Submain Supply 100a 100mA

[Tom Christopher]

Installing a 25mm 3core swa to feed an exisitng consumer unit due to the SEB moving the supply.

Planning to use a 100A 100mA time delayed rcd to feed the split load rcd board.

Sound ok?

 

[Ian1981]

Why a 100mA S type rcd upfront?
Is it a TT system?
Will the dual rcd board accommodate a 25mm into the earth bar?
Will there be a switch fuse isolator fitted If the supply is over 3 meters from the cut out?

 

[Dillb]

Will there be a switch fuse isolator fitted If the supply is over 3 meters from the cut out?

Why would it need that? Nothing in BS7671 about it, and the DNO may not specify it.

 

[Ian1981]

Why would it need that? Nothing in BS7671 about it, and the DNO may not specify it.

433.3.1 item (iii)
A device for Overload protection need not be provided at the origin of an installation where the distributor provided an overload device and agrees it affords overload protection to the part of the installation between the origin and main distribution point where further overload protection is provided.
The general consensus is that the DNO will allow 3 meters and no more for their cut out fuse to protect the tails.
Also 434.3

 

[Dillb]

433.3.1 item (iii)
A device for Overload protection need not be provided at the origin of an installation where the distributor provided an overload device and agrees it affords overload protection to the part of the installation between the origin and main distribution point where further overload protection is provided.
The general consensus is that the DNO will allow 3 meters and no more for their cut out fuse to protect the tails.

So as I say its speculation if its needed, nothing to say in this instance that the DNO require it fitting.

 

[Deleted member 26818]

My understanding is that the DNO will not generally allow their fuse to be used to protect any part of a consumer’s installation.
The 3m stipulation relates to the BS7671 requirement that overload protection must be provided within 3m of a reduction in the CCC of a conductor.

 

[Ian1981]

This is northern powers requirements anyway

 

[Tom Christopher]

Why a 100mA S type rcd upfront?
Is it a TT system?
Will the dual rcd board accommodate a 25mm into the earth bar?
Will there be a switch fuse isolator fitted If the supply is over 3 meters from the cut out?

PME

Yes dual board will take a 25mm

SWA will be made off into a metal enclosure with the 100a 100ma time delayed rcd. This will be mounted next to the main supply, so tails less than 3m

SWA will be above the plaster board so wont it need rcd protection?

I thought time delay to save both RCD trippings if there is a fault?

 

[Ian1981]

My understanding is that the DNO will not generally allow their fuse to be used to protect any part of a consumer’s installation.
The 3m stipulation relates to the BS7671 requirement that overload protection must be provided within 3m of a reduction in the CCC of a conductor.

Tho that is a regulation in the context you describe that has Nothing to do with the DNO tails
Read 433.3.1 and 434.3 or not

 

[Deleted member 26818]

RCD protection for cables concealed above ceilings and below floors is not an acceptable method for providing extra protection.
SWA however is.

 

[Deleted member 26818]

Tho that is a regulation in the context you describe that has Nothing to do with the DNO tails
Read 433.3.1 and 434.3

Not aware we were discussing DNO tails?
BS7671 does not apply to DNO equipment.

 

[Octopus]

^^ swa doesn’t need rcd ...

 

[Andy78]

PME

Yes dual board will take a 25mm

SWA will be made off into a metal enclosure with the 100a 100ma time delayed rcd. This will be mounted next to the main supply, so tails less than 3m

SWA will be above the plaster board so wont it need rcd protection?

I thought time delay to save both RCD trippings if there is a fault?

There is no need for RCD protection for those reasons if using earthed SWA. If it did, then you RCD you selected would not have been suitable anyway.

 

[buzzlightyear]

new sub mains from tncs to tt then .

 

[westward10]

We can only confirm if this is okay if you let loose what the earthing system is.

 

[Deleted member 26818]

Hoops or studs?
Pierced or clips?

 

[Tom Christopher]

We can only confirm if this is okay if you let lose what the earring system is.

PME

 

[LankyWill]

Out of interest ive never had to terminate a 25mm cpc into a cu, do you just fork it into two earth bar holes?

 

[westward10]

Not many CUs have an earth terminal to enable termination of a 25mm conductor.

 

[Cadgey123]

Out of interest ive never had to terminate a 25mm cpc into a cu, do you just fork it into two earth bar holes?

Like this one I found today. Right state.....

 

[westward10]

PME

Why the need for rcd protection.

 

[Andy78]

Out of interest ive never had to terminate a 25mm cpc into a cu, do you just fork it into two earth bar holes?

Un-insulated Reducing Pin - SWA - http://www.swaonline.co.uk/cable-terminations/copper-pin-terminals/uninsulated-reducing-pin

 

[Tom Christopher]

We can only confirm if this is okay if you let lose what the earring system is.

PME

Why the need for rcd protection.

So would you happy to run say a 16mm 3C swa from a 63a isolator to the consumer unit? No need for any RCD on the supply and above a ceiling/under the floor?

 

[westward10]

Yes providing the armour is effectively earthed. Additional rcd protection is not required and an s type 100ma rcd does not provide additional protection anyway.

 

[Des 56]

PME


So would you happy to run say a 16mm 3C swa from a 63a isolator to the consumer unit? No need for any RCD on the supply and above a ceiling/under the floor?

Why are you making reference to floors,ceilings and Rcd when considering swa

 

[Deleted member 26818]

Hoops or studs?

Why are you making reference to floors,ceilings and Rcd when considering swa

probably because it’s one of the acceptable methods for providing the extra protection required.

 

[DPG]

Why would it need that? Nothing in BS7671 about it, and the DNO may not specify it.

No, but as you know it's a common and well-known requirement.

 

[Wilko]

Hi - please confirm suppliers fuse, installation load, Ze, cable distance and installation method etc. Otherwise they're all going to argue pointlessly .

 

[Zdb]

My understanding is that the DNO will not generally allow their fuse to be used to protect any part of a consumer’s installation.
The 3m stipulation relates to the BS7671 requirement that overload protection must be provided within 3m of a reduction in the CCC of a conductor.

Where can I find this 3m rule in BS7671?

 

[Deleted member 26818]

Where can I find this 3m rule in BS7671?

Sections 433.2 and 434.2.

 

[Zdb]

Thanks