N-E joined at the incomer of your house

[Kev2632]

I was just wondering with the N-E being joined at the incomer, if i was to go downstream of a circuit which was "NOT" Rcd protected and tested between Neutral and Earth that would appear as a dead short between N-E is that correct? but if i was to go downstream of a RCD protected it wont be there is at that correct? as it cant get passed the RCD is that right?

Thanks.

 

[Rockingit]

I'M sorry but this thread reads like a child asking an adult WHY? WHY? WHY?

Who's to say the OP isn't? I could easily see a 14yr old me having asked just that kind of question.
(Apologies to the OP, just making a case that this an open forum!)

 

[morph]

goodnight

 

[Guest55]

N and E once joined never separate

wrong way round , once separated N and E never rejoin , starting at the distribution origin and working towards the consumers installation.

 

[Kev2632]

Some folk dont have patience... enough said there, MANY thanks to those who are willing to help, everybody has to learn eventually.

 

[Kev2632]

ive got my head round most of it now, but the only thing i cant understand is..

When on circuits where there is no RCD present, and the N-E joined together is present downstream of the circuit, why is the " Safety Feature anybody??

Thanks.

 

[snowhead]

wrong way round , once separated N and E never rejoin , starting at the distribution origin and working towards the consumers installation.

You're talking cables, I'm talking Neutral and Earth potential and therefore effect on RCDs

 

[snowhead]

again i was keeping it simple
i dont see you actually trying to help anyone here

On this comment, correcting your D.C flow, or on this thread?

 

[Rockingit]

ive got my head round most of it now, but the only thing i cant understand is..

When on circuits where there is no RCD present, and the N-E joined together is present downstream of the circuit, why is the " Safety Feature anybody??

Thanks.

What I think you're asking is how does this make it safer, right? The simplest answer is that by creating a dead short from the Live to the Neutral (via the Earth) it allows an enormous amount of energy to flow very very quickly. This energy surge then either burns a fuse wire, or trips an MCB so that the circuit is broken and then becomes dead, so safe again. In electrical terminology we call this type of protection "Automatic Disconnection of Supply" or ADS for short.

 

[Knobhead]

I like threads like this! :clap:

Are you playing devils advocate?

 

[Kev2632]

What I think you're asking is how does this make it safer, right? The simplest answer is that by creating a dead short from the Live to the Neutral (via the Earth) it allows an enormous amount of energy to flow very very quickly. This energy surge then either burns a fuse wire, or trips an MCB so that the circuit is broken and then becomes dead, so safe again. In electrical terminology we call this type of protection "Automatic Disconnection of Supply" or ADS for short.

So that was the way to protect circuits in the days before an RCD came into play is that correct ?

 

[Des 56]

As an apprentice trying to get to grips with basic 3 phase theory,I couldn't at first understand the return paths
At the time we were also being shown Star and delta configurations
Yours truley gets in one right puddle mixing this information like spagetti thoughts

I decided to ask the old man spark in the colliery I was at the outcome of this joining of winding ends

"What would happen if the three phases were linked at the outgoing bus bar of a panel,I asked in all sincerity
Son he said,see that roof above your head", "Yes sir.I do"

"Well son he said,remember it well, because the last you will see of it is when it disappears and joins Sputnic in orbit"

That seemed to help me know I needed to rethink this through
The op is asking questions that he considers thoughtfull and I for one see no problem answering his queries if at possible

 

[Kev2632]

As an apprentice trying to get to grips with basic 3 phase theory,I couldn't at first understand the return paths
At the time we were also being shown Star and delta configurations
Yours truley gets in one right puddle mixing this information like spagetti thoughts

I decided to ask the old man spark in the colliery I was at the outcome of this joining of winding ends

"What would happen if the three phases were linked at the outgoing bus bar of a panel,I asked in all sincerity
Son he said,see that roof above your head", "Yes sir.I do"

"Well son he said,remember it well, because the last you will see of it is when it disappears and joins Sputnic in orbit"

That seemed to help me know I needed to rethink this through
The op is asking questions that he considers thoughtfull and I for one see no problem answering his queries if at possible

Thanks Des 56, Much appreciated

 

[Rockingit]

So that was the way to protect circuits in the days before an RCD came into play is that correct ?

It still is! RCD's have not replaced fuses and breakers. An RCD will not trip on an overload like a fuse will (so say for example a circuit that is rated at 10A suddenly draws 100A, an RCD won't have a problem with that so long as it's 100A OUT the L and 100A BACK in the N). What the RCD will do is detect if in our 10A circuit, 9A suddenly returns via the Earth not the Neutral because a child has just dropped a drink into the fan heater....

 

[Kev2632]

It still is! RCD's have not replaced fuses and breakers. An RCD will not trip on an overload like a fuse will (so say for example a circuit that is rated at 10A suddenly draws 100A, an RCD won't have a problem with that so long as it's 100A OUT the L and 100A BACK in the N). What the RCD will do is detect if in our 10A circuit, 9A suddenly returns via the Earth not the Neutral because a child has just dropped a drink into the fan heater....

Yea, i understand what your explaining to me there, but the Neutral to Earth " Joined" wont be present downstream of an RCD protected circuit, so that wont help the Circuit for its " safety feature " as it would on a NON-RCD protected side? it will just Rely on the MCB for the overload is that correct?

 

[Goody]

This thread induced me to explore the PME system in details and here is an abstract that I lifted off from a website:

The great virtue of the PME system is that neutral is bonded to earth so that a phase to earth fault is automatically a phase to neutral fault. The earth-fault loop impedance will then be low, resulting in a high value of fault current which will operate the protective device quickly. It must be stressed that the neutral and earth conductors are kept quite separate within the installation: the main earthing terminal is bonded to the incoming combined earth and neutral conductor by the Electricity Supply Company. The difficulty of ensuring that bonding requirements are met on construction sites means that PME supplies must not be used. Electricity Supply Regulations forbid the use of PME supplies to feed caravans and caravan sites.