earthing conductor size

[shotgun1067]

Just tested a job where the supply to the house is 3phase via a 240mm 4core swa on a 160a 60947 MCCB, the Zs is 0.16. The earth is a 70mm seperate under ground and the armour of the cable is connected also, just trying to work out if this is acceptable? any thoughts?

 

[somersetsparks]

adiabatic equation would tell you, I can't be bothered to do it for you so you will have to look it up and calculate for yourself, sounds like it would be adequate though purely on the size of the armour. Is the armouring/earth also used as a bonding conductor?
Seems an odd way to supply a house I'm guessing the house belongs to the owner of an industrial site etc. I have only ever seen something similar at a local skip yard.

 

[MDJ]

Just tested a job where the supply to the house is 3phase via a 240mm 4core swa on a 160a 60947 MCCB, the Zs is 0.16. The earth is a 70mm seperate under ground and the armour of the cable is connected also, just trying to work out if this is acceptable? any thoughts?

More info required again,

whats the earthing type for starters? and more info about the house, with that size supply it isn't the norm obviously, so lets have more.

 

[bigbaddave]

Asthmatic equation....

 

[shotgun1067]

Its a large house with steam rooms, saunas etc so large loads, hence the large supply. The MCCB supplying the house is a schnieder 4pole 160a, but its turned down to 115a. The supply is TNC-S.

 

[KAS1]

Why are these questions usually someone's first post, I wish they would just ask how do I work out the size of the main earthing conductor because I don't know and am not competent enough to preform this EICR and then except they need to get someone in who does have the knowledge lol

Just tested a job where the supply to the house is 3phase via a 240mm 4core swa on a 160a 60947 MCCB, the Zs is 0.16. The earth is a 70mm seperate under ground and the armour of the cable is connected also, just trying to work out if this is acceptable? any thoughts?

 

[johnboy6083]

My first question would be is the Vd acceptable. Do a backwards cable calc.

 

[D Skelton]

So there is a seperate suppliers earth, plus the armour of the cable but the supply is TN-C-S?

 

[Norwich]

totally ok, .... the swa Armour alone is very likely to suffice, and the 70mm separate cpc would enhance this plus cover any many bonding requirements as 50mm is the max ever required for main bonding,

 

[Engineer54]

totally ok, .... the swa Armour alone is very likely to suffice, and the 70mm separate cpc would enhance this plus cover any many bonding requirements as 50mm is the max ever required for main bonding,

It won't for bonding purposes!!

You haven't been on any large projects have you??

This 240mm 4 core SWA cable must have been installed due to the distance between the source and load. Can't see any other reason if it's MCCB has been adjusted to 115A!! And as DS has pointed out above, why have they run in a separate 70mm earthing cable if the supply is PME (TNC-S)


Where is this 240mm cable supply coming from?? Is it a sub distribution cable coming from another building. It's doubtful it's a DNO cable as they rarely if ever use SWA cable to a service cut-out!! So, if it is part of a bigger installation, then i can understand the separate earthing cable being provided...

 

[somersetsparks]

The only time I have seen something this is at a skip yard owners house which was next to his skip yard, being fed from his commercial supply. (I believe the yard was there first). The 70mm is likely due to the rest of the installation which could be large and with it being PME require a large earth conductor. really need more info from OP

 

[scotsparky]

Th armour of the SWA may not always sufice!. If you use the adiobatic and K factor for a cable that size additional earthing must be run.
A good indication when using SWA is look at GN1 for the BGB page147 -150 it gives tables of what can and cannot be used.

240mm4c is ok if its thermosetting if operating at 70C but not at 90C but 240 3 core is to smal.

Dont rely on the SWA check first and prove it !!!!!!

 

[Engineer54]

Th armour of the SWA may not always sufice!. If you use the adiobatic and K factor for a cable that size additional earthing must be run.
A good indication when using SWA is look at GN1 for the BGB page147 -150 it gives tables of what can and cannot be used.

240mm4c is ok if its thermosetting if operating at 70C but not at 90C but 240 3 core is to smal.

Dont rely on the SWA check first and prove it !!!!!!

Even better if it's PVC insulated conductors as far as the CSA of the SWA. Either way, the armouring is not going to be of sufficient size to comply with TNC-S bonding requirements....

 

[shotgun1067]

The cable comes from a distribution panel next to the boards incomming supply. Its a supply to another distribution panel 100m away.
It is 70deg pvc 240mm 4core. I think that the steel armour equivelent in copper is 35mm??? and the seperate 70mm earth is to cater for the bonding at the other end (being 50mm)

 

[Norwich]

I take your point eng54 often main bonding conductors are specified by others larger than 50mm but I was using table 54-8 as my reference. (Large projects - cheeky) in this case I think 54-8 is fair reference