Power load issue: Your thoughts


  #1  
Old 11-13-19, 07:47 PM
A
Member
Thread Starter
Join Date: Feb 2012
Location: USA
Posts: 322
Received 0 Votes on 0 Posts
Power load issue: Your thoughts

I've read that the max load for a circuit with 12 gauge wiring is 1920 watts. I guess that's when run continuously for 3 hours?
If so, how much can you push it up to that 2400 limit that trips the 20 amp breaker?

I have an Airbnb guest suite and just discovered this potential load issue. The circuit has 12 gauge wiring (20 amp breaker). On this circuit are:
41 watts worth of outdoor lights (if all were turned on)
625 watt Weathermaker Infinity furnace
PLUS a bathroom with Nutone ceiling fan with 1300 watt heater, 7.5 watt watt night light and a fan (unknown wattage) and about 64 watts of vanity lights. I keep a 1600 watt hair dryer in the bathroom too.

I'm thinking that I need to just disconnect the ceiling heater. What do you think? If it was just me using the bathroom then I would just proceed with care, but I have to assume that guests can't follow instructions.
 
  #2  
Old 11-13-19, 09:30 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 62,687
Received 1,615 Votes on 1,487 Posts
First question..... why is this all on one circuit ??

I would definitely recommend disabling the bathroom ceiling heater.
Is there other heat in the bathroom to keep it warm ?
 
  #3  
Old 11-13-19, 09:47 PM
A
Member
Thread Starter
Join Date: Feb 2012
Location: USA
Posts: 322
Received 0 Votes on 0 Posts
Yeah. Best to disable this ceiling heater. Fortunately all I have to do is unplug it up there. Easy task.
This is just the way the house was wired -- Poorly! Built in the 50's and electrical upgraded at some point, but just not enough!
No other heat in the bathroom. Shower is nice and hot though!
If I do hold this place out on Airbnb during the Winter then I will only do so when the weather is forecast to be unseasonably warm (night time Southern California lows in at least the mid-50's). And of course I'll warn the cold sensitive people that this stay will not meet their expectations.
 
  #4  
Old 11-14-19, 01:52 AM
A
Member
Thread Starter
Join Date: Feb 2012
Location: USA
Posts: 322
Received 0 Votes on 0 Posts
And what about running 2000 - 2100 watts for 5 or 10 minutes? Is that doable?
 
  #5  
Old 11-14-19, 08:57 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 62,687
Received 1,615 Votes on 1,487 Posts
Yes..... that is do-able.
 
  #6  
Old 11-14-19, 10:08 AM
Z
Forum Topic Moderator
Join Date: Sep 2005
Location: USA
Posts: 5,820
Received 204 Votes on 182 Posts
All circuit breakers have what's called a trip curve. Looking at a common 20A breaker, a load of 20-25A should trip between 5 minutes, or never. At 30A, the breaker should trip between 30-10 seconds. At any significant load or short, it should trip within a single cycle or less (1/60th second).

The idea is that a short overload (like when an AC motor starts up) won't trip the breaker - but either a small overload for a longer time, or a high overload for a short time will.

BUT, I would never design or expect a circuit to take that much!

Published Trip curve of a 20A QO breaker
 
  #7  
Old 11-15-19, 12:54 AM
A
Member
Thread Starter
Join Date: Feb 2012
Location: USA
Posts: 322
Received 0 Votes on 0 Posts
The electrical code states that 12 gauge wiring can never continuously be loaded to more than 80% which equates to 1,920 watts. How long is "continuously? 3 hours?
 
  #8  
Old 11-15-19, 09:28 AM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: United States
Posts: 10,853
Received 114 Votes on 101 Posts
625 watt Weathermaker Infinity furnace

I'd also put that furnace on a dedicated circuit.
 
  #9  
Old 11-15-19, 08:52 PM
F
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,495
Received 36 Votes on 28 Posts
The electrical code states that 12 gauge wiring can never continuously be loaded to more than 80% which equates to 1,920 watts.
What "electrical code" is that? Please cite exact chapter and verse.
 
  #10  
Old 11-16-19, 10:52 AM
A
Member
Join Date: Mar 2010
Location: USA
Posts: 4,510
Received 139 Votes on 128 Posts
While the National Electric Code refers to continuous versus intermittent use, continuous means likely to being turned on for periods of time exceeding 3 hours.

Most of the time a general purpose branch circuit will have different items plugged in and turned on for different periods of time. One not so large item on for more than 3 hours does not make the whole circuit in violation of code because another item on for a short time broughj\t the circuit up to 100% of amperage..


Meanwhile ...

(copied from another forum) If there is an appliance or device that is is left plugged in for frequent use or that is hard wired, and that uses more than half the amperes or watts for which the circuit is breakered, then the circuit should not have receptacles for general purpose uses on it. Unplugging the ceiling heater from its ceiling receptacle and putting the ceiling grill back on will remedy this situation.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: