Checking and replacing fuses

Although we often think of fuses as a nuisance, they play an important safety role in preventing damage to equipment due to electrical overloading, thereby reducing the risk of electrical shock to patients and staff. You should not dismiss a blown fuse as an inconvenience. It may be a sign that a real fault has developed, giving you the chance to find and fix the problem before any serious damage occurs. Fuses degrade with time and will eventually fail. A blown fuse does not always mean that there is something wrong with the equipment, and in this article we will show you how to replace such a fuse. However, do not keep replacing a fuse if it blows immediately after you replace it. In these instances, call a qualifi ed biomedical equipment technician to service the equipment. A fuse is essentially a short piece of wire of a selected diameter and composition so that it conducts current up to a certain level, but melts or 'fuses' if the current rises above that level. It becomes an open circuit when it blows, interrupting the fl ow of current and preventing damage. In most cases, the fuse wire is mounted inside a small glass or ceramic tube, fi tted with metal end caps. The glass tube forms a physical guard for the fuse, so that when it blows the molten metal does not cause damage or injury. A glass tube allows you to see when the fuse has blown: there will be a gap in the wire or a metallic smear on the inside of the glass. Procedure Many electrical devices used in eye care have an externally accessible fuse near the electrical cord (Figure 1) that you can check and replace by following these steps. 1 Disconnect the device from the electrical system. 2 Remove the fuse from its holder. In some cases you may need a small screwdriver to unscrew the fuse holder cap. 3 Look at the fuse wire. If there is a visible gap in the wire or a dark or metallic smear inside the glass then the fuse is blown and needs to be replaced. If you cannot see whether the fuse is blown, follow steps 4 and 5. If the fuse is definitely blown, go to step 6. 4 Set a multimeter (Figure 2) to the resistance or Ω (Ohms) setting. 5 Place one of the …