Some Help Needed

[macwillis]

im a 3rd year apprentice and need some help on a few questions:

State the procedure and equipment required to perform each of the following tests

a ) insulation resistance for alarm cables

b ) continuity of alarm cables

c ) Safe isolation of a 230Vac supply

for b ) i was thinking multi-metre set on resistance shorting all the cores together at one end and testing between each one. and then checking them again un-shorted to make sure i dont have any shorts i shouldnt have.

and c ) was thinking metre set on voltage

test the supply at my IAP for 230v remove the fuse from my 3a unswitched fused spur and put the fuse in my pocket. test at IAP again making sure the supply is dead.

any help would be greatly appreciated

[james.wilson]

A) you need a insulation resistance tester ie megger. Because the cable is rated at a lower voltage, the minimum acceptable reading is lower than normal mains cable. It is in your reg book and onsite guide. Dont want to do it all for you.

B) Yes id agree

C) Whole other subject. If your 3rd year 236 then safe isolation should have been covered year 1. And its critical with the order and equipment used etc. Again well documented in your 'books'

James

[A-G]

b ) continuity of alarm cables

At end A, bear the wires and check there is no continuity between any of them.

then

At end A connect black to red, white to green and yellow to blue ....... at end B connect black to white and green to blue, then test between red and yellow and you should have continuity.

That saves all the walking back and forth

[macwillis]

i only have a copy of the 16th onsite guide.

and ive forgotten the safe isolation.

i work with a sparky and he says i would have to isolate the circuit from the board, locking off the breaker, removing the cables from the breaker. and sliding the slider over ( on a phased board)

but if its on a domestic premises and the fused spur is on a circuit with lets say the living room sockets or the kitchen lights or something.

i cant lock off the breaker becuase its a domestic board and it doesnt have the little slider.

[james.wilson]

agreed, but its the testing of isolation thats the bigger bit.

You doing your AM2?

dont think safe isolation has chnaged in the 17th anyway. But you should really have current ones, else your gonna find it hard. Borrow some from college to check.

[macwillis]

im doing NVQ3 in Security and emergency alarm systems.

have to design a system for a project.

if i ask at college im told to look in the regs but college dont have a copy.

usefull eh?

[james.wilson]

Amazed.

When i did mine we all got (couldnt take away) full relevent regs. We did buy our own as we needed em away from college but they should have them.

[macwillis]

its just for the safe isolation.

i would have said removing the fuse from the spur and putting a notice on it saying " Engineer at work do not touch" would suffice.

making sure the supply is dead at the panel .

but apparently not. i cant see me having to open up a DB exposing myself to live buzz bars when im not a qualified electrician just an security engineer.

[ispy]

A. Insulation resistance will be your Meggar set to 250M for selv circuits but make sure when test applied that cables is removed from source otherwise it may damage panel. Its to verify for poor insulation between conductors.

B. Low ohm continuity is best as its less likely to pick up false readings. as you say end to end is fine and your looking for the overall resistance of the cable.

C. safe isolation would be to use an approved voltage tester firstly tested with a prooving unit or a known source and retest after isolation. test between all live conductors and alllive conductors to earth. (neutral is classed as a live conductor)

[spider]

http://www.select.org.uk/downloads/publica...0Procedures.pdf