Insulation effect in wiring terminal blocks and fuse blocks 2

[thunderaxe]

Could anyone tell me what is the proper or most used method for stripping and securing wire in screw type terminal block? should bare wire be seen? Is it bad to have some insulation pinched in the connection? This is refering to 22awg to 18awg wire. Thanks

 

[advidana]

Yes it bad to have some insulation pinched in the connector because you are not getting a solid connection. Also make sure the strands are not cut or knicked and wires are not pinched. Some bare wire can show if it is not cable of shorting out to adjacent metal or other wires. Generally about 1/16" expose conductor from terminal is fine for voltages up to 480 volts. But it is best to check with the terminal manufacture for thier recommendations to comply with Terminal connection UL rating.

 

[buzzp]

Agree with advidana.

Insulation pinched in the connector is very bad. Any insulation under the screw clamp is unacceptable.

Bare wire can be seen as long as it can NOT short to an adjacent terminal/wire/etc.

 

[skiier]

Smaller wires tend to a pain in the ass. Stripping wire and leaving all the strands in place is rare. For smaller wires I tend to use "ferrules" and when they are not available I "tin" the wires with solder. I really dislike ferrules but they are good for smaller wires. Ferrules give the terminal something to compress so as to hold the wires in place but they limit the number of wires one can put in a terminal. Generally, good practise is not to have more than 2 wires under a terminal. Anymore than 2 and the wires tend to be compressed unevenly so that one wire may slip out of the terminal over time.

 

[Tofflemire]

Hello,

If you "tin" the wires, the screw terminal will vibrate loose over time, if the terminal block in a location prone to shock and vibration, because the tinned wires take a set. Make sure you use some form of anti vibration retaining mechanism on the screws.

Tofflemire

 

[jraef]

All good advice. The only thing I'll add is from noticing that you said "screw terminals". My preference is to use crimp-on lugs when connecting to screw terminals. I know that some manufacturers claim to have "saddle clamps" that will grip and compress stranded wire, but I have yet to see one that I think is ding a good job of it. Some even tend to bite so hard into the wire that you can begin to sever strands, making reconnection a problem. For another thing, as you rotate the screw to tighten it and the wire is on the left side of the screw, you are essentially pulling it in which can sometimes result in crimping the insulation. If the wire ends up on the right side of the screw, rotating the screw tends to push the wire OUT of the terminal and increase the chances of a bad termination.

Ring tongue terminals have the best safety record, but I find it to be a pain in the rear to always remove the screw. Fork tongues are easier to deal with, but have a risk of squeezing out sometimes (same risk as bare standard wire I suppose). My preference is what are called "locking fork tongue" terminals. They have a shape or protrusions that "snap" around the screw shaft to keep the terminal in place as you tighten the screw. Best of all worlds IMHO.

"Venditori de oleum-vipera non vigere excordis populi"

 

[ScottyUK]

My personal preference is for Weidmuller-Klippon's melamine RSF1 and RSF3 terminals which are designed to be used with a lipped blade style of lug. The design incorporates a spring which maintains electrical contact even if the clamp screw loosens under vibration, which can be a wonderful feature for CT connections. They are an excellent design which very rarely gives a bad joint. You must ensure that the electricians use the correct lug on the cable to get maximum benefit. I think this was developed in conjunction with the old CEGB in the UK to overcome the problem of terminals loosening over time.



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