...."Maybe it would help if I explained the situation in which multiple receptacles are typically installed on a 50A circuit, and why.
I'll use my own shop as an example. I have typical midrange/light industrial tools. For example, I have a Makita 2030 jointer/planer. It has a 2 HP motor and draws 18A when running. Typical startup current is double that, 36 A (double is a rule of thumb for motor startup).
Suppose I use a 20A circuit, with 10 guage wire, which appears to meet NEC for a motor circuit. I also use arc fault circuit interruptors and a GFCI. What happens when I turn on the motor? The breaker trips - the AFCI breakers respond quickly to overcurrent, unlike traditional breakers that respond slowly (if at all) to faults. If I use a traditional breaker, the motor will start, but the lights will dim and the motor voltage will drop, stressing the motor. That, and traditional breakers will only trip due to a sustained, significant overcurrent condition - so they often don't trip if a motor winding shorts, for example. (which is why AFCI's should be used for all circuits, even though that is not yet a code requirement - currently AFCIs are only required for bedrooms)
There are a couple of solutions to this problem. I could wire a dedicated 40A circuit with 6 guage wire to each machine. That would work, but is overly expensive. In addition, even with derating there are practical limits to how many such circuits I can legally put in my breaker panel. It's likely 200A service would not be sufficient if I am running my house off the same panel.
The better (IMHO) solution is to use a single 40A or 50A circuit with multiple 20A receptacles. I typically would wire this with 6 guage wire ( 4 is even better), which resolves the light dimming/motor drop issue. As noted previously, this meets NEC requirements. One significant benefit is that only one 40A or 50A circuit is added to the breaker panel, so I can still power my house with 200A sercvice. The only real disadvantage is that you can't start multiple machines simultaneously, but for most of us with small shops that's not a big deal. "
I didn't know that was possible either, like you I ain't an expert...
...but this guy is looney ....this is his response to some fella merely wondering what size breaker to install for a 12A saw. ......the WW conversation has entered the Twilight Zone since this EI?insists his way is OK
Re: woodworkers and electricity.....??#61759 02/02/0612:59 PM02/02/0612:59 PM
I don't know what thumb he is looking on that has a rule stating start-up is twice the full load current. Unless it is on an autotransformer or some reduced current starter the motor startup current is at least 6 X Full Load Current.
Should ask him why they don't only sell AFCI circuit breakers if the regular kind don't work. LOL
I think that this guy has been sitting too long in his shop smoking crack. LOL
[This message has been edited by RobbieD (edited 02-02-2006).]
Re: woodworkers and electricity.....??#61762 02/02/0609:25 PM02/02/0609:25 PM
Anyone remember that skit the Eddie Murphy used to do on SNL? He uses a lot of big words poorly put together. If you didn't know what the words meant, it might sound like it made sense, but knowing what they meant made it giberish.... Then they fade back, and he is in a prison cell. I think that is what you are dealing with.
Mark Heller "Well - I oughta....." -Jackie Gleason
Re: woodworkers and electricity.....??#61763 02/02/0610:48 PM02/02/0610:48 PM
Some subjects get me a little wound up, so I'll try to remain calm and be nice.:-)
First, remember that anyone can claim to be anything on the internet. Second, even if the qualifications or titles are correct, every profession has its' doofusses.
Finally, I am a little tired of folks whose world model has the electrician at the bottom of a "rank ladder," with inspectors, engineers, production managers, and someones' Uncle Fred "higher up." This is simply not true. While these other professions have their own place in the grand scheme of things, it is the electrician who is THE expert on things electrical. Period. Apprentice, Journeyman, Master...this is your area of expertise. Everyone else is in the supporting cast.
Finally, there is a reason it's called a SKILLED trade. Without learning the trade practices, and having the expiernce of seeing a variety of methods over time....there are large parts of the NEC that simply don't make much sense. I wish I had a dollar for every "code expert" I've met who casually disregards the part of the NEC wher it says "not to be used as a design manual!"
Back on topic....our "EI" has a flawed understanding of the code, motor controls, and even basic theory. Off the cuff, I'd venture that he has some power quality problems that are the direct result of his DIY electrical methods. He may also have some POS jury-rigged equipment. I find AFCI and GFCI technology great at catching sloppy or improper wiring methods.
Then again, there are those who believe a fuse blows because the fuse has a defect.
Re: woodworkers and electricity.....??#61764 02/02/0610:55 PM02/02/0610:55 PM