K
Knobhead
I know some countries use protection to guard against a broken neutral in PME systems.
Anyone know how they work?
Anyone know how they work?
Acording to E54 it never happens, so why bother.I know some countries use protection to guard against a broken neutral in PME systems.
Anyone know how they work?
Speak to the DNO ask them if you can fit an Earth Rod as a back up they will probably say no but do it anyway lol
J
Most of the underground PME joints to supply buildings are staked by the dnoThat is the way it is done in some countries an external electrode is connected to the N / E juncture within the service head.
That is the way it is done in some countries an external electrode is connected to the N / E juncture within the service head.
I don't quite get where he's saying it should be positioned in relation to it's effectiveness ? My CU has a 30mA non delayed RCD as a main switch will it trip out if the N drops out ? it's the same as his diagram isn't it ?
J
Doesn't the white wire on the RCD help with this?
It happened to my house years back.
I am thinking if 10 houses are on the same phase as me and the N drops off will I get all their fault load as well because my nice shiny new earth rod will provide a lower path of resistance than all their bonded extraneous water and gas ?
And if you have plastic gas/water coming in it gets worse.
J
i cant see how it would be a problem if all of the neutrakl curent was trying to go down one electrodwe. the laws of a certain mr ohm would take care of that. Aint you supposed to size the cable to the rod by best case resistance anyway? So in tother words, itys very unlikely that you would have a sub 10 ohms electrode. so the current that would flow would be 2.3 ohms. a 10mm cable for example would take that indefinately.
thy problem comeswhen people have undersized the cable to the rod, and you get a low current, long duration fault.
I can't help suspecting that there is a conspiracy of denial going on here.
Every electrician known to me, who's been in the game for a while has come across at least one failed neutral, that's not to say that it was open circuit, but more high resistance. As soon as the resistance rises beyond a few ohms it will begin to cause problems and will get progressively worse unless it is recognised and dealt with pdq.
I would certainly agree that spiking the MET at every supply intake will alleviate certain problems but will also hide them as well
You on the :54:
Its the touch voltage you need to consider.
Fair point about the touch voltage, but that is the point of CPC's and equipotential/supplementary bonding, so that even if the touch voltage is high, then there is no potential between any extraneous or eposed conductive parts.
in my inmd there is little difference between the physics of current flowing down a rod, or down a pipe to earth. Eitrher way, if the bonding cable is sized correctly, it shouldnt pose a danger to the end user of the installation.
No alcohol by the way, just rubbish at typing fluidly/accurately at the same time!
I take with a large pinch of salt, those that state they have seen numerous instances of broken neutrals on PME systems, it just doesn't happen, fortunately!!! I have a recently retired friend (DNO regional manager) that has only known of 3 such instances since joining, as was then, Eastern Electricity through to the time of his retirement in 2011, approx 35 years in total!!!
One of the easiest and cost effective ways of mitigating such problems to some extent, is to have a local earth rod at ''Each'' and every PME/TNC-S supply head, as they do in many European countries. But not at a numbty 200 ohm level, that would be a complete and total waste of time!
It would seem some countries use a RCD with a built in over voltage trip to protect the consumers equipment.
This vector diagram shows what happens with a floating neutral.
<snip> It is not a simple matter to retrofit TN-C-S distribution systems with such a facility. This is true for
TN-C-S systems (such as those in South Africa) that do not require the installation of a foundation
earth at the service entrance. Unless every consumer each have their own service entrance
foundation earth facilities, in the event of a break in the PEN conductor, the load current of all
other consumers may find a return path through those foundation earth connections that happen
to be present.
An extreme example would be the case of only one consumer having a foundation earth. In such
a situation, all the load currents of all consumers connected to that distribution system would try
to flow through the single foundation earth present. The consequential overheating together with
the related possibilities of incendiary ignition will be obvious.
so in an hour the DNO turn up and check the Ze and he says yep it was probelly like this from when they did the joint in the road, using wooden joint boxes.
Two options TT the house or get the occupier to apply for TNCS,the 3rd option from the chap who turned up was I PME the head and he would re seal if needed! I went with option 3 but re sealed it myself! There was no care of what the condition of the undrground joints were in. so to say...
I've never seen or heard of buried wooden cable joint boxes. In the early day's virtually all underground cable joints would have been heavy gage cast iron with plumed lead joints!!!
And if the DNO electrician came to any job i was involved with and spouted off that sort of crap, i'd have been on to his manager, asking a few pertinent questions. One of which, would have been allowing a jobbing electrician to undertake connection alterations to a service cut-out!!!