help with a few 2391 questions!!!

[dazsmith]

Had a go at a past paper and come across a few questions that i could do with a hand on!! your help would be much appreciated!!! Thanks

1.A SELV circuit is to be tested for electrical separation from a low voltage circuit which
shares the same pvc conduit containment system. State the
a) test voltage to be applied (1 mark)
b) conductors between which the test is carried out. (2 marks)

2.A 230 V circuit containing a surge protection device is to be tested for insulation resistance and the device cannot be disconnected. State the
a) conductors between which the test is carried out 1mark
b)test voltage applied 1mark
c)minimum acceptable resistance. 1mark

3.State the minimum IP rating for each of the following.
a)The top surface of an accessible distribution board 1mark.
b) The front face of a domestic consumer
15 Explain
a) the effect on earth fault protection provided by a BS EN 60898 circuit breaker if it is connected in the neutral conductor only 1mark
b) why the effect in a) above occurs. 2marks
unit. 1mark
c) An internal barrier within a distribution board. 1mark

 

[morph]

Had a go at a past paper and come across a few questions that i could do with a hand on!! your help would be much appreciated!!! Thanks

1.A SELV circuit is to be tested for electrical separation from a low voltage circuit which
shares the same pvc conduit containment system. State the
a) test voltage to be applied (1 mark)
b) conductors between which the test is carried out. (2 marks)


500v DC
all live conductors and all live conductors to earth

you can find the rest out your self ;-)

 

[tony mc]

Check the BRB on testing only a couple of pages and testing when surge protective devices can not be disconnected is covered you need to read that.

IP codes you will get these questions and you need to know IPXXD IP4X IP2X IPXXB GN3page 42 get to know these along with the other popular ones.

Re the neutral conductor in the protective device.

You need to know your earth fault path as this question comes up time after time and you can get 15 easy marks drawing it and identifying the main parts.

Basically if the neutral is in the protective conductor the mcb will not trip as when a earth fault occurs it does not go down the neutral conductor AS THE NEUTRAL IS NOT PART OF THE EARTH FAULT PATH.


1 Point of fault
2 CPC of cct
3 MET
4 Earthing caonductor TT Mass of earth TN Metalic return.
5 Main earth electrode of transformer Star point
6 Windings of transformer.
7 Line conductor back to point of fault but via MCB which would of now tripped .

Hope this helps

 

[mart8235]

Had a go at a past paper and come across a few questions that i could do with a hand on!! your help would be much appreciated!!! Thanks

1.A SELV circuit is to be tested for electrical separation from a low voltage circuit which
shares the same pvc conduit containment system. State the
a) test voltage to be applied (1 mark)
b) conductors between which the test is carried out. (2 marks)


500v DC
all live conductors and all live conductors to earth

you can find the rest out your self ;-)

SELV - Separated Extra Low Voltage, pretty sure its 250v dc for ELV

 

[tony mc]

If your taking the 2391 you need to know this.

The question is SELV cct to be tested for electrical separation from a LOW voltage cct

Morp has answered this .