Resource Library

What steps should I take to deal with earth leakage currents?

Earth leakage currents arise mainly from the EMC filters built into electronic equipment with switched mode power supplies.  Standards limit the leakage current from non-fixed equipment (i.e. equipment that plugs into a standard socket outlet) to less than 3.5 mA.  When a lot of electronic equipment is in use, the total leakage current in the protective conductor can become significant.  If there is a break in the CPC the earthed conductive parts of all equipment connected to the isolated section will rise to about half the supply voltage.  To reduce this risk, special rules apply when the leakage current in a CPC is likely to exceed 10 mA.   In the current edition of BS7671, these regulations are contained in clause 534.7, replacing section 607 of previous editions.

I am an architect looking for brass tubes in order to make handrails for a listed building where colour and appearance are important. What should I use? How may the surface be preserved?

The high copper brasses (gilding metals) such as CuZn10, CuZn15, CuZn20 and CuZn30 have a range of colours and are well suited for this application. Obtain samples to find the exact colour.

For handrails which come into contact with the public, the best protection would be given by periodically waxing using a natural wax such as Carnauba or beeswax. For rails which are only subject to atmospheric attack a lacquer such as Incralac should be used.

I am at the design stage of an engineering project, part of which may include the use of a copper alloy casting. Since considerable machining is involved I am interested in machining data for cast copper alloys.

Machining data for copper casting alloys are similar to those of their wrought counterparts. The most easily machinable are classified as Group 1 and include CC491K (LG2) with a rating of 90% (this rating is based on a 100% value for free machining brass CZ121,CW609N). The more difficult alloys to machine are classified as Group 3 and include the aluminium bronzes such as CC333G (AB2) with a rating of 20%. For further details see CDA publication 44 Machining Brass, Copper and its Alloys.

What surface treatments can be used to protect outdoor copper, brass and bronze objects?

Brasses will slowly tarnish in the atmosphere; outdoors the process is more rapid due to the effect of moisture, salt (in marine environments) and pollutants such as sulphur dioxide (acid rain) in industrial areas. The tarnishing can be greatly delayed and the range of colours, which give copper alloys their aesthetic appeal, maintained by either lacquering or waxing (or both).

Lacquering: one of the most effective lacquers is Incralac. Lacquers must be applied in dry, factory conditions and are not suitable for protecting components which are handled by the public, such as handrails, since acid levels of moisture in the skin (pH 5.5) damage the lacquer.

Waxes: copper alloys may be more cheaply protected by waxing. It is important to use natural non-reactive waxes such as Carnauba or Beeswax, not synthetic waxes which will eventually granulate and absorb water. Natural waxes are not affected by UV light.

I am considering making a heat exchanger from either 70/30 brass or austenitic stainless steel. What are the thermal conductivities of these materials?

For brass, 120W/m°C, and for stainless steel, 17W/m°C. As can be seen, the brass has a conductivity seven times better.

What type of bronze is used for modern works of art?

Bronze has been used for centuries to create statues, and is still the first choice for modern, striking works of art. The most widely-used alloys for such objects are leaded gunmetals, such as CC492K and CC491K.

I am designing a power lead connector for a large earth moving vehicle. The connector is crimped to copper wires to make electrical contact. I propose to machine this component from brass CW606N (CZ131) bar followed by tin plating. Any advice please?

The brass selected is free machining with good ductility and is an excellent choice for this application. I suggest that the component is annealed in the range 400 to 600oC to give maximum ductility to ensure that the crimping will be successful. There is no need for tin plating; in this environment the brass will darken with time with no loss of properties.

It is important that the lead content (1.6 to 2.5%) of this brass is maintained at the specification level in all of the connectors since higher lead levels may lead to cracking on crimping. With this in mind I suggest that the source of the brass is from the UK or Europe where full certification will be available.

What type of bronze is used for modern works of art?

Bronze has been used for centuries to create statues, and is still the first choice for modern, striking works of art. The most widely-used alloys for such objects are leaded gunmetals, such as CC492K and CC491K.

What are the critical pitting and crevice corrosion temperatures for copper-nickels in chloride environments?

Copper-nickels do not behave in the same way as stainless steels do towards corrosion by chlorides and these parameters are not appropriate to them. They do not have a critical temperature limit.

I have a brass table top which has been scratched. How can I restore the surface?

By hand polishing (buffing) using a soft abrasive such as T-Cut or Brasso. Follow this by waxing with a natural wax.

What type of copper is specified to make wire used to transmit electricity to trams, trolley buses or trains?

Pure copper is too soft for overhead wires and the copper alloys used are specified in BS EN 50149:2012. These are alloys of copper with respectively small amounts of silver, magnesium, tin or cadmium.

I am digging a well with water pH=5.8. Is this safe to drink?

Yes, the Drinking Water Regulations give a range of pH 5.5 to 9.5 for drinking water. However the ideal pH for water supplies is close to 8 if corrosion of the copper pipes is to be avoided. I suggest that you contact a water treatment company.