I have wired up a 220 circuit that also has a neutral leg. The reason for the neutral is so that through this circuit I can run both my 220v table saw and my 110v router (never at the same time).
Because my shop is also my garage, keeping the number of drop cords/trip cords to a minimum is important. I am using 12 gauge 3+1 (2 hot 110 leads on different poles, 1 neutral and a ground) heavy duty wire. I may not be using all the proper terminology here, so hopefully this makes sense.
My question is, if the router were to malfunction and cause a CB to need to trip, will the fact that the CB it is wired through is a 220v (coupled CB) cause it to not trip as it should?
The reason I think this should work is that some clothes dryers have 3+1 wiring, which would indicate, at least to my inexperienced mind, that there must be some 110v components that needed the neutral leg.
The 220 breakers are a paired set of breakers, so that an overload or short on either leg will cause both sides to be disconnected. Thus, if you have a router that is wired black plus white (110) trip its side, the whole shebang will disconnect (black, red and white are broken).
Sorry to hijack your thread but I have a question that I think I know the answer to.
If I have a 30a 240v CB does that mean that each leg could handle 30a it I were to run it as two 120v circuits? I'm not trying to do that just trying to get a better understanding. Here is my thinking. A 30a 240v CB is just two 30a 120v CB ganged together but since 240 uses both hots and no neutral the current is going to flow through both sides of the CB. That probably made no sense what so ever so I can elaborate on it further should anyone care.
In excess of the rated amperage will trip the 240 volt CB. That removes the "hot" power sources.
Never should a neutral (or white wire), or a ground EVER be switched.
It will work, and you can use 120 to the neutral from either hot leg (L1 or L2), but it isn't an advisable practice. (I have done that and some other "unorthidox" things in my shop)
Better is to pull a dedicated 240 volt with a ground for a dedicated pupose (TS). And run an appropreately protected circuit for your 120 volt needs.
If you use flex or conduit, you can pull the wiring you need in it as long as all wires are insulated for the highest voltage in the common conduit.
(I have a 240 volt, 30 amp TS circuit, and a 120 volt, 20 amp circuit within a common conduit (EMT) to my TS area.) :7
Yer right, Sonny. Don't know what I was thinking when I said that the white would be interrupted. Breakers don't do that. As you correctly said, you only interrupt the hot leads.
Another problem with the technique of running a white alongside a 220 circuit to allow you to create 110 circuits, is that the neutral (white) lead could be carrying twice the current of the hot leads but if you use the same gage wire, you will be seriously overloading the line.
To visualize this, think of a 220V 30A traditional circuit at full capacity. The black and the red leads are carrying 30A each. No problems. Now, imagine that you also had the white lead and loaded up the resulting two 110V circuits (red/white and black/white). Each could carry up to 30A and the circuit breaker would not trip. 30A on black -- fine. 30A on red -- fine. However, the neutral line is carrying the return for both of the hot leads, or a cumulative 60A! The breaker does not see this.
Unless you were to use a seriously larger wire gage for the white lead or run two 'independent' white wires, you would have a seriously dangerous situation.
As another way to seeing what is wrong with this, think of this as two completely separate circuit breakers, one feeding the red and one feeding the black, but you didn't run a neutral for both circuits, instead sharing one that is inadequately sized as a consequence.
... the current on line1 and line two effectively cancel each other at the neutral.
Lets say you have 20 amps on L1. And you have 25 amps on L2.
The current flowing back to the panel and ultimately to the utillities transformer on the neutral is 5 amps.
Not 45 amps.
That's why load balanceing is important. Better use of your power. ;)
Dumb question for the morning... is the cancelling thing why you don't always have a neutral line for a 220v run? After looking at the outlets in the store, the 15amp 220v outlets (two horizontal tabs + 1 ground) only let you hook up 2 hots and a ground.
Those are NEMA standards configurations so that the different plugs cannot be accidentally interchanged.
I use the 20 amp configurations myself, even though I have a 30 amp capacity on the TS, my compressor and cyclone are also 240 volt.
It should be remembered that the circuit breaker is to protect the wiring, not what is plugged into it.
So I standardized on 20 amp, 240 volt plugs and recepticals for my shop.
Since I am in a 20' x 20' garage, and for the convinence of always unplugging my TS to change blades, I put the receptical and the saws plug up front. But a secondary reason is for plugging in my bandsaw and jointer when I convert them over to 240 volts as well.
My booster blower and cyclone are remote controlled by X-10 moduals, so I can turn the DC on and off from 4 different places around the shop. As well as other auxillary types of equipment. Or in other words, turn it on over here, then turn it off over there after I'm done with everything I need it for.
As far as the current question, power systems for single phase residential supply have a transformer that takes a distribution voltages (high) and transforms it to 240 volts with a grounded center tap on the transformers secondary winding. That grounded center tap establishes a neutral, or zero current point between the windings of the secondaries of the transformer. Very Basically speaking.
In reality, it is easier to think of it as 2 phases, thus L1 and L2. (or line 1 and line 2).
In a three phase system (industrial for example) You have L1, L2, L3.
Or phases A, B, C.
When a motor is wired for 240 volt operation you are using both L1 and L2 to feed it. The current flows directly from one phase to the other and back magnetizing the motor to propell the rotor of the motor to turn the electrical energy back into rotational or phyisical energy.
At this point you are probably thourghly confused and may be getting a headache.
Suffice it to say, 240 volt supply is the better way to supply what you can change over in your shop. Not everything can be.
Just because you see the 1/2 of the amperage on the namplate, don't necessarily skrimp on the wiring. You still want the inrush current to have a "big tube" to run through. I have #10 @ 30 amps for my TS, and everything else (240 or 120) is #12 @ 20 amp CB's. (Including my lighting circuits).
Take two of your choice of pain relivers for your headache. :7
so... 120v has to have a return/neutral line because you only get the single 120 wave.
and... 240v has two 120 waves with opposing phases. No return line is used.
And (stretching here) the reason to run 240v on a 12/3 or 10/3 is for weirdo devices (dryers/ovens?) that internally branch off the 240 line to run some 120 components and thus require the return/neutral line.
So until I get a 240v tablesaw/dc/jointer/etc with an onboard computer that needs 120, there's no need for 12/3 or 10/3 runs? Does any wood working stuff need the x/3 cabling? Those fancy oneway lathes with digital variable speed controls?