Replacing Cooktop, Circuit Amperage Question - Electrical - DIY Chatroom Home Improvement Forum


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 07-18-2013, 01:12 PM   #1
Newbie
 
Join Date: Apr 2013
Posts: 8
Rewards Points: 10
Default

Replacing Cooktop, Circuit Amperage Question


I am replacing an old cooktop that was powered by a dedicated 30 Amp circuit. The circuit has 10 gauge wire. Many of the new cooktops I'm looking at require a 40 amp circuit, or the specs say 30Amps/208V or 40 Amps/240V.

If the specs of the appliance say 30Amp/208V or 40 Amps/240V can I use that cooktop on my existing circuit? What determines whether the appliance is drawing 30A/208v or 40A/240v? Is it the way the appliance is wired when installed or will the appliance only draw 30A/208V if its on a 30A circuit?

Thanks

Advertisement

diverdave is offline   Reply With Quote
Old 07-18-2013, 01:40 PM   #2
Licensed electrician
 
Join Date: Sep 2007
Location: Maryland
Posts: 8,054
Rewards Points: 2,906
Default

Replacing Cooktop, Circuit Amperage Question


The voltage affects the ampacity. Your house probably has 120/240 volt. 208 is commonly a commercial voltage.

Advertisement

__________________
Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.
Jim Port is online now   Reply With Quote
Old 07-18-2013, 01:45 PM   #3
Remodel and New Build GC
 
MTN REMODEL LLC's Avatar
 
Join Date: Sep 2010
Location: Colorado @ 7651'
Posts: 2,976
Rewards Points: 2,222
Default

Replacing Cooktop, Circuit Amperage Question


Quote:
Originally Posted by Jim Port View Post
The voltage affects the ampacity. Your house probably has 120/240 volt. 208 is commonly a commercial voltage.
Jim... I'm not going to understand commercial or three phase or anything.... but is there a relatively simple explanation why an appliance can run on a system with less volts and amps (30A/208) verse 40A/240.

Seems counter intuitive to me.

TIA

Best

Peter
__________________
Never stop learning (xcep fer speling en typeing)
MTN REMODEL LLC is offline   Reply With Quote
Old 07-18-2013, 01:48 PM   #4
Semi-Pro Electro-Geek
 
Join Date: Jul 2009
Location: Arizona, USA
Posts: 2,573
Rewards Points: 2,042
Default

Replacing Cooktop, Circuit Amperage Question


208V is not 240V. The current draw depends on the voltage (Ohm's law). So if you have a 240V system, which you probably do, then you need a 40A circuit.
__________________
I am a lawyer, but not your lawyer. And who cares anyways? We're here to talk construction. This is DIY advice, not legal advice.
mpoulton is offline   Reply With Quote
Old 07-18-2013, 01:51 PM   #5
Semi-Pro Electro-Geek
 
Join Date: Jul 2009
Location: Arizona, USA
Posts: 2,573
Rewards Points: 2,042
Default

Replacing Cooktop, Circuit Amperage Question


Quote:
Originally Posted by MTN REMODEL LLC View Post
Jim... I'm not going to understand commercial or three phase or anything.... but is there a relatively simple explanation why an appliance can run on a system with less volts and amps (30A/208) verse 40A/240.

Seems counter intuitive to me.
I=V/R

30=208/R

R=6.93 ohms

I=240/6.93

I=34.6A - round up to 40A.
__________________
I am a lawyer, but not your lawyer. And who cares anyways? We're here to talk construction. This is DIY advice, not legal advice.
mpoulton is offline   Reply With Quote
Old 07-18-2013, 02:01 PM   #6
Newbie
 
Join Date: Apr 2013
Posts: 8
Rewards Points: 10
Default

Replacing Cooktop, Circuit Amperage Question


OK, thanks. I understand now. So lets assume I'll need a 40 amp circuit for the new appliance. The current circuit has 10 ga wire, which I believe is rated for a max of 30A. Unfortunately I think I already know the answer to this question, but is there any way to upgrade the existing circuit to 40A without running higher capacity wire?
diverdave is offline   Reply With Quote
Old 07-18-2013, 02:06 PM   #7
JW
 
mm11's Avatar
 
Join Date: Apr 2013
Location: Maryland
Posts: 214
Rewards Points: 194
Default

Replacing Cooktop, Circuit Amperage Question


In a word- no. It would be a fire risk to terminate that #10 wire on a 40A breaker in your situation.
mm11 is offline   Reply With Quote
Old 07-18-2013, 02:16 PM   #8
Remodel and New Build GC
 
MTN REMODEL LLC's Avatar
 
Join Date: Sep 2010
Location: Colorado @ 7651'
Posts: 2,976
Rewards Points: 2,222
Default

Replacing Cooktop, Circuit Amperage Question


Quote:
Originally Posted by mpoulton View Post
I=V/R

30=208/R

R=6.93 ohms

I=240/6.93

I=34.6A - round up to 40A.
MPoul.....DUH.... Sorry... and thank you. I guess I got/was focused on the equivalent energy used by the cooktop.

Best

Peter
__________________
Never stop learning (xcep fer speling en typeing)
MTN REMODEL LLC is offline   Reply With Quote
Old 07-18-2013, 02:30 PM   #9
Newbie
 
Join Date: Apr 2013
Posts: 8
Rewards Points: 10
Default

Replacing Cooktop, Circuit Amperage Question


OK, that's what I thought. Thanks everyone for the quick responses.
diverdave is offline   Reply With Quote
Old 07-18-2013, 11:54 PM   #10
" Euro " electrician
 
frenchelectrican's Avatar
 
Join Date: Apr 2006
Location: WI & France { in France for now }
Posts: 5,369
Rewards Points: 2,000
Default

Replacing Cooktop, Circuit Amperage Question


If you have easy access to the cable or conduit ( pipe ) then you can able upgrade to #8 CU ( four conductor aka Black , Red, White et bare or green depending on which it used )

And double check the connection point some cooktops unit do required netural so make sure you check the installment instruction on that part.

Merci,
Marc
__________________
The answer will be based on NEC ( National Electrical code ) or CEC ( Cananda Electrical code ) or ECF ( Electrique Code France )
frenchelectrican is offline   Reply With Quote
Old 07-19-2013, 12:47 PM   #11
Member
 
Join Date: Jan 2009
Location: WV
Posts: 3,026
Rewards Points: 2,232
Default

Replacing Cooktop, Circuit Amperage Question


Quote:
Originally Posted by MTN REMODEL LLC View Post
Jim... I'm not going to understand commercial or three phase or anything.... but is there a relatively simple explanation why an appliance can run on a system with less volts and amps (30A/208) verse 40A/240.

Seems counter intuitive to me.
It does to me as well. Whatever the appliance is rated for, that's the wattage it will draw. Lower voltage would mean higher current. I eagerly await some pro's explanation of this.
md2lgyk is offline   Reply With Quote
Old 07-19-2013, 01:02 PM   #12
Remodel and New Build GC
 
MTN REMODEL LLC's Avatar
 
Join Date: Sep 2010
Location: Colorado @ 7651'
Posts: 2,976
Rewards Points: 2,222
Default

Replacing Cooktop, Circuit Amperage Question


MD.... I'm going to try this.... subject to a pro's correction/clarrification.

I assume that this appliance cooktop (non-inductive motor) can function at several wattages... within a range of wattage.

At 208/30, it just does not get as hot as if running at 240/35. (It's resistance remaining static/same).

I suppose it could "run/function" on 120V... just really crappy.

At 480V (as if I have any idea what that 3 phase stuff is) it would work really hot/good.... very temporarily untill the element burnt-up.

I'm interested in pro's input, because Ohm's law is Ohm's law, and I'm pretty sure Ohm was correct.

Best

Peter

EDIT: The only other thing I can think of theoretically, is if you had a resistance that varied in it's Ohm's resistance. Many years ago, I was learning about Ohms and tried to measure a "cold" light bulb... could not equate resistance to wattage using MM... then discovered a light bulb element does not take on it's "rated" wattage/resistance untill under load/hot. ... DUH on me
__________________
Never stop learning (xcep fer speling en typeing)

Last edited by MTN REMODEL LLC; 07-19-2013 at 01:10 PM.
MTN REMODEL LLC is offline   Reply With Quote
Old 07-19-2013, 01:33 PM   #13
" Euro " electrician
 
frenchelectrican's Avatar
 
Join Date: Apr 2006
Location: WI & France { in France for now }
Posts: 5,369
Rewards Points: 2,000
Default

Replacing Cooktop, Circuit Amperage Question


Quote:
Originally Posted by MTN REMODEL LLC View Post
MD.... I'm going to try this.... subject to a pro's correction/clarrification.


I will help you with something along the way.,


I assume that this appliance cooktop (non-inductive motor) can function at several wattages... within a range of wattage.

It will be diffrent wattage on heating elements all it will depending on the system voltage as you will read the rest of comment it will fall in place.

At 208/30, it just does not get as hot as if running at 240/35. (It's resistance remaining static/same).

They will loose about 20% of heating rating if ran on 208 volts instead of 240 volts and 208 volts is common found in commercal building and alot of larger condos flats and from time to time single family homes can get 208/120 volts if they get it off from POCO network distubation which it is common near large commercal buildings. ( there are speical rules to deal but will discuss about that later on the time realted to 208 networks )

I suppose it could "run/function" on 120V... just really crappy.

Oui., C'est simple 1/2 voltage and will result 1/4 of wattage of normal 240 volts element so like 2500 watt element @ 240 volts it will drop down to 625 watts on the same element.

At 480V (as if I have any idea what that 3 phase stuff is) it would work really hot/good.... very temporarily untill the element burnt-up.

Denfineity will burn up due it will be 4X of normal wattage so instead of common 2500 watt element it will become 10,000 watt element which it can blow up the 240 volt elements which I have see it happend but not very often.

I'm interested in pro's input, because Ohm's law is Ohm's law, and I'm pretty sure Ohm was correct.

Best

Peter

EDIT: The only other thing I can think of theoretically, is if you had a resistance that varied in it's Ohm's resistance. Many years ago, I was learning about Ohms and tried to measure a "cold" light bulb... could not equate resistance to wattage using MM... then discovered a light bulb element does not take on it's "rated" wattage/resistance untill under load/hot. ... DUH on me
My reply in bleu so you will know my answer there.

With heating elements the ohms laws will never change at all but the moteurs on the other hand it will change so lower voltage the more current it will draw for the same load on the moteur. ( all it depending on type and connection of the moteur.)

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

Last edited by frenchelectrican; 07-19-2013 at 01:51 PM.
frenchelectrican is offline   Reply With Quote
Old 07-19-2013, 01:40 PM   #14
Member
 
joed's Avatar
 
Join Date: Mar 2005
Location: Welland, Ontario
Posts: 8,388
Rewards Points: 3,570
Blog Entries: 4
Default

Replacing Cooktop, Circuit Amperage Question


Quote:
Originally Posted by md2lgyk View Post
It does to me as well. Whatever the appliance is rated for, that's the wattage it will draw. Lower voltage would mean higher current. I eagerly await some pro's explanation of this.
You are assuming the wattage stays the same. It does not. The resistance of the burners stays the same. Thus if the voltage is lower the current and the wattage are lower.
__________________
Do not PM with questions that can be asked in a forum. I will not respond.
joed is online now   Reply With Quote
The Following 3 Users Say Thank You to joed For This Useful Post:
md2lgyk (07-21-2013), mpoulton (07-19-2013), MTN REMODEL LLC (07-19-2013)
Old 07-19-2013, 01:43 PM   #15
Remodel and New Build GC
 
MTN REMODEL LLC's Avatar
 
Join Date: Sep 2010
Location: Colorado @ 7651'
Posts: 2,976
Rewards Points: 2,222
Default

Replacing Cooktop, Circuit Amperage Question


Quote:
Originally Posted by frenchelectrican View Post
My reply in bleu so you will know my answer there.

With heating elements the ohms laws will never change at all but the moteurs on the other hand it will change so lower voltage the more current it will draw for the same load on the moteur. ( all it depending on type and connection of the moteur.)

Merci,
Marc
MARC... MERCI MON AMI... (Edit X-post...and JOED...thank ya Bubbi)

Your clarrification really helps/confirms some basic electrical concepts/understanding for us non-pro's

Best

Peter

Advertisement

__________________
Never stop learning (xcep fer speling en typeing)

Last edited by MTN REMODEL LLC; 07-19-2013 at 01:51 PM.
MTN REMODEL LLC is offline   Reply With Quote
The Following User Says Thank You to MTN REMODEL LLC For This Useful Post:
frenchelectrican (07-19-2013)
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
Amateur Question - Amperage vs. Voltage Conjur Electrical 13 06-21-2013 02:30 AM
Quick electric cooktop wiring question pdp76 Electrical 1 04-09-2013 08:23 PM
Power Strips on 20 Amp Circuit Question... rudy2262 Electrical 7 06-27-2011 04:29 PM
Replacing a sliding glass door question cdm Carpentry 45 04-11-2011 05:12 PM
Replacing a circuit breaker PaulGray Electrical 3 05-13-2006 10:17 PM




Top of Page | View New Posts