10 mins in to Boil this happens YIKES !!!.....

[Jim]

Yes, many DIYers just don't realise the effect of poor quality joints in high current circuits.

The power dissipated is equal to the square of the current times the resistance, so as the current rises it becomes more and more important to have a very low joint resistance.

[weetabixface]

I have a sudden urge to open up my control boxes to check all the screw terminals

Out of interest, all those lives that are daisy chained, what is each driving?

W

[setmash]

3 are driving elements, one is driving pumps and a few other bits and pieces...max load in entire system 44 Amps (measured)

[chris_bobuk]

Another point people over look is thermal cycling. If it routinely carries a significant proportion of its maximum design current, the cable will be subject to repeated heating and cooling cycles. This in turn results in expansion and contraction which can loosen the terminal's grip on its conductor. With using 3kw or maybe more powerful elements it's something else to check with a total load of 44A being drawn.

[madprofessor]

As others have said, loose screw terminals can lead to heat.

It's Ohm's Law - power is current squared multiplied by the resistance. Power = how many watts of heat will be heating your connector block. A poor contact (eg due to loose terminals) leads to a bit of resistance and the whole thing heats up.

When using these screw terminals, IMO you should make sure that each conductor/wire passes along the whole length of the metal part in the screw terminals (but don't leave it so long that it pokes out of the other end). This way, as long as the screws are tight, each screw tightens down onto both wires. If you're /unlucky/ the two wires won't touch each other but you'll still have only a very short piece of connector carrying the current between the two wires ... in two places (ie at each screw). What will probably happen though is that the two wires will be tightly pressed against each other in the connector, and the connector itself would then carry very little current and therefore not really heat up much at all.

If the conductors are a lot thinner than the hole in the conductor, bare off a longer length so that you can double them over so that they better fill the hole and still have the doubled-over bared length run the full length inside the terminal so that the two conductors still overlap each other and are both clamped by both screws. This will help to get good contact between the conductors, and to the terminal block. It all helps.

Cheers,
Kingsley.