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Main switchboard has 2 main switches each with own seperate supply from a separate transformer (1400amps).

There is a bus tie changeover switch allowing only 1 main switch supply to be on at any time.

Each section has its own main neutral coming from its transformer, its own MEN link and its own main earth and earth electrode.

Looking like its 2 main switchboards beside each other

But there is just 1 earth bar and 1 neutral bar that goes cross into the 2 sections, so 2 MEN links on the same bar, also they are supplying the same outgoing circuits.

This is all in one joined switchboard / panel.

Probably supplying the same circuits is not diff then a generator supply etc but I'm not sure about 2 MEN links and 2 main neutrals from diff transformers and 2 main earths with the shared bars etc in regards to if some of this may be under part 1 or not?

If so what's required to satisfy the Inspector ?


I get the impression it's quite common practise do do it this way but I have not seen too many like this and woukd appreciate an explanation.

Thanks

Sounds the same as an arrangement with a generator changeover switch. It doesn’t sound non-compliant to me, although I don’t understand why they would double up on the ‘main earth’ & ‘MEN link’?

Anything under Part 1 requires a certified design; and 1.9.4 means this CD will be very clear about exactly which bits are Part 1.
If you've got all that documentation; then ESRs allow you to follow the CD in good faith; and the CD will also be what the inspector inspects to.
If you haven't got all that, then you're still in Part 2 territory.

Sounds like the setup is similar to Fig 7.1; which is really only intended to explain which ones are "main switches" and doesn't address the N & E side of things.

if this is one installation with one PoS, and 2nd supply is only for standby; I believe there should only be one main earthing system (including one MEN link).
The reason we have only a single MEN is to avoid load current flowing in earthing conductors.

However I suspect the intent is actually 2 separate installations, one from each supply, and the bus tie is only intended as an emergency measure in case one supply fails. In which case each side has to comply in its own; and each will be supplying a different bunch of circuits.
Under this set-up; if one supply fails and is isolated and the bus tie is closed to keep those loads running; the duplicate MESs can't cause any problems.

It is intended so if one supply fails it will be switched to the back up supply.

They both supply the same circuits.

Both supplies share 1 earth bar and 1 neutral bar so has 2 MEN links on bars.

Both supplies will be live all the time from their own transformer just one supply can only supply circuits at any one time via buss tie switch.

So there are 2 main neutrals/PEN.

Can this all be signed off under part 2?

Seems odd that anyone would have a supply that size that's simply a stand-by.
But can't see anything obviously non-compliant about it.

I'm assuming you didn't design this, and are simply installing it.
In that case you probably have a plan to follow; issued by the designer.
That plan is likely to qualify as a 'certified design" (as per ESR 58); in which case you are entitled to rely on it.

Hey,

Had this exact situation few months ago, but with three transformers, with three main switches, two bus ties between each "section" of the board all on to one switchboard. N + E bar common across all three boards, and it also had generator supply as well.

Each incomer had a MEN link, meaning there were 3 MEN links in the one board. This plant had be designed overseas but the NZ based electrical engineers for the HV and LV had us remove the N + E links in the transformers and keep all three in the boards. This was detailed on a revised CD document. All Earthing was common, earth mats and grid for the transformer bays to bar's in the transformer bays to the main earth bar at each incomer, then main earth conductors from each incomer cell earth bar to the earth grid and cad welded.

Not sure on theory behind it but obviously falls into the realms of Part 1 design as stated by Alec, just sharing my story as this set up is not uncommon in many large high current LV MMC/switchboards.

Thanks for the input.