20 amp wire on 15 amp breaker?

Status
Not open for further replies.

growler

Senior Member
Location
Atlanta,GA
romeo said:
Sounds to me like a home owner doing wiring thinking that he did a great job because he over sized the conductors,then violated the conductor fill.


How would reducing the the breaker size help with conductor fill? It's still a #12 wire and has to be counted as a #12.

I have wired many homes using #12 on 20 Amp. breakers. I buy deep boxes. What ever the load is that's normally plugged in will not change but the voltage drop will be less.

There is an added advantage to using 20 AMP circuits. A vacuum cleaner can be plugged into any circuit without tripping. Many people now have such things as treadmills and humidifiers. You don't know where people are going to plug in some of their heavier loads. Bedrooms often become home offices ( for at least one of the owners ).

The advantages of using #14 Ga. wire is that it's cheaper and easier to work with. If you check the voltage drop on #14 you will see that it gets above 10% on many long runs. Just because the 5% overall voltage drop is only a suggestion and not enforceable doesn't mean it's not a good idea.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
larry fine said:
The reason you can't place a 20a receptacle on a 15a circuit is that the slot shape of a 20a receptacle implies that the circuit is capable of supplying equipment that comes equipped a 20a plug

Larry,

I used to believe that was true and I always followed that rule of thumb. However, if you read 210.20(B)(1) you'll find that you can put a 20 amp single receptacle on a 15 amp circuit (although I don't know why someone would ) but you cannot put a 15 amp single receptacle on a 20 amp circuit.

If you see 20 amp duplex receptacles you can't assume that the branch circuit serving those receptacles is rated at 20 amps. The 20 amp rating is for the receptacle and does not imply that the branch circuit is rated for 20 amps. While I think it kind of wierd that someone would go to the expense of installing 20 amp receptacles on a 15 amp circuit, the NEC doesn't prevent you from doing this.

Phil
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
goldstar said:
Larry,



If you see 20 amp duplex receptacles you can't assume that the branch circuit serving those receptacles is rated at 20 amps. The 20 amp rating is for the receptacle and does not imply that the branch circuit is rated for 20 amps. While I think it kind of wierd that someone would go to the expense of installing 20 amp receptacles on a 15 amp circuit, the NEC doesn't prevent you from doing this.

Phil


Phil,

20 amp duplex receptacles are not permitted on a 15 amp circuit. Did you mean to say " 20 amp single receptacles"?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
infinity said:
Phil,

20 amp duplex receptacles are not permitted on a 15 amp circuit. Did you mean to say " 20 amp single receptacles"?
That's the oddity of it all why can't you use a 20amp receptacle on a duplex but you can on a single. I wonder if the wording of that was poorly done and that the intent was not to allow a single 20 amp receptacle on a 15 amp circuit. It doesn't make sense to me. I guess it doesn't much matter because very few of us would want to put a 20 amp receptacle on a 15 amp circuit anyway
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Dennis Alwon said:
That's the oddity of it all why can't you use a 20amp receptacle on a duplex but you can on a single. I wonder if the wording of that was poorly done and that the intent was not to allow a single 20 amp receptacle on a 15 amp circuit. It doesn't make sense to me. I guess it doesn't much matter because very few of us would want to put a 20 amp receptacle on a 15 amp circuit anyway


Part of the reason that it's permitted is that there are occasions when a larger single receptacle is used with a smaller OCPD. For example a 40 amp range circuit is often used with a 50 amp cord and plug and with a 50 amp receptacle.
 

iwire

Moderator
Staff member
Location
Massachusetts
Dennis Alwon said:
I wonder if the wording of that was poorly done and that the intent was not to allow a single 20 amp receptacle on a 15 amp circuit.

I think part of the problem is many people only think of 15 and 20 amp receptacles.

But 210.21(B)(1) is about all size receptacles.

Lets say I have a piece of mobile equipment that is cord and plug connected. This equipment requires 480 volt 3 phase 4 wire @ 65 amps.

I will have to use a 100 amp plug and receptacle as that is the next standard size, but there is no need to supply this receptacle with a 100 amp branch circuit. As a mater of fact this equipment with a 65 amp MCA might have a maximum overcurrent device rating of 80 amps.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
iwire said:
I think part of the problem is many people only think of 15 and 20 amp receptacles.

But 210.21(B)(1) is about all size receptacles.
I guess that's correct. I am thinking of 15 and 20 amp receptacles. Specifically it is hard to understand why one can put a single 20 amp receptacle on a 15 amp circuit yet they cannot put a duplex 20 amp receptacle. It seems more probable that a single 20 is more likely to get a larger load plug in but in either case the breaker is there to protect it at 15 amp so I don't see the issue. I understand the code I am just trying to make sense of it-- that may be an impossible task. Bob and Infinity thanks again for your willingness to go the extra mile for all of us.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
infinity said:
20 amp duplex receptacles are not permitted on a 15 amp circuit. Did you mean to say " 20 amp single receptacles"?
Trevor,

We had this discussion some time ago and I always thought you were not permitted to have 20 amp duplex receptacles on a 15 amp circuit but the majority of the respondents did not agree with me. I'll try to find the thread and post it here.

Regards,

Phil
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
I think the main reason I used 20A single receptacles on 15A circuits in residential was because that's all the supply house stocked regularly.

Generally, the single receptacle was used for a sump or something like that, on an individual branch circuit, that was unlikely to be unplugged (and would be used contrary to the intent of 210.8 if it were).

I have to admit, whenever I used a single receptacle, I never gave much thought to whether the circuit was an individual one or not, because I knew the load of the appliance I was connecting to it. Not good code-compliant practice, but I never gave it much thought.
 

iwirehouses

Senior Member
Wow...thats an odd code putting a single 20 recept. on a 15 amp breaker. I don't think I could ever do that. One thing that has flagged me about this thread though is the advantages to running 20 amp circuits versus 15 amp circuits. My brother and I have been trying to figure this out for a long time. I always run 12/2 on residential branch circuits no matter what. I could never figure out why there is so much 14/2 in a house. Honestly, with an electricians mentallity of "do it the best way the first time", I can't see the extra effort be a factor with laying 12/2 considering it will be there forever. And for the extra 20 bucks per 250ft. cost really isn't an issue either considering it will be there forever. This is why I always reccomend running 12/2, 20 amp circuits, no matter what. Am I wrong in thinking this? Once again, my brother and I have been pondering this for a long time? I think any quality electrician would rather deal with the extra effort to reduce the risk of homeowners tripping breakers.
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
iwirehouses said:
I think any quality electrician would rather deal with the extra effort to reduce the risk of homeowners tripping breakers.
There's more to the potential of tripping breakers than just the size of wire used. Circuit layout is nearly as big a component as wire size, IMO.
 

iwire

Moderator
Staff member
Location
Massachusetts
iwirehouses said:
This is why I always reccomend running 12/2, 20 amp circuits, no matter what. Am I wrong in thinking this?

I think your wrong if you simple always automatically, without thought choose 20 amp circuits.

I think any quality electrician would rather deal with the extra effort to reduce the risk of homeowners tripping breakers.

I have one 20 amp circuit with 8 duplex's connected to it.

I have two 15 amp circuits each with 4 duplex's connected to them.

Assume they all serve living rooms and bedrooms.

Which circuit is more likely to be overloaded?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
iwirehouses said:
I always run 12/2 on residential branch circuits no matter what. Am I wrong in thinking this?
I use to run the entire house with 12 gauge wire myself but it got more difficult with the more resent desire for decora switches and having to ground the switches. There are some disadvantages to 12 gauge beside the cost. 12/2 takes up more space in the switch box which in turn gives the switches and esp. the dimmers little room to breathe. Heat becomes a factor. At times with a 3 way and a 4 ways in one box with the 3 way as a dimmer it gets difficult to JAM those wires in the box. With some of the newer dimmers you can also dim from all the locations which in turns fills the box to uncomfortable levels. I still wire my receptacles in 12 gauge and I know many on this forum think it is a waste of money. In most cases they are probably right but I feel better knowing that if someone needs to plug in a heavier load there should be enough current there for that.
If you think about the lighting load ahead of time and don't load it up to capacity then there shouldn't be a problem using 14 gauge wire. There is always a chance the HO comes home with a fixture that will pull half the circuit ( I have had that) but if it is a big house you know that dining room and foyer and other area lights may be a watt hog, not a warthog.
 

bikeindy

Senior Member
Location
Indianapolis IN
iwirehouses said:
Wow...thats an odd code putting a single 20 recept. on a 15 amp breaker. I don't think I could ever do that. One thing that has flagged me about this thread though is the advantages to running 20 amp circuits versus 15 amp circuits. My brother and I have been trying to figure this out for a long time. I always run 12/2 on residential branch circuits no matter what. I could never figure out why there is so much 14/2 in a house. Honestly, with an electricians mentallity of "do it the best way the first time", I can't see the extra effort be a factor with laying 12/2 considering it will be there forever. And for the extra 20 bucks per 250ft. cost really isn't an issue either considering it will be there forever. This is why I always reccomend running 12/2, 20 amp circuits, no matter what. Am I wrong in thinking this? Once again, my brother and I have been pondering this for a long time? I think any quality electrician would rather deal with the extra effort to reduce the risk of homeowners tripping breakers.

We have been having this discussion in another thread. You are wasting money time and effort using all 20A branch circuits. It is all in the design, rethink how you are wiring homes is my oppinion. when you use 4500 ft of wire in a home tell me that $20/250ft doesn't matter, not to mention the difference in time to run it, and make it up.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
iwirehouses said:
And for the extra 20 bucks per 250ft. cost really isn't an issue either considering it will be there forever.
Why can't we have more guys like you competing in my area ???
 

romeo

Senior Member
20 amp wire on 15 amp breaker

20 amp wire on 15 amp breaker

growler said:
How would reducing the the breaker size help with conductor fill? It's still a #12 wire and has to be counted as a #12.

I have wired many homes using #12 on 20 Amp. breakers. I buy deep boxes. What ever the load is that's normally plugged in will not change but the voltage drop will be less.

There is an added advantage to using 20 AMP circuits. A vacuum cleaner can be plugged into any circuit without tripping. Many people now have such things as treadmills and humidifiers. You don't know where people are going to plug in some of their heavier loads. Bedrooms often become home offices ( for at least one of the owners ).

The advantages of using #14 Ga. wire is that it's cheaper and easier to work with. If you check the voltage drop on #14 you will see that it gets above 10% on many long runs. Just because the 5% overall voltage drop is only a suggestion and not enforceable doesn't mean it's not a good idea.

I must repeat. My question was for other than voltage drop what is the advantage to increasing conductor size? In this case a #12 on a 15amp breaker.

If you chose to wire a home using #12wire on a 20amp breaker that is fine because you have increased the ampacity of the circuit,but if you use 15amp ocp there is no advantage other than compensating for voltage drop.(and that is fine)

Vacuum cleaners treadmills and humidifiers are common appliances and I doubt that they would cause tripping of a 15amp circuit as they would not likely to be used at the same time

We all have often hear on this forum that what if is not a code issue,and it seems to me that your response is just that,but that is not a bad thing unless you are trying to price in a completive market.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
iwirehouses said:
And for the extra 20 bucks per 250ft. cost really isn't an issue either considering it will be there forever.
Why can't we have more guys like you competing in my area ???

Trevor,

I'm not sure I was correct in my original statement but here is the link from a discussion we had regarding this subject back in 2005. Bennie was still around at that time.

http://forums.mikeholt.com/showthread.php?t=64723&highlight=goldstar

BTW, where does it state (in the NEC) that you cannot put 20 amp rated duplex receptacles on a 15 amp circuit ?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
romeo said:
Vacuum cleaners treadmills and humidifiers are common appliances and I doubt that they would cause tripping of a 15amp circuit as they would not likely to be used at the same time.
Maybe not, but one reason I like separating lighting and receptacle circuits (and while I'm at it, maybe using one or two fewer circuits to cover the same area) is that vacuuming day is when all of the lights are most likely to be all full-on.

In other words, among the benefits of doing it in kitchens and other work areas, like garages. I'd hate to be under the hood of a car with a running engine and have the lights go out because of some power tool or others.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
goldstar said:
http://forums.mikeholt.com/showthread.php?t=64723&highlight=goldstar

BTW, where does it state (in the NEC) that you cannot put 20 amp rated duplex receptacles on a 15 amp circuit ?


Right here:

210.21(B)(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) specifies that a 15 amp circuit cannot have a duplex receptacle rated at more than 15 amps.
 
Status
Not open for further replies.
Top