Hi;
I am reading the 2005 NEC, and found this interesting:
210.21 Outlet Devices. Outlet devices shall have an ampere
rating that is not less than the load to be served and
shall comply with 210.21(A) and (B).
Then, subpart (3), and table 210.21(B)(3)
(3) Receptacle Ratings. Where connected to a branch circuit
supplying two or more receptacles or outlets, receptacle
ratings shall conform to the values listed in Table
210.21(B)(3), or where larger than 50 amperes, the receptacle
rating shall not be less than the branch-circuit rating.
Table 210.21(B)(3) Receptacle Ratings for Various Size Circuits
Circuit Rating
(Amperes)
Receptacle Rating
(Amperes)
15
Not over 15
20
15 or 20
30
30
40
40 or 50
50
50
So, if I read this correctly, a 20A receptacle cannot be used on a 15A branch.
This makes no sense to me, since there is really no difference between a 15A and a 20A receptacle; at least not in the ability of each to carry at least the 15A load.
Notice that the 15A doesn't have the horizontal on the neutral like the 20A does this is meant to keep people from plugging in a 20A device (with the appropriate plug) from being plugged into a 15A outlet, and constantly tripping the breaker
It's just a preventative measure to keep someone from tripping breakers as you mentioned. I assume the other way around, using 15amp outlets on a 20amp circuit would be fine.
Outlet. A point on the wiring system at which current is taken to supply utilization equipment.
Receptacle. A receptacle is a contact device installed at the outlet for the connection of an attachment plug. A single receptacle is a single contact device with no other contact device on the same yoke. A multiple receptacle is two or more contact devices on the same yoke.
Sliver.. you gotta watch out on this forum we have some pretty sharp fellas here and they like this stuff.....
I wouldn't be surprised if your instructor might get caught on what Chris75 proposed to you. His hint came with the word 'Single' in capitals. Take a look at 210.21(B)(1) and see if you catch on.
Also don't let conductor size fool you as to the branch circuit rating especially when looking at the small conductors of 240.4(D). The circuit breaker determines the branch circuit rating not the conductor size. Just something I observe from time to time that is confusing to some new at the trade.
So, the way I read 210.21(B); It is acceptable to use a 20A receptacle on a 15A branch if there are no other outlets on that branch (a dedicated line).
However, if there are 2 or more outlets on the branch, that 20A receptacle cannot be used on a 15A branch.
That doesn't seem to make sense. Why would the 20A receptacle be acceptable as the only outlet on a 15A branch, but not if there are 2 or more?
Either way, equipment using that 20A receptacle, and drawing more than 15A would trip the breaker.
Yea I agree. I'm not an electrician and haven't studied the code extensively, but what makes sense to me is that you shouldn't use 20amp receptacles on 15amp circuits, and it shouldn't matter whether there is 1 or more outlets. I don't see any problem using 15amp recepticales on a 20amp circuit.
I have been buying the 20A receptacles, only because I thought they were constructed better. I never bothered to actually compare them together with the 15A kind, and this was before I began studying the code.
To be honest, I don't think I've ever seen a 20A plug!
I'm not going to debate that something in the code is reasonable or valid, since it goes through a lot of review before an article is amended or added.
It just takes some interpretation to understand what was intended.
If you remove the face of a 15 amp and a 20 amp receptacle of the same manufacturer, and look at the base and contacts of each, you'll find them identical. Both will accommodate either 15 or 20 amp plugs. The face configuration determines the rating.
It's less expensive for a manufacturer to build all bases and contacts the same, and simply install different faces for different ratings.
Different grades of receptacles certainly are made differently though. Most manufacturers have 4 grades of devices, some have 5, and some have even more. They are residential, commercial (also known as 'specification grade', engineers like those technical terms!), industrial, hospital, and high abuse. Some other grades are marine, explosion-proof, oil-tight, and likely a few others I can't remember at the moment.
Each of these grades must meet certain design and test specifications. For example, one of the many high abuse receptacle tests involves forcibly removing an angled plug (like a dryer plug) from the device by dropping a weight attached to the cord straight down, thus ripping the plug out of the receptacle. No damage may occur to the receptacle. I don't think a residential grade receptacle would fare too well here.
I will never buy a residential grade receptacle or switch. I know I can get them for $0.59 compared with the $2.59 I pay for the commercial grade, but I sleep a lot better when I know that I have a quality device that I won't have to replace in a year because someone dragged the vacuum cleaner a bit too far, and it ripped the plug out of the receptacle.
I have also had the experience (way back when I was 20+) of literally destroying residential grade receptacles because I tried to tighten the screws on the conductors as hard as I would a commercial grade one. The force broke the plastic separating the two screws on one side of the receptacle.
I think I still have enough strength in my hands to do that today, even though I'm twice that age now<g>
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