Fitting a mains plug.

[Dave Moll]

I don't like the idea of a 5A fuse when the appliance runs at 2kW (which equates to over 8 amps). Maybe the fuse won't blow but would run pretty hot. Yes, I accept that the fuse is to protect the cable, but must be adequate for the running current of the appliance.

[Beobloke]

Originally Posted by Lancs Lad

Here it is!

Correct fuse for a table fan.

Legrand plug with unsheathed pins just because I really like those plugs!

So, now I'm in the firing line. What do you all think?

Tidy job, or not?

Go on, let me have it...

Looks like you’ve put the fuse in the wrong way round.

Don’t worry, though; it’s a common mistake.

[stevehertz]

Originally Posted by Dave Moll

I don't like the idea of a 5A fuse when the appliance runs at 2kW (which equates to over 8 amps). Maybe the fuse won't blow but would run pretty hot. Yes, I accept that the fuse is to protect the cable, but must be adequate for the running current of the appliance.

Clearly what this boils down to is matching the current rating of the mains cable to the appliance. Then a suitably rated fuse can be used that adequately and safely protects both.

[Lancs Lad]

How can you put a fuse in the wrong way round?

Please enlighten me!

[paulsherwin]

He was joking. As you say, it doesn't matter.

[Lancs Lad]

Was he?

I'm not so sure...

[Glowing Bits!]

Fuse orientation is critical, the electrons can only flow in one direction but not the other

[G6Tanuki]

Originally Posted by Glowing Bits!

Fuse orientation is critical, the electrons can only flow in one direction but not the other

Surely that only applies to the "Quantum Fuses" under recent discussion in another thread...

Personally I don't like running plug-fuses anywhere near their rated current: I've seen too many examples of this causing the fuse-clips to overheat with distinctly-negative outcomes both for the plug and the socket into which it is plugged; hence I only use 3A and 13A fuses.

[Lancs Lad]

What's wrong with 5 amp fuses?

I like them very much. Very useful.

I bought a toaster several years ago, and the sticky label on the plug said "Fitted with a 5A fuse", which I thought was unusual, but very correct at the same time.

Appliance manufacturers tend to fit 3 amp or 13 amp,don't they?

Although, I bought an LED 40" television in 2016, which has a 5 amp fuse in the plug, which I've never been terribly happy about.

Why would such a low current appliance be fitted with a larger fuse? The flex is just your standard two-core 0.75 mm.

I've never changed the fuse - but it's always niggling at me that I really should replace it with a 3 amp one.

Any thoughts?

Why would such a low current appliance be fitted with a larger fuse?

Surge current from the power supply, switched mode jobs do this.

[Heatercathodeshort]

To be honest I've welcomed the fitted plug from a customer point of view.
Unfortunately I have lost my 'Black Museum' photographs of horrendously fitted plugs on equipment that came in for service.

The most common fault was the neutral wired to the earth pin. This would produce a dead set when connected to my isolated bench!

Terrible wiring with bare wires hanging out of the plug and always a 13amp fuse. The loss of income from the sale of plugs was noticeable. I used to sell literally thousands and I often wondered what my customers did with them all! Happy days. John.

[G6Tanuki]

Quite a lot of modern stuff takes a significant switch-on surge; it's a characteristic of SMPS design. Using this sort of kit with a low-rated plug-fuse [they're not slow-blow!] can over time cause the fusewire to weaken - its resistance then goes up and it either fails-open or goes into heating-up mode.

In times-past I had to deal with a site where - during the obligatory PAT - the tester replaced the 13A fuses in the plugs with 3A ones without first seeking approval. These plugs were feeding a few hundred really-rather-large Trinitron CRT monitors on dealer-desks; a couple of weeks after the PAT had been completed we started having monitors fail to power-up in the morning, with blown plug-fuses.

The degauss, which fired every time the monitor was turned-on, drew a few cycles of really-rather-heavy current until its posistor warmed-up; this was enough to fatigue the under-rated fuses to failure in a few weeks.

Once the issue was identified I sent one of the team out to scour the local B&Q/Homebase stores and bring back every 13A fuse he could find, these were promptly fitted to every plug overnight. The techies were happy to be paid triple-time [London rates!] to do the work, the problem went away, the client [whose unit-of-downtime was dollars-per-minute] was happy, and he didn't employ that particular PAT-resting company again!

[G6Tanuki]

Originally Posted by Heatercathodeshort

The most common fault was the neutral wired to the earth pin. This would produce a dead set when connected to my isolated bench!

Thankfully, the coming of RCDs rapidly weeded out the transposed N and E connections.

I remember some plugs with colours on the inside to show which wire went where. And coloured sleeves on the power pins.

[mark_in_manc]

Originally Posted by Refugee

I also have a photo of a fully earthed and rooted plug complete with a snipped cable entry.

This passed without comment but I really enjoyed it - thanks!

[Beobloke]

Originally Posted by Lancs Lad

Was he?

I'm not so sure...

Yes, I genuinely was joking!

However, if you stray onto the Audiophoolery thread, you’ll find there are poor deluded souls out there that believe it does make a difference.

[Kentode]

I've used this for years and it works really well, although I'm going to include a loop in the earth wire from now on as it makes sense.

On a side note, buying good quality wire strippers which don't break or score the conductor strands are worthwhile, l know some on here use their teeth!

[unitaudio]

I aquired a suprising number of items over the years as not working due simply to one or more loose wires in the plug. Every time I get something new (to me) the first thing I do is check the plug. It's very often a nice simple "repair".

Regards,
Paul

[G6Tanuki]

Originally Posted by unitaudio

I aquired a suprising number of items over the years as not working due simply to one or more loose wires in the plug. Every time I get something new (to me) the first thing I do is check the plug. It's very often a nice simple "repair".

Yes! Same goes for domestic-things like vacuum-cleaners/irons/electric-drills/hedge-clippers/strimmers; these often develop an open-circuit in the flex a few inches from the plug [whether moulded-on or wired] due to repeated bending/stretching of the wire: though some people will just cut the plug off along with a few inches of flex and fit a new plug, I always replace the whole flex because if it's been flexed enough to break the cores close to the plug (or the appliance) chances are the rest of the flex has seen similar overwork and will not be far from the next failure.

Moulded plugs seem rather prone to another form of failure - where if they receive a sharp whack to one of the pins (like when winding-up an extension lead or letting a vacuum-cleaner retract its spooled-out flex) it can snap the brass bit off internally though the pin stays attached to the body of the plug. If you're lucky it's a clean break and the appliance fails; if you're unlucky the contact is intermittent, resistive, and eventually discloses itself in a shower of sparks and molten plastic.

[Refugee]

I can remember the plug on the vacuum cleaner when I was a teenager.
Dad was asked to have a look at it.
He wobbled the cable by the stop lozenge for the reeler and it revealed that the fault was elsewhere. It printed a black arrow on the wall pointing to the failed cord grip that had allowed the cable to pull out with audio.

I am not immune from acquiring stuff with badly wired plugs.
Three badly wired plugs by blunt screwdriver man