Newbee - stranded wires should not be tinned (unless done in factory). There are two reasons for that:
- Tinned stranded wires break easily, because stress point on the border of isolation is created (solder stiffens wire but stops short of going inside). It is just against common thought that tinning makes wire stronger.
- Connection is not reliable because solder "gives" over time (it is called cold flow). In some states (for instance Missouri) it is illegal (against code) to tin stranded wires.
This is clearly stated in BSEN 60950-1:2006 Information Technology equipment - Safety, Para. 3.3.8.
"3.3.8 Stranded Wire
The end of a stranded conductor shall not be consolidated by soft-soldering at places where the conductor is subject to contact pressure unless the method of clamping is designed so as to reduce the likelhood of a bad contact due to cold flow of the solder.
Spring terminals that compensate for the cold flow are deemed to satisfy this requirement.
Preventing the clamping screws from rotating is not considered to be adequate."
Stranded wire, flattened provides under pressure oxygen free connection while flattening increases contact area.
That's minor point and people do what worked for them before, but I absolutely agree with you that one has to be careful and examine connection from time to time.
- Tinned stranded wires break easily, because stress point on the border of isolation is created (solder stiffens wire but stops short of going inside). It is just against common thought that tinning makes wire stronger.
- Connection is not reliable because solder "gives" over time (it is called cold flow). In some states (for instance Missouri) it is illegal (against code) to tin stranded wires.
This is clearly stated in BSEN 60950-1:2006 Information Technology equipment - Safety, Para. 3.3.8.
"3.3.8 Stranded Wire
The end of a stranded conductor shall not be consolidated by soft-soldering at places where the conductor is subject to contact pressure unless the method of clamping is designed so as to reduce the likelhood of a bad contact due to cold flow of the solder.
Spring terminals that compensate for the cold flow are deemed to satisfy this requirement.
Preventing the clamping screws from rotating is not considered to be adequate."
Stranded wire, flattened provides under pressure oxygen free connection while flattening increases contact area.
That's minor point and people do what worked for them before, but I absolutely agree with you that one has to be careful and examine connection from time to time.