Mike Holts Basic Electrical Theory Study Manual

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ksue333

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There is a problem that shows a power example for a 230V rated device on a 240V circuit.

Q:What is the power consume by a 9.6kw heater strip rated 230V, connected to a 240V circuit.

A: P=10.45kW.

I thought the power consumed by a device/load is no more than the rating of the device/load.
:?
 

infinity

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When you apply a higher voltage (above it's rating) to a device that's a purely resistive load like a heater the output will also be higher. To solve this problem you need to find the resistance of the heater first and then use that number with the higher voltage in your power formula.

Welcome to the Forum. :)
 

ksue333

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Mike Holts Basic Electrical Theory Study Manual

The problem says 9.6kW is consumed by the heat strip. I assumed that this is the rating of the heat strip. So is the connection to the 240V circuit the problem?

Is there such thing as a 230V circuit?
 
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infinity

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At 230 volts the power consumed is 9.6kw. Increase the voltage to 240 volts and the power will go up as indicated by the answer. I would guess that the 230 volts is just for the sake of the question and is not a real world value.
 

Little Bill

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Most motors and some heaters are rate at 230V.
If you look at the table 430.28 it tells you the motors are rated 230V but nominal voltages can be used for calculations.
 

iwire

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Most motors and some heaters are rate at 230V.
If you look at the table 430.28 it tells you the motors are rated 230V but nominal voltages can be used for calculations.

A 230 volt tagged motor is designed to be supplied by a 240 volt nominal supply.

A 230 volt tagged heating element is not designed to be connected to a 240 volt supply.
 

Little Bill

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A 230 volt tagged motor is designed to be supplied by a 240 volt nominal supply.

A 230 volt tagged heating element is not designed to be connected to a 240 volt supply.

Some are and that's why they list the kw for different nominal voltages that may be used.
 

iwire

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Some are and that's why they list the kw for different nominal voltages that may be used.

No, a heater marked just 230 is not rated for 240.

If the element has multiple KWs on the label it will also have multiple voltages listed on them.

Not trying to be a pain, I just think it is important not to overdrive heating elements. They will run much hotter than designed. :)
 

GoldDigger

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So does that mean the heater would need an extra resistor installed?
That would not be practical (unless the extra resistor was a small section of eldment built into the assembly.
If you can not get a properly rated heater and the issue bothers you you should use a buck transformer. That would not waste much energy.
 

kwired

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240 volt nominal around here often runs at an actual 243-247, with little or no load maybe even up to 250 in many cases.

So does that mean we can not use heating equipment only rated 230 or 240 connected directly to a line that runs a little over 240?
 

George Stolz

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The point of the exercise is to drill it home that as voltage goes up on a fixed resistance, that the amperes will go up, and the power will go up proportionately.
 

kwired

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The point of the exercise is to drill it home that as voltage goes up on a fixed resistance, that the amperes will go up, and the power will go up proportionately.
Very well is, here we like to tie everything back to NEC since that is what this site is primarily about. The question originally asked wasn't necessarily intended to be a NEC related question/answer though.
 

iwire

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240 volt nominal around here often runs at an actual 243-247, with little or no load maybe even up to 250 in many cases.

So does that mean we can not use heating equipment only rated 230 or 240 connected directly to a line that runs a little over 240?

Did anyone say that or even hint that?
 

kwired

Electron manager
Location
NE Nebraska
Did anyone say that or even hint that?

No, a heater marked just 230 is not rated for 240.

If the element has multiple KWs on the label it will also have multiple voltages listed on them.

Not trying to be a pain, I just think it is important not to overdrive heating elements. They will run much hotter than designed. :)

Looks like that is exactly what you said, is rated for 230 only and probably shouldn't be run at any other voltage.

But yet you have before and probably will again suggest that a variance of 10% is probably acceptable for such things.

230 x 1.10 = 253.

Is true that if the VA rating on nameplate is based on 230 volts that the actual VA drawn will increase if operating even at just 231.
 
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