Agricultural installations

Anyone on here know section 705 inside out? specifically 705.537.2

I have a rewire that I'm pricing on a farmhouse with attached farm buildings.....

In the attached farm buildings there are several rooms,,,, stores, pens and shippens...... with loft rooms above.

Does each room need a separate circuit (lights via SWFS), it's own sub main or can I get away with 2 circuits for the lot (sockets & lights)?

This depends on the intended use of the rooms.

If, for example, one was to be used for something that was likely to cause power interruptions, or required regular isolation for washdown or the like, and another was running incubators, i.e. "life support", you wouldn't want them on the same circuit/means of isolation.

You could easily be OK, but the real answer is, it depends!

TBH I don't really know what uses they're being put to... except that there's a shippen, a few pens and a couple of store rooms on the ground floor with loft rooms above.

I'm assuming that the shippen and pens will have animals in them and the rest will be storage for tack (maybe), feed, fertilisers, tools, feed supplements etc... as far as I can gather this part of the building is about 20m long by about 5m wide (google maps is great  ).... it also looks like it has an overhead TNS supply (again from google maps)

It's the wording of 705.537.2 that has me....

"The electrical installation of each building or part of a building shall be isolated by a single device according to Chapter 46"

What defines ".... part of a building...."

Mains isolator switch,

as  a separate entity to the main building It needs an isolator, ie a small DB , which makes sense anyway.

binky said:

Mains isolator switch,

as  a separate entity to the main building It needs an isolator, ie a small DB , which makes sense anyway.

Click to expand...

Yeh,,, I figured that anyway and was planning on a SUB and CU to supply these "rooms"..... I might just feed the shippen & pen circuits through 4pole rotary isolators 

Don't forget RCDs for protection against fire. In some installations this might just be a suitability rated time delay 4 pole device at the orgin, but then your've got to be careful with discrimination (watch out for single pole rcbos!). If theres 'life critical' stuff there, then it'll need a more engineered approach to ensuring there is no loss of power to that

It probably wouldn't "need" RCD protection against fire as the supply is overhead TNS from what I can tell,,,, but I would probably be using double pole RCBO's anyway

As for "life critical" equipment... I haven't been told of any so I'm not quoting for it.... the spec is only one socket and one light per room (I'm going with WP accessories)

think I would split it upstairs / downstairs and run as radials for sockets.  It' just keeps it simpler for any future works.

NozSpark said:

It probably wouldn't "need" RCD protection against fire as the supply is overhead TNS from what I can tell,,,, but I would probably be using double pole RCBO's anyway

As for "life critical" equipment... I haven't been told of any so I'm not quoting for it.... the spec is only one socket and one light per room (I'm going with WP accessories)

Click to expand...

Don't forget that 705 says:

705.422.7 For additional fire protection purposes in some circumstances, RCDs shall be installed with a rated residual operating current not exceeding 300 mA. RCDs shall disconnect all live conductors. Where improved continuity of service is required, RCDs not protecting socket-outlets shall be of the type S or have a time delay.

So it depends on what they are doing in the locations.

NozSpark said:

It probably wouldn't "need" RCD protection against fire as the supply is overhead TNS from what I can tell,,,, but I would probably be using double pole RCBO's anyway

As for "life critical" equipment... I haven't been told of any so I'm not quoting for it.... the spec is only one socket and one light per room (I'm going with WP accessories)

Click to expand...

you dont get overhead TNS. its either TT or TNCS

Andy™ said:

you dont get overhead TNS. its either TT or TNCS

Click to expand...

I've seen it round here, it was a farm too!

Sidewinder said:

I've seen it round here, it was a farm too!

Click to expand...

really? thought DNO's wont supply TNS as overhead, too much risk of lost earth (although they will use the neutral as an earth.... )

You can usually recognise OH TN-S by the number of conductors but watch out for street lighting supplies. Another one to watch out for is neutral being at the top, the NE has home office approval for this.

Andy™ said:

you dont get overhead TNS. its either TT or TNCS

Click to expand...

 don't see it very often, but defo some in the SW.

Normally I suspect as mine was with a dedicated pole mount can Tx which is close to the property.

Think spheres of influence, it might be a hot site transformer to simplify things, or it might be a cold site with the LV rod close to the property.

last one I encountered was pole mount TX close to property.

Andy™ said:

you dont get overhead TNS. its either TT or TNCS

Click to expand...

This is what makes me think that it's TNS..... I've also priced for it being TT, just to cover the bases

TX is on the next pole (out of picture)...

NozSpark said:

TX is on the next pole (out of picture)...

Click to expand...

could be split phse, L1, L2, N? how many 11kv lines go into the transformer?