SWA- T&E Joint Earth

[redcove]

Hi

I am doing a joint of 10mm SWA to 10mm T&E using an IP66 60a junction box

My concern is the earth core joint, as the core is larger in the SWA than the T&E so my question is;

Should I run an additional earth cable from the consumer unit to the joint, to address this problem and if so what size earth cable???

 

[ricicle]

What does Table 54.7 or your adiabatic equation say ?

 

[ban-all-sheds]

I will be employing a qualified electrician to do the main work and are merely sorting the cabling side of things

Why isn't your electrician joining the cables?

 

[GaryMo]

What will this combination of cable be supplying? A garage consumer unit?

What's the rating and type of the protective device?

EDIT - Yes, it seems to be a garage CU

 

[bongos]

Should I run an additional earth cable from the consumer unit to the joint, to address this problem and if so what size earth cable???

2 or 3 core SWA? As ricicle suggests though, you can work it out using the adiabatic equation.

 

[redcove]

What will this combination of cable be supplying? A garage consumer unit?

What's the rating and type of the protective device?

EDIT - Yes, it seems to be a garage CU

Yes it is a garage consumer, running two lighting circuits, two socket circuits and a dedicated circuit for a compressor.

The protective device in the house consumer is a 40a MCB on the rccd side of the unit

 

[redcove]

Should I run an additional earth cable from the consumer unit to the joint, to address this problem and if so what size earth cable???

2 or 3 core SWA? As ricicle suggests though, you can work it out using the adiabatic equation.

3 core SWA

 

[bongos]

Table 54.7 shows if the protective conductor is of the same material as the line conductor, then where S is the cross sectional area of the line conductor in mm², if S ≤ 16, the protective conductor and line conductor must be of equal size.

Alternatively, use the adiabatic to work it out (you may be able to use a smaller size).

S= √I²t/k

 

[GaryMo]

Table 54.7 shows if the protective conductor is of the same material as the line conductor, then where S is the cross sectional area of the line conductor in mm², if S ≤ 16, the protective conductor and line conductor must be of equal size.

Alternatively, use the adiabatic to work it out (you may be able to use a smaller size).

S= √I²t/k

Considering the level of question, do you think he'll have any idea at all working out a minimum size of CPC via the adiabatic equation?

Like most people, he'll probably opt for table 54.7.

If he did work out the minimum size required from the adiabatic then he would probably find that the 4.0mm2 CPC within the t&e is adequate anyway.

 

[ColJack]

I think that he's concerned that the 10mm² T+E supply cable has a smaller CPC than the 3rd core in the 10mm² SWA..

I don't see a problem.. the T+E has been worked out by the makers as having a suitable CPC and the SWA CPC core is bigger..

 

[GaryMo]

Yes, along with the actual joint.

My concern is the earth core joint, as the core is larger in the SWA than the T&E

A suitably sized connector block (may even be included in his IP66 JB) with the 4mm2 CPC from the t&e doubled over will be fine.

 

[ban-all-sheds]

Yes it is a garage consumer, running two lighting circuits, two socket circuits and a dedicated circuit for a compressor.

The protective device in the house consumer is a 40a MCB on the rccd side of the unit

3 core SWA

Ah - you're back.

I will be employing a qualified electrician to do the main work and are merely sorting the cabling side of things

Why isn't your electrician joining the cables?

 

[Spark123]

Don't forget you need to also earth the armour of the SWA too.

 

[ban-all-sheds]

Surely his electrician will know that?

I will be employing a qualified electrician to do the main work and are merely sorting the cabling side of things

 

[redcove]

Don't forget you need to also earth the armour of the SWA too.

The SWA is clipped to a wall 3m above the ground so is not going to be penetrated by anything metal, so did not think it would require earthing??

If it does, can an earth wire be connected from the earthing ring on the gland into the existing earth joint in the junction box??