ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
AreMetal Ladders Ever OK For Electrical Work?
by HotLine1. 01/22/18 07:31 PM
Photocell
by twh. 01/22/18 05:06 PM
VDE 0100 to introduce AFCIs
by sparky. 01/20/18 05:09 PM
MRI LED lights dimmer control replacement - wow!
by Potseal. 01/19/18 08:52 PM
New in the Gallery:
Housebilding DIY wiring
SE cable question
Who's Online Now
0 registered members (), 16 guests, and 6 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
need some help #181853
11/03/08 10:23 PM
11/03/08 10:23 PM
E
Erick  Offline OP
New Member
Joined: Jul 2008
Posts: 5
Ut
Guy's I am a crazy with embarrassment but here goes: An electric heater is rated for 2400 watts at 240 volts. What power is consumed when the heater is operated at 120 volts? I=P/E, R=E/I, I=E/R, P=EI, I know the steps but with unequal voltages?? man I am so stumped, I know the answer it's (600) but don't know the formula Ohms law out the window to a point what am I missing?

Work Gear for Electricians and the Trades
Re: need some help [Re: Erick] #181854
11/03/08 11:17 PM
11/03/08 11:17 PM
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Watts = Amps times Volts
Volts = Amps times Ohms
therefore .. Watts = Amps times amps times Ohms
so ... amps times amps is a 'squared' relationship
that is, reducing the volts by half, and you cut the amps by four (2x2). Thus, 1/4th the heat.

Re: need some help [Re: Erick] #181855
11/03/08 11:22 PM
11/03/08 11:22 PM
C
canuck  Offline
Member
Joined: Jul 2006
Posts: 27
Canada
First, use this formula to calculate the resistance @ 240 Volts

p = e^2.......p = watts e = volts r = ohms(resistance)
.....---
.....R


2400 = (240)^2
.........------
...........R

R = ((240) x (240))
.....-------------
.....2400

R = 24 ohms

Then use the same formula to calculate the power at 120 volts:

p = (120)^2
.....------
.....24

p = 600 watts

Here are some more formulas that are helpful:
http://www.the12volt.com/ohm/ohmslaw.asp#pie



Last edited by canuck; 11/03/08 11:26 PM.
Re: need some help [Re: canuck] #181856
11/04/08 12:32 AM
11/04/08 12:32 AM
E
Erick  Offline OP
New Member
Joined: Jul 2008
Posts: 5
Ut
Thanks very much you guy's are great! Erick

Re: need some help [Re: Erick] #181858
11/04/08 01:13 AM
11/04/08 01:13 AM
S
SolarPowered  Offline
Member
Joined: Jul 2004
Posts: 625
Palo Alto, CA, USA
However, remember that the resistance of the heating element is likely to change with temperature, so 600W is only an approximation.


Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
cookcc
cookcc
California ,Long Beach
Posts: 28
Joined: May 2007
Show All Member Profiles 
Top Posters(30 Days)
Admin 21
sparky 15
Potseal 15
Popular Topics(Views)
243,599 Are you busy
180,406 Re: Forum
170,869 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.019s Queries: 15 (0.005s) Memory: 0.9668 MB (Peak: 1.1076 MB) Zlib enabled. Server Time: 2018-01-23 15:42:54 UTC