Spot the Faults.

[Knobhead]

i'll check the suppliers fuse tomorrow. it's probably 80A or 100A.

Tut Tut, naughty boy.

 

[pennychew]

Is it a job you are working on tel?

 

[telectrix]

yep. got to sort the mess out. basically, going to fit a 6 way DB and supply each SWA off it's own MCB.

 

[pennychew]

yep. got to sort the mess out. basically, going to fit a 6 way DB and supply each SWA off it's own MCB.

What are the SWA's supplying?

 

[telectrix]

caravan hook-ups. all on PME. that's the first phase - to earth the armours at source with the PME then TT rod each sub-main independently of the PME

 

[cotty]

Easy! The meter is in credit!

 

[happysteve]

caravan hook-ups. all on PME. that's the first phase - to earth the armours at source with the PME then TT rod each sub-main independently of the PME

If I read that right, are you saying at the moment (until you fix it) it's a PME supply supplying caravans?

If so, then gosh that's very bad (and against the ESQCR 2002).

So at the moment, in the (albeit unlikely) event that the black wire (supply service head neutral) going into the block where the earthing conductor is joined, becomes loose or is cut, then anyone who simultaneously touches any metal of their caravan - say, the door frame - and makes a good contact with Earth (wet grass) will probably die. RCDs will not save them. (Scenario 2 in the sketch below).



If I'm wrong in this (my understanding) then please correct me. I had always wondered what all the fuss about PME and caravans/boats/metal things was, until I drew it out.

 

[pennychew]

If I read that right, are you saying at the moment (until you fix it) it's a PME supply supplying caravans?

If so, then gosh that's very bad (and against the ESQCR 2002).

So at the moment, in the (albeit unlikely) event that the black wire (supply service head neutral) going into the block where the earthing conductor is joined, becomes loose or is cut, then anyone who simultaneously touches any metal of their caravan - say, the door frame - and makes a good contact with Earth (wet grass) will probably die. RCDs will not save them. (Scenario 2 in the sketch below).

View attachment 28628

If I'm wrong in this (my understanding) then please correct me. I had always wondered what all the fuss about PME and caravans/boats/metal things was, until I drew it out.

That's my understanding of it also, I watched a good YouTube video by John Ward on earthing systems and he talks about it on there

 

[happysteve]

That's my understanding of it also, I watched a good YouTube video by John Ward on earthing systems and he talks about it on there

Huh! Hadn't heard of that guy, or seen his videos. A good resource. (and pleased that my understanding has been confirmed).

 

[telectrix]

just love them pics happy. must be at least nvq3 in sketching.

 

[happysteve]

just love them pics happy. must be at least nvq3 in sketching.

Cheers! Notice how in scenario 2, the stick person has a sad face, reflecting his/her imminent demise? The devil's in the detail. (And I find drawing a sketch on paper, then taking a photo on my phone, much, much quicker than faffing about with a computer drawing package).

 

[pennychew]

just love them pics happy. must be at least nvq3 in sketching.

To be honest I don't think even eng54 could question Steve's credentials as a drawing engineer, lol!!

 

[telectrix]

Cheers! Notice how in scenario 2, the stick person has a sad face, reflecting his/her imminent demise? The devil's in the detail. (And I find drawing a sketch on paper, then taking a photo on my phone, much, much quicker than faffing about with a computer drawing package).

i did spot the sad face. i too, prefer to draw out with pen/pencil, then scan. these drawing software things are OK, but they take so long to do.

 

[Paul.M]

Tel, this has another great question attached????

Can you have 2 different earthing arrangements within the same SWA? The steel as PME and one of the cores as the TT????

This question was asked whilst I was having my first pint on a Friday evening in the beer garden. Interested if anyone can come up with a reg for this?

(ps Tel, this is how you get the Trainees to do "your" homework! SSHHH dont tell anyone )

 

[happysteve]

Don't see why not, as long as they are insulated from each other (542.1.3.3, the last bit) and there's no chance of an ordinary person being able to touch both at the same time.

Out of interest, why would you want to do this?