Resource Library

Some sources suggest painting busbars black to increase the current rating. Is this a good idea?

No. Black matt surfaces are better at radiating heat than bright shiny surfaces, and that is why painting is sometimes suggested. The efficacy of radiation is the emissivity of the surface; for a perfect radiator (matt black), the emissivity is 1 and for a perfect reflector, emissivity is zero. In practice, bright shiny copper has an emissivity of about 0.3, dull copper is about 0.7 and darkened copper – such as a busbar after a few weeks of service – can reach 0.9. Since only around 10-20% of heat is lost by radiation, the difference between dull copper and a matt black surface is only 3-6% of the total.  To achieve this apparent improvement, the 90% of the heat that escapes by convection has to pass through the thermal insulation provided by the paint layer, so the temperature of the bar increases rather than decreases.

There are a number of types of sprinkler heads, including concealed. If you saw a concealed sprinkler head in-situ what would you see?

Only the cover plate, a disc on the ceiling.

There are two types of compression joints - Type A and Type B. Which is ‘manipulative’?

Type B is manipulative, it requires the end of the tube to be flared.

How long has copper plumbing been used?

The earliest recorded use of copper for conveying water is a water conduit in Abusir, Egypt, which dates back to 2750 BC and is still in good state of preservation. Copper water pipes and cisterns were widely used by the Romans – examples can be found at the archaeological site of Herculaneum, destroyed by the eruption of Vesuvius in 79AD. At the beginning of this century, copper started being used again in Europe and North America.

We are experiencing difficulty with the performance of copper washers (CW 024A, C106) in service. In some cases they are too soft and they flow whilst others are so hard that they do not form a seal. What do you suggest?

You have the correct grade of copper.  I suggest that you require the half hard condition.  This is expressed now as H065 in EN1652.  The hardness range given is 65 to 95 HV.  You should carry out periodic hardness tests.

Warm roof or cold roof?

Warm roofs do not require ventilation and are suitable for all pitches and are preferred for low pitched and flat roofs. Cold roofs require ventilation and should not be used on low or flat pitched roofs.

How is copper used on a farm?

Copper sulphate, because of its fungicidal and bactericidal properties, has been employed as a disinfectant on farms against storage rots and for the control and prevention of certain animal diseases, such as foot rot of sheep and cattle.

How is the current carrying capacity of a busbar determined?

The current rating of a busbar is limited by the maximum ambient temperature and the maximum permitted working temperature. In use, heat is generated in the bar due to the resistance losses and is lost from the bar by convection and radiation.

At the working temperature, the heat generated is equal to the heat lost. The calculation process is to make an educated guess at the bar size and determine the heat loss at working temperature and then calculate the current that would produce this amount of heat.

The bar size is modified in light of the result and the calculation repeated until the result is close enough to the required rating. The result is the smallest possible bar size. As energy costs rise, it is worth considering the lifetime cost of a busbar system, including capital cost and the cost of waste energy.

How long has copper been used in agriculture?

The first recorded use was in 1761, when it was discovered that seed grains soaked in a weak solution of copper sulphate inhibited seed-borne fungi.

I am designing a rope guide in brass for a racing yacht. Which brass and manufacturing method should be used? Is chromium plating essential?

To resist the bending stresses in service, a high-tensile brass such as CW721R (CZ114) should be used. There is no need to chromium plate since it will increase the cost by 50% and is in any case merely decorative. Depending on the numbers required hot stamping (forging) could be used to make the component to near net shape.

Which copper alloys are currently available for aquaculture and do they have different applications?

Three alloys are currently commercially available: copper-zinc, copper-nickel and copper-silicon.

Copper-zinc is good for flexible mesh containment systems.
Copper-nickel is good for rigid (e.g. welded) mesh.
Copper-silicon is good where rigid mesh is needed, or where panels can have flexible connections.

We have produced a number of tin bronze castings which show extensive porosity. The result of this is that the castings have failed a pressure test and show fluid leakage. It has been suggested that weld repairs may be a solution. Is this so?

No, the usual solution for treating porosity in castings is by impregnation where the casting is placed in a vacuum and the porosity is filled with either a polyester or epoxy resin. This process is approved for military applications (except Class 1 castings).