2365/615 Question 5 Help please

[TClarney]

I'm just wondering if anyone can point me in the right direction with this question I'm struggling to work it out.

 

[timhoward]

Welcome!
Try this video - only 10 minutes, and if you still have questions come back and ask.

 

[TClarney]

Welcome!
Try this video - only 10 minutes, and if you still have questions come back and ask.

Thanks Tim,

I will give this a watch.

 

[timhoward]

Hopefully it helped. The starting point is that you are going to need the prospective fault current, so either
-they tell you what it is, or
-they tell you the Ze and the R1+R2 which add together to give the Zs and you can calculate the fault current ( 230 / Zs) , or
-if they are making you work very hard they will tell you 'so many' meters of a certain type of cable and you'll have to calculate the R1+R2 and then add it to the Ze, giving you the Zs, and calculate the fault current (230/Zs)
Having got the fault current you need to know how quickly it will trip the protective device from the relevant graph.

 

[TClarney]

Hopefully it helped. The starting point is that you are going to need the prospective fault current, so either
-they tell you what it is, or
-they tell you the Ze and the R1+R2 which add together to give the Zs and you can calculate the fault current ( 230 / Zs) , or
-if they are making you work very hard they will tell you 'so many' meters of a certain type of cable and you'll have to calculate the R1+R2 and then add it to the Ze, giving you the Zs, and calculate the fault current (230/Zs)
Having got the fault current you need to know how quickly it will trip the protective device from the relevant graph.

Hi Tim,

This is really the only info they are giving me I don’t know if I’m just being stupid but I can’t get my head around this.

 

[timhoward]

Ok, that's a start. 70 degree PVC singles in conduit and 16 amp protective device.

You are missing:
The length of the circuit - is there a diagram showing the room? Does a previous question address this?
The size of PVC singles (e.g. 1.5 sq mm, 2.5 sq mm. It can't be 1 sq mm as that can't carry 16 amps in conduit on a wall). This affects the resistance, and therefore the fault current.
The specific protective device (though one could assume a B16 MCB)
The earth loop impedance of the origin (Ze). (the resistance back to the supply transformer, which also affects fault current)

Do the previous questions get you to work out this, e.g. select an appropriate cable size for the fridges circuit for reference method B?

To use the adiabatic equation you need to know the actual prospective fault current for the actual circuit and right now you don't appear to have enough information.
I can only assume that other questions you have already answered are related to it too.

 

[Clemmie]

Has anyone got the full list of questions for this unit my tutor is away for weeks on end and what to start the assignment early as I like to keep on top of things.

 

[ajama21]

Ok, that's a start. 70 degree PVC singles in conduit and 16 amp protective device.

You are missing:
The length of the circuit - is there a diagram showing the room? Does a previous question address this?
The size of PVC singles (e.g. 1.5 sq mm, 2.5 sq mm. It can't be 1 sq mm as that can't carry 16 amps in conduit on a wall). This affects the resistance, and therefore the fault current.
The specific protective device (though one could assume a B16 MCB)
The earth loop impedance of the origin (Ze). (the resistance back to the supply transformer, which also affects fault current)

Do the previous questions get you to work out this, e.g. select an appropriate cable size for the fridges circuit for reference method B?

To use the adiabatic equation you need to know the actual prospective fault current for the actual circuit and right now you don't appear to have enough information.
I can only assume that other questions you have already answered are related

Hi Tim. Im also doing the same project. the pfc is listed in the photo how would i use it or can you show me what steps i should take for this question.

 

[westward10]

What do you think the value of PFC means in relation to the question?