It was thought by many manufacturers, and
perhaps still is, that to assemble a product from CE marked components
would result in a finished item which could be CE marked without
further test, i.e. CE+CE=CE.
We refer to this as CE+CE=CE (The Cop-Out Equation). We believe that, although in principle
that course of action should be possible, it is nevertheless a
very dangerous policy to adopt unless the manufacturer of the
finished product imposes his own EMC requirements on the component
parts.
Our version of the EMC equation is due
to Einstein (pictured [). CE+CE>CE, where E=MC².
This situation is particularly noticeable where the finished product
is assembled from a number of component parts from different manufacturers
and with differing specifications, such as a personal computer
system.
In the case of a personal computer (pc), the motherboard, monitor, expansion cards, mouse and keyboard are deemed to have an intrinsic function intended for an end user which is realised when the item is installed into the pc by that user. These parts must therefore be CE marked. On the other hand, the power supply is usually sold as part of the system unit case or as a service spare and therefore only requires CE marking for Safety and not for EMC. By comparison we have come across products which were marketed with a range of add-on expansion cards where the products were tested with just the main circuit board and not the optional cards on the grounds that the expansion cards were accessories and therefore exempt. It should be borne in mind that the addition of expansion cards is altering the function of the product and therefore is generating a new product which must still be compliant.
In the case of the pc, almost all the component parts have to be CE marked as relevant apparatus because the act of installation and putting into service can be carried out by the general public as well as a manufacturer. The manufacturer should however make sure that the main system has enough 'margin' to accommodate expansion products and peripherals, and the peripheral/expansion product will not compromise the CE marking of a typical 'host' system. In the case of products where the optional circuit boards are made available to customers (not the public), the manufacturer, who is effectively selling different products, should check that the CE marking remains valid with either all possible combinations or at least the worst case scenario.
Page last updated: 28 October 2007 17:18:19