20 amp plugs vs. 15 amp plugs

[Brian Vega]

Hi,
I am switching some of my larger tools to 240. I had a professional electrician install 240 20 amp circuit so I should be safe there.
I went out and bought plugs to put on my tools and realized that I picked up 20 amp plugs. My tools all say I should use plugs rated at 15 amp. If I put the 20 amp plugs on the tools will I be safe?

Thanks.
Brian

[Bas Pluim]

Yes. A 20amp plug will work perfectly fine on a tool that requires a 15amp plug. In fact, it's overkill. You're more than safe.

The other way around, a 15amp plug on a tool that needs a 20amp plug....that would be a bad idea.

[Mike Henderson]

I assume you're talking about tools that will operate at 240 volts and not your 120 volt tools. The plug for 240 volts is different from a 20 amp 120 volt plug and you should make sure you're using the 240 volt plug.

Beyond that, if you wire it up correctly there's no problem with using a higher amp rated plug.

Mike

[glenn bradley]

What Bas and Mike said.

[Brian Vega]

Thanks for the replies, I just wanted to make sure. This is my first time rewiring any tools. Those electrons make me nervous.

[Gary Curtis]

With two separate 220 circuits in and around my shop, I had to standardize plugs so I could move some of the machines around. The circuits have a breaker capacity of 30 amps each. But I had more 20 amp machines than 30, amp, so now my six 220 machines all have the 20amp size plugs.

Gary Curtis

[Tom Godley]

Often the reason the spec is for a 15amp plug and breaker is to protect the tool - wire/motor. Using a higher breaker (20amp) will not protect the electrical parts of the tool if something goes wrong. My grinder is very clear that it should be connected to a 15amp 240v circui.

The proper way to set this up is to plug the tool per spec and then match this to the outlet and to the correct breaker. It does make for more outlets.

I have a friend that got some 30amp plugs/outlets on the cheap and put his 240 volt tools on 30amp breakers. Wire was cheap years back and his runs were short -- but this is not a safe way to wire a shop.

[Norman Hitt]

I have a friend that got some 30amp plugs/outlets on the cheap and put his 240 volt tools on 30amp breakers. Wire was cheap years back and his runs were short -- but this is not a safe way to wire a shop.

Although it is considered "Overkill", It does not hurt anything to use a higher amp plug AND a corresponding larger wire on anything. It is the circuit breaker amp rating that controls the safety of the circuit, so in your friend's case, the circuit will be fine but he can replace the 30 amp Breakers with 20 amp breakers if he is trying to protect the tools with the circuit breaker, (even though that is NOT what the ckt Brkr is intended to protect). What IS truly unsafe is to use a smaller wire and lower amp plug than what is called for by the tool's specs, because the tool is then drawing more current than the wire and plug are designed to handle, which will cause the wire and plug to heat up and possibly catch fire. Additionally, the use of the lower amp circuit will eventually cause major damage to the tool's motor.

[Tom Godley]

I do not want to get into anything over this topic -- but this can be a very dangerous subject to overlook.

You do not want to place a higher amp plug and then by its very nature a higher amp circut onto any electrical device. The breaker is there to protect the entire circuit - not just the wire in the wall.

The overkill -- can kill.


If a tool has a 15 amp spec, the motor and other wires/ lineset are built around that spec, and to allow an overcurent is just not a good idea.

A motor built around a 15amp spec allowed 20amp with a locked rotor will tell you real fast it is not happy.


We are talking about TWO different items in a shop 240v circit.

The outlet must match the breaker rating with a wire gauged to at least match the rating of the breaker.

The tool rating is another matter - and you should not allow a tool to be installed in a circuit greater then its rated spec.

[Jim Becker]

Match the plug to the circuit...

[Bas Pluim]

You do not want to place a higher amp plug and then by its very nature a higher amp circut onto any electrical device.

I completely agree with the second part, but not the first. There is no reason why you can't use a higher rated plug. Likewise, I can run 10/2 wire for a 15A circuit as well. I don't need to, 14/2 will do, but it doesn't make it any more or less safe. My shop has 20A and 15A circuits. I don't have to swap the plug on my sander when I move it from one outlet to another.

The breaker is an entirely different matter of course. Always use the breaker appropriate for the wiring and usage.

Also, your advice on not using too large a circuit is great. Just because it works or because it's code doesn't mean you can't make it safer.

In theory, you could wire your whole house with 30A circuits, but then what's the point of having breakers to begin with? The previous owners of my house did this. There was a loose connection in an outlet, which would cause the breaker (15A) to trip. So, they replaced it with a 30A breaker. No more tripping. No more protection either!

Bas.

[Chris Barnett]

FWIW, on 115VAC, a 20 amp plug does not have the same pin orientation as a 15 amp receptacle.

[Tom Godley]

The original post was on the topic of replacing 15A plugs with 20A plugs so that they can then be installed on a properly wired 20A 240V circuit -- this is not correct - no way no how.

If the tool indicated that it should be on a max 15A 240V circuit it should have a 15A 240 plug connected to 15A 240V outlet and a 15A 240V breaker.

It will work changing the plug ....yes... but it is not correct. The same is true for placing a 30A plug on a 20A tool so you can plug it into a 30A circuit - also not correct.

Spending the small amout of money on the correct items greatly reduces the chance for problems ..... especially as parts age.

More is not always better. I'm finished

[Lee Schierer]

The original post was on the topic of replacing 15A plugs with 20A plugs so that they can then be installed on a properly wired 20A 240V circuit -- this is not correct - no way no how.

If the tool indicated that it should be on a max 15A 240V circuit it should have a 15A 240 plug connected to 15A 240V outlet and a 15A 240V breaker.


The ratings on all equipment are the requirements of that equipment. They are also the minimum ratings for any circuit or device they connect into. If your tool says 15 amps, then you can plug it into any receptacle on any circuit capable of supplying at least 15 amps. It does no harm to the tool at all to plug it in on a circuit our outlet with larger capacity than needed to run the tool as long as the voltage is correct. You can damage tools by placing them on circuits not capable of supplying enough volts and amps. You can safely plug a tool into a 100 amp circuit if the voltage is correct without damaging the tool. IF there is a problem internally in the tool, the circuit breaker is not likely going to come to your aid and prevent permanent damage to the tool. Motors are generally protected with overcurrent or over temperature devices internally.

Circuit breakers are designed to protect the wiring of the circuits they support not necessarily the devices plugged into them. Like wise receptacle ratings are designed to protect the receptacle from damage. You should not use a 15 amp receptacle or switch on a circuit that will be drawing more than 15 amps. The receptacles and switches should also match the circuit breaker rating since they are part of the wiring. Wiring size should never have less rating than the circuit breaker. You can use heavier wire if you want, but it is basically wasting money.

[Jason Hanna]

Am I missing something here? If you have a tool that states that it needs 15A MAX (I personally have not found this on any tools) and you have a 20A circuit with properaly sized wire, outlet, and breaker, then AS AN OPTION you could switch the breaker to a 15A breaker. Then your wire would be oversided, but the breaker would prevent the tool from receiving more than 15A.

I'm no electrical expert, but wouldn't this work?

[Lee Schierer]

Am I missing something here? If you have a tool that states that it needs 15A MAX (I personally have not found this on any tools) and you have a 20A circuit with properaly sized wire, outlet, and breaker, then AS AN OPTION you could switch the breaker to a 15A breaker. Then your wire would be oversided, but the breaker would prevent the tool from receiving more than 15A.

I'm no electrical expert, but wouldn't this work?

The crux of the matter is the interpretation of the rating. Tool ratings are what they consume to operate (I've never seen a tool with a maximum rating either). Ratings for extension cords, switches and receptacles are the maximum they should be asked to handle.

[Chris Friesen]

With two separate 220 circuits in and around my shop, I had to standardize plugs so I could move some of the machines around. The circuits have a breaker capacity of 30 amps each. But I had more 20 amp machines than 30, amp, so now my six 220 machines all have the 20amp size plugs.

Using 20A receptacles on a 30A circuit is a code violation, unless the circuits can reasonably be considered as dedicated motor loads.

[Jim Becker]

FWIW, on 115VAC, a 20 amp plug does not have the same pin orientation as a 15 amp receptacle.

The same is true for 240v connections.

[Rick Christopherson]

The original post was on the topic of replacing 15A plugs with 20A plugs so that they can then be installed on a properly wired 20A 240V circuit -- this is not correct - no way no how.
Sorry Tom, but this is correct. In full accordance with the NEC, youare permitted to install either 15 or 20 amp outlets onto a 20 amp circuit. You are also permitted to install 40 or 50 amp outlets on a 50 amp circuit. These are the only two exceptions, and all other circuit sizes and conditions must be equal.

Contrary to what I believe someone else may have stated, you cannot install a 30 amp outlet on a 20 amp circuit, nor can you install a 20 amp outlet on a 15 amp circuit.

[Tom Godley]

I am talking about the plugs -- not the outlets!!!

Yes you can have 15A or 20A outlets -- as is the case in kitchen 120v 15A outlets on a 20A circuit and yes you can have the 40A/50A on 240v to cover motor startup etc... on the 40A line.


But we are talking about the PLUGS that we install on our larger 240v tools -- most items, that the average person buys come with the plug already installed. I think that all 240v tools should come with the correct plug installed -- if you want to wire it direct you should be forced to remove it.
This would help in having things wired correctly -- It would still be a problem in duel volt setups.

Read the manuals -- both of my newest (just delivered) tools state very clearly that they should be installed on a 15A not 20A 240V circuit.

This type of direction is the norm -- check your split AC units -- it is the same thing.

The internal wiring of the tool is built to a standard not to exceed. Why do you think that there are so many different plugs!

I am sorry to sound like I am ranting -- But I really have been shocked (joke!!) at the mistakes -- that I have noticed in some shops that I have looked at since I began to plan my new one.

[Rod Sheridan]

The issue with tools or machinery and the maximum ampacity circuit you can connect them to, is due to the withstand rating of the tool or machine electrical component.

In a nutshell, a larger ampacity circuit will have lower impedance, and of course a larger ampacity breaker.

In the event of a fault in the machine or tool, the larger ampacity circuit can deliver more short circuit current than the tool or machine can withstand.

If the withstand ratings are exceeded, the tool or machine components can explode violently.

Anyone who has observed electric welding has seen a process that uses aproximately 25 to 30 volts at aproximately 100 amperes. Imagine the energy release and arc at 240 volts, 500 amperes.

A 30 ampere circuit with 3% impedance (usually the maximum allowed by code) is capable of delivering a maximum of aproximately 990 amperes of current into a fault.

The manufacturer of the tool or equipment, will design and test the tool to withstand the expected fault values. If you take a tool that is meant to operate from a 15 ampere circuit, and connect it to a 30 ampere circuit, you have doubled the available fault current.

If you aren't the electrical engineer responsible for the design of the tool, you have no way of determining whether that's safe. That is why machinery often specifies a maximum fuse or breaker size, and may even specify a certain time/current characteristic, or current limiting property for the fuse or breaker.


Regards, Rod.

[Tom Veatch]

...The tool rating is another matter - and you should not allow a tool to be installed in a circuit greater then its rated spec.

A trouble light is a tool. Assume it contains a 100watt bulb which is rated for much less than 15 amps. Does that mean I cannot safely use a trouble light on a circuit that is protected by a 15 amp breaker?

The rating on a tool indicates the minimum rating on the supply circuit, not the maximum. My Dust Collector has a FLA of 20.7 amps. It is supplied by a circuit wired with 10ga copper and protected by a 30 amp breaker. Do I need to replace that 30 amp breaker with a 20 or 25 amp breaker. No, of course not.

The purpose of the breaker is to protect the circuit components and is sized for those components, not for whatever devices might happen to be plugged into the circuit. The breaker has absolutely no function or responsibility for protecting anything beyond the receptacle.

[Kent Fitzgerald]

The original post was on the topic of replacing 15A plugs with 20A plugs so that they can then be installed on a properly wired 20A 240V circuit -- this is not correct - no way no how.

Tom, there's something you're overlooking: a 20A receptacle (either 120V or 240V) is intentionally designed to accept either 15A or 20A plugs. So, the assertion that a 15A plug is meant to prevent a tool from being plugged into a 20A receptacle is incorrect.

You mentioned in another post that "both of my newest (just delivered) tools state very clearly that they should be installed on a 15A not 20A 240V circuit." I'm going to take a wild guess that your new tools are... Grizzly. Grizzly has chosen to put this restriction in many of their manuals, but the rest of the world (and the NEC, and the UL), has absolutely no problem with plugging a 15A (or less) tool into a 20A circuit.

I hope this helps clarify things. Enjoy the new tools and shop!

[Josiah Bartlett]

This is why fused plugs are required in some parts of the world (like Britain).

They are a good idea if you can find them.

[Rick Christopherson]

I am talking about the plugs -- not the outlets!!!Yes, I realized this distinction right after I made my posting, but I left my posting to stand as-is because this still overlooks the basic concept of circuit protection.

As another poster already pointed out, because you can have 15 amp outlets on a 20 amp circuit, there is nothing preventing you from plugging a tool with a NEMA 5-15 plug on it into a 20 amp circuit. Moreover, a NEMA 5-20 receptacle is designed to accept both a NEMA 5-15 or NEMA 5-20 plug.

When the NEC says that you should refer to the appliance's manual, they are referring to a properly and accurately created manual; not the type you find with woodworking machinery. (I write manuals, so I know exactly how this erroneous information makes its way into poorly written manuals.)