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Connection capacity

IEC 60947-7-1/-2

Gauges (internal cylindrical gauge) of design A and B in accordance with IEC 60947-1  

Gauges (internal cylindrical gauge) of design A and B in accordance with IEC 60947-1

This mechanical test defines the connection of standard conductors according to the manufacturer's information.

Terminal blocks must be designed in such a way that conductors with the documented rated cross section and the rated connecting capacity can be connected. The specifications are documented by the manufacturer in metric [mm²] and Anglo-American AWG values.

Rated cross section means: the value of the maximum possible cross section of all connectable conductors (stranded and single or multi-stranded) that certain thermal, mechanical, and electrical requirements refer to.

Rated connection capacity means: the range encompassing the largest to the smallest connectable cross section (reduced by at least 2 increments) and the number of connectable conductors for which the terminal block is designed.

During the test, the terminal blocks are connected with the rated cross section and the rated connection capacity. Alternatively, the rated cross section can also be verified using gauges, see illustrations. It must be possible to freely insert conductors or gauges into or connect them to the open terminal point.

Terminal blocks from Phoenix Contact offer dimensions for the defined rated cross section that are well above those required by the standard. Thanks to appropriate design measures, the rated cross sections can also be connected with a ferrule and insulating collar for all terminal blocks from the CLIPLINE complete system.

Connecting aluminum conductors

UT and UKH series screw terminal blocks are suitable for the direct connection of aluminum conductors in accordance with the guidelines governing conductor pretreatment. Under pressure, aluminum yields more easily than copper due to a lower modulus of elasticity. It is said to “flow”. Furthermore, after stripping the aluminum conductor, an oxide layer forms on the conductor surface due to its reaction with air. This oxide layer leads to increased contact resistance between the aluminum conductor and the terminal point. The oxide layer must therefore be removed before wiring. In addition, the maximum current carrying capacity of aluminum conductors is lower than that of copper wires. In general, if the same current carrying capacity is required of the aluminum conductor, the selected cross section will be larger than for a copper wire. Based on the properties specified, UT ... and UKH ... series screw connection terminal blocks from Phoenix Contact have been qualified for the use of aluminum conductors through extensive tests. An important quality feature of this qualification is the 1000-hour current cycling test in accordance with IEC 61545. As part of this test, current is applied to the terminal block and aluminum conductor combination for an hour and is then switched off for an hour. The cycle is repeated 500 times. During the 1000 hours, temperature measurements are taken at the terminal points according to a defined schedule. The measured values must not exceed defined limit values. The table below lists all Phoenix Contact screw connection terminal blocks that have undergone these tests.

Round, single-stranded, Class 1, approved  

Round, single-stranded, Class 1, approved

Single-stranded aluminum conductors in round (RE) form up to 35 mm2 with the relevant approved cross section can be connected directly to the above-listed feed-through terminal blocks with screw connections. When connecting aluminum conductors that are 50 mm2 and above, only sector-shaped, single-stranded conductors (SE) may be used and inserted.

Sector-shaped, single-stranded, Class 1, α = 90°, approved  

Sector-shaped, single-stranded, Class 1, α = 90°, approved

When directly connecting aluminum conductors to UT ... and UKH ... series feed-through terminal blocks from Phoenix Contact, the following guidelines on conductor pretreatment must be followed:

  • Remove the oxide layer from the stripped end of the aluminum conductor using a blade (suitable knife, e.g., WIREFOX-D 13 stripping tool).
  • Immerse immediately in non-acid and non-alkali, neutral Vaseline.
  • The installation location must be kept free from humidity or aggressive atmospheres.
  • When using an aluminum conductor, tighten the screw in the clamping part of the screw terminal block with the recommended tightening torque of the respective terminal block. There is no need to tighten the terminal point.
  • The pretreatment must be repeated when connecting the conductors anew.
Example for UKH ...: connecting sector-shaped, single-stranded aluminum conductors  

Example for UKH ...: connecting sector-shaped, single-stranded aluminum conductors

Mount sector-shaped aluminum conductors in the terminal point of UKH terminal blocks. The rounded section of the conductor should be at the top so that the right-angled area of the aluminum conductor is positioned on the prism-shaped base of the terminal sleeve. Accessories, e.g., bi-metal cable lugs (Al/Cu compression cable lug), can be used to connect stranded aluminum conductors.

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