Silly Amperage/voltage Question - Electrical - DIY Chatroom Home Improvement Forum
Advertisement


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

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

Reply
 
Thread Tools
Display Modes
Old 01-09-2010, 09:48 PM   #1
Wire Chewer
 
Red Squirrel's Avatar
 
Join Date: Jun 2009
Location: Ontario, Canada
Posts: 3,550
Rewards Points: 528
Default

Silly amperage/voltage question


When sizing a breaker for a specific appliance, lets say the appliance uses 3000w and plugs into 240V, would a 15 amp double pole breaker do? Since 15x240 is 3600w So while it will only give 1800w on a single leg at 120v it will give 3600w at 240v, so technically the 3000w device should only pull 12.5 amps right?

Also 14awg would still be the minimum wiring used correct?

I don't have anything specific I'm working on though I do have a plan where this might come to play so it's more or less a theoretical question at this point.
Red Squirrel is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 01-09-2010, 09:53 PM   #2
Electrical Contractor
 
kbsparky's Avatar
 
Join Date: Sep 2008
Location: Delmarva
Posts: 3,368
Rewards Points: 2,000
Default


A 15 Amp 240 Volt circuit can supply a 3600 watt load .... but ...

If it's a continuous load the maximum on a 15 Amp circuit would be 2880 watts. This assumes a power factor of 100%, such as for electric resistance heating. If you have motor or other loads that operate on a lower power factor, then you will have to factor that into your calculations as well.

Note: Circuits for electric heating units are required to be sized at 125% of the connected loads.
__________________
-KB

Life is uncertain -- eat dessert first!!
kbsparky is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 01-09-2010, 10:01 PM   #3
Wire Chewer
 
Red Squirrel's Avatar
 
Join Date: Jun 2009
Location: Ontario, Canada
Posts: 3,550
Rewards Points: 528
Default


Quote:
Originally Posted by kbsparky View Post
A 15 Amp 240 Volt circuit can supply a 3600 watt load .... but ...

If it's a continuous load the maximum on a 15 Amp circuit would be 2880 watts. This assumes a power factor of 100%, such as for electric resistance heating. If you have motor or other loads that operate on a lower power factor, then you will have to factor that into your calculations as well.

Note: Circuits for electric heating units are required to be sized at 125% of the connected loads.
Yeah makes sense, you want to size higher. So in a real case scenario a 20 amp breaker would be better to use I guess.
Red Squirrel is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 01-09-2010, 10:01 PM   #4
Member
 
Join Date: Jul 2008
Location: Canada (s/w ON.)
Posts: 2,294
Rewards Points: 1,000
Default


Quote:
Originally Posted by Red Squirrel View Post
When sizing a breaker for a specific appliance, lets say the appliance uses 3000w and plugs into 240V, would a 15 amp double pole breaker do? Since 15x240 is 3600w So while it will only give 1800w on a single leg at 120v it will give 3600w at 240v, so technically the 3000w device should only pull 12.5 amps right?

Also 14awg would still be the minimum wiring used correct?

I don't have anything specific I'm working on though I do have a plan where this might come to play so it's more or less a theoretical question at this point.
Current is equal to the wattage, divided by the applied voltage!

I=P/E I=3000/240 I=12.5 amps

A double pole, 15 amp breaker on #14 wire is adequate. However, on a long run #12 would be better!
Wildie is offline   Reply With Quote
Old 01-10-2010, 08:22 AM   #5
Electrical Contractor
 
kbsparky's Avatar
 
Join Date: Sep 2008
Location: Delmarva
Posts: 3,368
Rewards Points: 2,000
Default


Quote:
Originally Posted by Wildie View Post
.... A double pole, 15 amp breaker on #14 wire is adequate.....
Not for continuous loads!
Quote:
Article 100.I Definitions

Continuous Load. A load where the maximum current is expected to continue for 3 hours or more.

210.19(A). Branch circuit conductors shall have an ampacity not less than the maximum load to be served. Where a branch circuit supplies continuous loads ... the minimum conductor size ... shall have an allowable ampacity of not less than ... 125 percent of the continuous load.

424.3(B) ... Fixed electric space heating equipment shall be considered continuous load.
The bottom line is dependent on what is connected to the circuit as whether is is adequate or not.
__________________
-KB

Life is uncertain -- eat dessert first!!
kbsparky is offline   Reply With Quote
Old 01-10-2010, 08:40 AM   #6
Inspector/Instructor
 
codeone's Avatar
 
Join Date: Dec 2009
Location: NC
Posts: 369
Rewards Points: 250
Default


So your circuit would be
I=P/E I=3000/240 I=12.5 amps x 125% = 15.625 amps = 20 Amp Circuit
codeone is offline   Reply With Quote
Old 01-10-2010, 10:21 AM   #7
Licensed Electrical Cont.
 
Speedy Petey's Avatar
 
Join Date: Feb 2004
Location: NY State
Posts: 7,828
Rewards Points: 2,006
Default


VERY little in a home is, or could/would be, considered a continuous load.

Electric heat and waters heaters are two automatic examples.
__________________
Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.
Speedy Petey is offline   Reply With Quote
Old 01-10-2010, 08:57 PM   #8
Wire Chewer
 
Red Squirrel's Avatar
 
Join Date: Jun 2009
Location: Ontario, Canada
Posts: 3,550
Rewards Points: 528
Default


Glad I was on right track. I was not taking into account other factors like continuous load requirements etc, was thinking mostly just in theory. In a real life situation I'd put such load on a 20 amp circuit and use 12 awg or even 10 awg wiring just to be on the safe side.
Red Squirrel is offline   Reply With Quote
Old 01-10-2010, 09:57 PM   #9
Super Moderator
 
joed's Avatar
 
Join Date: Mar 2005
Location: Welland, Ontario
Posts: 18,808
Rewards Points: 23,958
Blog Entries: 11
Default


The one other consideration you need to consider is the manufacturers direction for installation.
joed is offline   Reply With Quote
Old 01-10-2010, 10:02 PM   #10
Member
 
Join Date: May 2009
Location: Brooklyn, New York (NYC)
Posts: 1,124
Rewards Points: 500
Exclamation


Quote:
Originally Posted by Red Squirrel View Post
Yeah makes sense, you want to size higher. So in a real case scenario a 20 amp breaker would be better to use I guess.
With #12 AWG wire all the way. (Only common sense.)
spark plug is offline   Reply With Quote
Sponsored Links
Advertisement
 
Reply


Thread Tools
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
Simple electrical question (Amperage/voltage) Badfish740 Electrical 18 01-06-2009 11:35 AM
Basement Renovation Question KUIPORNG Remodeling 234 08-26-2008 08:19 AM
may be a silly question, but..... DangerMouse Electrical 20 07-21-2008 07:20 PM
hrv question indep HVAC 3 07-17-2008 10:39 PM
One furnace question and one thermostat question lh0628 HVAC 4 10-11-2007 10:17 PM




Top of Page | View New Posts