15A/20A wiring question

[Texas splinter]

I am in the process of wireing a new shop and am wondering about 15 amp vs 20 amp.
I plan on using 20 amp circut breakers and #12 wire (Romex) but when it comes to outlets, does it really made a difference? I can install 20 amp outlets, and use 20 amp plugs on everything (saw, DP, jointer, etc.) but then, how do I use my Craftsman autoswitch thingamajig that turns on my dust collector? it comes with 15 amp outlets built into it. So if I have a 20A outlet, 20A plug in it, but have to plug the saw into a 15A outlet on the autoswithc, , then what does that do to the saw?

[SARGE..g-47]

"What does it do to it"? It supplies it with the necessary current so it will run!

I have two 20 A circuit lines in my shop. One running down each side with a 20A outlet every 5 feet. I also have a 220V 30A line run in the center on the ceiling for appropriate machinery.

The 20 A line with 12 guage wire is correct for 20 A plugs and breaker. That fact does not mean that 20 A's are forced into whatever you plug it into. It just means that the wire gauge, circuit breaker and plug are capable of allowing 20 Amps through without over-heating. If you plug in a less than a 20Amp tool it will draw the current it needs. It does mean that if for some reason that tool with the 15 A plug were to draw too much current, the 15 A plug and tool would over-heat at the tool before the 20 A outlet or 20 A breaker over-loaded and tripped. With luck, your thing-a-ma-jiggy has an internal over-load breaker that would trip that particular tool.

Use the 20 Amp as you have planned to accomodate the need in most of your larger tools. Even though most (if they are under 2 HP will draw less than 20 amps, they will surge on start-up and possibly over 20 Amps on occasion briefly. If you are using two machines as a DC and TS at the same time on one 20 A line, that can trip the breaker.

Caution.. I am not an electrician. If anything I said is in-correct or could be explained better by a "certified electrician", jump onto correcting me. Also, if the various answers you get here confuse you even more, consult an electrician that is certified. Electricity is not an area that you should be left with any doubt about.

And that last statement is the best advice you get from someone non-certified!

Regards...

[LJR]

When you install a 20 amp 120 volt receptacle you are still able to plug in either a 15 or 20 amp cord plug with no changes necessary. A 15 amp receptacle will accept only a 15 amp plug and not a 20 amp plug.

There is no harm in plugging a 15 amp device into a 20 amp receptacle protected by a 20 amp breaker.

Breakers are meant to protect the wire connected to them.

The device being plugged in will have it's own (built-in) method of protecting itself against excessive current draw.

[Hellrazor]

Use a 20A breaker, #12 wire and all 20A outlets for your wiring. Its ok to plug 15A tools into a 20A plug. You can use 15A outlets on a 20A circuit if nothing is going to draw 20A on a single outlet. But I would skip that and use 20A outlets for future tool purchases.

I use #12 wire for 15A circuits too. You never know when you might need to upgrade a circuit to 20A for some reason. Changing outlets and a breaker is a lot easier then pulling new wire.

[Texas splinter]

Re: 15A VS 20A

I kinda got ramblng in my question, so will try to narrow it down.
I currently have my old shop wired with #12 wire, 20A breakers and 20A outlets. That said, when is the last time anyone has ever seen a tool come with a 20A plug? All I have seen that run on 110/115V come with a 15A plug installed. Even if thay have wire heavier than #14 in the cord to the plug.
And, I understand that the amperage available at the plug will not "force" its way down to the machine, it is just there, available.
That said, if the machine "wants" more than 15A and everything on either side of the plug is equiped for more than 15A, won't the plug just overheat and start to cause resistance in the circut?
Am I making any kind of sense here?
My new shop will be like my old one wiring wise, 15A breakers and #14 wire to lighting circuts only, all else 20A or higher and #12 or greater, depending on what the will be designed to feed. (Example, 30A breaker and #10 wire to my small welder, 50A breaker and #8 wire to my thru-the-wall heatpump.

[Garasaki]

That said, if the machine "wants" more than 15A and everything on either side of the plug is equiped for more than 15A, won't the plug just overheat and start to cause resistance in the circut?
Am I making any kind of sense here?

Anyone who makes a machine that "wants" more then 15amps yet puts a 15amp plug on it...

Will spend a lot of money on lawyers.

Your worrying way more then you need to.

Also, it's worth noting that not too many SINGLE devices will draw more then 15 amps. But what if you are running your drill, drawing say 12 amps, and your wife comes out and decides to vacuum (drawing, say, 12 amps) and plugs into the same circuit (special note: perhaps both have 15 amp plugs???). Now you have MULTIPLE devices, which on their own would be fine, but running simultaneously, overload your circuit.

(This is my point here: I would venture to guess that ciruit overloads, more often then not, happen because of multiple devices drawing current, NOT because there is one gigantically overpowered device running.)

Thank god you decided to run your lights on a dedicated circuit, otherwise your still spinning drillbit is navigating thru the darkness created by the blown circuit, right towards your hand....

[Hellrazor]

You are close.. voltage drop is another issue when figuring things out. A 20A breaker will easily feed something that requires 15A. A 15A breaker might not depending on the length of the run, etc.

[LCHIEN]

Don't worry about 15 amp outlets vs 20 amp outlets. Few appliances machines have 20Amp plugs. You really won't get into trouble plugging 15 amp appliances into 20Amp outlets.

Having the 20A wiring and 20Amp outlets provides extra power when you have multiple devices or the tool needs it. And has lower line loss due to the bigger wires - theoretically you'll get a couple of percentage better performance out of your 15Amp tools.

If your tool fails catastrophically due to wiring fault or shorts, then the breaker will still blow.

[gonesailing]

Plug types

One problem is that ther are several different types of 20 amp recpticals, and I think that is where the confusion comes from. Take a look at your normal wall outlet, two vertical slots and a (more or less) roung hole. That is a 15 amp receptical. A 20 amp recptical will have a horizontal slot comming off one of the vertical slots, but otherwise is looks just like a 15 amp receptical. I know that some plugs are pretty light weight and are rated for only 15 amps, but I would bet that almost all plugs on tools are rated at 20 amps.

There are, of course, special plugs and recepticals for special purposes, such as twist lock, or single outlets like the one for our washing machine.

Unless you have a special tool with a special plug, go with the 20 amp recepticals, they should be of a higher quality.

Mike L

[LCHIEN]

One problem is that ther are several different types of 20 amp recpticals, and I think that is where the confusion comes from. Take a look at your normal wall outlet, two vertical slots and a (more or less) roung hole. That is a 15 amp receptical. A 20 amp recptical will have a horizontal slot comming off one of the vertical slots, but otherwise is looks just like a 15 amp receptical. I know that some plugs are pretty light weight and are rated for only 15 amps, but I would bet that almost all plugs on tools are rated at 20 amps.

There are, of course, special plugs and recepticals for special purposes, such as twist lock, or single outlets like the one for our washing machine.

Unless you have a special tool with a special plug, go with the 20 amp recepticals, they should be of a higher quality.

Mike L

It would be against regulations and standard practice to have a tool that drew 20 Amps in normal use have a 15Amp plug on it.
For the record a NEMA 5-15 (15 amp, 120V) receptable looks like this:

and a NEMA 5-20 (20 amp, 120V) receptacle looks like this.

Note a standard NEMA 5-15 plug (the one we all know and love on most grounded, 3-wire power tool) will go into either receptable but
a NEMA 5-20 plu with one prong turned sideways will only go into the
NEMA 5-20 receptacle.

In terms of power handling, most stuff is made made heavier duty in at least 50% increments.
So I would bet that the basic design of the 15A plug and the 20Amp plug are probably the same contact size. The main purpose of the two different plugs is to prevent plugging a 20amp draw device into the 15AMp circuit. I doubt that comparable quality level plugs will be heavier duty from the 15 to the 20 amp level.

There is only one 20 amp, 120V straight blade receptacle in standard use, described above.
The twist lock devices referred to have contacts in a circular pattern and ratings 20-50 amps and the plug is inserted and twisted to lock in place. You might use these if you need higher current and retention of the plug under vibration or a lot of handling. They come in 3 and 4-contact versions and the contact sizes and the little bent tab on the end in different places to ensure mating only between matching plugs and receptacles.

[Tom Slick]

one benefit of twist locks is you don't have to tie your cord in a knot to keep it from unplugging. i.e. your circular saw doesn't unplug while you are climbing around framing a house.

a bit off topic
I see very little difference in the materials/beefiness between 208v, 240v, 480v, 20a and 30a single and three phase plug/recepticles. the only difference I see is blade configurations to make them incompatable with the wrong voltage/amperage.

[Texas splinter]

Re: 15A/20A question

Wow! Thanks guys for the great education! I will go ahead witht the 20A outlets and CBs with #12 wiring and not worry about the equipment plugs. Or mayby, just use the more expensive 15A outlets, instead of the "cheepies".

[Tom Slick]

I use nothing cheaper then "spec grade", "hospital grade" are top of the line I believe.

[gjat]

I've been in 'specialty' electrical construction for years. I AM NOT an electrician, but there are some basic rules of thumb.
The circuit breaker protects everything on the circuit, including multiple devices which can add up.
The CB is meant to 'trip' before the wire melts so it is safer to oversize your wire or undersize your breaker.
When sizing your wire and devices, in the scale homeowners or in, always tend to oversize the design because you may be underestimating the the load. (Why ruin the ship for a happeth of tar?)
The most critical aspect is having wire of adequate size. It must be sized for the breaker and account for voltage drop. (Larger IS better)
The second critical aspect is the amerage rating of the outlet. Especially in this world of mult-outlets, you may end up plugging in more tools than you thought. (Fan, dust collector, light, radio, saw, refridgerator). (Larger IS better)
The third critical aspect is the amperage of the breaker. DO NOT EVER oversize the breaker! It is intended to be the weak link. You want the breaker to trip before the wire gets hot, or the outlet fails. (Smaller (well, smaller than the wire rating) is generally safer).
The fourth factor is being able to turn off the power to work on the system. If you aren't an electrician, don't connect to the always 'hot' side of the main breakers. If you run wire to a remote building, have a means to disconnect the power at it's source. Could you imagine electrocuting yourself in your back yard moving your boat and striking the overhead to your garage, or your wife planting a bush and hitting the power to your shed. If there isn't a breaker, the amperage drain to fry you won't be enough to trip the power company's breakers.

I AM NOT AN ELECTRICIAN, I'm posting practical experience. Always hire a local electrician if you think a permit is need or you are unsure. Even if you do the work yourself, $100 for a licensed electrician to check things out is well worth it. You may be able to hire him/her to do the 'tie-ins' into your load center and design if for you. His/her advice may save you that much in providing advice for a more practical design. Just don't scrimp on wire size and good advice to save a few bucks.