PME to remote domestic dwelling

[mike box]

Hi guys,

thoughts on this would be appreciated.

I have a 3 phase 100 amp PME supply, feeding 3 domestic dwelling about 80 mts away. Done cable calc and have chosen 50mm 4 core swa using armour to protect cable.
In the 1st dwelling I have 3 phase metal DB feeding 3 sub mains, 1 to 1st & 2nd floor flats and 1 feeding separate dwelling. all have metal clad DB utilising RCBO protection on all circuits.

Should I TT at main DB or is it possible to use the PME system through out.

Any food for thought would be appreciated.

Regards

Mike

 

[Darkwood]

Welcome to the forum, I take it you have made an error in how you word your options, PME is a network system and you are not permitted to continue this, I assume you mean use the earth provided by the Networs PME by extending the equipotential zone.

Anymore details on the supply swa, what are the install methods and front end fusing, it sounds a tad small for a buried cable at 80m with 100amp fusing?

 

[Leesparkykent]

Hi guys,

thoughts on this would be appreciated.

I have a 3 phase 100 amp PME supply, feeding 3 domestic dwelling about 80 mts away. Done cable calc and have chosen 50mm 4 core swa using armour to protect cable.
In the 1st dwelling I have 3 phase metal DB feeding 3 sub mains, 1 to 1st & 2nd floor flats and 1 feeding separate dwelling. all have metal clad DB utilising RCBO protection on all circuits.

Should I TT at main DB or is it possible to use the PME system through out.

Any food for thought would be appreciated.

Regards

Mike

Hi Mike, welcome to the forum. The armour wouldn't be adequate as a bonding conductor...Would you mind sharing your calculations? What type of overcurrent protective device is protecting each distribution circuit?

 

[mike box]

To your 1st point, yes I mean extend earth system provided by DNO.
I plan to install 80 amp 3 phase switch fuse at incomer, 50 mm 4 core to DB 1. Sub mains to 2 flats and 1 house

 

[mike box]

According to IEE sheet I have on 4 core 50mm armour steel is ok to use as CPC. Main DB has 3 X 63 amp mcb sub mains feeding 3 DB fully loaded with RCBO

 

[mike box]

Standard 100 amp DNO pme supply, then to 3 phase 80 amp switch fuse, feeding 50 mm 4 core SWA. To DB 1. 3 63 amp MCB sub mains to 3 to 3 flats each with single phase DB loaded with RCBOs

 

[Darkwood]

Is the SWA buried or clipped direct? This can have a big bearing on its size hence I queried your front end fusing and methods, before we start advising on earthing etc we need to establish your design is correct to suit. I asked because it rang a few alarm bells if I made a few basic likely assumptions.

 

[Leesparkykent]

Standard 100 amp DNO pme supply, then to 3 phase 80 amp switch fuse, feeding 50 mm 4 core SWA. To DB 1. 3 63 amp MCB sub mains to 3 to 3 flats each with single phase DB loaded with RCBOs

yes would be fine as circuit protective conductor but not a bonding conductor due to the resistivity of the steel. Having multiple 60898 circuit breakers in series will not provide discrimination.

 

[davesparks]

According to IEE sheet I have on 4 core 50mm armour steel is ok to use as CPC. Main DB has 3 X 63 amp mcb sub mains feeding 3 DB fully loaded with RCBO

It might be ok as a CPC but probably won't be as a main bond. What is the steel CSA of the armour? Off the top of my head it would have to be over at least 90sqmm

Mcbs protecting a submain is very poor design, why aren't you using fuses?

 

[telectrix]

completely agree.^^^^^^.