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

 DIY Chatroom Home Improvement Forum Silly amperage/voltage question

01-09-2010, 09:48 PM   #1
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## 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.

 01-09-2010, 09:53 PM #2 Electrical Contractor     Join Date: Sep 2008 Location: Delmarva Posts: 3,368 Rewards Points: 2,000 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!!

01-09-2010, 10:01 PM   #3
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Quote:
 Originally Posted by kbsparky 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.

01-09-2010, 10:01 PM   #4
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Quote:
 Originally Posted by Red Squirrel 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!

01-10-2010, 08:22 AM   #5
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Quote:
 Originally Posted by Wildie .... A double pole, 15 amp breaker on #14 wire is adequate.....
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.
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 01-10-2010, 08:40 AM #6 Inspector/Instructor     Join Date: Dec 2009 Location: NC Posts: 369 Rewards Points: 250 So your circuit would be I=P/E I=3000/240 I=12.5 amps x 125% = 15.625 amps = 20 Amp Circuit
 01-10-2010, 10:21 AM #7 Licensed Electrical Cont.     Join Date: Feb 2004 Location: NY State Posts: 7,828 Rewards Points: 2,006 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.
 01-10-2010, 08:57 PM #8 Wire Chewer     Join Date: Jun 2009 Location: Ontario, Canada Posts: 3,579 Rewards Points: 586 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.
 01-10-2010, 09:57 PM #9 Super Moderator     Join Date: Mar 2005 Location: Welland, Ontario Posts: 20,539 Rewards Points: 32,366 Blog Entries: 11 The one other consideration you need to consider is the manufacturers direction for installation.
01-10-2010, 10:02 PM   #10
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Quote:
 Originally Posted by Red Squirrel 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.)

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