Overhead PME

[Justinsane]

Is it common to see overhead pme systems? I went to a job the other day which had an overhead supply.
The main earthing terminal has the cable coming out of the enclosure and down the wall into the ground.

The external earth loop was 0.26....I phoned the supply authority and apparently they upgraded all the overhead supplies from TT to PME.

anyone else come across this?

 

[Spudnik]

Quite common nowadays.

They normally PME TT systems at the base of about every 3rd pole and when requested in a domestic situation they can easily supply it.

The supply companies, i believe,have until 2013 to convert most supplies to PME from TT anyway.

 

[chocolate]

Does that mean that by 2013, all TT supplies to houses will need to be concentric cable and not separate line and neutral conductors as most presently are ?????

With a TT supply ( separate conductor supply ) , even with PME, isn't there still a risk that should the neutral conductor be broken, you automatically lose your earth ? So PME or not, there's still a risk to the customer.

Can you use an earth electrode to compliment a PME supply ?

 

[Dazza1212]

You are right with the problems of pme it is a cheap fix for the supplyers but if you staked the property and lost the neutral and had a n-e fault ( with most places have) the results would be catosphropic thats why there should be a hold on contactor fitted at the disturbutions side of ervy pme head as like i say the results of a neutral failing is a bad situation to have say a village sub lost a neutral and some one had a neral earth fault the villages load would all try to go through that if they was on the right side of the fault i hope this helps

dazza1212

 

[Justinsane]

the property i was at had the line and neutral coming in overhead separately, not one cable,
the earth then came out of the earthing terminal and disapeared down the side of the house and into the ground. There are three seperate cables coming out of the enclosue on the wall of the house....
I don't understand how this can be pme?

 

[Spudnik]

If you have a reading of .26 then i would say that you do have PME.

However, as you probably know, PME is derived out of the side of the head into, normally, an MET.

Can you trace the ME from the CU to see where that goes?

 

[Justinsane]

I've looked all round the property and have found an old earth rod which has been disconnected.
Other than that i dont know where its going. Where the neutral and earth cables come into the box there looks like some kind of join........theres a transformer at the bottom of the garden which has a cable running down into the ground but i don't know where that goes.

 

[Spudnik]

Hmmm.

Any chance you can get some pics posted up sometime?

Would be interested to see this arrangement and it also might help us establish whats going on.

 

[Justinsane]

I'll take some photos tomorrow and post them up....

 

[Dazza1212]

without sounding rude in any way but did u do a loop with all the bonds disconected,
also where the netral block is at the head is there an earth wire coming out of that to i hope i am not insulting ur inteallagence i only wish to help

 

[Justinsane]

yep, i did loop without bonds connected. I have spoken to WPD and they are sending someone out to confirm the earthing arrangement. What i don't understand is how they gave me earth loop impedence values without knowing what it was??

I have spoken to someone who told me that WPD will convert a TT system to PME as long as all the relevent bonding is in place. They crimp the neutral and earth cable together just outside the box but tend to leave the old earth rod connection there.....

I've spoken to three different people at WPD with regards to this property and each time they tell you something different!

 

[Spudnik]

I have spoken to someone who told me that WPD will convert a TT system to PME as long as all the relevent bonding is in place. They crimp the neutral and earth cable together just outside the box but tend to leave the old earth rod connection there.....

Sounds like this may be what you have.

Did you get any pics to post up?

 

[Justinsane]

I'll sort some out tomorrow......