EAL Assignment

[joesparks]

Evening guys, I'm a newbie here. I'm studying an EAL domestic installers course, don't panic i'm not after seting up on my own when i've finished the course just using it to help me get on the bottom of the ladder.

I've got a few questions that i'm stuck on though, hoping you guys could point me in the right direction and help.

Explain why the following information, relating to the characteristics of supply is required during the design stage of the electrical installation.

a) Prospective earth fault current?

B) The value of Ze?

c) New assumed current demand of the installation?

d) Disconection time of an external bulkhead type luminaire?

a? to make sure you choose the right MCB to trip in time?

b? it will affect the speed of operation of the MCB?

c? could mean upgrading the CCU eg. from 60A to 100A if demand equires it?

d? pass

thanks for any help guys.

 

[Apache]

Hello and welcome

 

[Jono Pashley]

A) To ensure the protective devices used can break the maximum possible fault current on the installation safely

B)To check that you have a suitable method of earthing on the supply best to find any problems before you come to commissioning

C)Correct

D)Depends on the supply type, but you would need to know if the Zs value at that point would allow be low enough to allow enough current to flow under fault conditions to operate the circuit protective device, or if other protective measures would be required.

 

[SPECIAL LOCATION]

Evening guys, I'm a newbie here. I'm studying an EAL domestic installers course, don't panic i'm not after seting up on my own when i've finished the course just using it to help me get on the bottom of the ladder. I've got a few questions that i'm stuck on though, hoping you guys could point me in the right direction and help.

Explain why the following information, relating to the characteristics of supply is required during the design stage of the electrical installation.

a) Prospective earth fault current?

B) The value of Ze?

c) New assumed current demand of the installation?

d) Disconection time of an external bulkhead type luminaire?

a? to make sure you choose the right MCB to trip in time?

b? it will affect the speed of operation of the MCB?

c? could mean upgrading the CCU eg. from 60A to 100A if demand equires it?

d? pass

thanks for any help guys.

Hello Joesparks...

Guiness DrinkGuiness DrinkGuiness Drink

grab a virtual beer and have a mooch around! :^O

a) if a direct short circuit fault occurred across Live-Neutral or Live-Earth

a maximum "prospective fault current" will flow..

All switch gear fuses must be able to handle the Prospective 'worst case' fault current without blowing themselves off the wall!

B) Ze, 'External earth fault loop impedance' this is the "AC Resistance" of the suppliers live & earth conductors as it appears at your fuse box, back to the generator supply.

c) How much current an installation is going to need, e.g. what size fuse the supplier has to provide to the installation, Typical domestic property 80A or maybe 100A.

All main isolator switch have a MAX current rating, and new CUs' typically have 100A rated main switch,

but some older type CU's may only have a 60A or 80A rated switch....

not good if you are running 100A through it!

d) All circuits should disconnect within a specified time in the event of a short circuit type fault between a live conductor and an exposed conductive part (earth potential),

see regs 411.3.2, pg 46 onward in the big red book BS7671!

HTH

ASK again If I have missed something or not explained very well.

Or if I have had too many of these Guiness DrinkGuiness DrinkGuiness Drink

and missed the bleeeding obvious!:_|Blushing

I am sure the other guy will add more better stuff later!

 

[SPECIAL LOCATION]

hello again:^O

have you got a copy of the regs yet?

BS7671 around

 

[joesparks]

Thanks for the help guys, I've got the 7671 ( big red book ) though i have read easier books :_|

 

[Zeespark]

I know of someone that has memorised the BRB/OSG/GN3 as he was a house hubby at the time and looking after his kids.

Bugger thatApplaud Smileyheadbang

AndyGuiness Drink

 

[Theorysparky]

I know of someone that has memorised the BRB/OSG/GN3 as he was a house hubby at the time and looking after his kids.Bugger thatApplaud Smileyheadbang

AndyGuiness Drink

ah thats Specs then !!! :^O :^O

 

[Evans Electric]

Thanks for the help guys, I've got the 7671 ( big red book ) though i have read easier books :_|

I'd agree with you on that, welcome to the Forum.