![]() I recognize that many mfgrs dump the responsibility of device current 'protection' on the systems guy, but this is really bad form. So AC43 has given mfgrs and maintenance folks a task at which all have failed, and is likely impossible. In fact, virtually any device needing more than a few amps can make smoke without tripping its rated protection device. If a 2A device develops a serious issue, it can easily make smoke without tripping a 5 or 7A breaker that's protecting multiple devices. ![]() Consider examples where multiple relatively low current devices are on one circuit. Take a look at virtually any certified a/c, and you'll see one protection device on a circuit feeding multiple devices. That's one of those cases where it could just be FAA-speak semantics, but it's either deceptive or wrong (it's probably both). I personally prefer working with #20 wire for convenience but would still use the same 5A breaker. I read that as taking the manufacturer's recommended breaker size even if you happen to use a larger wire size.Īs an example, the Garmin G5 calls for a 5A breaker and #22 wire. Protective device rating, including its timecurrent Wires must be sized to carryĬontinuous current in excess of the circuit A circuitīreaker must always open before any component Wire attached to it is exceeded, or before theĬumulative rating of all loads connected to itĪre exceeded, whichever is lowest. That it will open before the current rating of the House wiring uses a minimum 14 g wire, no skinnier 120 volt wiring around.įrom the FAA bible - AC43.13 - my highlight -ĭevices must be sized to supply open circuitĬapability. it depends sometimes on the actual load being protected. You won't find any 0.5A breakers in the panel to protect your wall wart cell phone chargers. If that doesn't make sense, look at your house wiring. ![]() Then size the circuit protection to protect the wire. Size the *wire* for the load, with acceptable voltage drop and heat rise. Note: if You are unsure, contact a local certified electrician for more information, including local laws and regulations.Respectfully, that's backward. Also, weaker electric circuit breakers may trip too often, so, they are not recommended either. Unlike wires, which can be somewhat thicker, for a 50 Amps circuit, one should NEVER use a stronger circuit breaker. When looking for a proper circuit breaker, finding proper amperage if the circuit breaker is very simple - for a 50 Amps circuit, one needs 50 Amps electric breaker. Note: Never, but really never use thinner cables than required - for example, don't go for AWG 8 wires (or thinner) for 50 Amp circuits. ![]() Ampacity: 70 Amps 85 Amps and 95 Amps thicker wires, in this example, AWG 4 instead of AWG 6, decreases energy losses and the operating temperature of the wires.īut, just note that thicker cables also require more space, they are heavier, thicker, often more difficult to work with, etc. If we check the wire chart, we will find that there is no wire with an Ampacity value of 62.5 Amps, so we will choose the next best thing:Īs one can see, different maximum temperatures also mean different wire sizes - some electricians may consider AWG 4 wire an overkill for a 50 Amps current, especially if the wires are not extra long, but better safe than sorry. So, for a 50 Amps wire, we will choose the wire with the Ampacity of AT LEAST 62.5 Amps and the required temperature. Choosing a lower temperature adds an additional safety level.Īnother important requirement for 50 Amps wire size is the "80% Rule":įor example, when calculating wire size for 50 Amps circuit, we will go for the wire that features Ampacity of: Note: Wire thickness is very often calculated for temperatures of 167☏ (75☌), but 140☏ (60☌) is already a hot enough temperature to prevent an adult to hold the cable with an unprotected hand for more than a few seconds. When looking for the right wire thickness for 50 Amps current, first we have to find the proper wire thickness at the required temperatures as listed in the chart. Note: Ampacities are given for enclosed wires ambient temperatures.
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