Hi all, bit of an introduction and a rant! (soz lol)

[djrichie_t]

Hi all, Yep this is my 1st post so thought i'd introduce myself before ranting on about something of a safety issue.

I am a fully qualified electrical engineer, trained by the electricity board where I started my 5 year apprenticeship as an electrical fitter in 1990, finished that and went on to qualify as a craft engineer and then a year after that guess what - I got made redundant!

So, any project type or 'out of the ordinary' questions, feel free to message me as im used to working on anything from small electronics upto 132,000 volt systems - also im authorised to work over and above BS7671 which has caused a few heated conversations with some normal sparkies but i do try to get on with everyone



Anyway heres my rant:

I had a call this evening from someone who put lots of christmas lighting up round their house, looking very nice indeed. However guess what... the main switch in the consumer unit had melted! This was caused by the terminal screw on the incoming 25mm tail not being tightened properly.

All sorted now, changed switch over and bobs your uncle. with a constant load of 6kW of lighting (all on a green tariff) it doesnt take things long to heat up.

So always check and double check tightness of connections. A 9kW shower on for 20 mins will not cause enough heat to cause this sort of problem due to the short duration the shower is used.

A 3kW kettle definately wont (unless the connection is extremely bad)

6kW of load for 6 hours a day will cause probs on a bad connection.

When terminating conductors, especially 2.5mm inside the back of a socket, always double the copper conductors where possible. The idea is to fill the whole with as much copper as possible so that when the screw tightens, its not just pinching on the 1 strand of copper, but gripping twice the surface area, hence half the resistance

Obviously its impossible to double over larger conductors in cooker sockets etc, however in this case its good to use equipment that has two termination screws where the cable enters the terminal, and not just the one screw.

Ive had this argument with sparkys lots of times, they sometimes dont care, as long as the test results are fine (which they will be at 1st) - try again after 6 months of heavy use and you will get a big increase in resistance. - resistance = heat = hotspot = flames! This will not always trip an mcb or rcd either!

It doesnt matter who your registered with, NICEIC, Part P with the council.... its the quality of workmanship that counts. I've seen some horrendous work done by registered people so use your instinct!

if someone is not doubling conductors over then question it by all means!

I'm usually much more chilled out than this just this eve it got my back up lol!

Any questions/advice feel free to fire away!

Regards

Rich.

 

[GaryMo]

also im authorised to work over and above BS7671 which has caused a few heated conversations with some normal sparkies but i do try to get on with everyone

What does this actually mean, also, authorised by whom?

 

[djrichie_t]

Sorry i should have clarified that bit, its by the ESI - Electricity Supply Industry. Long winded one but basically I can make decisions and take the rap as usually its to do with decisions made on an emergency/contingency basis

 

[RF Lighting]

I've seen some horrendous work done by registered people so use your instinct!

Hello, for more examples of horrendous work, just have a search for RF Lighting's Picture of the week!™

Oh, and welcome to the forum.


Infact, Click Here

 

[securespark]

RichT, I beg to pick a few holes in what you've said:

You don't have to have a large load to cause a build up of heat, even a loose light switch connection can build up enough heat to break into flame. I had this once on a 60W lamp when I was S/E- 0.26A. As I took the switch off (power still on!!), it burst into flame.

It's the loose connection that toasted the main switch. The load through that connection will only affect the speed of deterioration, surely?

In my experience, a 9kW shower will deffo cause problems if there's a loose connection, even if only on for short periods.

How many burnt-out shower switches (and all other types of accessory, come to that) have I changed in 20-odd years?

Just wanted to be the first to "lock horns" with you...

 

[djrichie_t]

Yeah I get what youre saying, I was just generaslising as if to say bigger loads can cause big probs.

Just that now the can of red bull has kicked in i can think clearer lol. Its ohms law at the end of the day, if you have resistance, you have heat, its the volt drop across the loose joint which is proportianal to the power dissipated in heat but thats starting to get technical

As for changing shower switches, its very rare you have to change a british-made one isnt it

its when i see 'made in china' i start to shudder

 

[securespark]

I change all sorts! If it's got a loose connection, it'll burn, British-made or not!

 

[ricicle]

.......but thats starting to get technical

No it's not, it's a basic understanding of electricity and any electrician who does not understand it should not be allowed anywhere near it.

 

[djrichie_t]

hehe you'll be amased. There even exists some electricians who do not fully appreciate the reason of a neutral conductor being .... neutral (or as close to 0 volts as poss) gave me a headache explaining to one of them the probs of floating neutrals on older systems.

Pen, paper, big diagrams and still they didnt get it. I even used coloured pens!

 

[Pensdown]

Sorry i should have clarified that bit, its by the ESI - Electricity Supply Industry. Long winded one but basically I can make decisions and take the rap as usually its to do with decisions made on an emergency/contingency basis

I'm intrigued? What sort of emergency decisions are you authorised to make and for whom?

 

[bernardgreen]

Its ohms law at the end of the day, if you have resistance, you have heat, its the volt drop across the loose joint which is proportianal to the power dissipated in heat but thats starting to get technical

Add the effect of increasing heat on the materials and contact pressure and it gets complicated. I am told the calculations include the use of calculus equations. di/dt etc etc....

So keep it simple , do the screws up properly........

A soft joint ( screws not tight enough but wire fixed ) heats due to the resistance of the small area of contact. A loose joint heats due to arcing.

 

[IJWS15]

Rich

Since you were having a rant . . .

"I am a fully qualified electrical engineer, . . . . . "

So are you a paid up member of the Institution of Electrical and Electronic Engineers (i.e. an MIEE) and the Engineering Council (a CEng.) ?

Or are you a qualified electrician?

 

[djrichie_t]

qualified engineer, thats qualified on big systems upto and including 132kV. did an apprenticeship and went on to be made up as an engineer.

 

[ricicle]

qualified engineer, thats qualified on big systems upto and including 132kV. did an apprenticeship and went on to be made up as an engineer.

HNC/HND etc ?

 

[viewer]

This is interesting. I was told to double over if one conductor entered the terminal, but not if two (i.e. a socket on a ring). I have found that it is possible to put two "singles" into a socket and tighten them, only to find that they will pull out a week later even though initial tests were fine. The use of shrouded terminals (MK/Crabtree) means that it is difficult to see how the wire cores are arranged. As said earlier, it is the contact area which is important and the physical resistance to movement. The latter will not always be shown in higher electrical resistance. I'd be pleased to hear further experiences (not arguments about qualifications- I've a PhD, but it doesn't qualify me to change a fuse).
Many thanks
V