Connecting a self-supporting insulated wire (SIP) to circuit breakers - a task faced by both professional electricians and private home owners when installing input distribution devices (ASU). The main difficulty is that aluminum SIP conductors require special preparation before connecting to the copper terminals of the machines. Incorrect ferrule crimping results in overheating of contacts, oxidation and even fire. In this article we will look at how to avoid mistakes, choose the right tips and tools, and also consider a step-by-step crimping algorithm taking into account the requirements PUE 7.1.34 and GOST R 50571.5.52-2011.
Many people mistakenly believe that it is enough to simply strip the wire and insert it into the terminal of the machine. However, aluminum is a soft metal with a high coefficient of thermal expansion, and without proper crimping, the contact will weaken over time. This is especially critical for introductory machines, where large currents pass (25–63 A). We will analyze common myths and compare types of tips (NSHVI, NASHVI, TML) and show you how to check the quality of crimping without special instruments.
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Why can’t you connect SIP to a machine without tips?
Aluminum SIP conductors in direct contact with the copper terminals of the machines form galvanic couplewhich accelerates corrosion. Even if the connection seems strong, three critical problems arise over time:
- 🔥 Local overheating — due to the oxidation of aluminum, the contact resistance grows, which leads to heating to 100–150°C (risk of insulation melting).
- ⚡ Sparking — when the contact loosens under load, microdischarges occur that destroy the terminal of the machine.
- 🔌 Terminal block burnout — in 80% of cases, the cause of failure of the input circuit breakers is precisely the incorrect connection of the SIP.
According to Rostechnadzor, up to 30% of fires in electrical panels are associated with poor-quality crimping of aluminum wires. At the same time Even factory lugs do not guarantee reliability if they are selected without taking into account the cross-section of the core or are crimped with the wrong tool.
Another reason to use tips is mechanical strength. SIP cores consist of several thin wires, which can break or “fluff” when the screw terminal of the machine is tightened. The tip fixes the beam, distributing pressure evenly.
Types of tips for SIP: which one to choose for the machine?
There are more than 10 types of lugs for aluminum wires on the market, but only three main types are suitable for connecting to automatic machines. Their key differences are in design, material and crimping method:
| Tip type | Material | SIP cross-section, mm² | Benefits | Disadvantages |
|---|---|---|---|---|
| NSHVI (Insulated pin sleeve lug) | Tinned copper | 10–50 | ✅ Cheap, easy installation ✅ Suitable for most machines |
❌ Requires additional insulation ❌ Cannot withstand high currents (>63 A) |
| NASHVI (Aluminum pin sleeve insulated tip) | Copper coated aluminum | 16–120 | ✅ Optimal for SIP ✅ Corrosion resistant |
❌ More expensive than NSHVI ❌ Requires special tools |
| TML (Tubular copper-tinned) | Tin Plated Copper | 16–240 | ✅ High current load ✅ Durability (>20 years) |
❌ Difficult installation (requires hydraulic mandrel) ❌ High price |
For household panels (current up to 63 A) is optimal NASHVI — it combines accessibility and reliability. For introductory circuit breakers rated at 80–100 A, it is better to use TML, despite its cost. Important: The cross-section of the tip must correspond to the cross-section of the SIP core. For example, for SIP-4 2×16 mm² you need a 16 mm² tip, not 10 or 25!
Crimping tool: what to buy and what to save on?
The quality of crimping depends 70% on the tool. Let's look at the minimum and recommended set:
- 🔧 Press jaws - the main tool. Hand pliers are suitable for NSHVI/NASHVI Knipex 97 53 08 or IEK PKVk-10>. TML requires a hydraulic press (for example, HT-35T).
- ✂️ Stripper for SIP — strips the insulation without damaging the cores. Alternative: knife NWS 1840 with cutting depth limiter.
- 🧴 Quartz-vaseline paste — applied to the core before crimping to protect against oxidation. Will do KVT or ContaClip ALU-Paste.
- 📏 Vernier caliper - to check the diameter of the crimped tip (must comply with the standard
GOST 23469.3-79).
Saving with risk: some craftsmen crimp NSHVI with pliers, but this leads to uneven compression and cracks in the tip. If your budget is limited, it is better to buy budget pliers Bison EKOM-16 (~2,500 ₽) instead of professional ones Weidmüller (~10 000 ₽).
Before purchasing press pliers, check whether the kit includes dies for crimping aluminum ferrules - many models are designed only for copper wires!
Step-by-step instructions: how to crimp a SIP with a tip for a machine
Let's look at the process using a connection example SIP-4 2×16 to the introductory machine ABB S201 C40 using a tip NASHVI-16.
- Step 1. Stripping the insulation
Remove 30–40 mm of insulation from the SIP core with a stripper. Important: do not damage the wires - cuts reduce the cross-section by 15–20%. If using a knife, move it at a 30° angle to the wire.
- Step 2. Preparing the core
Twist the wires with your fingers into a tight bun. Apply a thin layer of quartz vaseline paste to the exposed part. This will reduce contact resistance and prevent oxidation.
- Step 3: Install the tip
Put it on NASHVI onto the core so that the wire insulation extends 2–3 mm under the ferrule collar. This will protect against moisture.
- Step 4: Crimping
Insert the tip with the wire into the die of the press jaws corresponding to the cross-section (there is usually a marking on the handle). Squeeze the handles all the way and you should hear a click. Check the tip for cracks.
- Step 5. Quality Control
Pull the tip towards you with a force of 10–15 kg - it should not move. Measure the diameter of the crimped part with a caliper: for NASHVI-16 it should be 7.5–7.8 mm.
Stripping 30–40 mm without cutting the cores|
Quartz vaseline paste applied|
The tip is pushed all the way in (insulation under the cuff)|
Correct jaw die used|
Pulling force tested (>10 kg)-->
Common mistake: crimping “in two steps” (first the end of the tip, then the beginning). This leads to uneven pressure and increases contact resistance by 30–40%. Always crimp one at a time!
Mistakes when crimping SIPs and how to avoid them
Even experienced electricians make mistakes that shorten the life of the connection. Here are the top 5 mistakes and their consequences:
- 🔌 Incorrect tip section - if you take NShVI-10 for SIP 16 mm², the contact area will decrease and the tip will overheat. Solution: Always check the cross-section correspondence table.
- 🔧 Using pliers instead of press jaws — leads to pinpoint pressure and microcracks. Solution: For one-time installation, you can rent a tool.
- 🧴 No protective paste — without it, aluminum oxidizes in 6–12 months. Solution: use ALU-Paste or analogues.
- ✂️ Damage to cores during stripping — reduces the cross-section and increases resistance. Solution: use a stripper with adjustable cutting depth.
- 🔥 Tightening the machine terminal screw - deforms the tip. Solution: tighten with a force of 2.5–3 Nm (use a torque screwdriver).
What happens if you crimp SIP without paste?
Without a protective paste, aluminum reacts with oxygen, forming an oxide film with a resistance 10 times higher than that of pure metal. After 1–2 years, the contact heats up to 80–120°C, which leads to:
1) Melting of the tip insulation.
2) Burning of the terminal of the machine.
3) False activations of the thermal release.
In the worst case, there is a short circuit and a fire in the panel.
Case study: When examining a panel in a private house after a fire, experts discovered that a 25 mm² SIP was crimped with a 16 mm² tip. The temperature at the point of contact reached 180°C, which caused the fire.
How to connect a crimped SIP to a machine: installation nuances
After crimping, the tip must be correctly installed in the terminal of the machine. There are several critical points here:
- Tip position
The tip must fit into the terminal perpendicular plane of the machine. If it is installed at an angle, the contact area is reduced by 20–30%.
- Screw tightening
Use torque screwdriver with force:
- 2.5 Nm - for automatic machines up to 40 A;
- 3.5 Nm - for automatic machines 50–63 A;
- 4.5 Nm - for input circuit breakers 80–100 A.
If there are vibrations in the panel (for example, near a transformer), fix the wire plastic clamp to DIN rail. This will prevent the screw from unscrewing itself.
Important for multi-core SIPs: if several wires are inserted into the machine (for example, two phases), use double tips or bus splitters. Never twist the wires together - this will break PUE 2.1.21.
After connection, check the terminal temperature after 1–2 hours of operation under load. If the tip reaches more than 40°C (warm but not hot), the connection is correct. A hot terminal (>60°C) is a sign of poor contact!
Alternative ways to connect SIP to the machine
If ferrule crimping is not possible for some reason, consider these options (with their pros and cons):
| Method | Pros | Cons | When to use |
|---|---|---|---|
| Soldering aluminum | ✅ Reliable contact ✅ No need for tips |
❌ Difficult to solder without experience ❌ Requires flux F-64 |
For temporary connections or repairs |
| Bolted connection | ✅ Easy to install ✅ Suitable for large sections |
❌ Takes up a lot of space ❌Regular check of tightness is required |
For input circuit breakers >100 A |
| Twisting with Wago | ✅ Fast and without tools ✅ Sealed terminals |
❌ Current limitation (up to 32 A) ❌ Expensive for large sections |
For lighting or socket groups |
Warning: twisting of SIP with copper wire without adapter terminals (Wago 2273 or KBM) is prohibited PUE 2.1.21 due to the risk of galvanic corrosion.
Frequently asked questions about crimping SIPs (FAQ)
Is it possible to crimp a SIP with a copper tip (NSHVI) without tinning?
No, this is a gross violation PUE 2.1.21. Aluminum and copper form a galvanic couple, and without a protective coating (tinning or aluminum-copper transitions) the contact will last no more than 1–2 years. Use only NASHVI or TML.
What color should the crimped tip be?
After crimping, the aluminum tip (NASHVI) should remain silver (aluminum color). Darkening or blackening indicates overheating during crimping - such a tip needs to be replaced. Copper tips (NSHVI) may be slightly faded, but should not have cracks.
Do I need to insulate the ferrule after crimping?
If used insulated tip (for example, NASHVI-from), additional insulation is not required. For non-insulated tips (TML) be sure to wear heat shrink tube or wrap PVC electrical tape in 2 layers.
What should I do if, after crimping, the ferrule wobbles on the core?
This means that:
1) Incorrect tip cross-section (diameter too large).
2) Insufficient force of the press jaws (the dies may be worn out).
Solution: cut the core and crimp a new tip, first checking the correspondence of the sections.Is it possible to use SIPs without lugs if the machine has aluminum terminals?
Yes, but only if:
- The machine is certified for direct connection of SIP (for example, ABB S200 with Al/Cu terminals).
- The core cross-section does not exceed 16 mm².
- You use quartz vaseline paste and check the tightness every 6 months.
Risk: even in this case, the contact will weaken over time due to the “fluidity” of the aluminum.