PME METAL OUTBUILDING

[Rkidcd]

Scenario encountered:
New submain looks to have been taken from a PME supply in 4c 10mm SWA with no copper earth to a external metal feeder pillar.

The SWA has been glanded into new metal clad DB within the feeder pillar effectively incorporating it into the PME supply. A Earth has also been taken from the banjo to a earth rod within the feeder pillar.

The feeder pillar is intended to go on to feed a metal fabricated building with sub circuits and that’s what we have potentially come in to carry out.

Issues I can see but may be barking up wrong tree:

For me surely it would have been better to isolate the PME and TT this DB and all of its sub circuits?

As there is no internal copper earth in the SWA - PME hasn’t effectively been exported at all so bonds are currently ineffective?

 

[westward10]

The armour of that cable is inadequate to support PME bonding. So yes your only option is to isolate from the source earth and create a TT system.

 

[Rkidcd]

Thanks for the reply.

Things have developed further since this morning - when I took a Zs at the DB with the supplementary Rod connection disconnected leaving me just PME I achieved a Zs of well over 2 ohms on a B63 MCB with no associated RCD!!

Am I right in saying if I isolate the source earth pre DB it still leaves the armouring up to this point with no fault protection?

Am I going mad here? BTW the run is around 400m

 

[westward10]

Sounds like a pretty poor design 400m of 10.0 swa but yes the armour stills requires protection from fault.

 

[Wilko]

Agree - with 4 core I would TT at the far end. Just confirming - the distribution circuit (400m of 10mm) has Zs more than 2 Ohms and is protected by B63 (?). Voltage drop won't out well either I'm afraid, with about 1.5V drop per Amp if my fat fingers haven't botched it.

 

[Octopus]

New submain looks to have been taken from a PME supply in 4c 10mm SWA with no copper earth to a external metal feeder pillar.

By whom and whats your involvement?

 

[Strima]

New out building 400m from source sounds like a farmer trying to save some money.

 

[richy3333]

New out building 400m from source sounds like a farmer trying to save some money.

And possibly de-ice his track in winter

 

[Rkidcd]

Another quick question about the same job but completely different subject. How would you go about zones in the following scenario:

A wildlife hut which is semi open to the elements. Half of hut is solid ground the other half vaguely described as a pool, pond or collection of water (through excess site water runoff) which is to be utilised by the wildlife.

Client would like fittings throughout the hut and the ceiling height isn't particularly high.

Thoughts?

 

[Rkidcd]

By whom and whats your involvement?

No involvement to date, just looking into the feasibility of installing circuits from this extremely poorly designed DB/supply

 

[Wilko]

A wildlife hut which is semi open to the elements. Half of hut is solid ground the other half vaguely described as a pool, pond or collection of water (through excess site water runoff) which is to be utilised by the wildlife. Client would like fittings throughout the hut and the ceiling height isn't particularly high. Thoughts?

Reading 702.11 Scope "Except for areas especially designed as swimming pools, the requirements of this section do not apply to natural waters ..." So a nice TT and plastic IP rated installation perhaps?

 

[Strima]

Another quick question about the same job but completely different subject. How would you go about zones in the following scenario:

A wildlife hut which is semi open to the elements. Half of hut is solid ground the other half vaguely described as a pool, pond or collection of water (through excess site water runoff) which is to be utilised by the wildlife.

Client would like fittings throughout the hut and the ceiling height isn't particularly high.

Thoughts?

ELV, the animals would be at risk but also the keepers when they enter for cleaning etc.

Without knowing the full layout or requirements socket outlets could possibly a no no if you have animals bigger than a penguin trying to eat them...

 

[Rkidcd]

Gonna potentially be flamingos and other similar birds - lighting would be within a 2m height of the solid ground/water sections.

IP rated a must? ELV recommended?

 

[Lucien Nunes]

So at 4mV/A/m and even allowing for 5% VD in the submain, you've got a maximum of 7A available at the far end, so the B16 that will be needed to protect the cable will be ample although hard to achieve discrimination with. As it's TP+N that's 4.8kVA, which might or might not be enough to keep the hippos warm. Or is is SP+N with pairs of cores paralleled?

If the hippos want an electric shower, they will be in need of a pair of transformers. At 1000V you can get six times as much juice down the cable.

 

[johnduffell]

vaguely described as a pool, pond or collection of water (through excess site water runoff) which is to be utilised by the wildlife.

At least you've found somewhere for the earth rod that won't dry out!