What's wrong here then?

[steptoe]

I have always learned a general rule of 3mA per item of IT kit, therefore a max of 4 X double sockets on any one 30mA device.

 

[kme]

the cpc wire is longer whilst not being a problem it's bad practise????

As this is in the student area, and hasn`t been picked up.

Gavin: On the contrary, the CPC should always be the longer conductor; for the same reason the earth pin is always the longest. So its GOOD practise.

I`m not going to say why - I`d like YOU to have a guess mate

 

[sb_89]

Hi integ earthing is something I have never seen the point in personally, if you do all your dead tests and prove its a ring, what is the point ?! I'd be interested if somebody could actually give a decent reason.

 

[Manator]

High integrity earthing is not the same thing as a rings earth. Extra earthing is supplied to those sockets that have a high number of PC's connected. Often called a clean earth by some.

 

[gavindrummond]

Sorry kme I don't think I explained my self correctly. I didn't mean the entire length of the cpc conductor I know that should be longer when terminating anything. I was referring that it was coming through the back where it's been terminated. Its not even doubled back.

 

[SPECIAL LOCATION]

Hi integ earthing is something I have never seen the point in personally, if you do all your dead tests and prove its a ring, what is the point ?! I'd be interested if somebody could actually give a decent reason.

First thing to remember is that high integrity earth is not just a ring final requirement..

it is also applicable on a radial circuit.... and the concept is probably easier to grasp on a radial circuit.....

e.g.

10+ PCs off a radial circuit all high high leakage current..

if the CPC get disconnected at socket number 3...

All the earth current on all of the equipment connected further up the radial is now sitting on the metal work of any class I equipment.. {e.g. maybe PC tower}

So the regs say on a radial a duplicate earth path must be provided back to the CU earth bar AND connected onto its own a separate terminal at the earth bar.

With ring finals there is already a duplicate earth path..

but they are allowing for the common occurrence that we have all seen..

where two CPC's have been twisted and stuffed in the same screw terminal...

Maybe in a socket or at a CU or where a radial has been spured off the ring...

But one has actually broken off and is only relying on the twisted grip around the terminated conductor.

We get enough questions on the forum about people doing PIR's and finding the ring continuity has been broken somewhere..

It is a common occurrence!

Larger CSA CPC's are less likely to break off and produce a stronger mechanical joint.

So for example in conduit wiring larger CSA CPC's can be a solution..

But in practice with standard T&E wiring we are stuck with the CSA of the CPC that is inside the cable..

The general assumption is that,

Smaller CSA CPC's terminated into their own screw terminal are stronger than shared terminal

So in a nutshell its..

Two smaller CPC individually terminated

or one big fatter CPC!

It is similar in concept to bonding conductors that can be smaller if they have mechanical protection,

but bigger if no mechanical protection.

Further reading an be found at.

543.7 thro 543.7.2.101 pages 165 - 166 BGB

section 7.5 On Site guide pages 77 - 79

section 8.1 Guidance Note #1 "selection & erection" pages 93 - 98

:coffee

 

[sb_89]

It seems like massive over kill to me, again if your tests have been carried out correctly and you installed the circuit well, what's the point In dragging in an extra earth to do the job of the earth that's already there, earths don't just disconnect themselves. I understand the point, I just personally think its over the top. Maybe it's a better safe than sorry.

 

[roys]

I did fit a batch of twin 13A sockets once, that no matter how hard I tightened the connection screws on the back of them they would slacken off after about 6 months. Had to use a spot of stud lock on the screws in the end. No more problems after that but weird. We put it down to rubbish manufacturing and bluffed about 50Hz being the resonant frequency of the screws. Not sure how relevent to this thread, sorry if I have digressed it a little.

 

[SPECIAL LOCATION]

I did fit a batch of twin 13A sockets once, that no matter how hard I tightened the connection screws on the back of them they would slacken off after about 6 months. Had to use a spot of stud lock on the screws in the end. No more problems after that but weird. We put it down to rubbish manufacturing and bluffed about 50Hz being the resonant frequency of the screws. Not sure how relevent to this thread, sorry if I have digressed it a little.

Actually it is relevant I think...

All screw terminals work loose over time..

{Which is why they must be accessible for inspection & testing 526.3}

That includes the earth terminals on the backs of sockets..

All sockets are susceptible to vibration from plugs being inserted and removed...

any vibration around a loose screw terminal can cause poor electrical connection...

Even though the ring continuity may have been tested at install..

10months down the line one or more joints could be weaker....

I have seen loads of sockets that have loose screws..

But I am confident a majority were tightened up originally...

Massive overkill fitting CPC's into different terminals in the back of a socket? :C

You don't have to drag an extra earth for a ring..

Just terminate them individually! :|

 

[sellers]

It seems like massive over kill to me, again if your tests have been carried out correctly and you installed the circuit well, what's the point In dragging in an extra earth to do the job of the earth that's already there, earths don't just disconnect themselves. I understand the point, I just personally think its over the top. Maybe it's a better safe than sorry.

I don't think its over the top. Its what the whole electrical world is based on. being fail safe. Faults occur and measures are put in place to prevent injury and damage. Same goes for Hi Integ earthing its a form of fault/shocl prevention.

I don't know how many installs you've seen, but earths do disconnect themselves it happens!

 

[NozSpark]

IMHO I think that earth terminations undo less often than Live ones,,, but then again the CPC usually only carries a current during fault conditions. With these circuits we are designing them in the knowledge that they will be carrying some current "normally"

 

[apprentice87]

What is with the lug on the right hand side of the box?? looks like the screw is still in place?? Has it pulled through the socket front plate??

john..

 

[Sidewinder]

Wire ends and screw down terminals will also distort their shape "creep" under heat cycling, which you may well find in an electrical termination due to the load cycles, if you see what I mean.

This creep can cause them to become loose, hence the requirement as has been said earlier, to have them accessible for inspection.

 

[apprentice87]

Hi Paul,

I know exactly what you mean, so loctiting them as has been suggested previously, is a VERY bad idea.. You will merely never be able to tighten them, you have in fact then, to all intents and purposes made them "inaccessible"

john...

 

[NozSpark]

What is with the lug on the right hand side of the box?? looks like the screw is still in place?? Has it pulled through the socket front plate??john..

John,

What you're looking at is the backbox earth terminal, the lug is above that

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Hi Paul, I know exactly what you mean, so loctiting them as has been suggested previously, is a VERY bad idea.. You will merely never be able to tighten them, you have in fact then, to all intents and purposes made them "inaccessible"

john...

That would depend on the type of thread lock that you use,, Loctite make many different versions for different applications... and you can pretty much free any thread locked screw/nut, you just have to use the right method

 

[steptoe]

Loctite make many different versions for different applications

you disappoint me here John,

as Noz rightly points out, Loctite do indeed make many different types of locking compound,

virtually every nut and bolt on our race bikes gets the loctite treatment, but they still get took apart on a regular basis, depending on the locking compound used,

most of them are simply damping compounds (I think) that stop the screw/bolt moving under vibration.

you also get different compounds depending if you are applying to the bolt or nut, dunno what difference that makes TBH :C

 

[Sidewinder]

They are almost all insulating though, thus unsuitable for use in electrical connections!

I would not put thread locking compound of any type on them unless it was that specified by the manufacturer of the electrical connection.

 

[apprentice87]

Hi Steps!!

I have not used that much loctite!! but i know it comes in "undoable" grades, and "well and trully stuck" grades too!!

The stuff i have used though, cost a fortune!!!! It was high strength retainer. Believe me, this stuff is strong!!! I know it is not meant to be used as thread lock, and you would shear the bolt before you undid it, trully amazing stuff!!!

Other stuff they do though is much more useful.. Obviously if you want you thread locking compound to work as the maker intended, you will have to COMPLETELY degrease the items. But they also do grades that can be used without degreasing.. Presumably these just "fill the gaps" to dampen the bits against vibration in the way that you describe...

Bought a new driller today too. Only wanted it for spares for mine, but it is MUCH too good to strip for spares, i hate stripping machines anyway, it is like murdering them....

Got two drills the same now..Ho hum. A fool and his money are soon parted!!!!!

john...

 

[alextrician]

the back box is not earth, and there is a (earth)wire sticking out (no basic protection achieved)

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also i can see that the earthing sheath is pushed down into the earth terminal, therefore an improper earth connection connection.