We had a cheap Homemaker brand HT7145KM heater come in for recycling.  This one had two of the halogen heating lamps rattling around in the bottom because the ends had shattered and the third on was on the way out as well.  I thought I would take it apart for a bit of a laugh.  And look what I found.

One of the case screws had pierced one of the wires, in this case it was carrying the voltage going to the oscillating motor.  This is pretty poor manufacturing quality to say the least!  Fortunately the screw is recessed about 20mm down a hole otherwise it would be a serious safety issue.

Another worry is that if the wire strands were cut by the screw would the remaining wires have created enough heat to melt and burn the plastic?  Possibly not given that the oscillating motor is quite low current.

This heavy duty extension cord had been quite severely severed.  This is certainly a serious safety situation.

It must have happened while it had current flowing through it because there has been severe sparking in the severed section.

Stay safe!

This cable came in as part of a whole bunch of other stuff from an IT company.

Not sure why someone would want to make one of these.  A mains plug to IEC connector cable is pretty easy to get hold of.  We get them as new and used by the millions – well lots anyway.

The taped up joint is a bit dodgy!  The Electricity (Safety) Regulations 2010 says that cables are unsafe if they “are inadequately protected against the risk of damage by the nature of their covering or their method of installation”.  The AS/NZS 3760 In-service safety inspection and testing of electrical equipment standard says that tape should not be used, and I would agree on that point.

The wires were soldered and heatshrinked under the tape so it is not as bad as some of the others that I have seen.

This is one of the reasons why this type of mains plug should not be used in wet areas. It had arced between phase, neutral, and earth when wet, which carbonised the plastic of the plug.

The other reason is for electrical safety.

An extension cable can traverse wet areas but the plugs and sockets should not get wet, unless they are rated for wet areas.

I came across this real dodgy modification.

This plug board came in for recycling. The original cord has been replaced with one that has no earth. Also, the replacement cable is the older two core type without an outer sheath.

This is really unsafe.  There is no earthing on the sockets.  If something that wasn’t double insulated was plugged in that had leakage from phase to the metal you can get a belt off it and possibly get electrocuted.

The lesson here is: Don’t modify something unless you know what you are doing.

Ecotech Services now offers electrical safety testing (test and tag) for plug in appliances both on site and delivered to our workshop.  This is a logical extension to the work that we have been doing to date.

Alan Liefting, the founder and Managing Director of Ecotech Services, has extensive experience with the safety of electrical appliances: “About 99% of the safety issues can be discovered with a visual inspection.  The other 1% are picked up with PAT testing and knowledge of appliance reliability.”

Anecdotal evidence and first hand experiences by Alan Liefting suggests that  there are a number of “cowboys” carrying out electrical safety testing.  Ecotech Services is committed to offering a high quality service and improving electrical safety rather than maximising profits.

See our electrical safety testing services page and the electrical safety page in our knowledge base for more information.

Check out these 300mm long cables that came out of some gear that we recycled!

I managed, with some difficulty, to get three tight coils out of  it.  The label is a complete waste of time, and I think some of the other ones I came across did not have the labels.

Some of you are probably wondering why you see these warning labels on cables, especially extension leads and retractable vacuum cleaner leads. It is due to the temperature rating of the cable.  Most cables used on appliances are PVC sheathed and PVC has a maximum temperature rating of 105°C.  If the cable is coiled up and has a load plugged into it it will heat up more than if it was uncoiled.  How much the cable heats up depends on how tightly it is coiled, the current though the cable, the resistance of the cable, the air flow (if any) though the coiled cable, and the ambient temperature.

We can do some maths on it.

Total resistance of the cable (300mm long with two conductors of 0.75 mm²):

R = ρ L/A = 1.68 x 10^-8 x (2 x 0.3)/0.75 x 10^-6 = 0.013 Ω

Power dissipated at the maximum loading of 10 amps:

P = I² x R = 10² x 0.013 = 1.3 W

That does not equate to a lot of heat.  My head is spinning with all of this maths so I am not going to do any more to figure out the temperature rise. I know from experience that 1.3 W is not going to give much of a rise in the cable temperature.

So I guess the labels were slapped on the cables by the production staff when they were made in the factory because they are put on the longer ones.  They did not consult the engineers about whether they were needed.

Or are we in a really risk averse world?

Save

I have just done my electrical safety refresher course and when I was changing yet another blown light bulb in our house I began thinking about the safety of the actual sockets.

All sorts of work, backed up by regulations, is done to make things as electrically safe as possible, such as doing periodic safety checks, limitations on who can do what, insulating sleeves around the live and neutral on mains plugs, a protruding shroud on extension cord sockets, prohibition of the sale of some second hand electrical goods, to name just a few.

So then why is it that it so easy to stick your finger into a live lamp socket? Sure, most lamp sockets are on the ceiling but there are plenty of desk lamps, bedside lamps, wall mounted lamps etc from which you can get zapped. On a technical point, and I don’t want anyone to test this, the shock received would only be across a couple of centimetres of skin so it may not be fatal.  The fatal electric shocks are those where the electricity passes though the chest area where the heart is located.