Help please

[lee sandland]

Hi all,
i am doing a domestic electrical installer eal level 2 course with olci and came across a question "if i had to wire a immersion heater 10meters away from the cu would i use 11 meters of cable and would i use the same cable size for a 8kw shower

 

[cbw]

No and No

How long is a bit of string (CABLE) it depends on what, how and where it needs to run.

3kw/230=13.04 amps
8kw/230=34.8 amps

You look at installation methods and let us know what cable sizes you think.

The other things to bear in mind is heat resistant flex for the heater side of circuit and I think the power triangle calculation for emersion heaters is based on 240v so it comes in under 13 amp (May be wrong)

 

[lee sandland]

No and No

thanks but that did't help

 

[cbw]

thanks but that did't help

Sorry was busy typing the rest, me and computers!!!

 

[lee sandland]

Sorry was busy typing the rest, me and computers!!!

ok sorry,but the question is "10 meters away from the cu,so i will put 11 meters thanks for your help

 

[cbw]

Sorry Lee, I dont understand the 10M/11M bit of the question, If you were to wire mine here at home it is about 8 meters from the CU but you would probably need 16M of cable to get there

 

[lee sandland]

Sorry Lee, I dont understand the 10M/11M bit of the question, If you were to wire mine here at home it is about 8 meters from the CU but you would probably need 16M of cable to get there

ok i understand i will just have to guess what there trying to say thanks anyway

 

[Amp David]

What sort of question is that for them to ask you? Do you get any more options for your answer?

 

[lee sandland]

What sort of question is that for them to ask you? Do you get any more options for your answer?

hi dave ,i will right you the question
"Make a material list of all the components and accessories necessary to install the following circuit:
1) 3kw immertion heater circuit, 10 meters from the cu
2) 8kw electric shower circuit , 15 meters from the cu

 

[Jason Smith]

Easy peasey lemon squezy mate. They are exploring loads of your knowledge here, Cookers and Immersions go on their own circuits. Average immersion is 3KW, so its 2.5 to a fused switch, then a meter or so of heat resistant to the immersion. All goes back to a 16 or 20 amp MCB. The cable length written into the question could be about voltage drop, but not even a consideration at 10-11 meters, the Wire size is to be able to carry the current for the load (immersion) the MCB size is to protect the wire from catching fire in an overcurrent situation.
Any suggestion of bogging into the shower circuit is out because both have their own circuit back to the board. If they are suggesting can you use wire big enough to draw 8.5 kilowatts down it for the immersion yes you can, as it only draws 3kw.
These questions are easy if when designing, you start with the load and design a circuit for it, right back to the board, learn which circuits have to stand alone. This question is all about watts dived by volts equals amps, and loads of regs.

 

[lee sandland]

thanks jason

 

[cbw]

So how come no thanks to me????

Not jealous but I did try to help...........

Have you worked out the cable sizes?

 

[Amp David]

hi dave ,i will right you the question
"Make a material list of all the components and accessories necessary to install the following circuit:
1) 3kw immertion heater circuit, 10 meters from the cu
2) 8kw electric shower circuit , 15 meters from the cu

Well now you've actually posted the question being asked, it make sense now.

 

[lee sandland]

Well now you've actually posted the question being asked, it make sense now.

HI so is jason right, thanks

 

[ezzzekiel]

its actually a stupid question to ask, and if thats the best the di can come up with then they all should be shut down