Dwelling Unit Receptacle Circuits

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WA_Sparky

WA_Sparky

Electrical Engineer
Location
Vancouver, WA, Clark
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Electrical Engineer
Hello all,

Typically whenever I design a dwelling unit plan (because of my commercial experience), I always default to 20A breakers and #12. I know many residential spaces end up getting 15A/1 breakers. I cant imagine the material cost reduction would be that significant since you can get bulk wire at discounted cost? Is the choice of 15A/1 over 20A/1 specifically due to material cost?

Second question. I have put a treadmill in a guest bedroom and it keeps tripping the breaker anytime I turn it on. I've figured out a surge protective device could be a potential solution. Even though that solution will work for me, I wouldn't want a future client to have to resort to that for a new build.

Do you think the problem wouldn't occur if the circuit had actually been 20A/1?
Do you think the problem is specific to the sensitivity of the AFCI breaker.
I may be totally in left field here, but ive been reading up on different types of breakers and their tripping characteristics (Type B, Type C, Type D). Do you think an alternate solution for preventing moderate inductive loads (treadmill) from tripping its breaker, would be specifying (or interchanging) the breaker with a Type C or Type D breaker for that given circuit?

I don't typically ever specify breakers this small unless there is a Fault current issue for series ratings so this whole type B,C,D is new turf for me.

Thanks,
 
wire prices crazy now but. A typical house 2-2.2 k sq ft. would cost around $500 more with all 12ga
2250' 14-2. and 700' 14-3 .
I did 69 apartments. I did everything :units, common areas, complete FA and video bla bla bla
you engineers always specify 12 ga. Ive done 4 or 5 large projects apartments, assisted and independent living buildings. 12 ga raises total costs $12-15k
you first have to determine if CB is tripping due to magnetic, arc fault or equipment level ground fault current
 
A treadmill is on the top of the list of things that trip AFCI breakers.
As far as the 12AWG vs 14AWG, along with the slight difference in price (any increase in price these days adds up) 15A is plenty large enough for most areas of the house. I use to use only 12AWG for new houses. Then after service calls in "McMansions", I saw that most general purpose outlets were 15A with no problems. So now I use 15A for all lights, and that really helps with box fill in multi-gang boxes, and also lowers the costs some. Of course, I have to run 20A circuits w/12AWG for the required 20A circuits. But unless I know there would be possible heavy loads, I run 15A for most all of everything not required to be 20A circuits.
 
Hello all,

Typically whenever I design a dwelling unit plan (because of my commercial experience), I always default to 20A breakers and #12. I know many residential spaces end up getting 15A/1 breakers. I cant imagine the material cost reduction would be that significant since you can get bulk wire at discounted cost? Is the choice of 15A/1 over 20A/1 specifically due to material cost?
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Well it isn't millions but it can be $500 or so. Now picture a community with 100 homes and you are given the op to wire them. Save even $100 on each unit then you have saved $10,000

Question. I have put a treadmill in a guest bedroom and it keeps tripping the breaker anytime I turn it on. I've figured out a surge protective device could be a potential solution. Even though that solution will work for me, I wouldn't want a future client to have to resort to that for a new build.
Click to expand...
Do you think the problem wouldn't occur if the circuit had actually been 20A/1?
Click to expand...

I pretty sure the threadmill is not tripping on overcurrent but rather as Little Bill mention, AFCI. Notoriously a problem for exercise bikes and treadmills.

Do you think the problem is specific to the sensitivity of the AFCI breaker.
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Yes

I may be totally in left field here, but ive been reading up on different types of breakers and their tripping characteristics (Type B, Type C, Type D). Do you think an alternate solution for preventing moderate inductive loads (treadmill) from tripping its breaker, would be specifying (or interchanging) the breaker with a Type C or Type D breaker for that given circuit?
Click to expand...

I know nothing about the type breakers or even if available in afci and small sizes for panelboards.
 
Thank you all for your input. Makes much more sense now why #14's are preferred. One of my biggest complaints when designing projects is the overall cost impacts, with respect to labor and material, are unknown. Lighting manufacturers do not share cost and it's hard to get an EC to sit down and clarify how they would have done the project differently, so thank you. I'll be sure to take advantage of the 15A/1 when possible to make everyone's lives (and wallets) better.
 
Dennis Alwon said:
Well it isn't millions but it can be $500 or so. Now picture a community with 100 homes and you are given the op to wire them. Save even $100 on each unit then you have saved $10,000
Click to expand...
For dwelling units if you use 20 amp circuits can't you use less circuits than if you used 15 amp circuits thus saving on costly afci breakers?
 
WA_Sparky said:
Thank you all for your input. Makes much more sense now why #14's are preferred. One of my biggest complaints when designing projects is the overall cost impacts, with respect to labor and material, are unknown. Lighting manufacturers do not share cost and it's hard to get an EC to sit down and clarify how they would have done the project differently, so thank you. I'll be sure to take advantage of the 15A/1 when possible to make everyone's lives (and wallets) better.
Click to expand...


Back in the days of olden we used, and still do, #12 on receptacles. We did that because many of the homes we wired were passive solar design and the people didn't want heating systems especially large systems. I decided that many of these people were going to end up with portable heaters so I wanted to be certain they didn't blow the circuit. Each bedroom had it's own circuit....

The point is sometimes it may be a good idea to think about what you are wiring. Certainly a MacMansion will probably not want portable heaters all around the house so #14 should be fine.
 
James L said:
14 vs 12

14 requires less box volume
14 is much faster to make up
14 goes on devices much faster
14 costs less
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14 requires a greater number of circuits to supply a given amount of available power in a given area.

I prefer using 20a circuits for receptacles (unknown loads) and 15a circuits for lighting (known loads).
 
Dennis Alwon said:
Back in the days of olden we used, and still do, #12 on receptacles. We did that because many of the homes we wired were passive solar design and the people didn't want heating systems especially large systems. I decided that many of these people were going to end up with portable heaters so I wanted to be certain they didn't blow the circuit. Each bedroom had it's own circuit....

The point is sometimes it may be a good idea to think about what you are wiring. Certainly a MacMansion will probably not want portable heaters all around the house so #14 should be fine.
Click to expand...
I am a big fan of dedicating a circuit for all bedrooms. I have a couple EE buddies that live together in an house. BR1 and BR2 are sharing a 15A circuit. BR3 and BR4 are sharing a 15A circuit. House is not equipped with AC, so BR1 and BR2 (sun beat walls) have window AC units. Each BR has their own Computer/workstation. Finally their Comcast router is also located in BR1. Because of the (2) window AC units (2) workstations sharing a 15A circuit, their router tends to drop quite frequently when their breaker pops.

Without rewiring the house their only temporary bandage of a solution was to get UPS's/surge protectors to keep their computers and routers online.
 
WA_Sparky said:
I am a big fan of dedicating a circuit for all bedrooms. I have a couple EE buddies that live together in an house. BR1 and BR2 are sharing a 15A circuit. BR3 and BR4 are sharing a 15A circuit. House is not equipped with AC, so BR1 and BR2 (sun beat walls) have window AC units. Each BR has their own Computer/workstation. Finally their Comcast router is also located in BR1. Because of the (2) window AC units (2) workstations sharing a 15A circuit, their router tends to drop quite frequently when their breaker pops.

Without rewiring the house their only temporary bandage of a solution was to get UPS's/surge protectors to keep their computers and routers online.
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I recently ran into a situation almost exactly like that. The lady was using her three-story home as a boarding house. Each person was running some kind of business out of their room, and everybody had window air conditioners. Blowing Breakers all over the place.

We ran 20a circuits to the exterior walls and piped up the outside and then back in, and around the room with wiremold.

Each room got a separate circuit for the receptacles. The lighting got left alone.
 
infinity said:
For dwelling units if you use 20 amp circuits can't you use less circuits than if you used 15 amp circuits thus saving on costly afci breakers?
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You can, but it's probably a trade-off

If you figure 20 ft of wire for each receptacle, you would add $2.40 per recep to go with #12

By the time you add more labor to work with the #12, you have matched the savings of your breakers
 
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