Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Electrical

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 07-13-2011, 12:33 PM   #1
Newbie
 
Join Date: Jul 2011
Posts: 16
Rewards Points: 10
Default

12 AWG wire adequate for 20A 240V (~19A continuous load)?


I am getting wiring done by an electrician for a ductless split AC system and for the condensor, this is the spec from the manufacturer.

It specs ~19A @ 208V with the voltage drop taken into account for all evaps operating, but only calls for a max breaker size of 20A.

I have two questions:

1. At startup, would the transients cause the breaker to trip even if its momentary?

2. Operating with all indoor evaps "ON", and drawing ~19A, there is only a 5% derating factor, I would be happy with at least 20%, are my assumptions incorrect? Should I have him run a 25A or 30A wire instead?

Any help is greatly appreciated and thanks in advance.
Attached Thumbnails
12 AWG wire adequate for 20A 240V (~19A continuous load)?-currentdraw.jpg  

ChootarLaal is offline   Reply With Quote
Old 07-13-2011, 01:52 PM   #2
Licensed Electrical Cont.
 
Speedy Petey's Avatar
 
Join Date: Feb 2004
Location: NY State
Posts: 6,858
Rewards Points: 2,020
Default

12 AWG wire adequate for 20A 240V (~19A continuous load)?


May I ask WHY you are questioning this???

Also, this is NOT a continuous load.

If the specs call for a max breaker of 20A then that is all you can do. NOT 25 or 30.
#12 is FINE for this.

Speedy Petey is offline   Reply With Quote
Old 07-13-2011, 01:56 PM   #3
Newbie
 
Join Date: Jul 2011
Posts: 16
Rewards Points: 10
Default

12 AWG wire adequate for 20A 240V (~19A continuous load)?


Ofcourse I would keep the 20A breaker, that is not what I am questioning. I am questioning the 20A wire rating versus the ~19A continuous load on it. I like the idea of derating and would like to have at least a 20% margin, so thats why I was asking if I should have my electrician run a 25A or 30A rated wire.

How is this not a continuous (steady state) load? What is that number then? Peak or transient?
ChootarLaal is offline   Reply With Quote
Old 07-13-2011, 02:16 PM   #4
Licensed Electrical Cont.
 
Speedy Petey's Avatar
 
Join Date: Feb 2004
Location: NY State
Posts: 6,858
Rewards Points: 2,020
Default

12 AWG wire adequate for 20A 240V (~19A continuous load)?


It is not continuous since it is not intended to run at full capacity for three hours or more.
The 19A is the full running load amps. It is not 19A all the time, just when everything is running.
My question is WHAT good would it do to oversize the wire, unless of course the run was very long, like over 100'??? What is the purpose of this "20% margin", and who told you you need it?
Speedy Petey is offline   Reply With Quote
Old 07-13-2011, 02:21 PM   #5
Newbie
 
Join Date: Jul 2011
Posts: 16
Rewards Points: 10
Default

12 AWG wire adequate for 20A 240V (~19A continuous load)?


Its an industry practice to derate, isn't it? I was simply taking a 20% derating factor into account for the wiring, even if it would run for <3 hrs, I don't think the accumulated heat over that period of time is good for the wire.

The run isn't very long, only about 25'. Isnt it just good practice to upgrade to a 30A wire, for example, to be on the safe side for this application?
ChootarLaal is offline   Reply With Quote
Old 07-13-2011, 02:31 PM   #6
Electrical Contractor
 
jbfan's Avatar
 
Join Date: Jun 2004
Location: Newnan GA
Posts: 5,855
Rewards Points: 2,106
Default

12 AWG wire adequate for 20A 240V (~19A continuous load)?


No!

You are pulling 16+/- amps at 240 anyway.
The manufactorer has already figured the calculations and i s safe with the rating they have posted.
It is also a code violation to not follow the name plate of the unit!
__________________
Yes I am a Pirate, 200 years too late. "Jimmy Buffett"
jbfan is offline   Reply With Quote
The Following 2 Users Say Thank You to jbfan For This Useful Post:
gregzoll (07-13-2011), Speedy Petey (07-13-2011)
Old 07-13-2011, 02:37 PM   #7
Member
 
joed's Avatar
 
Join Date: Mar 2005
Location: Welland, Ontario
Posts: 7,828
Rewards Points: 2,450
Blog Entries: 4
Default

12 AWG wire adequate for 20A 240V (~19A continuous load)?


#12 wire wire has a rating of 25 amps in the NEC tables. So that should satisfy your concerns. Other code sections limit its use to 20 amps maximum on general purpose circuits
__________________
Do not PM with questions that can be asked in a forum. I will not respond.
joed is offline   Reply With Quote
The Following 2 Users Say Thank You to joed For This Useful Post:
ChootarLaal (07-13-2011), Speedy Petey (07-13-2011)
Old 07-13-2011, 02:53 PM   #8
Licensed Electrical Cont.
 
Speedy Petey's Avatar
 
Join Date: Feb 2004
Location: NY State
Posts: 6,858
Rewards Points: 2,020
Default

12 AWG wire adequate for 20A 240V (~19A continuous load)?


Quote:
Originally Posted by ChootarLaal View Post
Its an industry practice to derate, isn't it?
Not in the way you are thinking. Not even close.

You are trying to out think the NEC. Personally I think you are over analyzing this whole thing. Let the electrician do his job.
Speedy Petey is offline   Reply With Quote
The Following User Says Thank You to Speedy Petey For This Useful Post:
Anti-wingnut (07-14-2011)
Old 07-13-2011, 08:23 PM   #9
Lic Elect/Inspector/CPO
 
Join Date: Apr 2011
Location: NJ
Posts: 369
Rewards Points: 250
Default

12 AWG wire adequate for 20A 240V (~19A continuous load)?


Quote:
Originally Posted by Speedy Petey View Post
Not in the way you are thinking. Not even close.

You are trying to out think the NEC. Personally I think you are over analyzing this whole thing. Let the electrician do his job.
I agree. The mfg and electrician know what is required.
NJMarine is offline   Reply With Quote
Old 07-13-2011, 10:04 PM   #10
Newbie
 
Join Date: Jul 2011
Posts: 16
Rewards Points: 10
Default

12 AWG wire adequate for 20A 240V (~19A continuous load)?


I didn't refer to any of the NEC tables. If NEC has already taken the derating into account, then that answers the question, thanks for all your help.

I was under the impression that the actual wire rating is its continuous load rating at 100%.
ChootarLaal is offline   Reply With Quote
Old 07-13-2011, 10:12 PM   #11
Wire Chewer
 
Red Squirrel's Avatar
 
Join Date: Jun 2009
Location: Ontario, Canada
Posts: 3,211
Rewards Points: 2,000
Default

12 AWG wire adequate for 20A 240V (~19A continuous load)?


I would not see anything wrong in derating it, but as said, you don't really have to. It actually takes quite a lot to get a "wall grade" wire even warm, let alone hot to the point of melting.
Red Squirrel is offline   Reply With Quote
Old 07-14-2011, 01:29 PM   #12
Newbie
 
Join Date: Jul 2011
Posts: 16
Rewards Points: 10
Default

12 AWG wire adequate for 20A 240V (~19A continuous load)?


Actual vs maximum current rating
Nominal Rated Circuit Capacity Continuous Rated Circuit Capacity
5 amps 4 amps
10 amps 8 amps
15 amps 12 amps
20 amps 16 amps
30 amps 24 amps
50 amps 40 amps
100 amps 80 amps
200 amps 160 amps
Most commonly available circuit breakers are rated to carry no more than 80% of their nominal rating continuously (3 hours or more) (NEC Art. 100). 100%-rated circuit breakers are manufactured for and may carry 100% of their nominal rating continuously.

Source:
http://en.wikipedia.org/wiki/National_Electrical_Code

So my concern was, is the 20A 12AWG wire rating at 80% derated or at 100% maximum current rating? In this part of the city, they require arc-fault breakers too, so I dont think it will accept any current draw over 20A even for a brief moment, at startup transients for example. But at full capacity, it will be running at ~19A.
ChootarLaal is offline   Reply With Quote
Old 07-14-2011, 02:10 PM   #13
Licensed Electrical Cont.
 
Speedy Petey's Avatar
 
Join Date: Feb 2004
Location: NY State
Posts: 6,858
Rewards Points: 2,020
Default

12 AWG wire adequate for 20A 240V (~19A continuous load)?


Quote:
Originally Posted by ChootarLaal View Post
Most commonly available circuit breakers are rated to carry no more than 80% of their nominal rating continuously (3 hours or more) (NEC Art. 100).
Correct. This is called a continuous load.
Like you have been told several times, yours is NOT a "continuous load".




Quote:
Originally Posted by ChootarLaal View Post
So my concern was, is the 20A 12AWG wire rating at 80% derated or at 100% maximum current rating?
Again, this is not a continuous load so the 80% rule does not apply.




Quote:
Originally Posted by ChootarLaal View Post
In this part of the city, they require arc-fault breakers too, so I dont think it will accept any current draw over 20A even for a brief moment, at startup transients for example. But at full capacity, it will be running at ~19A.
This circuit does not fall under arc-fault requirements.
Also, ANY circuit breaker IS designed to carry much more than it's rated capacity for a certain amount of time. A 20A breaker for instance will run at 22-24 amps for possibly hours before tripping.



I get the impression that you will not be satisfied until you are told just what you want to hear. In this case tell your guy to use #6cu wire for this 20A circuit, on an arc-fault breaker, fed through a GFI protected relay, just to be safe.
Speedy Petey is offline   Reply With Quote
The Following User Says Thank You to Speedy Petey For This Useful Post:
Anti-wingnut (07-14-2011)
Old 07-14-2011, 03:23 PM   #14
Newbie
 
Join Date: Jul 2011
Posts: 16
Rewards Points: 10
Default

12 AWG wire adequate for 20A 240V (~19A continuous load)?


I understand that "continuous load" is defined to have a load for >3 hours but if I have all evaps running at full capacity for >3 hours, isnt that a continuous load? plus what exactly does that ampacity mean then, ~19A?
ChootarLaal is offline   Reply With Quote
Old 07-14-2011, 03:37 PM   #15
Master Electrician
 
Join Date: Mar 2010
Location: Indiana
Posts: 2,894
Rewards Points: 2,044
Default

12 AWG wire adequate for 20A 240V (~19A continuous load)?


Quote:
Originally Posted by ChootarLaal View Post
I understand that "continuous load" is defined to have a load for >3 hours but if I have all evaps running at full capacity for >3 hours, isnt that a continuous load? plus what exactly does that ampacity mean then, ~19A?
So have the #10 installed and be done with it. No one here should continue to try and convince you otherwise. Time is money. Stop wasting yours.

brric is online now   Reply With Quote
The Following User Says Thank You to brric For This Useful Post:
tweak (07-16-2011)
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
240V Electric Heater install - 3 wire vs. 4 wire? dhgarage Electrical 7 12-12-2008 10:49 PM
Neutral Wire? 4x15mph Electrical 8 11-24-2008 01:00 PM
hooking up dryer....bronx ny code SURFBUG Appliances 6 10-14-2008 09:41 PM
Load vs. line wire gvernea Electrical 5 01-16-2008 12:50 AM
Wire sizes based on actual connected load BigJimmy Electrical 7 08-21-2007 08:30 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.