Calculating fuse size, current and voltage in a circuit

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Discussion Overview

The discussion revolves around calculating various electrical parameters in a circuit, including conductor and fuse size, current, voltage, and power under different conditions. Participants explore scenarios involving normal operation, overload situations, short circuits, and open circuit conditions, with a focus on homework-related calculations in an electrical installations context.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant requests calculations for conductor and fuse size, current, voltage across the load, and power consumed under normal conditions.
  • Another participant questions the absence of a fuse in the provided diagram and seeks clarification on what is needed to determine the appropriate fuse size.
  • Some participants express uncertainty about the problem statement, noting it lacks specific details such as source voltage and load resistance.
  • There is a suggestion that the blue rectangles in the diagram may represent fuses, though some interpret them as resistors for conductor resistance.
  • Participants discuss the relevance of wiring length in determining conductor size and express concerns about the adequacy of the problem statement.
  • One participant mentions using Ohm's law to calculate current and expresses confusion about the next steps after calculating current.
  • Another participant suggests starting a new thread for similar questions to maintain clarity in the discussion.

Areas of Agreement / Disagreement

Participants generally agree that the problem statement is incomplete and lacks necessary information for accurate calculations. Multiple competing views exist regarding the interpretation of the diagram and the approach to solving the problem.

Contextual Notes

Limitations include missing assumptions about the circuit configuration, lack of specific voltage and resistance values in the initial posts, and the ambiguity surrounding the diagram elements.

Who May Find This Useful

Students and practitioners in electrical installations or related fields who are working on circuit calculations and seeking peer input on similar problems.

Jon Canine
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circuit.jpg


(a) Calculate the size of Conductor and Fuse, the amount of Current through the conductor, Voltage ACROSS the existing LOAD and power consumed by the EXISTING LOAD under normal circuit condition (when the switch of the above circuit will be closed).

(b) Calculate the overload current, voltage and power if additional two 30 OHMS loads are connected in parallel across the existing load. (When the switch will be closed).

(c) Calculate the short circuit current, voltage and power if the LOAD is shorted. (When the switch will be closed).

(d) What will happen to this circuit if HOT” CONDUCTOR COMES IN CONTACT WITH METAL RACEWAY OR OTHER METAL OBJECT.

(e) What will happen to this circuit under open circuit condition? Calculate the open circuit current, voltage and power if one 30 OHMS load IS connected across the existing load under this open circuit condition? (When the switch will not be closed).

Homework Equations



I = E/R

The Attempt at a Solution


[/B]
I know:

240 = 7.992 or 8amps.
24 + 0.001 + 0.001 + 0.001

How do i figure out fuse size and voltage?

i know this is very basic... Any help is greatly appreciated.
 
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I don't see any fuse in the drawing. Do you understand what fuses DO? What do you need to know to know what "size" fuse you need?
 
@phinds, I figure those blue capped rectangles are meant to be line fuses.

The problem statement is incomplete as it doesn't specify the source voltage or the load resistance. However, judging by the attempt at solution clues (I say clues because they aren't proper equations) I'm guessing that the source voltage is 240 V and the load resistance is 24 Ω.

We also don't know the length of the wiring, so determining the conductor size (assuming copper) from its given resistance is not possible. Of course, this may be some sort of Electrical Code test question where a normal residential circuit is assumed and wire gauge is determined by the load current.
 
Last edited:
gneill said:
@phinds, I figure those blue capped rectangles are meant to be line fuses.
Yeah, I thought that might be the case but since the label said "conductor resistance" I took them to be resistors representing the conductor resistance.

The problem statement is incomplete as it doesn't specify the source voltage or the load resistance. However, judging by the attempt at solution clues (I say clues because they aren't proper equations) I'm guessing that the source voltage is 240 V and the load resistance is 24 Ω.

We also don't know the length of the wiring, so determining the conductor size (assuming copper) from its given resistance is not possible. Of course, this may be some sort of Electrical Code test question where a normal residential circuit is assumed and wire gauge is determined by the load current.
You're probably right ... I just have an antipathy to inadequate problem statements.
 
damn... sorry. this part didn't paste:

Given that the VOLTAGE OF THE SOURCE =240V, LOAD RESISTANCE = 30 OHMS
 
Jon, can you clarify the nature of the question? Is it an Electrical Code or Standards type question? Otherwise I don't see enough information to be able to determine a conductor size.
 
Jon Canine said:
damn... sorry. this part didn't paste:

Given that the VOLTAGE OF THE SOURCE =240V, LOAD RESISTANCE = 30 OHMS
And you still have not answered the questions I asked you in post #2.
 
This is just an electrical installations course. @phinds, you are correct - the fuses would be the blue rectangles by the switches. I understand what fuses do and I thought I needed: I (Amps) = P (Watts) ÷ V (Voltage) to figure it out...
 
Jon Canine said:
This is just an electrical installations course. @phinds, you are correct - the fuses would be the blue rectangles by the switches. I understand what fuses do and I thought I needed: I (Amps) = P (Watts) ÷ V (Voltage) to figure it out...
Well, I suppose you could do it that way, but I don't see why you would want to do it the long way by computing power when you can just use ohms law directly
 
  • #10
Jon Canine said:
View attachment 78635

(a) Calculate the size of Conductor and Fuse, the amount of Current through the conductor, Voltage ACROSS the existing LOAD and power consumed by the EXISTING LOAD under normal circuit condition (when the switch of the above circuit will be closed).

(b) Calculate the overload current, voltage and power if additional two 30 OHMS loads are connected in parallel across the existing load. (When the switch will be closed).

(c) Calculate the short circuit current, voltage and power if the LOAD is shorted. (When the switch will be closed).

(d) What will happen to this circuit if HOT” CONDUCTOR COMES IN CONTACT WITH METAL RACEWAY OR OTHER METAL OBJECT.

(e) What will happen to this circuit under open circuit condition? Calculate the open circuit current, voltage and power if one 30 OHMS load IS connected across the existing load under this open circuit condition? (When the switch will not be closed).

Homework Equations



I = E/R

The Attempt at a Solution


[/B]
I know:

240 = 7.992 or 8amps.
24 + 0.001 + 0.001 + 0.001

How do i figure out fuse size and voltage?

i know this is very basic... Any help is greatly appreciated.

I have the same question, however it supplied the voltage at 120 and a load resistance of 20 OHMS. Also, it says to consider that the length of both, black and red hot conductor is 50 feet. I calculated 5.99910 amperes so 6 amps but not sure what to do next? Any ideas
 
  • #11
Mature student said:
Any ideas
Yes, start a new thread, with your own diagram.
 
  • #12
Has anyone figured this out? I have the same (a) (b) (c) (d) (e) questions above. my voltage is 120 , load resistance of 20ohms
Also, consider that the length of both, black and red hot conductor is 50 feet. I calculated 5.99910 amperes so 6 amps but not sure what to do next
 
  • #13
@Mature student & @basede92 -- Please start your own threads here in the homework forums with your question. Please be sure to fill out the Template with the Relevant Equations and show your work. Kind of strange that you both have such similar problems, but maybe the problem is from a distance-learning problem set or something.

This old thread is closed.
 

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