Number of Main Switches

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JamieP
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Number of Main Switches

Post by JamieP »

"2.3.3.2 Number of main switches
The number of main switches shall be kept to the minimum practicable to
provide for effective operation in an emergency.
Domestic electrical installations, including each separate domestic
electrical installation forming part of a multiple electrical installation, shall
be provided with not more than one main switch for—
(a) each separately metered supply; or
(b) where there is more than one separately controlled supply from a
meter, a main switch for each of the separately controlled supplies."

Now I'm well aware you can have more than one main switch and I can see that this number should be kept to a minimum but the second half there only applies to domestic installations

In a non-domestic installation what other situations would call for multiple main switches?
Last edited by JamieP on Mon Apr 20, 2020 9:13 pm, edited 1 time in total.
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Re: Main Switches

Post by gregmcc »

JamieP wrote:
Fri Apr 17, 2020 8:58 pm

In a non-domestic installation what other situations would call for multiple main switches?
In a commercial building where there are multiple tenancies, typically a main installation switchboard which may or may not have metering for each tenant.
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Re: Main Switches

Post by JamieP »

I see, makes sense, cheers
AlecK
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Re: Main Switches

Post by AlecK »

safety services eg fire pumps, , lifts, etc 9see 7.3) must each have separate main switch.
For outbuildings; if supply > 100A + has a switchboard, or if supplied by more than one submain [2.3.4]
Back to domestic; each separate tenancy must have own main switch; though not necessarily within the tenancy
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Re: Main Switches

Post by JamieP »

Understood, thank you
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Re: Number of Main Switches

Post by AngryClient »

Well I came here to make an inquiry on this very requirement. Moved house just before the lockdown and found that there are 2x Main Switches (both labelled as such) in the house. Me thinks an email to the contactor is in order.
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Re: Number of Main Switches

Post by AlecK »

There's no requirement for the various main switches that may be required, eg for controlled & uncontrolled loads, to be linked.

For domestic multi-tariff supplies;, I would regard linking (or use of a multi-pole device) as best practice where it's practicable, but once you're past 3 tariffs it becomes difficult.

And where they are required for other reasons; linking is not only impractical but forbidden; because we need to be able to isolate each supply / type of load individually.
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Re: Number of Main Switches

Post by JamieP »

AngryClient wrote:
Tue Apr 21, 2020 3:56 pm
Well I came here to make an inquiry on this very requirement. Moved house just before the lockdown and found that there are 2x Main Switches (both labelled as such) in the house. Me thinks an email to the contactor is in order.
Provided this was done under current rules, wouldn't 2.3.3.4 (b) call for better labelling than them both just being main switch to be compliant?
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Re: Number of Main Switches

Post by AngryClient »

JamieP wrote:
Tue Apr 21, 2020 8:25 pm
AngryClient wrote:
Tue Apr 21, 2020 3:56 pm
Well I came here to make an inquiry on this very requirement. Moved house just before the lockdown and found that there are 2x Main Switches (both labelled as such) in the house. Me thinks an email to the contactor is in order.
Provided this was done under current rules, wouldn't 2.3.3.4 (b) call for better labelling than them both just being main switch to be compliant?
Recently completed domestic dwelling so we should assume it was required to be under current rules. I cant see any benefit to what has been done.
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Re: Number of Main Switches

Post by AlecK »

yes if multiple switches are used, they must be properly labelled as to exactly what they control.
Agree that for most domestic, there's no advantage (to user, which is what matters) from having separate switches compared to linked switches.
And having been involved in the EWRB complaints process (luckily not as the complainee) where "main" switches were one of the issues; I'm certain they would take a dim view of using multiple switches even though it's clearly compliant.
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Re: Number of Main Switches

Post by AngryClient »

Ok so I'm getting conflicting information here. I think its not compliant.

This is what we have:
Mains from street into Meter Enclosure terminated to "Main Switch"
From there it goes across to the Switchboard where terminated into "Main Switch". This is also where the MEN link and Main Earth is.

So from the outside there are 2x Main Switches. Both are essentially on opposite ends of the Meter and Switchboard.

Simple enough right? Complies or not?
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Re: Number of Main Switches

Post by DougP »

Once you provided the actual arrangement, it is simple for any electrician to tell you the answer.

The first switch in the metering enclosure is not the main switch for the installation. It is a metering isolator, or main isolator - or whatever the locals wherever you live want to call it. It shouldn't be labelled "main switch".

Only the switch on the main switchboard is the main switch in your case.
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Re: Number of Main Switches

Post by gregmcc »

2.3.3.2 says that domestic installations shall be provided with not more than one main switch for (a) each separately metered supply or (b) where there is more than one separately controlled supply from meter, a main switch for each of the separately controlled supplies.

So for a domestic installation, In the meter board simply remove the label that calls it a "Main Switch", as far as commercial and industrial installations as many as you like, but keep them to a minimum practicable to provide for effective operation in an emergency
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Re: Number of Main Switches

Post by AngryClient »

Ok thanks for the clarification. So the point is that the labelling, which was clearly provided by the installing electrical worker, is incorrect; therefore not compliant.
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Re: Number of Main Switches

Post by AlecK »

That sort of error is very common;; the industry including lots of people who use words carelessly rather than as they are defined.
Eg earth electrodes being called "pins", "stakes", "rods"; and just about every switch being called 'isolating" regardless of whether they actually provide isolation.
Or in this case thinking that the "main switch" is always the first (most upstream) switch of an installation.

As others have said, the key here is that the isolating switch in the meter enclosure is not a "main switch".
In fact it's not required at all by Wiring Rules (though it may be specified by the metering provider and / or the network connection requirements). That said, putting on my AMC hat, such switches are a great idea, because they allow safe - ie isolated - work on the meters without needing to access network's supply fuse.

The reason it's not a "main switch" is that 2.3.3.1 states that "main switches" are located at the "main switchboard"; and this switch isn't at MSB.
Fig 7.1 illustrates a number of switch functions that can be on line side of the "main switches"; either within the MSB or elsewhere.
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Re: Number of Main Switches

Post by AngryClient »

Should I add that the "switch" in the Metering enclosure doesn't isolate the meter, it is on the load side. So what is the point of it at all?

Agree though that a switch to isolate the meter would be useful for maintenance purposes.
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Re: Number of Main Switches

Post by AlecK »

Agree that seems silly, as well as the labelling being non-compliant.

Another place where switches are often wrongly labelled as "main switches" is the isolators for incoming submains to DB - which mostly are not "main switches and in fact are often not required at all.
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Re: Number of Main Switches

Post by TPower »

Where domestic PV is concerned, and there’s a main switch/circuit breaker for the PV, and a separate main switch for the grid supply, which is pretty standard. Is this acceptable under 2.3.3.2? I would’ve thought it would be better to gang them together?
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Re: Number of Main Switches

Post by AlecK »

Perfectly acceptable; as long as they are properly & correctly labelled.

For an inverter that only runs as supplementary supply (co-generation; could argue that linking is sensible.
But with modern multi-mode inverters that can also act as alternative supply, the last thing you want is linked switches
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Re: Number of Main Switches

Post by TPower »

Thanks Alec. I came across a Fronius grid connected inverter that has islanding capability, to act as alternative supply if the grid fails. It has a contactor arrangement so it won’t back feed.

I guess it just concerned me a bit, as imagined an electrician coming to work on the switchboard, isolating the grid main switch and thinking this would isolate everything, however power would still be on supplied from the inverter.

But I guess this is why having adequate signs & labels is very important.
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Re: Number of Main Switches

Post by AlecK »

the labelling of main switches is absolutely crucial.

"3000"; 7.3.3 requires that any generation system must have an isolating switch at the swbd it is connected to.
It also requires no back-feeding; with Exception if network agrees - as for a grid-connected inverter

7.3.4 then adds a number of requirements WRT isolation.
However the Exception says that arrangements that comply with 4777 series are OK.

For generating sets, the principles for alternative supply include that when load is connected to one supply, it must be isolated from the other supply.

Most contactors do not provide isolation (one of the reasons that ATS for alternative supplies are expensive beasts).
So you have cause to be concerned.

A key question would be establishing whether the unit does comply with 4777 in all modes.
It may be that when in grid-connect mode it complies with 4777.2, but could well be that the alternative supply mode is non-compliant.
I suspect that 4777 series sets no requirements for this mode, simply because the entire series is all about grid-connect.
And if there are no requirements set; difficult to claim compliance with them.

Basically we have a grey area, with equipment development being well ahead of rules development.

I believe that in order to safely & compliantly make use of the cleverness now available in "multi-mode" inverters;
a separate change-over device is required same as for a genset c/o. Probably manual on grounds of cost.
Reliance in internal switching (especially electronic switching) is not sufficient because it doesn't provide isolation between sources.
Same for relays, & (most) contactors.
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Re: Number of Main Switches

Post by TPower »

The inverter has a ‘certificate of suitability’ indicating compliance with 4777.2, and the manufacture supplies instructions/wiring diagrams for the contactor arrangement to prevent back feed when operating as backup supply. Certainly is a bit of a minefield trying to navigate this stuff with regards to compliance though.
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Re: Number of Main Switches

Post by AlecK »

Title of "4777.2" is
Grid connection of energy systems via inverters; Part 2 inverter requirements".
so hardly surprising that it's focussed on the aspects that relate to connection to grid.

2015 edition does include some info on multi-mode inverters (clause 6);
but the first statement is: "unless otherwise stated, the modes in the following clauses are for the grid-interactive port of the inverter".

6.4.1 sets some requirements that apply when in "standalone mode" (ie operating as alternative supply); bit again thse relate to the grid-connected port rather than the standalone port.
Including when the inverter is disconnected from the grid, any standalone port shall ensure that all active conductors are isolated from the grid-interactive port.
Seems like in your case the manufacturer is relying on external, third-party-supplied, contactors to meet this requirement.
But unless the contactors have an isolation rating (contact gap etc); isolation will not be achieved.

It's basically been left to "3000" to set the rules for alternative supply via inverter; unlike for gensets where we have "3010" to provide detailed requirements.
And "3000" simply has not yet addressed the issue in any detail.
In fact 7.3 assumes that every inverter, other than a UPS, is grid-connected.
It was written at a time when PV / inverter system didn't include batteries.

7.3 is expected to get a full work-over in next edition.
meantime we need to proceed with extreme caution.
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