Loose Connection

[chalkmycue]

Hello

Could one of you confirm i have understood this properly?

If you have a connection which is badly terminated you could get burning at the connection due to the fact that only part of the copper is in contact with the terminal, which is going to reduce the csa of the conductor causing overheating.

If you suspected this was the case could you just do a continuity test to confirm this?

Please note i dont have this situation i was just trying to get a better understanding of it.

Thanks Ricky

 

[jj4091]

In theory what you say colud be true, but burning more likely to be caused by a loosely connected wire/terminal arcing between the conductor & terminal.

 

[Taylortwocities]

Continuity test MIGHT find it but its unlikely.
The loose connection tends to break down when the current is high. There is only a miniscule current flowing when you do a continuity test.

 

[bernardgreen]

only part of the copper is in contact with the terminal, which is going to reduce the csa of the conductor causing overheating.

If you suspected this was the case could you just do a continuity test to confirm this?

A continuity test would show continuity, that there was a continuous conductive path, but would not show the quality of that path.

A resistance measurement with a multimeter might show there was a higher than expected resistance but would not for certain identify it as a poor connection. But this only uses a very low current so a weak joint would not be noticed.

That is like testing a water pipe with a trickle of water, a kink or other constriction in the pipe ( which is equivalent to a poor electrical joint ) won't prevent a trickle flowing.

So to see if there is a poor joint in a circuit a large test current must be used in the same way that the kink in the water pipe will only have an affect if there is a lot of water trying to flow through the pipe.

 

[ban-all-sheds]

So to see if there is a poor joint in a circuit a large test current must be used.

As used to be done with conduit systems....

 

[NotHimAgain]

The loose connection is a 'strength and capability' issue (See the electricity at Work Regulations - Regulation 5).

Strength and capability testing is not usually carried out on low voltage electrical installations - its too dangerous . We generally rely on inspection to identify problems such as loose connections. Whilst an instrument test might reveal a fault, there is no certainty that it will.

Circuits may have to carry fault currents of several thousand amperes without failing. To put this in prospective - if we assume a fault current of 1000A flows for 0.1 seconds before it is interrupted by a protective device - the potentially destructive energy that flows into the circuit would be

1000 * 1000 + 0.1 = 100,000 A²s

The average continuity tester producing 0.2A for, say, 10 seconds would deliver a whopping

0.2 * 0.2 * 10 = 0.4 A²s during the test.

Even the more specialised loop impedance testers would typically only produce

25 * 25 * 0.04 = 25 A²s.

Hardly an effective test of strength and capability is it .

This short clip shows why we don't do strength and capability tests .

http://www.youtube.com/watch?v=SCupx469UBY&NR=1