residential circuiting

[ryan_618]

I am interested to know from some of the residential electricians out there how the requirement of AFCI's has changed the way you wire a house. Two examples that, as an inspector, I see are:
1) More devices on a circuit
2) Wires stapled much more gently.

 

[hurk27]

Re: residential circuiting

I'll bet you see more rooms on one circuit too as they will try to cut down on how many arc-fault breakers they have to use.
Had one the other day that had all the bedrooms on one circuit. The home owner was complaining of blowing the breaker.

 

[russellroberts]

Re: residential circuiting

Hasn't changed much for us. We generally always put bedrooms on their own ckt. before.Unless they were realy small.

I've always tried to staple romex as lightly as possible anyway.

We used to pull a 12-3 feed to adjacent bedrooms,now we pull 12-4 if feasible.

Other than the cost of the afci breaker,it just hasn't made much difference.

Russell

 

[ctroyp]

Re: residential circuiting

I agree that the reason for adding more devices to the arc-fault circuit is because the cost increase with the use of additional AFCI breakers. In most cases, except for small bedrooms, there are more that ten outlets that need to be served per BR circuit. I try to use ten as a rule of thumb, but have always streched it to twelve if needed.

As far as loose stapling, I wouldn't think it would be something that has changed just because of the introduction of AFCI breakers; since it has always been a possibility to short across the hot and another conductor and not just the neutral and another conductor. Although now we especially have to assure that there is no contact between the egc and the grounded conductor throughout the complete circuit to eliminate nuisance tripping and improper breaker functionality.

Back to the number of outlets, how do some of you other guys decide on the number of outlers per circuit? Just curious...

 

[bthielen]

Re: residential circuiting

I don't intend to sound critical so if I do please accept my apology. Since I am not a licensed electrical contractor I don't bid on electrical projects. Do you find that when bidding on projects the added cost difference of using two or three AFCIs really makes or breaks the sale? I recently purchased AFCIs for my home and they cost about $30.00 each retail while regular breakers cost about $12.00. This means that in my home I had to spend an additional $34.00 for the two AFCI breakers to use instead of regular breakers. It seems that if I were in the business and bidding an entire home or portion of a residential project, this added cost would be negligible. There really isn't any additional installation cost that I am aware of. Am I missing something?

ctroyp,
I rewired my entire home. There are calculations to determine the maximum number of outlets per circuit, although I don't recall the spedific code references as it was about 6 years ago. I do remember that the circuit calculations indicated a floor space area of service and 600sq.ft. for 15A and about 800sq.ft. for 20A circuits come to mind. If I remember correctly, I derated it to 500sq.ft. and 700sq.ft. just to be safe and my inspections passed without issue.

Bob

 

[ctroyp]

Re: residential circuiting

Originally posted by bthielen:
There are calculations to determine the maximum number of outlets per circuit, although I don't recall the specific code references...
Bob

Bob:
Thanks for the reply. From my understanding, there is no NEC article that specifies an exact number of outlets required--someone correct me if I'm wrong. Although, I do see that there may be standards used for estimates within a company.

To comment about the significance of the cost difference between standard breakers and AFCI's, I don't believe it is a large issue when estimating. I agree, $30 is not that significant. When bidding, all competitive estimates should cover this additional cost and no one should be dipping into their profit margin. In contrast, to cover what Ryan is asking, I believe that some contractors try and take the easy way out. Same reason they back stab devices instead of using the screws--which I disagree with. They are adding additional outlets to a circuit instead of running another feed. Maybe this is because they cannot run 14-3 feeds anymore for two circuits--who knows. lol

 

[tom baker]

Re: residential circuiting

Recepetacles in a dwelling unit are part of the general lighting load at 3 w/sf, see article 220 in the NEC. There is no NEC maxium number per circuit, however there may be local codes and ordinances. A typical limit is 12 to 13 per circuit, essentially the same as a commerical occupancy, which is computed at 180 VA per strap.

 

[Guest]

Re: residential circuiting

In the old days people plugged in 60 watt table lamps, or maybe a 100, or a 3-way bulb with a 150 watt. Now people plug in irons, 1500-watt hair dryers, 400-watt computer systems, 400-watt home theaters (or more), torchiere lamps at 300-watts, retrofitted track lighting, etc.

I used to figure 1.5 amps per receptacle-- so about 10 per 15-amp, and 13 per 20-amp. The 180-VA rules ends up being about the same. Anytime I have pushed beyond this I have gotten bit in the behind and had to retrofit another circuit in somewhere to split the load. This might involve sneaking out a piece of tongue-and-groove wall paneling, or cutting some pull-holes in the sheetrock-- and the patching that never quite looks right.

I'd rather throw in an extra circuit or two upfront than do a retrofit circuit split. Even being cautious there is always a chance for a gremlin.

[ September 16, 2003, 06:34 PM: Message edited by: awwt ]

 

[bthielen]

Re: residential circuiting

awwt,

You bring up a good point. The demand on the circuitry in both residential and commercial areas has increased dramatically over the years. Especially in the last couple decades. I wouldn't be surprised to find revisions in the code to address this issue. Either requiring minimum 20A circuits and/or increasing the calcuated 3VA load constant and/or setting limits on the number of outlets to name a few possibilities.

30 years ago the typical home didn't have all the electronic gadgets we consider common items today. Home computers, DVDs, VCRs, Microwaves, high power home entertainment systems, etc., in many cases were either too expensive or didn't exist yet.

Bob

 

[brejay]

Re: residential circuiting

As a matter of course we charge for each AFCI circuit so the more the better. As far as wiring for them try 14-2-2 or 12-2-2. It is meant to address the issue of two circuits one pull for AFCI's and GFCI'c. I find it to be cost effective.

With the addition of the cost and two new items to stock it has no effect on how we wire. We also have experienced no call backs in two years.

Jay

 

[tonyi]

Re: residential circuiting

Originally posted by brejay:
...try 14-2-2 or 12-2-2. It is meant to address the issue of two circuits one pull for AFCI's and GFCI'c.Jay

Cutler Hammer (and recently GE) make two pole AFCI breakers. Last I looked, the Cutlers were a bit pricy, but I bought some GE's for $70/ea at GE Supply in Miami. Still a bit more than two singles, but you can use a 14-3 or 12-3 and not have to contend with an up front 80% derating if its going through a hot attic. Southwire says the 14-2-2/12-2-2 stuff is supposed to be derated as if its run in pipe.

In a coolish area you're still OK, but in a 114+ degree attic (fairly common), the #12 will wind up having to be on a 15A breaker due to ambient temp derating added to the 80% the manufacturer says to derate up front.

The 14-2-2 becomes unusable if ambients go over 131 degrees. I've measured over 130 degrees in my mom's attic in FL on an 85 degree day where there was little breeze. On a 95 degree windless day I'm sure it could soar over 140.

 

[Guest]

Re: residential circuiting

Originally posted by tonyi:
<snip>I've measured over 130 degrees in my mom's attic in FL on an 85 degree day where there was little breeze. On a 95 degree windless day I'm sure it could soar over 140.

Christmas is coming. Maybe it's time to buy mama an attic ventilator

 

[russellroberts]

Re: residential circuiting

Doesn't nm-b use 90 deg.C rated conductors?

Russell

 

[tonyi]

Re: residential circuiting

Originally posted by awwt:
Christmas is coming. Maybe it's time to buy mama an attic ventilator

Indeed, that's one of the things on my to-do list for the place. During the day it gets so hot up there it almost takes your breath away. I'll go up, make a few splices in a j-box and come down soaking wet streaming sweat. The batteries in my 18V Milwaulkee only last about 1/2 as long as normal up there. At least I haven't passed out and fallen through the ceiling yet

 

[tonyi]

Re: residential circuiting

Originally posted by russellroberts:
Doesn't nm-b use 90 deg.C rated conductors?

Russell

Yes, it doesn't mean you can run that conductor up to 90 degrees though, you only get to derate from the 90 degree column, and then can't use that result as an excuse to exceed its nominal 60C degree ampacity, table 210.24 still applies.

At 100 amps or less we still have to treat it as 60C degree wire for other than derating calcs purposes.

 

[roger]

Re: residential circuiting

What do we use for adjustment, the highest temp ever recorded for the area, the lowest, or the average?

How long do we have to monitor the area one year, one decade, one century (they use one hundred year flood statistics)?

The 100 amp 60 deg rule is only if the componets aren't rated for 75 deg which is becoming the norm that most are 75 deg rated.


Roger

 

[tonyi]

Re: residential circuiting

Originally posted by roger:
What do we use for adjustment, the highest temp ever recorded for the area, the lowest, or the average?

CYA and Murphy's law IMO. If you use anything other than a worst case scenario, there could be liability issues if something bad happens. Some PI lawyer would eat you alive if it could be shown a system didn't consider reasonable variations in temps or possible failures of cooling gear like vent fans. There's some precedent in that insurance companies use things like 100 year flood planes.

My own feeling is planning for at least 140F in south FL attics is not unreasonable. The lights I put in mom's place near the peaks I did with #10 on a 15A breaker (there's aslo a receptical on that branch, so loads could go up with tools running). I also measured more than a 10 degree gradient from the peaks to the floor.

 

[roger]

Re: residential circuiting

Tony,

My own feeling is planning for at least 140F in south FL attics is not unreasonable

in reality even though south FL is over populated, begging for water from north FL, to stupid to curb development, test their lift station generators more strenuously than hospital specs, (obvious reason due to sardine can conditions) pump treated water into the aquifer, etc... they do not have a monopoly on the 140 deg attic temps. I would bet 90% of the Continental U.S. experiences these temps every summer.

Roger

 

[russellroberts]

Re: residential circuiting

Just for the record,I wasn't looking for an "excuse" to exceed a conductors ampacity,just asking a question.

Russell

 

[roger]

Re: residential circuiting

Hello Russell, I didn't take your question to be you were looking for an excuse to get around anything. (We know you better than that)

My question, although I agree with Tony , is not defined in the NEC.

The average residential circuit would never be loaded enough that attic temps would need to be considered in calculating an adjustment into the conductor.

Of course in my statement above I had not consulted (there's that word again) Chicken Little

Roger