Copper connectors that absorb vibration in high-current systems are now a standard that is hard to do without. Whether it is a new transformer, the supply to a metallurgical furnace or the joint between busbar runs, we always use an expansion joint to absorb the vibration caused by the current in the busbars.
There are many kinds of flexible connectors and at least two different raw materials for making them. You can use flexible connectors made of thin copper laminations that are press-welded, welded or riveted (PE), or the very popular flexible connectors made of flat copper braid.
In this article I focus on connectors made of copper braid.
How are copper braided connectors (PG) made?
A flexible connector made of flat copper braid is a set of several copper braids of a given length (their number depends on the total cross-section required), finished at both ends with a flat terminal made of a pressed copper tube. The length of this terminal, commonly called the ferrule, usually depends on the width of the connector.
This means that a 100 mm wide connector normally has a 100 mm long ferrule. The photo below shows such a ferrule.
Such a connector is very flexible, so it can be installed in places that are hard to reach and at various angles, when the busbar terminals are not aligned symmetrically.
Flexible braided connectors are made from copper braids woven from wires of high-grade Cu-ETP copper, usually 0.2 mm in diameter. The braids come in a range of cross-sections, from a few to several dozen or even several hundred mm².
For each connector we choose the braids that best match the current rating required for the whole connector. If, for example, the connector needs a cross-section of 1,200 mm², we use ten braids of 120 mm² each.
Ferrules in PG flexible connectors
The ferrules are made from a special tube ordered from the copper mill. An ordinary tube for heating or plumbing installations will not do, because it is usually made of Cu-DHP copper, which conducts current much less well.
How to recognise poorly made ferrules
Why does the ferrule matter so much? Because a wrongly chosen tube diameter has an enormous effect on the quality of the connector. It usually shows in the following:
- the edges of the ferrule are rounded too much (the diameter was too small);
- the edges of the ferrule are not filled with braid;
- the contact surface is uneven (the diameter was too large or the tube wall too thin);
- the collar of the tube has no chamfered edge, which can eventually damage the pressed braids.
Ferrule thickness
The thickness of the ferrule depends directly on the cross-section: it should correspond to the number of braids plus the wall thickness of the copper tube pressed onto the ends. A smaller cross-section automatically means a thinner ferrule.
Crushing the ferrule under the press with excessive force just to make it as thin as possible is not advisable. Sometimes, however, it is necessary because there is little space between the copper busbars the connector is attached to.
Tin plating and current rating
Both the copper braids and the ferrules can be tin-plated, and the ferrules can even be silver-plated. The customer specifies the coating thickness; as standard we tin-plate to 12 µm and silver-plate the terminals to 5 µm.
The ferrules are always plated before they are pressed onto the braids: we cut a suitable length of tube, prepare it for electroplating and then plate it with tin, silver or, less often, nickel.
Interestingly, a connector does not need a tinned braid to have tinned terminals. The options can be combined freely, although a tinned braid with a bare “red” copper ferrule makes little sense in terms of performance.
Whatever the finish, remember that the contact itself is critical and must not be contaminated in any way.
The connector can also be protected with heat-shrink sleeving, but its performance is then noticeably lower because heat is dissipated less well. As physics tells us, the higher the temperature of the copper, the higher its resistance.
Current rating table for copper braided connectors (PG)
Types of copper braided flexible connectors
Copper braided flexible connectors can be made to customer requirements in many ways. We have often made custom connectors with quite unusual terminals. It all depends on whether the connector the customer wants can physically be made.
These are the most popular types of flat copper braid connectors we make:
In practice there can be many more end configurations; it all depends on what the project needs. Sometimes a transformer has to be connected at such an angle that a standard connector shape, flexible as it is, would make installation much harder.
Length of copper braided connectors
The length of a flat copper braid connector can be given approximately, but it is better to overestimate than to underestimate it. As a rule, we add 30–60 mm to the distance between the two terminals being connected.
Even when it is longer than needed, a braided connector is still easy to install, and it is better if it is not under tension. This is a clear advantage when you cannot be sure that the distances in the system where the connector will be used will not change slightly.
What are copper braided connectors used for?
Braided connectors have a very wide range of uses. They are, however, more expensive than press-welded connectors made of copper laminations, so it makes sense to use them where they are really needed.
Flat braided flexible connectors are most often used:
- to connect transformers to busbar trunking;
- in equipment and places that move;
- where the connector “works” hard both horizontally and vertically;
- in oil-immersed transformers;
- wherever connectors with heat-shrink sleeving are required.
What about aluminium braid?
Flexible connectors are also made from braided aluminium strip. Their performance is, of course, much lower than that of copper connectors. They are used mainly because the raw material is much cheaper.
I would question both the performance of such connectors and how well they hold up in long-term service.
To find out more about flat copper braided flexible connectors, use our contact form or call +48 71 303 62 09 and talk to our expert about what these connectors can do.
Would you like a quotation or the current rating for your connector? Send your enquiry to biuro@izar.pl.
