Earthing Cattle Sheds ? 2

[RBE]

HI

Q Which would you say was the safest method of earthing a cow shed ie connect & bond to the supply PME earth terminal or use an earth rod & rcd making a TT installation.
Ive Always Assumed that a properly bonded system was safe on PME. However Ive just been reading about an incident in Ireland where six bullocks were electrocuted in a PME earthed installation where all the earthing & bonding was upto code. apparently there was a fault on the supply cable to another part of the farm. the information isnt specific but I suspect a brocken neutral
So Im wondering would TT be safer. ?

 

[jbartos]

Suggestion: Visit

http://www.ile.org.uk/documents/REC_Earthing.pdf

http://www.cbibreakers.com/papers/29/Loss of Neutral.pdf

etc. for more info

 

[jbartos]

Small encore:

http://www.cired.be/docs/CIRED01_RT_Earth.doc

 

[RBE]

Hi Jbartos

yes verry interesting sites But non have specific reference to my question as both earthing systems have their merits & both meet BS7671 requirements what Im asking is there any reccomended preference. given the incident I refered to. I personaly prefer pme. but how can back feed be prevented if a break in neutral occurs as the source is via overhead cables.

 

[jbartos]

Suggestion to the previous posting. When it comes to a malfunction of the electrical equipment, it may become dangerous to everyone, not only to cows. Therefore, various potential malfunctions have to be anticipated, identified and an appropriate protection designed, i.e. protective relays, monitoring, annunciation and sensing.

 

[RBE]

it seems to be an area that no one can give a straight answer to
The conclusion in the artical I refered to merely stated that the installer should have checked the rest of the sites installation even the there is no guarentee that it would have been prevented. RCD relays are a standard requirement but are useless under sutch circumstances

 

[jbartos]

Suggestion: The equipment manufacturer tech support is supposed to provide a suitable guidance or application notes.

 

[RBE]

Hi
I was not suggesting that the Rcd was faulty or incorrectly installed, if you go to

http://www.reci.ie/newssept2000.htm

Electrocution of cattle.
you will understand me better.

 

[Walden]

This almost happened to me when I was on "The Tools"! I quoted a farmer for the electrical installation of a new milking parlour in an existing shed. I lost the job to the farmer's brother-in-law who did the work at weekends. Two months later, 6 of his cows fell down dead as he was milking them!

The problem with PME is making sure everything else is on PME too! A voltage sensitive relay/breaker could be used to monitor the rise in earth/neutral voltage without, I believe, breaking any European regulations.

I have some information on this problem, if you contact me on tmp@fridgecontrols.co.uk I can email it to you.

 

[RBE]

Martinpirrie

Thanks for the info. this backs up my own oppinion to use a TT system with Rcd protection. as opposed to connecting to the Recs Pme earth Based on the fact that it is less likely that stray current from other instalations can back feed onto the installation ok fault disconnection is dependant on the Rcd Opperating But this seems to offer the best protection for livestock. & loss of overhead CNE would not impose dangerous voltage on the earth/Bond in the building. as the Rcd would Trip.

Regards RBE

 

[jbartos]

Suggestion: It is not the voltage that is so dangerous, actually it is the excessive current that causes discomfort. The system with isolated ground and properly protected are safer. Even, if the system is isolated from the ground, there will be need for proper protection and monitoring, since insulation faults do happen and the insulated power system from the ground can also become dangerous.

 

[scotsparky]

Working for a local REC I would suggest the TT system ,and earth spike each and every shed . This will prevent as mentioned tranfering earth fault currents and will prevent reverse polarity problems occuring with the pme system. Most overhead installations have been found to have poor or non existing earthing ,and remember if there is a problem with the earthing found from the incoming overhead the REC will only service an existing supplied earth and will not provide one if not already done. Its the live/neutral thats guaranteed not the earth .

 

[RBE]

scotsparky

I just wondered what your oppinion was on a site using both
ie house Workshops & grainstore on PME.
cow shed & stables on TT earth spike & Rcds
the buildings are seperate so cross bonding isn,t a problem
& water pipes are pvc.

 

[Walden]

Is it still possible to buy a voltage operated earth leakage breaker like the old Crabtree E60?

 

[RBE]

Martinpirrie

I may be wrong but I thought the IEE had banned the use of voltage opperated trips,

 

[scotsparky]

RBE
I would check the incoming earthing first, just to see how good or poor the earth is. If the origional installation is conventional and you can take an earth loop reading, you really will have to stick to the Less than 0.8 ohm rule.

However having experience with a conventional setup in normal housing ie seperate live/neutral/earth and relying on the overhead earth, in windy conditions this can become detached at some point without neccessarily falling down and you then have the problem where any small live to earth (or neutral to earth)fault will energise all earthed metal work.
If the offending overhead earth-wire then falls onto a phase conductor you will then have the full 230 volts on your earth and god forbid it falls onto the wrong phase you will have 415 between live and earth and 230 between neutral and earth or you could end up with 0 volts between live and neutral...aarrgghhh potential disaster and then the sky falls down!.
I have come across this problem where a 30mA rcd will not trip because there is no other leakage path,(especially with the new split boards) that is until someone touches the sink etc!
In my experience I would stick to a conventional earthing setup and stick in my own earth spike and RCD in each building. I would never use PME from an overhead although I dont think I have seen it provided from this REC.
I think I`ll take up plumbing.

 

[jbartos]

Suggestion: The system and equipment grounding can be shown on drawings, e.g. grounding schematic diagram, grounding layout, grounding details, etc. This way there is not any difficulty to follow it.