Earth Requirement

[Michaelwgroves]

I need to run several new supplies for studios. 16mm T&E is fine for the supplies. But I'm worried the earth may not be big enough. Longest run is 12M from Meter. I could just run cable then if it fails test run 16mm earth. But would be interested to learn the calculation so I can be sure from the outset.

Thanks
Michael

 

[Michaelwgroves]

That changes things. I've not run cable yet, so may or may not be burried less than 50mm. Glad you mentioned that, thanks.

 

[Michaelwgroves]

Okay, looking at everything. It just makes sense to use 16mm 2 core SWA. So does anyone know how big the armour would calculate to. I assume bigger than 16mm ?

 

[Sintra]

20.3mm copper equivilant for BS 6346 70 degree SWA and ONLY 13.5mm for BS 5467 & 6724 XLPE 90 degree.

 

[Michaelwgroves]

So which one do I use, or just go with adiabatic ?

 

[telectrix]

use 3 core then you know it's sufficient. and as for the buried in walls<50mm deep, read 522.6.101/102. any cable

 

[Engineer54]

The CSA of the steel armour on a 16mm 2 core is 46mm for PVC, and 41mm on XLPE.... The difference arising from the XLPE's thinner overall insulation of the conductors!!

 

[Michaelwgroves]

The CSA of the steel armour on a 16mm 2 core is 46mm for PVC, and 41mm on XLPE.... The difference arising from the XLPE's thinner overall insulation of the conductors!!

What am I missing here, Sintra advised "20.3mm copper equivilant for BS 6346 70 degree SWA and ONLY 13.5mm for BS 5467 & 6724 XLPE 90 degree" ?

 

[Engineer54]

Taken from this table......... Which is a table for compliance for using SWA as the circuits/cables CPC!!

Blue = min CSA of cables SWA to comply.

(Red) = Cable does not comply.

Table for 70[SUP]0[/SUP]C Thermoplastic PVC SWA cables.

Conductor CSA​	Minimum CSA of SWA to meet 54G​	CSA of armour 2 core​	CSA of armour 3 core​	CSA of armour 4 core​
1.5​	3.4​	15​	16​	17​
2.5​	5.7​	17​	19​	20​
4​	9.0​	21​	23​	35​
6​	13.6​	24​	36​	40​
10​	22.6​	41​	44​	49​
16​	36.1​	46​	50​	72​
25​	36.1​	60​	66​	76​
35​	36.1​	66​	74​	84​
50​	56.4​	74​	84​	122​
70​	79.0​	84​	119​	138​
95​	107.2​	122​	138​	160​
120​	135.3​	(131) ​	150​	220​
150​	169.2​	(144) ​	211​	240​
185​	208.6​	(201) ​	230​	265​
240​	270.6​	(225) ​	(260)​	299​
300​	338.3​	(250) ​	(289)​	(333)​
400​	403.9​	(279) ​	(319)​	467​

Table for 90[SUP]0[/SUP]C Thermosetting SWA cables operating at 70[SUP]0[/SUP]C.

Conductor CSA​	Minimum CSA of SWA to meet 54G​	CSA of armour 2 core​	CSA of armour 3 core​	CSA of armour 4 core​
1.5​	3.4​	16​	17​	18​
2.5​	5.7​	17​	19​	20​
4​	9.0​	19​	21​	23​
6​	13.6​	22​	23​	36​
10​	22.6​	26​	39​	43​
16​	36.1​	41​	44​	49​
25​	36.1​	42​	62​	70​
35​	36.1​	62​	70​	80​
50​	56.4​	68​	78​	90​
70​	79.0​	80​	90​	131​
95​	107.2​	113​	128​	147​
120​	135.3​	(125) ​	141​	206​
150​	169.2​	(138)​	201​	230​
185​	208.6​	(191) ​	220​	255​
240​	270.6​	(215) ​	(250)​	289​
300​	338.3​	(235) ​	(269)​	(319)​
400​	451.0​	(265) ​	(304)​	452​

​

​

 

[Michaelwgroves]

Thanks Engineer54, that is really helpful.