Fuse and Wiring Education For Your Air Conditioner Or Heat Pump

All H.V.A.C. equipment is meant to be protected with fuses and or circuit breakers that are sized to handle the "amp" draw of a normally operating piece of equipment. The fuse and wiring sizing is spelt out by all manufacturers in their installation instructions and many times on the equipment itself. An improperly sized wiring job and or fuses or breakers can lead to equipment failure at the least and a worst case of serious fire danger! In this article we will be discussing a split system air conditioning condenser as would be found on a typical home. You will usually find a disconnect box near your outdoor condenser (air Conditioner) or Heat Pump.

They are also used at Electric Furnaces or Air Handlers. Their purpose is to shut the main power (usually 240 Volts ) off between your main electrical panel and the HVAC equipment. Disconnect boxes that have fuses in them are called fused disconnect boxes, while boxes that are simply a disconnect don't have fuses. There are many different types and colors of these boxes. Some of them have a circuit breaker in them instead of fuses. Which type you have, will most likely be decided by your City or County Codes. Which ever type you have, you should not change to a different type before checking with your City or County Official! Also, NEVER substitute a different size fuse or circuit breaker than what you have (assuming what you have was sized correctly ). Some times people buy a home and un be known to them, the seller of the home may have changed the fuse or breaker to the wrong size out of ignorance. Also NEVER assume that just because you pull the disconnect out, that the power to the equipment is REALLY off! We have seen MANY disconnect boxes that have been jumped out rather than being replaced! Remember, you are working with 230-240 Volts here! If unsure of what you may have, please use a Volt meter to be sure the power is actually off to the equipment. If unsure of YOURSELF please call a HVAC Technician or Electrician to do this work! Shown is a fused disconnect box in the closed position.

The aluminum lugs will be marked Line (main power into the box) and Load (power into the equipment from the box). Removing the white disconnect "Breaks" the power going to the equipment (if it hasn't been jumped out!) It is a good idea to use a fuse puller to remove and replace these fuses and even better, to shut the main power off at the main panel!

Fuses range from 15 amps to 60 amps. There are always two per box on residential equipment. Most people will want to keep an extra (2) on hand.

While lightning accounts for some of the blown fuses we see, there are also situations such as aluminum wiring (should be removed for safety), loose connections, tight compressors, or other mal functions. Make sure the fuse or breaker is sized correctly per your equipment documentation and that you are using Time Delay Fuses and not the usual hardware store One Time Fuse! Time delay fuses can take a higher amount of amp draw for a brief period that one time fuses can not withstand.