Advice on regulation 521.5.1

[Paul.M]

It's actually quite a good thread paul.

Theres a bit of silliness and provoking language but it's not too bad and the main thing is everyone is actually contributing, unlike in the past where there would have been posts solely designed to cause offense.

Let's see if the music has helped :smile5:

Yes it is a good thread but it has been reported and we thought a bit of chill out music was the best option. Next time DW is picking the track

 

[HappyHippyDad]

Yes it is a good thread but it has been reported and we thought a bit of chill out music was the best option. Next time DW is picking the track

You do realise I now have Nina Simone blaring out! The link lasts for 1 hour 15 minutes and 33 seconds!!

 

[andyb]

It's actually quite a good thread paul.

Theres a bit of silliness and provoking language but it's not too bad and the main thing is everyone is actually contributing, unlike in the past where there would have been posts solely designed to cause offense.

Let's see if the music has helped :smile5:


ps... Although as for whether the Main CPC should go through the same hole as the tails I'm far more confused than when I first read the reg!! I think I'll stick to what the reg says and have all three together, thus it avoids any problems with those eddies and complies with BS7671.

I agree with all this hhd, I must admit that until this thread I was unaware that the protective conductor of a circuit needs to enter with the live conductors. (I'm talking about a ferrous metal enclosure for any pedant out there)

As an aside, how much current and for how long would need to flow through a conductor for it to be a problem?
It seems to me that if a fault current flows for long enough and does not operate the ocpd then you have a bit more of a problem that a piece of metal getting warm.

 

[Deleted member 26818]

Rather than asking the NICEIC for advice on what the Regulations mean, perhaps you should try asking the IET.

 

[Risteard]

Although as for whether the Main CPC should go through the same hole as the tails I'm far more confused than when I first read the reg!! I think I'll stick to what the reg says and have all three together, thus it avoids any problems with those eddies and complies with BS7671.

How is there any confusion? The Earthing Conductor is a protective conductor so the Regulation is clear and explicit.

I don't understand the confusion. A number of years ago I flagged up the issue during initial verification where the three phases and the neutral entered a switch fuse through one entry and the Earthing Conductor through another. The NICEIC Approved Contractor I was working for tried to tell me that I was wrong about protective conductors being subjected to the same rules as the live conductors but it is and always has been stated very clearly in the Regulations.

 

[HappyHippyDad]

How is there any confusion? The Earthing Conductor is a protective conductor so the Regulation is clear and explicit.

I don't understand the confusion. A number of years ago I flagged up the issue during initial verification where the three phases and the neutral entered a switch fuse through one entry and the Earthing Conductor through another. The NICEIC Approved Contractor I was working for tried to tell me that I was wrong about protective conductors being subjected to the same rules as the live conductors but it is and always has been stated very clearly in the Regulations.

You're confused about the confusion and I'm confused about your confusion about the confusion!

 

[davesparks]

As an aside, how much current and for how long would need to flow through a conductor for it to be a problem?
It seems to me that if a fault current flows for long enough and does not operate the ocpd then you have a bit more of a problem that a piece of metal getting warm.

Considering that fault currents can be in the thousands of amps it will probably take a fraction of a second for the eddy currents to become a problem. Don't forget current has more effects than just heating the conductor, the magnetic fields will cause mechanical stress at those levels.

 

[Dave OCD]

No, I hate children
Wtf does having kids have to do with it?

Why does this not surprise me ?

 

[davesparks]

Why does this not surprise me ?

Which bit?

 

[Dave OCD]

It just came into my head Dave, bit strong saying you hate kids though, you were one once ? :smiley2:

 

[interlude]

Why spin?
it has always been acceptable, whilst ill advised to run a "separate" earth (cpc) alongside an SWA, as both the SWA & the "earth" must be capable of carrying the full fault current and suitably terminated to meet the requirements, so it is just a waste of money to do this.
So nothing has changed.
It is still stupid to waste money on a separate cpc, so why bother?

This is something we have always adhered to, but what regulation does it actually come from?

 

[Deleted member 26818]

It doesn't come from any Regulation.
There is a requirement where high integrity earthing is required for both CPCs to be selected so that each satisfies the requirements for a CPC.
However there is nothing in standard circuits to prohibit the use of two conductors which will only satisfy the requirements for a CPC when combined.

 

[netblindpaul]

This is something we have always adhered to, but what regulation does it actually come from?

543.1.1

 

[Deleted member 26818]

411.3.2.6

 

[netblindpaul]

Where does supplementary bonding come under the realms of a circuit protective conductor?

 

[davesparks]

It just came into my head Dave, bit strong saying you hate kids though, you were one once ? :smiley2:

Hate as in I have a phobia of them. I cannot stand to be in close proximity to small children and babies.

 

[Darkwood]

Hate as in I have a phobia of them. I cannot stand to be in close proximity to small children and babies.

Your life must have been hell at school then

 

[andyb]

Considering that fault currents can be in the thousands of amps it will probably take a fraction of a second for the eddy currents to become a problem. Don't forget current has more effects than just heating the conductor, the magnetic fields will cause mechanical stress at those levels.

Have to take your word for that Dave, it's a science that I know nothing.
I did a job a couple of weeks back where the lives to a three phase board were all taken into the board through their own neatly drilled 20mm hole. At the time each phase was drawing about 20a, there was no heat or sign of any damage. It had been like this for 20 years.

 

[Midwest]

Thought I would invest in the latest copy of Guidance note 1, Selection & Erection. Curious, I looked up 'Ferromagnetic enclosures, cable entering; (521.5.1) All the conductors of a circuit should generally follow the same route. Live cables of the same circuit may cause overheating if they enter a ferromagnetic enclosure through different openings (page 97, 7.4)

 

[shanky887614]

Thought I would invest in the latest copy of Guidance note 1, Selection & Erection. Curious, I looked up 'Ferromagnetic enclosures, cable entering; (521.5.1) All the conductors of a circuit should generally follow the same route. Live cables of the same circuit may cause overheating if they enter a ferromagnetic enclosure through different openings (page 97, 7.4)

exactly what i was getting at, the earth is only live during fault conditions

 

[Risteard]

exactly what i was getting at, the earth is only live during fault conditions

That isn't true. There will be a certain amount of legitimate earth leakage from appliances. Don't forget that there is functional earthing as well as protective earthing.

And as pointed out, under fault conditions there could be a significant current flowing.

 

[Deleted member 26818]

Also there will be some voltage and current on the earth conductor where PME conditions apply.

 

[R G]

So are the wylex tail glands with the 2 holes only not be used then?

Wiska make glands that have 3 holes in and made for this purpose ..

 

[Dave OCD]

Hate as in I have a phobia of them. I cannot stand to be in close proximity to small children and babies.

That's an unusual one, I have the same problem with snakes.:smile5:

 

[Lucien Nunes]

When the SWA is used as the CPC outside the box, and a length of 6491X lugged onto the banjo bolt serves on the inside, the low resistance path connecting them together is via the brass of the banjo and the bolt, rather than through the enamelled steel enclosure which might make relatively poor contact and is of lower conductivity compared to the brass. So in the event of a fault the banjo bolt carries most of the fault current through a separate hole.

What's the solution? Single hole banjo? Moebius bolt that goes through both holes and back to where it came from? Slot the banjo bolt hole across to the gland entry?

 

[R G]

That's an unusual one, I have the same problem with snakes.:smile5:

Funny that I have the same , must stay off this forum ...

 

[netblindpaul]

When the SWA is used as the CPC outside the box, and a length of 6491X lugged onto the banjo bolt serves on the inside, the low resistance path connecting them together is via the brass of the banjo and the bolt, rather than through the enamelled steel enclosure which might make relatively poor contact and is of lower conductivity compared to the brass. So in the event of a fault the banjo bolt carries most of the fault current through a separate hole.

What's the solution? Single hole banjo? Moebius bolt that goes through both holes and back to where it came from? Slot the banjo bolt hole across to the gland entry?

Do like I do and put the banjo inside?
Not an issue really outside or inside, the contact area is greater inside, than out.
Don't drill the enclosure, why would you?

 

[Dave OCD]

That isn't true. There will be a certain amount of legitimate earth leakage from appliances. Don't forget that there is functional earthing as well as protective earthing.

And as pointed out, under fault conditions there could be a significant current flowing.

There is no functional earthing in a domestic installation.

 

[Risteard]

There is no functional earthing in a domestic installation.

There mightn't be much, but I wouldn't say none (on appliances).

 

[Lucien Nunes]

Indeed, functional earthing is where most legitimate leakage current comes from. Not that it has anything much to do with eddy currents - they start being a problem with hundreds of amps, not a few mA.

 

[Risteard]

Indeed, functional earthing is where most legitimate leakage current comes from. Not that it has anything much to do with eddy currents - they start being a problem with hundreds of amps, not a few mA.

Completely agree. Just pointing out that it isn't correct to state that there can be no current on the Earthing Conductor without a fault current.

 

[Dave OCD]

There mightn't be much, but I wouldn't say none (on appliances).

I was thinking along the lines of the installation rather than connected appliances.:smiley2:

 

[shanky887614]

Indeed, functional earthing is where most legitimate leakage current comes from. Not that it has anything much to do with eddy currents - they start being a problem with hundreds of amps, not a few mA.

thats my point, you wouldn't get 100amps flowing on the earth in a domestic property

in commercial/industrial yes it is something to consider because of the size of the supply etc.

now i will follow the reg but im just saying in my opinion its belt and braces with reguards to the earth

if people have safely put the earth in the board for the last 100+ years i doubt it is cause for concern

 

[Dave OCD]

Maybe momentarily under extreme fault conditions but unlikely.

 

[shanky887614]

Maybe momentarily under extreme fault conditions but unlikely.

a fault current that high would melt the copper where the fault is located and clear it before the eddy currents would start to work on the earth

i doubt 6ka fault current would be enough to instantly cause noticble affects on the install before it trips the breaker

 

[Dan]

Just bumping some threads in the Electrical Wiring Theories and Regulations forum category here on our Electricians Forums. If this specific topic isn't current, just ignore it, it'll drop off the list in no time. However, if it's something you'd like to contribute to, feel free to reply and bring it back into current discussion.

 

[HappyHippyDad]

You chose to bump this thread Dan!!!
Could get interesting if the same characters are still around