Replies

1. 
   cliffy | Jan 29, 2008 06:51pm | #1

   With the exception of camping trailers I can't think of any devices that require 120 volt 30 amp circuits.

   Have a good day

   Cliffy

1. 
   JDLee | Jan 29, 2008 07:04pm | #4

   I wasn't thinking of a single 120v device that would require that much juice.  I was thinking about a circuit I'd like to add to my garage which might have a couple of fairly heavy 120v loads running at the same time.  What do you think?

2. 
   IMERC | Jan 29, 2008 07:46pm | #8

   water heaters, some range tops 

   Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming<!----><!----><!---->

   WOW!!! What a Ride!Forget the primal scream, just ROAR!!!

3. 
   McDesign | Jan 29, 2008 08:29pm | #13

   < camping trailers >

   Yep; got one to plug my camper (office) in in the barn so I have AC and refridge and all.  Special plug.

   Forrest

2. 
   Scott | Jan 29, 2008 06:59pm | #2

   I don't think there is anything wrong with it. Just make sure you have the right receptacle and plug. As said above, it's common with RV applications.

   I have both push-in and twist lock 30 amp connections. I prefer the twist lock.

   Scott.

   Always remember those first immortal words that Adam said to Eve, “You’d better stand back, I don’t know how big this thing’s going to get.”

3. 
   RobWes | Jan 29, 2008 07:02pm | #3

   Common on boat docks also

4. 
   renosteinke | Jan 29, 2008 07:14pm | #5

   In theory one might; this is sort of what is done in commercial places, where a particular piece of equipment is moved about.

   For your house, though, there are a few problems.

   The 'normal' receptacles, of both the 15 ans 20 amp ratings, are all required to be able to handle 20 amps. They are not rated for more than that.

   The 'normal' receptacle circuit is something of an exception to ordinary practice. The normal practice is to size a circuit to it's load, choosing the wire and breaker to provide the maximum amount of safety. That is, an appliance that needs 27 amps will get a 30 amp breaker, while a 23 amp appliance will get a 25 amp breaker. We want that breaker to trip as quickly as possible, should there be a fault.

   With your 'convenience' circuits, we have no idea what appliances will be used. It is considered that it is more important that there be little reason to use extension cords, so the bias is on having more receptacles. Overload protection is, as a result, nowhere near as good as with a dedicated circuit. So, the breaker often will trip only for a major fault. In a very real sense, that breaker is there to protect the wiring - not the appliance.

   Commercial application often ave something that could be considered as the equivalent of a massive 'branch circuit' powering many machines. It is critical to note that these arrangements had separate overload protection at each 'tap' or machine on the circuit ... household appliances do not have this protection.

   Finally, there is the very real practical drawbacks to using larger wire. #10 wire is a lot harder to work with, or to fit in the box.

1. 
   JDLee | Jan 29, 2008 07:40pm | #6

   Thanks for the response.  That's some very good, logical information.

   Here's my particular situation:  I have one wall that is only 15' from my breaker box.  I would like to install a few workbench outlets and an outlet that someday might be used for a refrigerator or freezer.  On the opposite side of that wall, I'd like to put an outlet that might be used for a treadmill.

   I'm guessing that a treadmill is the type of load that might require a dedicated circuit.  And I'm pretty sure an outlet for a refrigerator should have that.  But I'm certainly not sure where my treadmill might end up,  and I don't know that I'll ever have a garage refrigerator (I'm against it for conservation reasons, but I may need one).

   It seems that you are saying the main drawback with making this a 30 amp, 120v, 10 awg circuit would be the increased overload it would take to trip the breaker if a single device that doesn't need 30 amps were to malfunction, and that makes sense.  Hmmm...  I'm at least tempted to wire it with 10 awg (as I have enough on hand that I'd probably never otherwise use) and make it a 20 amp circuit and see if I ever trip it with that before considering going to 30 amp.  (The same way that some people wire 15 amp circuits with 12 gauge for safety and less resistance.)

1. 
   drh | Jan 29, 2008 07:51pm | #9

   How much room is left in your panel?If I understand correctly, you are just wanting to add regular receptacles (which are 15 amp), and are concerned that with the stuff you will be using, the circuit will get overloaded?If you have room to add two breakers, why don't you have one duplex receptacle dedicated to one 20 amp breaker, that you could use for the fridge, or treadmill, or whatever, and then do the rest of your receptacles on a second 20 amp breaker.I think that normal 15 amp receptacles are only designed to be used with #14 or #12 wire. As well, you don't want a 15 amp receptacle on a 30 amp breaker.Someone with more electrical knowledge can probably jump in and comment on the treadmill, but FWIW, everyone I know with a treadmill just has it plugged in wherever it is convenient.

1. 
   JDLee | Jan 29, 2008 08:11pm | #11

   That's a good point.  I can't remember why I didn't want to do that.  I'm partly just asking for informational purposes.

2. 
   renosteinke | Jan 30, 2008 04:10am | #20

   In a situation such as you describe, we have an accepted way of making everybody happy. We install a 'sub' panel. In your example, you might put a two-pole 30 amp breaker in your panel, and use that to supply a small panel located elsewhere. This new panel will have a variety of 15 and 20 amp breakers, to serve the various loads. Since you are unlikely to ever be running everything at full power, at the same time, the feed to that panel will never come close to using the full capacity of that 2 pole breaker ... yet, each branch circuit will be protected at a reasonable level.

2. 
   rasconc | Jan 29, 2008 07:45pm | #7

   Great explaination.  He could go ahead and run 10 to the first box and then go to the others with 12  and put it all on a 20 amp.  Would help with VD (but not other std's (:-)).  But not a great idea in case someone saw the 10 in the panel and decided to replace it with a 30 not being aware of the downstram 12ga. 

1. 
   JDLee | Jan 29, 2008 08:10pm | #10

   You're right about somebody confusing that later.  I would never mix cable on a circuit for just that reason

3. 
   BillHartmann | Jan 29, 2008 08:18pm | #12

   "The 'normal' receptacle circuit is something of an exception to ordinary practice. The normal practice is to size a circuit to it's load, choosing the wire and breaker to provide the maximum amount of safety. That is, an appliance that needs 27 amps will get a 30 amp breaker, while a 23 amp appliance will get a 25 amp breaker. We want that breaker to trip as quickly as possible, should there be a fault."BS. Look at any motor or AC circuit.On motor circuits you can have, depending on the type of circuit overload protection, of 175% to 800% of the motor load..
   .
   A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

1. 
   renosteinke | Jan 30, 2008 04:03am | #19

   Bill, you know better than that. There's no honor in setting up a straw man, only to knock it down. Motor circuits are like every other circuit - with the sole exception of out general purpose convenience circuits - where the size of the load determines the size of the overload protection.
   OK, maybe "nature of the load" is more accurate than saying "size." The code recognizes at least ten different types of loads, besides the general convenience circuit. Motors are but one of these instances (AC another).... and, like every other type of load, the code details overload selection as well as wire sizing. Nor, for this thread, is there any reason to differentiate between 'overload' and 'overcurrent' protection. What does matter is that the equipment to be used on a circuit has an important role in designing the circuit ... except when you're designing a general purpose convenience circuit. The loads on a convenience are completely unpredictable, and relatively small. Therefore, we place many more receptacles that we'll probably need, in the hope that some of them are in convenient spots. Such circuits are, however, limited to 20 amps. If you need more than that, then you need more than one circuit.

5. 
   BillHartmann | Jan 29, 2008 08:47pm | #14

   There are two basic type of circuits.

   General purpose, which have multiple receptacles and/or lights on it. And it is expected that any equipment from a 7 watt night light, to a 1500 watt heater, to an electric drill.

   The other type are dedicated circuits. Dedicated circuits the load is known and the wiring and overload protection can be carefully taylor to the application. Motor circuits often allow breakers and several times the motor load and the what is appropriate for the wire size.

   But the motor has it's own protection. Either internal overloads (which are common on most WW stationary equipment motors {-3 hp induction motors}) or motor starters for larger motors. The purpose of the overload device is only to protect the wiring from faults and not overloads from the equipment.

   A general purpose circuit is different.

   You have no idea of what combination of equipment that can be used a gneeral purpose circuit at only time. This the overload needs to protect against both small overloads, and large shorts.

   Also while the NEC ignores any protection of loads, it is clear that a combination of history in the developement of the code along with developement of the loads, via UL and the like, have coordianted the safety of the loads with the supply.

   And there MIGHT be reasonably levels of safety have device with common 15 amp plugs on circuits protected by 30 amps. But the standards have not developed that way. SO the research has not been done on that combination.

   One solution to this would be to run 2 circuits side by side (or one multi-wire circuit) and leapfrog the receptacels. You can use two different colors to id which is on which.

   Loads that draw more than 50% of the circuit capacity are suppose to be on a dedicated circuit.

   I like the British ring system. A circuit will be 30 amps/230 v and wired so that it starts and ends at the panel. I think that the wire size is about the same as #12. The plugs have fuses in them that are sized to the load.

   Basically is a distributed system with a sub-panel at each receptacle.

   Doing this you have both high power and some protection for the loads.

   .
   .
   A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
6. 
   DanH | Jan 29, 2008 10:21pm | #15

   You can't put standard outlets on a 30 amp circuit.

   If your view never changes you're following the wrong leader
1. 
   junkhound | Jan 29, 2008 10:30pm | #16

   You can't put standard outlets on a 30 amp circuit

   Think you mean 'the code does not allow' vs. 'can't put' ? <G>  Have seen a bunch of 20 A hospital grade outlets in non-buried conduit boxes on 200 C 10 AWG on a 40 A breaker even in one barn - (I know, bad, bad code breaker<G>)

    

1. 
   DaveRicheson | Jan 30, 2008 12:28am | #17

   Don't think you are likely to overload that puppy, but I bet you can slag those recepticles.

2. 
   JDLee | Jan 30, 2008 01:00am | #18

   For my garage and outside (and for something like a treadmill), I always use Leviton industrial outlets (not pro, not commercial, but industrial).  I hate the way extension cords tend to pull out of regular outlets.  I do protect them with GFI.