am I overloading my 15 amp breaker - Page 2

pvtschultz · 02-15-2012, 04:36 PM

Sorry to keep beating this horse, but I think that I've satisfied my curiosity and can put this to rest. I'm assuming that residential breakers are not rated at 100% but I can brew an entire batch of beer in under 3 hours so I'll pull 30 amps all I want and not worry about it.

Quote:

NEC 210.19, 210.20, 215.2, 215.3 and 230.42 permit conductors and overcurrent protection to be rated for 100 percent rather than 125 percent of continuous current “where the assembly, including the overcurrent devices protecting the [circuit] is listed for operation at 100 percent of its rating.” An important factor is that the assembly, meaning the switchboard, panelboard or similar equipment, is listed for operation at 100 percent of its rating as well as the OCPD. The additional current flowing will cause additional heat. If the assembly has not been listed for this application, temperatures may easily become excessive for the conductors and insulation.

http://www.iaei.org/magazine/2002/03/overcurrent-protection-and-the-nec/

**ajm163** · 02-15-2012, 05:21 PM

Quote:

Originally Posted by pvtschultz

I wish people would stop spreading the lie about the 80% rule on this forum, or at least use it appropriately. If you have a 15 amp breaker on a branch, you can use 15 AMPS CONTINUOUS, 24/7/365.25. 14 ga wire is rated for 20 amps minimum in residential settings per the NEC. But, the NEC also requires overload protection of 15 amps for 14 ga wiring. If you do the math, 15/20 = 75%. YOU WILL NOT EXCEED 80% CAPACITY IN YOUR HOME! I hate to yell like that, but internet electricians have been pushing this false fact for as long as I have been coming to this forum.

Source:
http://ecatalog.squared.com/pubs/Circuit%20Protection/Miniature%20Circuit%20Breakers/QO-QOB%20Circuit%20Breakers/0600DB0103.pdf

Now, I am a mechanical engineer, not an electrical one, but I know enough to know how to read and I have taken my share of EE courses. I do encourage someone to disprove me though if I am off base here.

As for wire ratings, I run 25 amps continuous through 14 ga conductors in my control panel. That 15/20 amp rating is only for bundled conductors. The rating is higher for single conductors in open air like in chassis applications. It all comes down to temperature rise and the NEC rules for residential applications are VERY conservative just because you never know.

Source - pg 184
http://std-wire.com/downloads/SWC_Catalog.pdf

I am an Electrical Engineer and I have to say the NEC differs with you greatly here. For circuits under a continuous load you should not size the circuit for more than 80% of the breaker size. I have designed equipment for the charging of electric cars that run at 32 amps and guess what they require a 40A breaker per the NEC. It is always better to be safe than sorry and follow building codes

cravej · 02-15-2012, 05:50 PM

Quote:

Originally Posted by pvtschultz

Sorry to keep beating this horse, but I think that I've satisfied my curiosity and can put this to rest. I'm assuming that residential breakers are not rated at 100% but I can brew an entire batch of beer in under 3 hours so I'll pull 30 amps all I want and not worry about it.

Scientifically, theoretically and by code, you can pull 30 amps for 2 hours and 59 minutes on a 30A breaker, but I've seen enough burned up switchboards that I wouldn't intentionally run it at it's maximum. The breakers do have thermal trips in order to drop the load when it starts to overheat, but what would happen if the breaker failed to trip?

redm18 · 02-15-2012, 05:55 PM

So based on the spirited debate here I could probably run everything on the circuit but as I am sitting somewhere around 15 amps if every single load is running at the same time its not the best idea in the world but likely won't burn my house down. I think I will probably just hook everything accept the mini fridge. My neighbor is an electrician and he has offered to help me install an additonal circut out to the garage so I will have him do that when he gets the time. Does this plan seem reasonable?

pvtschultz · 02-15-2012, 06:06 PM

The thing that will get you in trouble redm18 is the inrush or start-up current of the devices. Most appliances will have two current draw ratings, the starting current and the operating current; with the start-up being considerably higher than the operating for motors and other induction loads. Having extra capacity in the garage is never a bad investment; I wish that I had more than 20 amps available in mine.

wildwest450 · 02-15-2012, 06:16 PM

Quote:

Originally Posted by pvtschultz

The thing that will get you in trouble redm18 is the inrush or start-up current of the devices. Most appliances will have two current draw ratings, the starting current and the operating current; with the start-up being considerably higher than the operating for motors and other induction loads. Having extra capacity in the garage is never a bad investment; I wish that I had more than 20 amps available in mine.

Yes, but everything would have to start at the exacxt same time to overload it. That's a slim chance. Like I said, 3 freezers on one circuit, no problems.

pvtschultz · 02-15-2012, 06:28 PM

^^^Agreed^^^

redm18 · 02-16-2012, 04:44 AM

Upon closer inspection its a 20 amp breaker so a lot less worried

adam01 · 02-22-2012, 01:26 PM

The breaker is sized to protect the wire in the wall. I would recommend getting a second circuit from the elec nbr. ask him about up sizing the breaker. Or you could get a kill-a-watt and measure the actual amps used by each device.