maybe i missed it in the other thread on this subject, but here’s my question-
i’m wiring my shop space and have 35′ wall that i want a sh!tload of outlets running along- say, on average a 4 outlet box every 4′ or so- but i want them on two separate 20a circuits. if possible, each double receptacle in the box (of the pair in a box) on a different breaker from its mate. so maybe all the outlets on the left sides of the 4 outlet boxes are on one breaker and the rights on the other. does this make sense? it’s basically so i can run a big shop vac and task lighting at the same time as a sander, miter saw or router, plugged in more or less next to each other but still have them on separate circuits.
someone suggested i could run one 12/3 instead of two 12/2’s and use a common neutral and ground. also, how would you guys suggest arranging/marking the receptacles (no matter how they’re wired) so someone in the future doesn’t make the mistake of shutting off the breaker to only half of the hot outlets- with predictably exciting results? is there a way to use one 2-pole breaker (usually for 240v circuits) for both sides with this set-up? what size? still 20a?
any suggestions?
thanks,
mitch
Replies
I'm not an electrician, and I'm Canadian so this advice is worth less than 2 cents...
You can run 12/3, common ground, common neutral. You understand you have to break off the connecting tab to turn the receptacle into a split receptacle? You would have two single pole 20A breakers supplying the 12/3, with a tie-bar connecting the two breakers, or a double pole breaker.
There is nothing you have to do to the outlet to notify future thrill seekers. Anyone working on the outlet in the future should immediately notice the 12/3 wire because a single outlet will have a red and a black wire connected to the hot terminals. Also, the breaker tie-bar should force them to clue in. If they're oblivious to that, they shouldn't be working with electricity. Or maybe they should...some people should be eliminated from contributing to the gene pool.
Regards,
Tim Ruttan
Edited 8/17/2003 11:49:59 PM ET by TRIMBUTCHER
"You understand you have to break off the connecting tab to turn the receptacle into a split receptacle? "
No need to do that. No need for the split receptacle.
He want to have two duplex devices in each box. One whole receptacle will be on one leg and the other device on the 2nd leg.
so just to make sure i've got this straight-
run 12/3, shared grounds (bare wire) and neutrals (whites), black to one 2 outlet/duplex unit, red to the other, then use A) one 2-pole/240v 20a breaker OR B) two single pole 20a breakers? will option A be safely triggered with an overload on one circuit or the other? if that works ok, then it would seem to be the safer choice because an overload on either (or intentional manual operation of just one switch) will shut off both circuits on that wall, not just half of them.
next question- what is the preferred method (code?) of wiring a long run of outlets on a circuit? A) stripping the insulation in the middle and looping it around each screw, thus making for a continuous, unbroken run of copper wire- which would seem to be the best way, but a minor pain to strip that way (except for grounds which are already nekkid and only have one screw to attach to) and a major pain to pull the cable into the boxes, or option B) which is to cut the conductors then use both screw connectors and the intact trim tabs to continue the circuit? (I do know not to use the "poke in" connections, and they're only on 15a units anyway, aren't they?) any advantage to using just one screw for both wire ends instead of the connector tab to bridge/continue the circuit? it would keep the copper in direct contact but would whatever you might gain just be offset by the problem of cramming two wires under a crowded screw head?
if option A), which really does seem better, electron flow-wise anyway, any helpful heloise hints on stripping wire in the middle and pulling continuous runs of cable into the boxes? (ain't NO WAY i'm pulling romex up thru one hole then back out another in a run of 7 or 8 boxes! i'm not picky enough- or stupid enough- to do that with 14/2, let alone 12/3)
btw- loved the idea of colorcoding the outlets- i think i can get grey, white and orange industrial quality outlets.
thanks,
mitch
Edited 8/18/2003 9:25:48 AM ET by mitch
A couple things to consider:
1. GFCI's, if required, cannot share a common neutral (at least in Michigan). This means if you go the root you are suggesting, and are in a basement, for example, or other area where they are required, you will be buying a LOT of GFCI's. I did the same thing you are referring to (except I only ran a single duplex in each box, but every other box was on a different circuit), and it cost me an extra $100 after I found out this little tidbit...
2. Don't even try to strip the middle of a wire and wrap it around a screw to create one continuous loop - it isn't worth the effort, isn't allowed in many places, and would prevent you from pulling out just one outlet (since it is now connected to its neighbor via its ground and neutral) to work on it. Use wire nuts and be done with it.
3. Consider using extra deep boxes - I ran all 12 ga wire (since I did 20A circuits) and it was a PITA to work with. I used double boxes to give me extra room and it made a HUGE difference....
d-
"will option A be safely triggered with an overload on one circuit or the other? if that works ok, then it would seem to be the safer choice because an overload on either (or intentional manual operation of just one switch) will shut off both circuits on that wall, not just half of them."
Yes, but it is not really important to shut off both sides on an overload. But I think that it is safer when working on the circuit. Some one could just trip one leg and test the outlet on that leg, but brush against the other outlet that is on the other leg. So I would recommenc a 2 pole breaker when they are in the same box.
When you have a multi-wrie cirucit (sharted neutral) the code does require that the neutral be pigtailed and not run "through" a device. The reason being that if you removed that device or had a bad connection then you can have 240 volts on some of the other outlets.
And in general stripping wires in the middle of a run is a real PITA. Hard to get a good job on it. Even more so if you are using NM.
AFAIK there is nothing in the code prohibit doing this. And while you can use the terminals to join the "income" and "outgoing" circuits (except for grounds and multi-wire neutrals) most people feel that pigtailing all of the connections are the best way to go.
" (I do know not to use the "poke in" connections, and they're only on 15a units anyway, aren't they?)"
The "back stab" connection are limited to #14 on new devices. And BTW, you don't need to use 20 amp devices on a 20 amp branch circuit as long as you have more than one outlet (and a duplex counts as more than one). I have never seen anything that has a 20 amp plug on it. And outside of the residential grades the guts are the same in both 15 and 20 amp devices, it is just the difference in the slots in the faceplates.
I don't know if this is universal, but I had this discussion in anohter forum and so I downloaded Levitions catalog. The Residential grade devices, some with back stab and some without, where only availabe in 15 amp devices.
Once you went to commercial or industrial spec grade all of the devices where avaialable in both 15 and 20 amp "version". So use whatever is readily available.
When you have a multi-wrie cirucit (sharted neutral) the code does require that the neutral be pigtailed and not run "through" a device. The reason being that if you removed that device or had a bad connection then you can have 240 volts on some of the other outlets.
ok- this means wirenutting two pigtails to the incoming and outgoing neutrals- 4 wires total- with the pigs going to each duplex receptacle? (same for grounds) and does NOT allow for inbound neutral to outlet screw, pigtail from other screw to other outlet, then outbound wire attached to second screw on #2 outlet?
thanks again!
m
this means wirenutting two pigtails to the incoming and outgoing neutrals- 4 wires total- with the pigs going to each duplex receptacle? (same for grounds) and does NOT allow for inbound neutral to outlet screw, pigtail from other screw to other outlet, then outbound wire attached to second screw on #2 outlet?
You got it ...............................Ed
damn- it would be so much cleaner and easier the other way. thanks.
m
And BTW, you don't need to use 20 amp devices on a 20 amp branch circuit as long as you have more than one outlet (and a duplex counts as more than one). I have never seen anything that has a 20 amp plug on it. And outside of the residential grades the guts are the same in both 15 and 20 amp devices, it is just the difference in the slots in the faceplates.
Something people tend to overlook in this regard is that the NEC states that each device installed be derated to 80% of it's nominal value when designing the system. So a 15a receptacle is rated at 12a and a 20a receptacle is rated at 16a. This means that design-wise if you have a tool drawing more than 12a then a 20a (nominally)-rated device needs to be installed.
Ed
Edited 8/19/2003 5:52:23 AM ET by Ed
Edited 8/19/2003 5:55:27 AM ET by Ed
"Something people tend to overlook in this regard is that the NEC states that each device installed be derated to 80% of it's nominal value when designing the system."
You will never find any such statement in the NEC.
Now there are a number of 80% "rules", but there is no one that is as broad as you say. And they depend on the applications. For example some of then only affect circuits that are used continously (more than 3 hours).
This is probably the seconds that are closes to this application. "15 and 20 amp branch circuit. ....The rated of any one cord and plug connected utililazation equipment shall not exceed 80% of the BRANCH CIRCUIT RATING. ...."
last question, i swear (then you can bill me for consulting) -
yea or nay on running the hots "thru the device"- inbound to one screw, outbound off the other, or do i need to pigtail all of those too? (the box is filling up fast)
THANK YOU!
m
It is legal to run the hots through the device.
But I think that is "just works better" to pigtail them and run a single wire to the recpetecal. For one think you only have to work 3 #12 wires back into the box rather than 4.
You be wrong dude. We're talking 15/20a 120v duplex receptacles here, not every receptacle on the NEMA chart:
NEC 2002 Table 210.21(B)(2) : For a 15a or 20a branch circuit supplying more than one receptacle (which we clearly have here) w/15a rated receptacle, the maximum cord-and-plug connected load (per receptacle) is 12a. For a 20a circuit w/20a-rated receptacle the maximum allowable cord-and-plug connected load is 16a.
Nothing to do with the continuous (3-hr.) 80% branch-circuit you're referring to.
So it makes sense in a shop to use 20a-rated devices.
Ed
Ed, that makes no sense at all. If, as a dumb user, I see a plug rated at 15 amps and I plug in a 1500 watt heater (continuous use) the heater will pull 13.6 amps at 110v and 12.5 amps at 120v.
However, if the 15 amp rated plug is designed at 18.75 amps (%80 derated from design ) then just looking at the rating of the devices, I am covered.
If I as a dumb user have to know the NEC before I can plug in a device, we would be having a lot more fires than we do now.
Look how many 1500watt devices with 15amp plugs are in common use in a home. at 120v each one of them is drawing more than allowed current as per your statment.
SamT
Sam -
You lost me somewhat with that thing about 18.75. The values being derated are 15 and 20, to 12 and 16.
You as a user don't need to know the Code. But those who install should (IMHO). And that table referenced is part of the Code.....you can get a copy and look at it yourself.
A 0.5a additional load (over 12a) on a 15a receptacle is hardly going to suddenly start a fire if the system is well installed. The Code has some built-in safety margins. The reason portable heaters are commonly 1500W is just so they CAN be plugged into 15a circuits/receptacles without overloading. If a full 15a draw would actually work safely on these circuits, then the heaters would being built at 1800W.
Ed
Edited 8/20/2003 10:29:39 PM ET by Ed
BTW......your math is wrong in the first sentence. If a simple resistance heater is designed to operate at 120v and use 1500W of power, then reducing the voltage to 110v would have a significant effect on the amp draw .....because of Ohm's Law.
The resistance is fixed (agreed?) Volts=Amps X Resistance. 120 divided by 12.5a = 9.6 . So the resistance of the heater is 9.6 ohms. Apply 110V to that and 11.5a flow. 110 X 11.5 = 1265 Watts. Big difference in output.
Ed
Ed, My math is correct, your understanding of what I said is wrong.
18.75 x %80 = 15
1500W @ 110V = 13.63636363... Amps That is %13+ higher than your 12 amps actual for a 15 amp rated socket.
And the NEC will never require that the actual allowed amperage be lower than the rated amperage.
The following does seem to support you:
copied from http://www.ultraviolet.org/mail-archives/beowulf.2002/2685.html
For what it's worth, an earlier section (B)(2) is also of interest (B)(2) Total Cord-and-Plug-Connected Load Where connected to a branch circuit supplying two or more receptacles or outlets, a receptacle shall not supply a total cord-and-plug-connected load in excess of the maximum specified in table ...
circuit rating/recep rating/max load 15 or 20 / 15 / 12 20 / 20 / 16 30 / 30 / 24
Although, how the NEC expects an electrician to control this, or a home owner to know this is beyond me.
The code does allow 15A rated sockets on a 12ga line and a 20A socket (not a 20/15) does not allow one to plug in a 15A plug.
SamT
Hi Sam -
I had to think about this a while before replying 'cuz I don't want to get into a hassle w/you (or anyone else here). There's a lot of confusion and disagreement of electrical theory and Code out there, even amongst electricians and inspectors.
So, one thing we do when we debate is to cite the Code. I stand by my statement that NEC 2002 Table 210.21(B)(2) limits the design current to 80% of the nominal value of a 15a or 20a 120v receptacle on a multi-outlet circuit. If you or anyone else disagrees, then please cite a specific section of the Code that supports your argument, or look at the Table and explain to me why it doesn't apply. I am always happy to expand my understanding of (what to conscientious electricians is) "The Good Book".
Re: 1500W @ 110v.................I was confused by your remarks because the electrical grid supplies, nominally, 120/240V to residences. So as far as I know , appliances made for this country are rated at 115v-120v. I thought you were making a common mistake, which is to think that the wattage of a simple resisitive appliance is fixed and that if less voltage is applied, then the amperage increases. But I understand that you were talking about 2 different heaters.
I agree with you that once the wiring is done you can't control what someone will do with it. We can only do the best we can to provide a safe reliable system. The Table is a "design" criteria. This means that when the system is installed, the electrician keeps in mind the usage of that system. This prevents for example the installation of a 15a duplex when you know that a large air-conditioner is going to be plugged in there. If you're wiring a work bench and there are going to be a couple of tools using 8a each, then it would require you to install at least two 15a receptacle outlets or one 20a duplex receptacle outlet.
And BTW, if you look at a NEMA chart, you'll see that a 20a125v receptacle is designed to accept both a 15a and 20a plug. There is no "20a plug only" straight-blade 120v receptacle that I know of.......I also looked in Leviton's catalog and they don't make one.
Peace and love.......................Ed
Edited 8/30/2003 8:38:49 AM ET by Ed
Ed,
Don't worry about pissin' matches with me. I am NOT an electrician, I AM an Electronics Technician with more training than some EE's.
In the house I am in now, all heating is with space heaters, so when I was remodeling I wanted to use 20A outlets, ran down to the bigbox and grabbed a handful... so, when I goes to install them, they had one blade at a 90° to the other. Could not use a 125V plug with them.
copied from http://www.ultraviolet.org/mail-archives/beowulf.2002/2685.html
For what it's worth, an earlier section (B)(2) is also of interest (B)(2) Total Cord-and-Plug-Connected Load Where connected to a branch circuit supplying two or more receptacles or outlets, a receptacle shall not supply a total cord-and-plug-connected load in excess of the maximum specified in table ...
circuit rating/recep rating/max load 15 or 20 / 15 / 12 20 / 20 / 16 30 / 30 / 24
************************************************
So, if I was wiring a house where the owner might use a 1500W, 12.5A space heater, then I would want to use 12ga wire and 20A outlets in all the wall outlets in order to meet code with a dumb HO like myself?
Don't take me wrong, please. I am really trying to learn here. I do understand that the code is the bare minimum and not the best possible.
SamT
Those receptacles that you got sound like they NEMA 6-20R's. Those are for 240 volts. The matching plugs look like the same as the 120 volt, 20 amps (5-20), but they are mirror images of each other.
Here is a chart of the different devices.
http://www.networkcable.com/pages/components/nema_nonlocking.html
Now "nominal" voltage ratings are a strange thing. While "everyone" calls them 110/220, the actual design standard is closer to 120, EXCEPT IN CALIFORNIA. It is a little confusing as it is not actually spec'd as a design standard value, but rather max and min's. I found some references to this online ast some point and in CA they lowered the miniumum spec a couple of years ago when they where having the power outage.
At one time, probably about 20-30 years ago 117 volts was nominal.
And for some historic reasons. motors are rated at 115 volts, while all other loads else rated at 120.
BUT, wiring devices are rated at the "maximum" voltage, so they are labeled 125/250 volts. I use "maximum" because, if I remember correctly, that report that I found allowed 127 or 128 for the maximum allowed supply voltage. And actually there are too different sets of standards. One is the allowed range at the meter, the other is the allowed range of voltages at the outlets.
And other interesting thing that I found was that with all of the standardization that is going on in the European common market that while all of the contries used "240", 50 hz different countries had different ranges of values for the voltage. Some might have been 225-240, other 230-250, other 2435-250. So they just said that equipment had to work over the full range of voltages.
So, if I was wiring a house where the owner might use a 1500W, 12.5A space heater, then I would want to use 12ga wire and 20A outlets in all the wall outlets in order to meet code with a dumb HO like myself?
Right. And you could go home and sleep well knowing you had done a nice installation that would hold up for a long time.
Don't take me wrong, please. I am really trying to learn here. I do understand that the code is the bare minimum and not the best possible.
SamT
Thanks Sam...........talk to you again..................Ed
"If you're wiring a work bench and there are going to be a couple of tools using 8a each, then it would require you to install at least two 15a receptacle outlets or one 20a duplex receptacle outlet."
Or ONE 15amp DUPLEX receptacle.
There is even a footnote in that section refering to the definition of a receptacle in seciton 100.
Well, somebody makes those receptacles. I have a duplex one in a drawer out in my shop. Bought it at the local farm supply store. Then never used it.<G> Have the cord end to plug into it too. It takes a 20 amp plug, but won't take normal straight blade plugs. Was gonna use it for a 220 outlet.
I didn't use it because I found some twist lock 3 and 4 pin 30 amp male and female cord ends at the local hardware store. They were clearancing them for a quarter each, so I bought all they had. Best $3 I ever spent.<G>
Did you check out the link that I posted.
I suspect that you have a 240 volt device.
I didn't check out the link. I think it was rated for 20 amps 220. But, the plug fits a 110 20amp outlet, so it could be used for either.
Not totally sure why you'd want to put in a 110 outlet that took special plugs that don't work in anything else, but you could. When I bought it I just wanted something different for a 220 outlet that couldn't be plugged into a 110 by mistake. Opps, my garage now has all 20 amp outlets, so if I used this, that 220 device could plug in anywhere. Doubt I'll ever use the receptacle anywhere.
I did buy a used pressure washer that draws 17 amps. I may put the plug on the end of the cord so that it can't be plugged in to a normal extension cord, then building a heavy extension cord that'll take 20 amp plugs. That thing got plugged into a 16 gauge extension cord once, opps. Bogged way down then popped the breaker.
Only problem is that the outside outlets and bathroom outlets are on the same GFI circuit. I try to make sure that the curling irons ect. are turned off when the pressure washer is going. Need to add some exterior outlets on another circuit.
Hey Mitch, i ain't an electrician and not even a canadian,but why not use conduit and pull 12ga. wire from 3 colored spools to each box. Where there's A wheel there's a way, got any wheels?
First you can use too different color recptecals one for each leg.
By code you don't need to use a 240 breaker as eacy device will only 120 volts on it. But there is no reason why you can't use the 240 breaker and yes it is still 20 amp.
Well, several options.
If you need the outlets GFI protected (good idea in a garage), then the easiest way is to run it with two runs of 12-2. That way the first outlet in each string can have a GFI outlet in it which feeds all outlets downstream. This way you can buy cheap GFI's ($6-7 ea.). Cheap GFI's are rated at 15 amps, but 20 amp feed-through. Which means they're capable of supplying a full 20 amps to the downstream outlets.
I've read that a 220 GFI breaker will work with 2 110 legs sharing a neutral, but am not certain of this, and wouldn't do it this way myself unless I was. But, in your situation, I'd try to find out, because if this works, it'd reduce the wires in each box from 12 plus pigtails to 8 plus pigtails which'd be a big help. If you can use a 20 amp 220 GFI breaker, which I think you can, that's how I'd do it.
Otherwise, I'd put in a 20 amp 220 breaker and use 2 legs of 12-2 wires. The first box would contain 2 GFI outlets which would feed the rest of the string. The 220 breaker would ensure if it was shut off everything in the box would be dead.
As far as the best way to wire the outlets in. I think it's with pigtails. The wires coming into the box are wire-nutted to those going out of that box to the next box, with a short length of wire connecting the outlets (the pigtail). This is fairly quick, and very reliable, also easy to modify later if needed, and no downstream outlets are dependant on those upstream (excepting in a GFI outlet). Green grounding wirenuts (the type with the hole in the top for running a wire through) will help make the inside of the box neater. Don't forget to ground the metal boxes if used (I'd use metal boxes myself for the increased durability).
If you don't need GFI protection, then 12-3 works fine. I'd personally still wire it to a 220 breaker so both outlets are shut off when the breaker is shut off. This also helps balance your power load, since you're running things on both legs of your electrical service. With two 110 breakers, you could be running both of the same leg of incoming power, unless you're careful to make sure they're plugged into different legs at the panel.
I'll be quiet now, hope my blather didn't just confuse things further.
it's basically so i can run a big shop vac and task lighting at the same time as a sander, miter saw or router, plugged in more or less next to each other but still have them on separate circuits.
Just a thought, my preference is to run the router, saw or sander through the shop vac - and use a vac that automaticly switches on and off as you use the tool. Then you only "need" two outlets - 1 for the lights and one for the vac.
actually i have a fein turbo II that i can do that with for some stuff, but a few of the bigger toys exceed the amp rating for the vac outlet and/or the total breaker capacity. it doesn't take many amp-sucking 110v tools to go over 20a- just the vac and a 3hp router or scms will do it. i also prefer to minimize voltage drop and general strain on the system by making everything as much below capacity as practical.
m
In some respects it's lucky I live in Australia where a standard outlet is 240V at 10A. My Festo vac can power a 2.7 hp tool through its switched outlet.