earthing armouring

[adammid]

Just looking at another forum on here and saw a picture where the electrician had used a conductor in 3 core armoured cable for an earth. Where the armoured terminates in the cu they had connected the aforementioned earth conductor straight onto the earth bar and then run 2 x 2.5mm conductors also from the earth nut to the earth bar in the cu.

My question is:- should the earth conductor used in the armoured not connect straight onto the earth bar in the cu? And then run a seperate 4mm from the earth bar onto the earthing nut to earth the armouring?

Or am I being pedantic?

 

[Steve3948]

Whatever floats your boat

 

[johninlondon1]

By connecting 2 x 2.5mm cables they can not be sure that the fault current (if any) will split equally between both conductors. So the conductor used should be of sufficient size to carry the full fault current.

 

[adammid]

Yes, I think he was aware of that as he didn't have any 4mm at the time. My question is though is it acceptable to connect the earth conductor onto the earth nut first and then from the earth nut onto the earth bar.

I would have thought the earth conductor should connect straight onto the earth bar and then a separate 4mm to connect from earth bar to earth nut but then if the 4mm can take the fault current then I don't see why it should matter.

 

[ajkend]

Not most peoples way of doing it, but as long as the cpc is the right size then no problem.

More than one way to skin a cat.

 

[Steve3948]

They must be the same size and length, as with parallel supplies.

 

[steptoe]

Just looking at another forum on here and saw a picture where the electrician had used a conductor in 3 core armoured cable for an earth. Where the armoured terminates in the cu they had connected the aforementioned earth conductor straight onto the earth bar and then run 2 x 2.5mm conductors also from the earth nut to the earth bar in the cu.My question is:- should the earth conductor used in the armoured not connect straight onto the earth bar in the cu? And then run a seperate 4mm from the earth bar onto the earthing nut to earth the armouring?

Or am I being pedantic?

I think you have got mixed up a bit here,

either that or Im reading something wrong. :|

 

[samson337]

^ plus one I think you need to re read the first part, then the second

 

[adammid]

My apologies guys. What I meant to say in the first part was the electrician had connected the earth conductor in the armoured cable straight into the earth NUT and then run 2 x 2.5mm conductors from the earth NUT to the earth BAR.

My question is should the earth conductor used in the armouring not connect straight onto the earth BAR and then run a separate conductor from the BAR to the NUT to earth the armouring.

I think that how it should be done is best practice but can't think of a scientific reason why it can't be done the way the other electrician had done it.

 

[welchyboy]

I would of personally run both to the met but this set up it ok

The main point is that the armour is sufficiently earthed and a gland and banjo has been used which seems to be a rare thing now days

As said above running 2x2.5 earth is ok as long as they comply with the same principles as the parallel supply regs, but is a bit lazy , not really called for in place of a bit of 6 or 4mm

 

[adammid]

Thanks Welchyboy. I thought the same about taking both straight to the MET. Can't see it as a prob if not tho if the conductor can take the fault current.

 

[Sidewinder]

adammid,

Not perfect, and IIRC he said that he had made an error when cutting the cable back, had wanted to get the supply running and had no 4mm sq on the van, thus used 2x2.5mm sq in parallel, of equal lengths.

Not perfect, no, as he freely admits, but it would comply with BS7671, and in fact would possibly exceed the minimum requirements.

Many people would have used a banjo & locknut on the polymer enclosure and connected to that, which would not have been a good solution.