I'm in the planning stage of my electrical wiring within my shop. I'm going to be placing separate 220v circuits about the shop. What amperage should I use? BTW, I already have my PSI switched to 220 and have a 20 amp circuit in place for that . The rest of my equipment is still 110 but in the future, I see a cabinet saw and jointer that could be run on 220. TIA
-- Tim
-------- See my page @
IME, just about anything you can convert to 220, and most 220v shop tools, will run on a 220v, 20A circuit. Might want at least one 30 A for a dust collection system..
FWIW, I used 10 ga wire on all my 220v circuits, even the 20 A circuits ... that way I have a choice of going to 30 A with a breaker and new receptacle if/when the need arises.
Doing it now, while you have a case of the endeavors, is the best bet ... DAMHIK.
What amperage do the cabinet saw and jointer require? That's what you should provide.
-- Regards, Doug Miller (alphageek-at-milmac-dot-com)
...think previous post already had the answer...converting 120v motor to
240v isn't going to change the answer at all if the existing stuff runs ok on 120v. Great idea about using 10g wire though...not that much more $$$ per foot as long as you are at it and don't have any serious bends to make.
I'd run #10 AWG wire with 2P-30A c'bkrs for everything except say a 5HP air compressor which will require a 2P-40A and #8 AWG to handle the inrush.
Remember one thing, the c'bkr protects the insulation on the down stream wire, not the load connected to it.
As far as NEC is concerned, that $1,000.00 tool can go up in smoke as long as the insulation on the wire feeding it is protected.
Protecting that $1,000.00 tool requires the installation of an overload relay which is a whole different kettle of fish.
HTH
I've noticed that going from 12-gauge to 10-gauge is quite a bit more expensive, unless (perhaps) you're buying in 1,000-foot spools. Places around here practically give 12-gauge away at a loss just to get you in the store. But again, 10-gauge is a good idea anyway!
steve
The few 5-HP machines I've looked at have had maximum amp draws of around 27 amps, a 30-amp 220 circuit will run them just fine.
As for handling the inrush current without tripping the breaker, I wouldn't worry. I haven't seen a breaker yet that isn't EXTREMELY generous at tripping. The brand-new, 20-amp circuit breakers that I've tested have taken as long as 5 minutes to trip when put under *30* amp draws. I've heard people telling horror stories about Square-D breakers, but none of these were Square-D. I've come to believe that they're all that way. Maybe I'm wrong, maybe there are some "strict" breakers out there, but I sure haven't been able to find them from Square-D, GE, or ITE/Siemens! Of course, as the current draw gets higher, they trip more quickly.
steve
Not true.
The allowable full load for a c'bkr in an enclosure such as a panelboard is
80% of the nameplate value.The 100% rating is for a c'bkr in open air only.
Thus a 30A c'bkr is rated to handle 24A on a continuous basis which is why you need a 40A c'bkr for that 27 FLA motor.
Unless you have about $100,000.00 of rather sophisticated test equipment at your disposal, you will be unable to properly test c'bkrs.
How is measuring the current draw, and seeing how long it takes to trip not "proper"?
steve
No problem with that procedure as far as it goes; however, you are dealing with a thermal-magnetic c'bkr.
To check the thermal portion of the c'bkr, requires as you suggest, applying a controlled current and measuring the time required to trip; however, it also requires controlling the ambient temperature while testing.
Since the thermal trip curve represents and inversely proportional relationship, it require multiple test points to get a complete picture.
Translation:
It's a PITA, time consuming test since you must wait for the c'bkr to cool down after a test before you can run the test at a different test point.
Testing the "magnetic" portion of the c'bkr is a whole different kettle of fish which your applying a current and measuring the time to trip doesn't address.
It requires very high currents and high speed recording devices, all very expensive.
I once saw a film of a 3P-100A safety disconnect switch that had a bolted fault wired on the secondary side (Literally a copper bar bolted across the terminals) that had a 100,000 amp current applied to it.
The camera that recorded the event was behind a special piece of bullet proof glass.
The safety switch exploded right in front of the camera like a bomb had exploded inside the switch.
If the camera had not been behind that glass, it would have been history.
It was an attempt to demonstrate the effects of high current short circuits, and IMHO, was very effective.
BTW, the lab where that test was run cost over $1,000,000.00 to build 20 years ago.
HTH
Watch your conduit size, number of wires and number of bends with that 10 ga wire. The stuff is a bit harder to pull then 14 or 12 ga. Use condulettes or boxes instead of pulling ells. IMHO!
Something to keep in mind.
The locked rotor starting current of a motor can be in the order of 6-10 times the nameplate FLA of the motor.
Using your example above, the inrush current could have been as high as 280 amps for perhaps as long as 1/2 second.
No wonder you tripped that little 1P-20A c'bkr.
Older motors are not as efficient as the newer ones. It may have a higher inrush current as well. Besides, you shouldn't be running a 28amp max machine on a 20 amp circuit.
On Wed, 13 Aug 2003 10:04:01 -0600, "Steve Wolfe" pixelated:
I got a 250' spool of 12/2 grounded for $20. The 10/2g was $35 or something for 250', and even less per foot in 1k' spools. MAN that
10ga stuff is hard to wind around an outlet or switch terminal! I had to resort to REAL needlenose pliers when I installed the 10/3 A/C feed wiring while the old Xcelite (electronics) needlenose pair worked fine with the 12ga. I think the 10/3 was $0.49/ft, quite a bit more expensive for 25'.- Press HERE to arm. (Release to detonate.) -----------
That's one of the reasons you can get back wired as opposed to side wired devices.
They are usually industrial or hospital grade and thus are a little more expensive than commercial grade devices sold at Home Depot.
They "stab" into the back but the resemblance to the fire hazard cheap sockets ends there. The industrial or "spec" grade use the side screw to clamp the wire once it is inserted into the back. The cheap sockets use a small bent spring to hold the wire in place.
-Bruce
It is interesting to me that in Denmark, where I spent some time, they do not have wire nuts. Instead they use a plastic-covered metal tube with set screws -- like I have seen on a wiring block but I cannot remember the name
-- and you put the wires in from either end. At first I thought it was too cumbersome and expensive (a simple switch box there was >$6) but then I realized that there was unlikely to be a problem when bending the wire back into the box and having the connector fall off. (It is also easier over there because w/ 220 the wire is half the size.) It seems much, much safer than our wire nuts. In fact, I'd like to use them here in the US if I could find them and they were legal.
You will see these in commercial wiring too but usually only on larger sized conductors. There are some listed down to 14ga wire so they are "legal", just pricy.
That's certainly true for very long wires (i.e. transmission lines) and/or high frequencies. I suspect it's not true for the length runs you're likely to find in a residential wiring job.
I did a quick google search on "skin effect" and came up with a few references filled with more calculus than my few remaining brain cells are still capable of dealing with. Here's one reasonable reference:
Are you talking about the stab holes in the back for 10 ga wire?
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