Which variant is better for a copper cable 2.5 mm²- a non-insulated tin-plated copper cable lug ТМЛ or an insulated tinned copper terminal НКИ?

The first issue that you need to consider before making your choice is what cable you are dealing with- is it a solid or stranded wire. Insulated tin-plated copper cable lug НКИ is designed only for work with stranded wires. Non-insulated ТМЛ can be used for both, stranded and solid wires.
In some cases when you deal with a copper wire you might not need a terminal or lug at all.
There are several points that prove that insulated НКИ is a better choice:
- НКИ terminals 2.5 mm² are less expensive than ТМЛ (Russian standard GOST 7386-80)
- There are more various mounting ends in НКИ types- 4 of them. Compare with 2 mounting ends of ТМЛ.
- The types of mounting end in НКИ are as follows: pin, ring, fork, and hook.
- НКИ have an insulation cuff in its design. If you use ТМЛ you will have to care about a heat-shrinkable tube or sleeve beforehand.
- Insulation cuff of НКИ can be made of nylon or PVC, so if your connection could be subjected to high temperature, you’d better choose terminals with nylon cuff.
- НКИ are of a more compact in size than ТМЛ
- After installation, you can double-check the crimping result as there is an indent sign on each cuff that tells about the size of the die used for crimping. It is not possible to do such a double check in ТМЛ lugs.
- Colors of the cuffs are more comfortable for easy and quick identification of the terminal size.

How can I make a connection leak-proof?

The easiest way is to use non-insulated ferrules together with adhesive lined heat shrinkable tubes with shirk coefficient 3:1 or 4:1. This method is used for the connection of underwater pumps and in most cases when contact with water is possible. Short recommendations for installation: peel insulation by 1\2 of the ferrule length. Measure and cut a heat-shrinkable tube so that after installation it covers 2-3 cm of cable insulation at both sides, add some length for possible longitudinal shrinkage. Crimp a ferrule with a corresponding tool, put a tube on the place of connection and shrink it with a heat gut. Glue pressed out of the sealed part proves the good leak-proof connection. In case you need more confidence shrink one more heat-shrinkable tube over the first one. The second tube should cover the first one. In case you need a leak-proof connection in cross-section range from 0.5 to 6 mm², use heat shrinkable insulated butt connector ГСИ-Т made by KBT.
If you need a leak-proof connection for cables consisting of 2, 3, 4 or 5 wires, use common insulated butt connectors ГСИ together with adhesive lined heat shrinkable tubes with shirk coefficient 4:1.

Can vibration resistant male and female disconnectors be crimped by means of the tool for crimping of common male and female disconnectors?

Yes, you can, as the same dies can be used in both cases.

Can vibrations resistant PVC male and female disconnectors be used also as general PVC insulated male and female disconnectors, just because they are the same but of better quality?

Yes, it is true. ВРПИ vibration resistant disconnectors have an additional copper cuff, just like all brass disconnectors made by American and European manufacturers. The contact part of such a disconnector is made of brass that is only 0.4 mm in thickness. So the contact part after crimping is not that reliable like in lugs made of brass with 08.-1 mm in thickness.
Moreover, the copper cuff works for a safer connection even is the orientation of dies was chosen wrong.

How can I install a branch on a wire?

If you need to keep the cable and do not plan to cut it, it is better to use branch connectors ОВ or OB-T made by KBT. An additional advantage of nylon branch connector OB-T is that you can leave the cable without further connection until the time when the connection will be necessary by simple input of a wire ended with nylon-insulated male disconnector РПИ-П(н).
If cutting off the wire is possible in your case, you can also use a branch disconnector with female socket and male plug РПИ-О made by KBT.

What is the difference between nylon-insulated ferrules and PVC-insulated ferrules except for the material of insulation?

There is no big difference between them. The contact part is the same- made of copper tube and with a length stopper inside. The difference is only in the material of insulation. Nylon is more resistant to high temperatures; it is transparent for the possibility of visual control.

Can I connect two cables simultaneously to one terminal НКИ?

In theory, it could be possible if not for the insulation cuff, its size will make it impossible. If your imagination lets you find a decision on how to place two wires inside one cuff, it could become possible.

When it is better to use disconnectors РП-М and РП-П?

Their main advantage is crimping in two spots: over the wire and over the insulated part of the cable. As a result, you receive a very good and reliable connection, which makes it possible to use these connections in environments with vibration and high temperatures.

Are there any peculiarities in the installation of insulated terminals?

Any operation has its nuances. Please take your time to read our recommendations for each type on this website.

What do the figures 1, 2 and 6 mean? I saw them pressed on the cuffs after crimping.

Most likely your question deals with die 01 made by KBT. This die has three crimping profiles that are indicated with yellow, red and blue color. After crimping you can see an indented number: 1, 2 or 6, which corresponds to color indication also. This feature was added by KBT as an additional way of control of a correct choice of crimping profile for the particular size of the terminal. 1 for cross-section range from 0.5-1.5 mm², 2 for cross-section range 1.5-2.5 mm² and 6 for 4.0-6.0 mm².
For example, if you notice number 2 on a red cuff you definitely know that there was a mistake in the choice of crimping profile and crimping result cannot be reliable.