Energy Safety advises that polystyrene insulation can turn common Tough Plastic-Sheathed (TPS) building wiring cable brittle and become a fire hazard.
Two ways to prevent this occurring are either to prevent contact between the cable and the polystyrene using a suitable duct or sheath, or to use a migration-resistant cable, says Energy Safety.
Where standard TPS cable is installed in contact with polystyrene insulation, the wiring should be checked out every few years, because there is "a small probability that it will cause a problem".
Retrofitting polystyrene insulation, e.g. using loose fill polystyrene beads in the wall cavity, should be avoided where direct contact with standard TPS cable is likely.
Building wiring cables under investigation
Energy Safety also just advised that the compliance of building wiring cable from "a number of suppliers" is currently under investigation.
"Our preliminary investigation has identified that some cable in the New Zealand market has inadequate certification, or appears not to have been manufactured in accordance with the certification requirements," it says in a statement.
Energy Safety reminds us that suppliers of building wiring cable must have a valid supplier Declaration of Conformity (SDoC) for the product before offering it for sale or supply.
Compliant cable must also be "durably and legibly marked" with compliance-related information.
If any cable or its packaging is not marked with all of this information, it is not compliant with a relevant standard and must not be sold, supplied or installed.
The concern is that cable which is incorrectly labelled "may have other significant safety deficiencies that make it unsuitable for use as building wiring".