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Topic Title: New TT supply, More earthing questions.
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Created On: 15 May 2013 11:33 PM
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 15 May 2013 11:33 PM
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Energent

Posts: 5
Joined: 29 March 2011

Hi All,

We have a new TT supply going into a new Barn which will have a 50kW PV array on the roof. I've been pretty much exclusively involved in PV at a domestic and small commercial level for the last 3 years seem to have forgotten most things about everything else.

I'd just like to run through my current interpretation of the regs for TT supplies and section 705 and ask that I be put right if astray.

705 requires a 300 mA MP RCD, and a TT supply Can have this if the Ze is <167ohms reliably. The TL inverters can cause nuisance tripping on any more sensitive RCD's so 300 is what we have to aim for at the intake. We can then have 30mA's on the socket outlets etc. downstream.

Pretty much everything in the vicinity should be bonded back to the MET if livestock are going to be present. The building is not intended for livestock but it cannot be ruled out long term.

All accessories should be IP44 or better, guessing this includes switchgear etc.?

That seems to be the important stuff from my point of view.

e
 16 May 2013 03:57 PM
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AJJewsbury

Posts: 11462
Joined: 13 August 2003

Sounds about right to me. As your inverters are transformerless, you might need B-type RCD, unless the manufacturer can confirm that the construction of the inverters are such that d.c. fault currents can't be fed into the mains.

Presumably it's a G59 rather than G83 setup (as it'll be over 16A/phase) - so you'll have DNO involvement in the particulars of that.

- Andy.
 17 May 2013 07:36 AM
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Energent

Posts: 5
Joined: 29 March 2011

Hi,

Thanks for the reply,

The inverters don't require a type-b, i'm yet to use one that does.

The DNO have designed the new supply for a 50kW feed so it's just a case of doing the G59 notification after the install, nice and simple(fingers crossed)

Do you know a supplier of TT earthing lattices?
 20 May 2013 05:38 PM
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AJJewsbury

Posts: 11462
Joined: 13 August 2003

Do you know a supplier of TT earthing lattices?

'friaid not - someone here might though.

What's the barn's construction? ... just wondering if it's steel framed that the frame/foundations might make a decent electrode.

- Andy.
 20 May 2013 07:18 PM
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anastasis

Posts: 583
Joined: 01 September 2009

Originally posted by: Energent
Do you know a supplier of TT earthing lattices?


Furse or Speedwell
 20 May 2013 08:49 PM
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slittle

Posts: 3510
Joined: 22 November 2007

With a well driven (maybe extended) rod or two I would of expected to get a reasonably low reading on a farm unless you are on rock.

Barn legs can be good but other times are next to useless if the concrete pads are near the surface.


Stu
 20 May 2013 09:46 PM
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alancapon

Posts: 5768
Joined: 27 December 2005

Originally posted by: Energent
. . . new supply for a 50kW feed so it's just a case of doing the G59 notification after the install, nice and simple . . .

If you are lucky. Often with G.59 on the larger systems, there will be a degree of site specific parameters, and the DNO wishing to witness that the inverter will operate correctly according to the settings.


Regards,

Alan.
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