You’ll have to look pretty hard to find a new vehicle or farm machine that still uses glass-tube electrical fuses, although there are still many older working machines equipped with them; and some other electrical gadgets still use them. New vehicles and farm machines now almost exclusively use blade style, also known as plug-in, fuses.
Many people are used to looking for the Amp rating stamped into the nickel-plated ends of glass-tube fuses. On blade fuses, the Amp rating is shown on the top of the plastic body. Depending on the manufacturer, that rating may be embossed into the plastic or only printed on. And if it’s just printed, the number can wear off over time, which can leave you wondering what rating a blown blade fuse had when you need to replace it.
Fortunately, blade fuses are also colour coded. So even if the Amp rating number is illegible, you can still determine the fuse rating by its standardized body colour (see below).
There are three common blade fuse sizes: the small minis (ATM), mid-sized regular (ATC/ATO) and the large maxis (APX). There is also a low profile version of the mini, the APS, which uses the same universal Amp colour coding system.
The regular-sized ATC fuse is more common than the ATO. The ATC has a fuse element that is closed (hence the “C” in the code) inside the plastic housing, sealing it from the environment to prevent corrosion from developing. The ATO fuse is open on the bottom, exposing the fuse element between the blades. ATC fuses are the best choice for use on machinery where they could be exposed to the weather. The high probability of corrosion build up could eventually interfere with current flow on an ATO type exposed to moisture.