" as these are plugin units, like plugin RCDs. There is no fuse, internal or external, I've just had one open again. Live goes to one pole of the relay and to a couple of diodes.

[Mike Clarke]

Probably a fusible section of track or a key electronic component expected to burn out and go open circuit in the event of a high current fault. Either way the "protection" is to avoid further heat and fire - the device itself will usually be deemed to be a write off.

[Harry Bloomfield]

It happens that Dave Liquorice formulated :

So the relay is only protected by the 32amp MCB back at the mains.

[Mike Clarke]

Depends on the source of the overcurrent. If it's a fault in the appliance or its lead then the fault current will be limited by the plugtop fuse. If the relay develops fault sufficient to cause a short then yes it'll be the MCB in the CU but the relay will already be beyond repair and the MCB will protect the circuit from damage caused by the faulty relay.

[Dave Liquorice]

Yes, though in our case a 30A bit of fuse wire... B-) The relay is rated for 240v AC @ 10A.

The track from the terminal where the live in connects to the PCB and relay pole to the two diodes is probably only 1.5mm wide and 20mm long what does that equate too in terms of fuseabilty? The two diodes are ordinary plastic encapsulated ones, normally having a 1A rating. If the track doesn't fry the diodes will.

[Tim Watts]

Worse than you might think!

The two diodes

[Chris J Dixon]

I use a similar device occasionally, though not for a computer. I have noticed that it can be switched off (fortunately never on, so far) by radio car keys. Might be a problem if it crashes your PC.

Chris

[Dave Osborne]

Can't say. It depends on the actual width of the track, the thickness of the track and the heat-sinking effect of the terminals at the end of the track. further, in the event of a fault current, it depends on the rate of rise of temperature of the track (i.e how fast the glue melts vis-a-vis the buckling of the track due to thermal expansion).

The two diodes

I don't quite see your argument. If the load causes a fault current, the diodes may or may not be affected. They will almost certainly not fail due to long-term over-temperature of the copper track.

If the electronics in the unit fail and cause an over-current, then the diodes may fail. However, the most likely failure mode is that one of the diodes fails and takes out the electronics.

HTH