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240v Air Compressor Wiring

4.8K views 53 replies 9 participants last post by  chandler48  
#1 ·
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Hello

I don't have much electrical experience beyond basic home wiring. I just recently purchased a 240v air compressor, that has a 20a factory plug. Currently I have a garage heater that plugs into a 240v 50A outlet.

My question is - If I just purchase a new 240v 50A power cord and re-wire the compressor motor, am I safe to plug that into the same outlet as the heater? (obviously not at the same time) The motor has an overload switch on it that I would think protects the compressor from overheating.
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#2 ·
#3 ·
#4 ·
A 50 amp breaker will "overprotect" the circuit, placing your wiring as a "fuse". It already has a proper plug, so why not do it right? Not expensive. Less expensive than rewiring the motor and modifying the plug.
 
#7 ·
But if the motor has a built in breaker, wouldn't that be the protection? I understand why you wouldn't want to install a 20a outlet in a 50a circuit.

And I've already looked into running a new line and it's very expensive just because of the layout of the house. My house is on a slab.

I just get confused because everyone plugs in small motors rated for less amps than their circuit all the time. For example a box fan might be rated for 5 amps, but no one cares about plugging that into a 15 or 20 amp circuit. I'm sure there's more to it but I'm just trying to understand.
 
#8 ·
I just get confused because everyone plugs in small motors rated for less amps than their circuit all the time. For example a box fan might be rated for 5 amps, but no one cares about plugging that into a 15 or 20 amp circuit. I'm sure there's more to it but I'm just trying to understand.

If the outlet and plug is rated for the correct amperage, wouldn't the breaker on the motor protect anything else?
 
#12 ·
What size wiring is supplied to the 50 amp receptacle? Is it protected by a 50 amp breaker. Is that breaker in the house? Post a picture of the receptacle and its wiring. You have limitations of how you can run wiring. What is the nameplate amperage of the heater. There may be a way.
 
#13 ·
The real answer is maybe depending on certain circumstances. The breaker in this type of circuit rarely "protects" the wire from thermal, similar to the "5 amp" load on 15 or 20 a circuit but is an off/on switch and for short circuit interruption. In some circumstance several of these could be connected to larger circuit, part of that may be cord size. You are on the right track realizing you can't put the 20 outlet on a larger circuit.
 
#21 ·
I can see we have work to do with this. The breaker protects the wire from thermal mainly on general circuits with multiple outlets. A circuit with a single outlet (or hard wired) is protected by the calculated load. An appliance, ul listed, nema etc is designed to load to 80% for example and breaker small enough for fault protection within up to a point incl it's cord and large enough to pass the current without tripping.
Welder circuits are often wired this way, an electric range is a perfect example. It's a collection of elements that are wired with 12 so to speak, they will not overheat the individual wires and as a collection will not overheat the 6 cord, breaker needs to pass required current and be small enuf for fault protection of all the wires. Might have additional fuse for clocks and controls on newer models but rely on load size to thermal protect.
 
#22 ·
A welder circuit is kind of "exaggerated or magnified" example of this fundamental design principle our "whole system" is based on taps and feeders etc but 50A breaker to 10 cable to 50A outlet connected to a machine with a 12 cord.
 
#23 ·
The current limited magnetic breaker is limited for short circuit. An outlet "cept for couple exceptions",,,, "says" 3 things. It says the wire is adequate, the breaker will pass the listed current and is current limited,, yss.es it will limit thermal but it's not it's primary design intent in specific circuits.
 
#30 ·
Other than wiring it the proper way, you can use one of these.
It has a a built in 20 amp breaker.
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#31 ·
I have another idea. Since it is such a small compressor, rewire the peckerhead to 120 volts, replace the plug with a 120v plug and use a regular receptacle.
 
#42 ·
Here is another example. 60 fuses panel. Number 10 wire connected to the 60 feed thru lugs to 1 arm bandit with 30 fuses,, or 20 to water heater or air comp,, fuses limit the load when placed after the wire.
I got nothing.... :ROFLMAO: You guys get in. Are we talking about a 60A SUBPANEL?? You know, with dedicated breakers for individual and safe cirqueets