WOULD THESE ANSWERS BE ACCEPTABLE?? or along right lines...bit of help pls :( exam on thursday

[Dave A]

1)state the likely cause of each of the following faults

a)complete loss of supply at the origin of the installation

b)the motor contactor starter fails to hold on

c)a circuit breaker in a distribution board operates but fails to hold on

answers

a) the main fuse in the board has gone causing a loss of supply

or

a)would it be due to loose tails or M.E.T?

b)the contactor coil has gone

c) short circuit- (obviousley expand a bit more in the exam)

2a) identify three electrotechnical systems/equipment where precautions should be taken during fault diognosis?

b)identify hazards/risks

answers-

-overide timer fan- permanent live?

-solar pv- could be distributing energy elsewhere

- dimmers and lighting transformers??

 

[Andy™]

loose MET will not cause loss of supply (loss of life possible though)

if contactor coil was gone, it would not work in the first place. if it doesnt hold on, then its usually the aux contact

solar PV - panels will always be live

 

[ProDave]

Last time I went to investigate a total loss of supply, the L was there but the neutral wasn't.

I suspected a corroded and ruptured outer core of a concentric feed cable and called the DNO. I was right, they had to dig up his drive and half the street to lay a new cable.

 

[Dave A]

i know u cant really give me the answers but theses are the questions i am really struggling with, could i get your opinion and maybe the answers which u would say so i can compare with ones i have?

---------- Post Auto-Merged at 19:00 ---------- Previous post was made at 18:59 ----------

is the DNO same as SWA?

---------- Post Auto-Merged at 19:01 ---------- Previous post was made at 19:00 ----------

MY BAD JUS READ UR COMMENT AGAIN LOL

 

[ProDave]

SWA = Steel Wire Armoured cable (mains cable you can bury underground)

DNO = District Network Operator, the electricity company that maintains the supply network.

Most likely cause of total loss of power in most cases is the main fuse blown. That is the responsibility of the DNO and it is them who you contact to come and replace it. Us humble sparkies are not permitted to replace a blown main fuse.

If you customer has chosen a different energy supplier to your local DNO you may get the run around between the two, but that is less likely if you make it clear it's an emergency and they have lost all power.

 

[Evans Electric]

No, DNO is the company supplying power to the property.

SWA means Steel Wire Armour as in Armoured cable .

 

[Dave A]

Hi there proDave

You seem a knowledgable sparkes i wonder if u could help me with this question which has had me stressed for days... identify three electrotechnical systems/equipment where precautions should be taken during fault diognosis?

b)identify hazards/risks

answers-

-overide timer fan- permanent live?

-solar pv- could be distributing energy elsewhere

- dimmers and lighting transformers??

they were the only answers i could think of

 

[Evans Electric]

Electrotechnical systems !!!! Where does that come from ?? Sometimes I think I've been at it too long TBH

An Electrotechnical System Eh!

Precautions have to be taken with everything , even a simple light fitting .

I sometimes wonder about the logic of these questions . Why don't they say what they mean .

I see where Andy is coming from with the PV stuff and the DC still feeding in even after switching the board off, if this is what the examiner is looking for , why not say .

Don't see a problem with a fan TBH , turn off 3pole isolator .

Dimmers !! :C

Hazard would be with a motor that starts automatically so you lock it off before changing a belt etc.

As Andy says , PV panel with an isolator for the DC and the AC .

 

[Dave A]

what about these Q and A's....

1)state the likely cause of each of the following faults

a)complete loss of supply at the origin of the installation

b)the motor contactor starter fails to hold on

c)a circuit breaker in a distribution board operates but fails to hold on

answers

a) the main fuse in the board has gone causing a loss of supply

or

a)would it be due to loose tails or M.E.T?

b)the contactor coil has gone

c) short circuit- (obviousley expand a bit more in the exam)

 

[Evans Electric]

a) Service fuse or network fault .

B) Motor jammed, overloads tripping, starting load too high, fault on the hold-on circuit. Hold-on not wired correctly.

c) Short circuit. Overload . Faulty breaker . Trying to switch on with loads of IT stuff plugged in .

 

[ProDave]

Hi there proDaveYou seem a knowledgable sparkes

Steady on, let's not start rumours

As for these "electrotechnical systems" not heard that phrase before.

Common sense really, anything with permanent live, e.g timer fans, pir lights even humble light switches. Of course you have been taught all about safe isolation, test for dead etc haven't you?

Also rotating machinery has it's own hazards.

 

[batty]

well in my area the most likely cause of lose of power will be EDF have got a fault again it is actually getting quite a regular thing.

 

[apprentice87]

Hi ProDave,

You say;

"Last time I went to investigate a total loss of supply, the L was there but the neutral wasn't.

I suspected a corroded and ruptured outer core of a concentric feed cable and called the DNO. I was right, they had to dig up his drive and half the street to lay a new cable"

Funnily enough, a western power cable jointer told me they have this problem quite often, and that they have many more problems with the "modern" cables than they ever did with the old lead and paper ones....

Was it a TNCS supply?? the sort where the DNO GUARANTEE that they will never lose the neutral!!!!!! Wired in concentric i rather suspect it would be!! [unless it was TT'ed]

Were there any other problems?? people dead in the garden holding class one electric drills and the like!!!!

john..

 

[ProDave]

The supply hadn't gone completely. If you turned a light on, on would glow very dim, but turn anything bigger on and the light went dimmer still.

As far as I could tell the incoming neutral had ruptured and the only return path allowing it to work at all was via the water and gas pipes.

I didn't hang about doing any more tests, as soon as I realised what was going on, I switched off the CU and called the DNO.

Lets just say I could light my neon screwdriver from the MET!!!!! So I think the touch voltage exceeded 50V.

 

[Technician]

Only an observation; if the supply fails in this manner

who pays for rectification? Consumers never had to

pay BUT, when supply heads are being renewed the

guys take a live Ze reading. In some areas of the

country Ze is creeping up and PME has to be installed;

and the customer is paying for it, in part if not all of it.

Interesting comments in your post Pro Dave.

 

[Andy™]

if the fault is before the meter, then its upto DNO to fix FOC

 

[a1]

is the DNO same as SWA?

No mate: See attachment (to your right) for a useful demo: It involves hovering Mouse.

Lets just say I could light my neon screwdriver from the MET!!!!!

You have a Neon Screwdriver Dave? And you used it?? :innocent

the guys take a live Ze reading.

As one would expect, Techy. Or else it would be a Calculation or Enquiry. :innocent

 

[Technician]

Yes Admin, I take Andy's point and yours.

One of the guys doing live working in houses

where this was done told me that there was

a charge for the installation of the PME (Protective

Multiple Earthing) irrespective of the earthing

arrangment. I was (mildly) surprised.