Proper Calculation For Circuit Size - Electrical - DIY Chatroom Home Improvement Forum

 DIY Chatroom Home Improvement Forum proper calculation for circuit size
 Register Blogs Articles Rewards Search Today's Posts Mark Forums Read

02-13-2012, 07:20 PM   #1
Newbie

Join Date: Feb 2012
Posts: 2
Rewards Points: 10

## proper calculation for circuit size

I am about to run wire for 8kw double oven, 120/240 4 wires, 80 feet one way. instruction says 'protection circuit recommended 40A'. However, i want to double check with calculation. not sure which method to use or none at all.

method A
8000 / 240 = 33.33
then
33.33 x 1.25 = 41.66
go for 50 amp breaker???

50 amp breaker x .8 = 40 amp limit.

method B
10% over 8kw
hence
8000 x .1 = 8800
8800 / 240 = 36.67
go for 40 amp breaker???

method C, no calculation needed, variance already built in???

02-13-2012, 07:47 PM   #2
Master Electrician

Join Date: Mar 2010
Location: Indiana
Posts: 3,746
Rewards Points: 3,748

A range is NOT a continuous load. 40 amps is correct.

 The Following User Says Thank You to brric For This Useful Post: withoutlicense (02-13-2012)
 02-13-2012, 07:53 PM #3 " Euro " electrician     Join Date: Apr 2006 Location: WI & France { in France for now } Posts: 5,369 Rewards Points: 2,000 Moi aussi 2X as above not a contionous load at all. Just wired 8-3 avce 40 amp breaker and be done with it. Just be aware of junction box location so you will have to check the manufacter specs on location due it will varies a bit so be on safe side check it out. Merci, Marc __________________ The answer will be based on NEC ( National Electrical code ) or CEC ( Cananda Electrical code ) or ECF ( Electrique Code France )

 02-13-2012, 08:11 PM #4 Newbie   Join Date: Feb 2012 Posts: 2 Rewards Points: 10 It figures. just had a brief look at the definition of continuous load. vague description but thanks anyway.
 02-13-2012, 10:43 PM #5 Member   Join Date: Nov 2007 Location: Nashua, NH, USA Posts: 7,918 Rewards Points: 1,442 Note that ovens cycle on and off to maintain the desired temperature. It is highly unlikely that both ovens would have cycled on and remained on together for a period of more than 3 hours, which is the defnintion of a continuous (as opposed to intermittent) load. __________________ The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit. Last edited by AllanJ; 02-13-2012 at 10:46 PM.
 02-13-2012, 10:48 PM #6 retired elect/hvac/plumb     Join Date: Jan 2010 Location: south east of omaha/The island of misfit contractors Posts: 2,921 Rewards Points: 2,020 Being that far of a run I might suggest upgrading the wire size to a 6/3 wg instead of an 8/3 wg ,keeping the same 40a breaker __________________ "facts" have no relevance to this discusion Posting from a concrete bunker under a non descript barn
 The Following User Says Thank You to plummen For This Useful Post: ben's plumbing (02-13-2012)
 02-13-2012, 10:50 PM #7 Member   Join Date: Oct 2009 Location: South TX outside San Antonio Posts: 153 Rewards Points: 152 Not to hijack his thread, but if you know an appliance will run continuously like an air conditioner in south Texas, should it be considered a continuous load? My two 7.5 ton units run 18 hours per day in our 110 degree heat. They never cycle until we close the door and turn off the lights. David
 02-13-2012, 11:01 PM #8 retired elect/hvac/plumb     Join Date: Jan 2010 Location: south east of omaha/The island of misfit contractors Posts: 2,921 Rewards Points: 2,020 I dont know if i would consider that a continuous load or a cry for help myself Have you had them serviced lately to figure out why theyre running so much? Maybe its time for a replacement/upsizing __________________ "facts" have no relevance to this discusion Posting from a concrete bunker under a non descript barn
02-13-2012, 11:24 PM   #9
" Euro " electrician

Join Date: Apr 2006
Location: WI & France { in France for now }
Posts: 5,369
Rewards Points: 2,000

Quote:
 Originally Posted by n175h Not to hijack his thread, but if you know an appliance will run continuously like an air conditioner in south Texas, should it be considered a continuous load? My two 7.5 ton units run 18 hours per day in our 110 degree heat. They never cycle until we close the door and turn off the lights. David
David.,

I can understand the nature of southern Texas with heat wave it is simauir to our most southen France on tempture wise it is not too far off from there.

But did the HVAC contractor did look at the unit to make sure it is sized properly if sized properly it will cycle from time to time if it was undersized may have to upgrade to twin 10 tonnes units but there is a clevation with it is you will have to check the supply to see if they can handle addtional load for the A/C units.

But I can understand some unit that can run almost contionuns they will design the circuit properly to handle that.

The last 7.5 tonne unit I have see one Trane unit it did have dual compressours so it will adjust the compressour as need to for addtional load to keep it up on hevey demand.

Merci,
Marc
__________________
The answer will be based on NEC ( National Electrical code ) or CEC ( Cananda Electrical code ) or ECF ( Electrique Code France )

 02-14-2012, 08:17 AM #10 Member   Join Date: Nov 2007 Location: Nashua, NH, USA Posts: 7,918 Rewards Points: 1,442 The 8 gauge copper wire will be fine for the 80' (160' round trip) run in terms of wire resistance (.64 ohms per 1000'). The voltage drop at maximum draw (34 amps) will be about 3-1/2 volts or about 1-1/2 percent of 240 volts. When sizing the conductors for voltage drop purposes you do not multiply amperes by 1.25 for continuous loads. Then given the conductor size for amperage and, if applicable, continuous load and the conductor size for voltage drop, you choose the larger of the two. Air conditioners are considered continuous loads. The installation instructions should give a recommended breaker rating. Sometimes there is a maximum allowable breaker rating as well. __________________ The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit. Last edited by AllanJ; 02-14-2012 at 08:28 AM.
 02-14-2012, 11:46 AM #11 Retired "Double E"     Join Date: Feb 2012 Location: Mid Missouri Posts: 2 Rewards Points: 10 Here is a link for a number of electrical calculators. http://www.electrician2.com/calculators/elcal.html Last edited by MoHawk; 02-14-2012 at 12:02 PM.
02-14-2012, 11:52 AM   #12
retired elect/hvac/plumb

Join Date: Jan 2010
Location: south east of omaha/The island of misfit contractors
Posts: 2,921
Rewards Points: 2,020

Quote:
 Originally Posted by AllanJ The 8 gauge copper wire will be fine for the 80' (160' round trip) run in terms of wire resistance (.64 ohms per 1000'). The voltage drop at maximum draw (34 amps) will be about 3-1/2 volts or about 1-1/2 percent of 240 volts. When sizing the conductors for voltage drop purposes you do not multiply amperes by 1.25 for continuous loads. Then given the conductor size for amperage and, if applicable, continuous load and the conductor size for voltage drop, you choose the larger of the two. Air conditioners are considered continuous loads. The installation instructions should give a recommended breaker rating. Sometimes there is a maximum allowable breaker rating as well.
Im more worried about actual heat generated in the wire over that 80' when youve got a turkey sitting in there for 8 hrs getting ready for thanksgiving/christmas dinner than I am about the voltage drop,although they both have the same basic cause resistance
And the 6/3 wg does cost that much more for peace of mind
__________________
"facts" have no relevance to this discusion
Posting from a concrete bunker under a non descript barn

02-14-2012, 12:24 PM   #13
Retired "Double E"

Join Date: Feb 2012
Location: Mid Missouri
Posts: 2
Rewards Points: 10

Quote:
 Originally Posted by plummen Im more worried about actual heat generated in the wire over that 80' when youve got a turkey sitting in there for 8 hrs getting ready for thanksgiving/christmas dinner than I am about the voltage drop,although they both have the same basic cause resistance And the 6/3 wg does cost that much more for peace of mind
+1 on this post!
During my 36 years working for a large electrical utility, I've seen a number of disasters from customer wiring without proper knowledge. If your calculations are in doubt or borderline I always recommend installing the next larger wire size. When cooking a holiday dinner many ranges are operated at or near maximum amperage for many hours which can generate a lot heat in the conductors & connections.

Last edited by MoHawk; 02-14-2012 at 12:41 PM. Reason: content

 The Following User Says Thank You to MoHawk For This Useful Post: plummen (02-14-2012)
 02-14-2012, 05:18 PM #14 Member   Join Date: Nov 2007 Location: Nashua, NH, USA Posts: 7,918 Rewards Points: 1,442 For a given wire size and a given number of amperes the number of BTU or calories of heat generated per foot of wire is the same regardless of the length of the wire. __________________ The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit. Last edited by AllanJ; 02-15-2012 at 09:00 AM.
02-14-2012, 05:50 PM   #15
retired elect/hvac/plumb

Join Date: Jan 2010
Location: south east of omaha/The island of misfit contractors
Posts: 2,921
Rewards Points: 2,020

You dont think there would be more resistance /heat built up in that wire over 80' than there would be in a piece of 6/3 going the same distance with the same load on it?
Either way I guess its not a big deal,we're just beating another dead horse here

__________________
"facts" have no relevance to this discusion
Posting from a concrete bunker under a non descript barn

 Tags breaker , oven , wire sizing

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are Off Pingbacks are Off Refbacks are Off Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post avtck Remodeling 2 05-22-2011 07:27 AM Doug Crf General DIY Discussions 20 02-26-2011 12:29 AM RyanD Building & Construction 3 06-28-2009 11:33 PM Suzuki91vx800 Electrical 36 06-23-2009 05:18 PM deck hand Flooring 4 04-08-2009 05:42 PM

Top of Page | View New Posts