15 Amp Devices on 20 Amp branches

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  #1  
Old 07-16-02, 05:45 AM
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15 Amp Devices on 20 Amp branches

I just realized I've been using 15 amp rated devices (outlets & switches) on 20 amp branches.
-Old house
-All 12 ga BX
Should I replace all of the devices with 20 amp rated?
or
Replace the breakers with 15 amp rated?
None of the outlets really require 20 amp service
 
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  #2  
Old 07-16-02, 05:56 AM
timgeorge
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The experts can verify this, but if the branch circuit is rated at 20 amps, you're fine with 15 amp devices. You shouldn't go the other way, 20 amp devices on a 15 amp branch since you'd pop the breaker all the time. I don't see any reason to downgrade the breaker to a 15 amp.

Hope this helps.
 
  #3  
Old 07-16-02, 07:27 AM
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I agree with Tim. What you have is perfectly fine. Millions of other homes have exactly the same thing.
 
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Old 07-16-02, 08:40 AM
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I disagree. The intent of the circuit breaker is to protect everything that is on the other side of it. If you have a 15 amp plug pulling 16 amps of current through it... it could cause some problems... the breaker would never blow though as long as it stays under 20 amps.
I know millions of houses use this, but that doesn't make it any safer. You probably will never have a problem with it, most devices rated at 15 amps will usually work higher than that. But that doesn't make it right either.
 
  #5  
Old 07-16-02, 09:11 AM
Sparksone42
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The overcurrent device is designed to protect the circuit conductors, not the equipment they are connected to. That's why they call these circuits general purpose circuits.
It has been a long standing practice to put 15amp receptacles on a 20amp circuit in the kitchen. There has never been any documented evidence that this practice has caused any kind of a fire. If there had been the code would be amended to change this long standing practice. One good example is the refrigerator, we run a #12 wire to the fridge and put a 15amp receptacle in to serve it. Have yet to see a fridge with a 20 amp plug, other than a subzero in multi-million dollar homes.
The code allows you to put receptacles of a smaller ampacity on a larger circuit. It will not however, allow you to put a larger receptacle on a smaller circuit. That would be a sure FIRE.
Rest assured that your installation is fine as it stands and I am sure that any local inspector in your area will confirm this for you. Give them a call explain your question and get their opinion.
As for the breaker not blowing as long as it stays under 20 amps, this is not correct. 20 amp breakers are designed to begin there trip cycle at approx. 16 amps. that would be 80% of the circuits rated capacity. If you look in the NEC, it will tell you that general purpose branch circuits shall not exceed 80% of their rated capacity. Even though the circuits we are talking about are more than likely in the kitchen and they would be considered small appliance circuits, they are still general purpose receptacles as they have no designated load. It could be a toaster, mixer, radio, TV etc. Don't bother with replacing the rec's. or the breaker that feeds them, you are a homeowner i am sure that something else will come up that will need attention!
 
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Old 07-16-02, 09:14 AM
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A 15-amp receptacle is called that because it accepts 15-amp plugs, not because it can only handle 15 amps. Since most of us don't have a testing laboratory handy, we rely on such testing to tell us what is safe. And they're telling us that 15-amp receptacles on 20-amp circuits are sufficiently safe. But we each get to decide for ourselves what makes us feel safe enough, so if anyone feels that they need 20-amp receptales for their comfort, there's no problem with using them on 20-amp circuits.
 
  #7  
Old 07-16-02, 08:20 PM
Wgoodrich
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John was right in his original reply to this post. Check out Table 210.21.B.2 and you will find that 15 or 20 amp duplex receptacles are allowed on 20 amp branch circuits whether commercial or dwelling settings.

As I read the rule that applies to all other receptacles whether 15 or 20 amp single receptacles or any receptacle rated in amps above 20 amps the receptacle must be sized equal to the amp rating of that branch circuit it serves. Read the following and see if you read the same.

406.7 Noninterchangeability.
Receptacles, cord connectors, and attachment plugs shall be constructed so that receptacle or cord connectors do not accept an attachment plug with a different voltage or current rating from that for which the device is intended. However, a 20-ampere T-slot receptacle or cord connector shall be permitted to accept a 15-ampere attachment plug of the same voltage rating. Non–grounding-type receptacles and connectors shall not accept grounding-type attachment plugs.

Hope this helps

Wg
 
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Old 07-17-02, 02:43 PM
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ok, so I was mistaken. And after your explanations I learned a few things. Thank you.

However, I still disagree that a 20 amp breaker will trip at 16 amps. They tell us to only load 80% because it gives us room for error... not because they blow at 80%. That extra 20% is a built in buffer to keep people from overloading circuits with poorly tested equipment. Imagine if they said 99% how many shortcuts and problems there would be.

Then again, I've been wrong before. Show me.
 
  #9  
Old 07-17-02, 03:08 PM
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kuhurdler, you are completely correct. A 20-amp breaker should not trip at 16 amps. If it does, it is defective. A properly functioning 20-amp breaker will handle 19.99 amps continuously for years. The 80% rule exists for other reasons, not because of how a breaker functions.

Sparksone42 was oversimplifying when he said that "if you look in the NEC, it will tell you that general purpose branch circuits shall not exceed 80% of their rated capacity." The NEC 80% rule only applies to a limited number of specific situations, and does not apply in general.
 
  #10  
Old 07-17-02, 04:07 PM
Matt Marsh
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There really is a simple way to look at this.

There are only two basic reasons that a 20 amp receptacle is ever needed. The first is where a 20 amp circuit has only one single (not duplex) receptacle, and the second is when you have a specific appliance that requires a 20 amp receptacle.

If an appliance requires a 20 amp receptacle, the manufacturer should have supplied it with a 20 amp plug. A 20 amp plug is one that has its neutral blade perpendicular to the hot blade. How many appliances like this do you have in your home? In all my years as an electrician, I have encountered just a few (you see them mostly on larger sized window type air conditioners).

Table 210.21b2 of the NEC limits the size of cord and plug connected loads that receptacles can supply where there is more than one receptacle installed on a branch circuit. It limits a 15 amp receptacle to a maximum of 12 amps, and it limits a 20 amp receptacle to a maximum of 16 amps. If a particular appliance draws more than 12 amps, it should have been supplied with a 20 amp plug.

Many moons ago I discussed this with a factory rep at a trade show. He claims that in most cases, the metal bussing inside a 15 amp receptacle are just as beefy as that of a 20 amp receptacle of same spec models. He also said that if anything, a combination 15/20 amp receptacle ( one with a T-slot) is more apt to loosen or wear out over time because of the more complicated contact assembly needed for the neutral side because it must accept both 15 and 20 amp plugs.

So as you can see, unless the plug on a particular appliance has been improperly modified, the maximum load ever supplied by a 15 amp receptacle is 12 amps. It has been my observation, that manufacturers tend to require a dedicated circuit when a specific appliance even nears the 12 amp mark, even though it was supplied with a 15 amp plug. Matt
 
  #11  
Old 07-17-02, 10:05 PM
reprosser
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Oh man ! I just replace 8 "15"amp (39 cent) outlets with "20" amp ($2 )outlets. Should have done more research, rather than accepting the first response (on a different forum) that I read.

I guess I have a 20 amp circuit with 20 amp outlets if I need it...maybe a new tool shop
 
  #12  
Old 07-18-02, 06:55 AM
Zathrus
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On the upside, those 20 amp outlets are far, far better constructed than that cheapo $.39 outlet. The 20-amp ones have a metal strip going around the back of the outlet, have much better quality screw downs, and probably use screw tensioned "push in" terminals rather than the cheap (and dangerous) unclamped push in terminals. Odds are the face is made out of unbreakable nylon composite instead of cheap plastic.

I avoid the $.39 outlets if I can find a decent 15 amp outlet for only a $1 or so more. It's worth the extra quality to me.
 
  #13  
Old 07-18-02, 08:41 AM
Sparksone42
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I think some of you misread what I wrote. I said that a 20 amp breaker will beging it's trip cycle at 16 amps! I did not say it would trip at 16 amps!!
Yes the extra 20% is a buffer. The fact that I referred to this as a general purpose branch circuit is absolutely correct. These circuits are general purpose because it is unknown when the house is built what specific appliance will be used with these outlets. Therefore, the general purpose designation applies.
When I say that the breaker will begin it's trip cycle at 16 amps that is kind of like a wake up call to the breaker. Those last four amps are critical in the trip sequence. The breakers that we use everyday are known as inverse time circuit breakers meaning that the amount of time it takes for the breaker to trip is inversely proportional to the amount of current flowing through the breaker. If you think that a 20 amp breaker will carry a full 20 amps before it trips you are mistaken. In the twenty years that I have been in this field the only 20 amp breaker that I have seen that will allow 20 amps to flow across it is an original FPE breaker. In my experience doing service work, any time a circuit has had 16 amps of load on it, as measured with an amprobe on the circuit in question, after about twenty minutes that breaker would trip. I am just relaying information that I have actually seen and this was not a one time event.

There are only a few limitied parts of the code where it will allow you to load a circuit to 100%. In fact in article 430 it will allow you to oversize the overcurrent protection as much as 250% for an inverse time breaker. Keep in mind that in this section they allow that because you are sizing all of the equipment in a specific manner spelled out in the article, so it is no longer general purpose.

Remember the code is interpreted differently by everyone who reads it. Get 8 inspectors together in one room and give them one question and maybe two of them will agree on what the code says about it.

Bottom line to all of this discussion is that it is perfectly ok to put a 15 amp rec. on a 20 amp circuit. I think that horse has been beat!!
 
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Old 07-18-02, 02:30 PM
Wgoodrich
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sparkone42, you said;

Remember the code is interpreted differently by everyone who reads it. Get 8 inspectors together in one room and give them one question and maybe two of them will agree on what the code says about it.

Opinion;

The statement you said is absolutely true to a fault. This fact that you stated probably is one of the most important positive results of these forums. The more deep discussions we have occur tend to help draw together a more uniform interpretation of the NEC. We have had many deep discussions providing many different view points on just one sentence in the NEC, yet in the end even if on very few occasions we come to an agreement as a whole what the true intent of that rule in the NEC means. That seeking of true intent of the NEC rules is the goal of many who frequent and read these forums. In my opinion and personal experience after the introduction of these forums on the net the uniformity of interpretation of the NEC has grown by leaps and bounds. When I travel to conventions and to teach seminars I have pleasantly experienced much more uniformity in the knowledge level and uniform interpretation of hte NEC. While the many instructors throughout the world make a huge impact, it is my opinion that these forums have made just as huge of an impact in uniformity and level of knowledge concerning the NEC. YOu and many more of us in this forum have attributed to the gain in knowledge and unifromity of interpretations of the NEC. While it is true that we have a long road to go, we have made great strides in the increased knowledge and uniformity of interpretations of the NEC thoughout the electrical industry.

Everybody stay in there we are all learning almost daily.

Wg
 
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Old 07-18-02, 05:41 PM
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Just as a point of reference, most smaller circuit breakers take just a few electrical cycles (about 100 milliseconds) of time to open. Once the mechanism is activated, it is an immediate response to open. There is no gray area between 80% and 100% where the breaker begins to open. Most breakers reach there trip value at 1000 seconds, as seen by the trip curve at the web site below.
http://www.geindustrial.com/products.../GES-6202A.pdf
From 1000 seconds on, the manufacturers don't document the characteristics of the breaker trip, but it is directly vertical.
 
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Old 07-18-02, 07:24 PM
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Ron, thanks for the graph. The key point for our discussion here is that at no point does the line on the graph go below the "1" multiple of current rating. This means that when the breaker is functioning as designed, it will never trip when carrying current below its rating (at least out to 1000 seconds, and it looks like the curve is asymptotic to the "1" line).
 
  #17  
Old 07-19-02, 06:32 AM
Wgoodrich
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Matt, just a thought on a rule found in the 2002 NEC that may change the outlook of using a 15 amp plug in a 20 amp receptacle. Try looking at the following rule found as a copied section of the 2002 NEC;

406.7 Noninterchangeability.
Receptacles, cord connectors, and attachment plugs shall be constructed so that receptacle or cord connectors do not accept an attachment plug with a different voltage or current rating from that for which the device is intended. However, a 20-ampere T-slot receptacle or cord connector shall be permitted to accept a 15-ampere attachment plug of the same voltage rating. Non–grounding-type receptacles and connectors shall not accept grounding-type attachment plugs.


Just a thought

Wg
 
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Old 07-19-02, 07:18 AM
Matt Marsh
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WG,

I guess I'm missing your point. But it could be because I just got home from working a midnight shift and my brain is mush LOL. You might have to spoon feed me this morning.

406.7 use to be 410-56(i). There was a slight change to the article in 99, but as far as I know the basic rule has been the same for quite a few years. They are just refering to a T-slot 20/15 combo receptacle. What am I missing? Matt
 
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Old 07-19-02, 07:39 AM
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Many thanks!!!

Many thanks to all for your responses to my question regarding 15/20 amp devices and breakers.
The strick interpretations are always very helpful.
-Then there's the practical application.
I'm going to stay with the 15 amp devices on 12 ga/20 amp circuits.
In the future, I'll use 20 amp devices.
 
  #20  
Old 07-19-02, 05:16 PM
reprosser
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After all this, I am not sure what the official answer is, but it seems that you can't go wrong with 20A breaker and 20A outlets. 15A outlets are probably not much risk, but the practical question is what the inspector will say when he finds 15A outlets on 20A line.

very interesting thread...
 
  #21  
Old 07-19-02, 05:37 PM
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the practical question is what the inspector will say when he finds 15A outlets on 20A line
Nothing at all.
 
  #22  
Old 07-19-02, 05:52 PM
Wgoodrich
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John is right saying nothing at all. It is most common that people use 15 amp receptacles and switches on 20 amp branch circuits and in generally accepted.

Matt, the above question is why I posted that rule allowing 15 amp equipment to be plugged into 20 amp T style receptacles. The way we have been answering this question caused me to fear that people would think that they shouldn't put 20 amp receptacles on a 20 amp branch circuit for fear they could not plug into them. We just never pointed out that while most common practice is to install 15 amp receptacles on 15 and 20 amp circuits, there is nothing wrong with using the 20 amp T style receptacles for general lighting use in a dwelling. Just didn't want all we were saying to mislead our intent on the subject and lead people to using only 15 amp receptacles thinking that all they should use.

Sorry if I didn't make my intent clear.

Wg
 
  #23  
Old 07-19-02, 05:53 PM
Matt Marsh
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Yep, I concur with John, the inspector will say nothing.

Again, the only time that the NEC requires a 20 amp receptacle on a 20 amp circuit, is either when you have an appliance that has a 20 amp plug (rare), or if the 20 amp circuit only serves a single (not duplex) receptacle.

I see now WG. Yes, if you want to install 20 amp receptacles, thats fine too. Matt
 
  #24  
Old 07-19-02, 08:09 PM
reprosser
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Thanks !

My thanks to everyone who provided information, and especially those who took extra time to make <even clearer> explanations to readers like me who are easily confused.
 
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