Protection on Tncs / tt system

[cliffed]

Pme Swa sub main supplying external tennis courts.
Because of cable size,tt system will be installed.
The original Pme supply comes from main distribution area,from a Bill Switchfuse isolator,63 amps.
The new tt system is ze 13 ohms,the Pme earthing system is 0.35 ohnms.
No connection to the Pme system exists in the new install.
The wire netting around the tennis court as zs of 11 ohms.
All main bonding completed
With the metal DB what would happen if the live had an earth fault to the tt system,there is no Rcd protection @ present on the Swa supply.

 

[Ian1981]

The sub main if supplied via a TT arrangement will require fault protection via a suitably rated S type rcd.
If your using a TPN DB downstream then I suggest you install DP rcbos as a neutral to earth fault will disconnect an upfront rccb unless you use DP rcbos.

What is the issue regarding cable size?

 

[westward10]

What do you think would happen, Uo 230v, Ze 13 ohm.

 

[westward10]

The sub main if supplied via a TT arrangement will require fault protection via a suitably rated S type rcd.
If your using a TPN DB downstream then I suggest you install DP rcbos as a neutral to earth fault will disconnect an upfront rccb unless you use DP rcbos.

What is the issue regarding cable size?

Assuming his submain is using the PME the s type rcd would have to be at the point it converts to TT.

 

[Ian1981]

I read it as the submain is protected by a TT arrangement?

Assuming his submain is using the PME the s type rcd would have to be at the point it converts to TT.
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[telectrix]

fried tennis balls. serve with chips and peas.

 

[cliffed]

I read it as the submain is protected by a TT arrangement?

Pme sub main,protected by 63 amp switch fuse,Swa sheath used for cpc .
This cpc not used,size of swa not suitable,system made into TT system,for new Db,rcbo’s used for lighting circuits.

 

[cliffed]

What do you think would happen, Uo 230v, Ze 13 ohm.

My concern would be failure of protecting devices.

 

[cliffed]

Assuming his submain is using the PME the s type rcd would have to be at the point it converts to TT.

Rcbo’s are used @ new Db,tt system

 

[westward10]

Nothing

My concern would be failure of protecting devices.

Ze of 13 ohm, fault to earth then nothing will happen unless rcd protection is provided. It will remain live as your fault current is about 18A.

 

[Ian1981]

What size is the swa?
Why is the armour not suitable as the cpc, is it because of extraneous conductive parts at the tennis court building end?

 

[cliffed]

Y

Nothing

Ze of 13 ohm, fault to earth then nothing will happen unless rcd protection is provided. It will remain live as your fault current is about 18A.
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What size is the swa?
Why is the armour not suitable as the cpc, is it because of extraneous conductive parts at the tennis court building end?

yea,16mm 3 core Swa,the main earth bond to the existing building is 50mm earth cable

 

[cliffed]

Nothing

Ze of 13 ohm, fault to earth then nothing will happen unless rcd protection is provided. It will remain live as your fault current is about 18A.

Will look @ Fault charesteristics of the protection device.
Concerned if the fault happen on the tt system,the fuse would not protect.

 

[Lucien Nunes]

This is the same problem as with meter tails in an Amd. 3 domestic CU on TT. The only thing that is not protected is the line upstream of the RCD going down to the TT earth. Could solve by putting RCD in separate insulated enclosure at tennis court end so that by the time the cables enter the DB they have local RCD protection. Can't do that in domestic install hence the magic glands etc to minimise risk of short.

 

[cliffed]

This is the same problem as with meter tails in an Amd. 3 domestic CU on TT. The only thing that is not protected is the line upstream of the RCD going down to the TT earth. Could solve by putting RCD in separate insulated enclosure at tennis court end so that by the time the cables enter the DB they have local RCD protection. Can't do that in domestic install hence the magic glands etc to minimise risk of short.

Thanks,exactly what I was trying to say.