Any danger of running lower amp tool on 20 amp circuit


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Old 07-09-19, 01:53 PM
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Question Any danger of running lower amp tool on 20 amp circuit

I'm new to this forum and I'm very impressed with the quality of the threads.

I am upgrading my shop and will be installing a few dedicated 20 amp circuits with 12-2 wire and a GFI on each. This is in anticipation of running higher amp tools in the future. My question is re: lower amp tools on a 20 amp circuit; do lower amp tools anticipate a lower amp circuit breaker and rely on it in case of an overload? It seems like any tool that is lower than the breaker max would be dangerous if that were true but I thought I should ask.
 
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Old 07-09-19, 02:16 PM
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No, it is perfectly acceptable to run plug-in loads less than the breaker size. The breaker is sized to protect the wiring. But, if you are worried about it, install a 15-A breaker until later.
 
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Old 07-09-19, 02:32 PM
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Welcome. This is not meant in any way as a criticism, but if you mean that you are going to upgrade the service yourself you might want to read a bit on basic electricity, which will help you understand how all of this fits together. You will find that while a 120 volt 20 amp circuit provides 120 volts, it has the potential of providing up to 20 amps, meaning that a tool rated at 15 amps will draw only 15 amps, not 20. And the amps of various devices plugged into that circuit can be simply added up to determine how many total amps are being drawn on that circuit. So if you are running say a 6 amp drill and have a 2 amp fan plugged in, both on the same circuit, the circuit is providing 8 amps total and all is well. Now, if you have a table saw, say rated at 15 amps plugged into the circuit, and your buddy decides to cut something, POP!, your total load has just become 23 amps and you tripped the breaker. As far as a tool of lower rating being dangerous on a 20 amp circuit, no. First of all, the purpose of the breaker is to protect the circuit, not the tool. Second, if the tool and the circuit are properly wired, that tool protects itself and you by the fact that it is either properly grounded via the circuit or is what is known as double insulated, in which case there is no ground prong, but the tool is insulated such that you in turn are insulated from any metal components of it. I'm sure others may offer other and/or additional explanations, and some may be somewhat contrary because it takes a little more than a simple explanation, but that's sort of a layman's version.
 
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Old 07-09-19, 02:22 PM
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Yeah, I don't expect to ever use anything that I'm not actually running by hand so I would know what it's doing. I suspect it's safe but I thought I should ask. I'll ask the electrician how big a deal it will be to run 15-A now and switch to a 20-A later. Thanks!
 
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Old 07-09-19, 04:18 PM
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By the way, thought about this later but if you want any proof of how safe a circuit can be with a smaller load than the circuit is rated, go to any circuit in your home. Unless it's an older home, the counter receptacles in your kitchen are 20 amp circuits, but the coffee make doesn't require all of that. Or go to the living room, likely 15 amp circuits, possibly 20, but either way the television, lamps, whatever don't add up to the rated capacity, and you've probably never thought about that because everything works and that's all that matters, right? Your wires and receptacles are rated for it so stick with the 20 amp breakers in your shop and you'll be fine, plus you won't have any problems when you decide to plug in a circular saw or whatever. And a whole other issue, but another thing with shops is that extension cords often come into play, and of course you want a properly sized cord, but even then, particularly with a long cord on a hot day, current draw, i.e. amps, goes up, so a higher load like with a saw, router, etc. can draw a bit more than rated. I'd stick with the 20 amp breakers.
 
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Old 07-10-19, 06:20 AM
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In the US plug-in appliances, tools, etc are designed to run on either 15A or 20A circuits. Hardwired appliances and tools should come with instructions from the manufacturer on acceptable circuit sizes.

Running 20A circuits for a shop/garage area would be good practice.
 
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Old 07-15-19, 07:06 AM
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Thanks for all your input, guys. My second cousin who has background as an electrician and is an electrical engineer is going to do the board for me. My question about load was really more focused on how good power tools are at managing the load. I think I understand the cumulative effect of amperage at the receptacle which is another reason I wanted to go with 20 amps and independent circuits. My vision was to have enough capacity so more than one tool could be run at a time when others are helping me work on cars, etc. I'm pretty sure the counter top plugs are 15 amps but there is a 20 amp circuit for the refrigerator. Good idea to have my cousin check that however.
 
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Old 07-16-19, 11:12 PM
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Your tools are safe. 110v is 110v. Amperage is watts per time. Everything runs a 110 v (difference in charge) but some appliances need 1200 watts (microwave) and some use 40 (nightlight) Your appliance/tool DEMANDS amperage. It isn't something shoved out from your panel, it's simply available if you need it. You can not overpower or burn out tool that runs on 110v by having additional current (amperage). Think of your system like plumbing. The more amperage you have the wider the supply pipe is. So even though every faucet will give you the exact same amount of water per minute (110v), if you have a fatter supply pipe (more amperage) means your wife and daughter can shower at the same time as you do the dishes (lol), it has the reserves to supply more simultaneous demands.

its not just having a breaker with a higher amp rating. You need fatter, more expensive, lower guage wire to safely handle more current aka amps, i.e. more appliances.
 
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Old 07-17-19, 06:59 AM
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In industry, with larger motors, things called magnetic motor starters are used, that have built-in heater elements that are set for external motor protection. There is a little wheel that is turned to correspond to the protection value for that particular motor, or a fixed heater value is speced, depending on the motor rating. The motor is hardwired to the starter. Also, typically wired as to not "self-start" without pushing a button.

In a home, with various sub-3 hp motors, there are typically internal thermal protectors integral with the motor. Usually, self-resetting thermostats, sometimes though manually reset (think garbage disposer).

If you want to get into more sophisticated motor protection, then check this type of stuff out.
https://www.automationdirect.com/adc...bodycontentppc
 
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Old 07-22-19, 06:10 AM
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Great tutorials and much appreciated. I'll let you know how things are going.
 
 

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