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?
Discuss PME & Broken neutral in the Electrical Forum area at ElectriciansForums.net
As the N/E are shared at the head can you see any problem with taking a rod from MET ? I am struggling to find a reason how this wouldn't improve the safety of the installation if you lost the NeutralThat is the way it is done in some countries an external electrode is connected to the N / E juncture within the service head.
This is looking at loosing the incoming neutral, before the Neutral / Earth connection, the normal C.U RCD can't detect that.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 ?
The old MEM RCD did have a functional earth but that was years back. the only time Ive seen the functional earth now is on RCBO's. With any normal front end RCD if the neutral is lost before its split then the RCD wont become unballenced.Doesn't the white wire on the RCD help with this?
This is the problem I had years back. I had 40A+ going down to the rod.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 ?
You on the :54: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 think it more a case of PME never being fully accepted in the UK by the older electricians, having been brought up, as it were with TN-S and TT systems. A single incident somehow turns into multiple incidents, and many electricians are simply telling of someone else's experience as their own, ...it soon spirals out of all recognition then.... Not so in the vast majority of Europe where you rarely, if ever hear any scaremongery about PME/TNC-S installations, that and TT systems is all they have ever known...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
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.You on the :54:
Its the touch voltage you need to consider.
Several problems,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!
Strange that 25 of them years I would have been a sparks, and had meetings at rayleigh EEB main office. (sadly a meter changer for a year) And my father was a chair man Of the ECA and was well up there as to SAY!(knew everyone) and your friend only told you of 3 such incedences!! yep its been well coveredI 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!