DIY Home Improvement Forum banner

Replacing Cooktop, Circuit Amperage Question

3K views 23 replies 11 participants last post by  stickboy1375 
#1 ·
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
 
#3 ·
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
 
#4 ·
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.
 
#6 ·
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?
 
#10 ·
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
 
#12 · (Edited)
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.:laughing:

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
 
#13 · (Edited)
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 :huh: 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.:laughing:

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
 
#16 ·
So basically heating elements (resistive load?) will use less wattage at lower voltage, and motors will likely draw more current at lower voltage. This is why you see dual amperage/wattages appliances like water heaters, If they are marked for both 208/240 volt.

Makes sense. :yes:

I enjoy reading all of this info from the pros.
 
#17 ·
So basically heating elements (resistive load?) will use less wattage at lower voltage, and motors will likely draw more current at lower voltage. This is why you see dual amperage/wattages appliances like water heaters, If they are marked for both 208/240 volt.

Makes sense. :yes:

I enjoy reading all of this info from the pros.
Kyle... me too... really helps...

Really uneducated discussion/guess here... but I think it is just inductive motors that respond/operate as you mention above.... but I have no knowledge/understanding of that or motors.
 
#19 ·
This is not what I learnt in school.......


http://www.ohmslawcalculator.com/ohms_law_calculator.php


Use 4500 watts and change the voltage only

Leave everything else blank and hit calculate ...



Notice the difference in amperage ...

If voltage is lower and watts are the same then current/amperage must be higher...
Philly... That would be a mathmatical truth, but not the facts of the circumstance. Wattage (energy heat factor) does not remain the same under reduced voltage.
 
#22 ·
Philly, take a dryer for a perfect example, ever notice that almost every unit is 120v motor and 240v heating element? This is simply because they will work in more applications, So you can take this one product and use it in a 120/240v residential service, or a 3phase 208/120v building. Of course, the caveat is that your clothes will take much longer to dry in the 208v building. But, you won't smoke the motor either. ;)
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top