Thoughts on two circuits and two gang switch ?

[ban-all-sheds]

537.2.1.3 applies to any situation where the actual live 'parts' can be re-energised from more than another supply.

That's not what it says.

This situation will never arise with a multi gang light switch. Because to isolate a switch you identify the circuit at the db and pull the fuse. So even if the db has dual supplies, you're still completely safe because you have isolated the individual circuit.

It's not the DB which has dual supplies, it's the light switch.

537.2.1.3 requires a warning notice because the live parts inside the switch enclosure cannot be isolated from a single point.

Thats why 537.2.1.3 does not apply, the teminals 'parts' maybe adjacent but they are different 'parts' individually supplied and/or isolated.

Where an installation, item of equipment or an enclosure contains live parts connected to more than one supply..."
Do you not consider a switch to be an item of equipment?

Do you not consider the box it's mounted in to be an enclosure?

It is for the individual switches.

A multi-gang switch is one item.

The box it is in is an enclosure.

If the circuits supplying the one item, or the enclosure, can't be isolated at a single point then 537.2.1.3 applies - it says so quite clearly.

If you're ascerting that multi gang switches need one point of isolation then take it up with the IET.

I am asserting that in cases where more than one circuit is supplying the switch and they can't be isolated at a single point.

And I have no need to take it up with the IET, as what they say about it is unambiguous.

You could also point out non compliance with the EAWR, because you have to dismantle a grid modules before you can test for dead.

And ordinary switches have to be removed before you can test for dead.

Equipment covers have to be removed before you can check for dead inside them.

Those are not contraventions of the EAWR.

 

[JohnW2]

Where an installation, item of equipment or an enclosure contains live parts connected to more than one supply..."
Do you not consider a switch to be an item of equipment?
Do you not consider the box it's mounted in to be an enclosure?

As I've said, holmslaw may actually be right about this one. I don't think there's any argument about 'item of equipment' or 'enclosure' - the issue is about what they mean by 'more than one supply'. You appear to think, as I did initially, that it meant 'more than one circuit', but holmslaw has suggested that it means 'source' (mains supply, generator, PV etc.). Whilst BS7671 does not define 'supply', use of the word in other places in BS7671 (e.g. 514.15) suggest that he may be right.

Kind Regards, John.

 

[sparkticus]

Where an installation, item of equipment or an enclosure contains live parts connected to more than one supply..."
Do you not consider a switch to be an item of equipment?
Do you not consider the box it's mounted in to be an enclosure?

As I've said, holmslaw may actually be right about this one. I don't think there's any argument about 'item of equipment' or 'enclosure' - the issue is about what they mean by 'more than one supply'. You appear to think, as I did initially, that it meant 'more than one circuit', but holmslaw has suggested that it means 'source' (mains supply, generator, PV etc.). Whilst BS7671 does not define 'supply', use of the word in other places in BS7671 (e.g. 514.15) suggest that he may be right.

That is why I asked the following questions earlier in this thread:
QUOTE:

1) In what context is it written? holmslaw indicates it is for multiple generator situations which is what others have told me.
2) What does "supply" mean in this context ? Does it mean the generator(s) source of electrical energy feeding that enclosure and the related parts of the installation or does it mean the final circuit causing parts to be live within that enclosure?

UNQUOTE.

There seems to be a sense that it means the source or sources of electrical energy. It appears that it does not mean multiple final circuits (on individual CBs) emerging (for functional switching or other reasons) within an enclosure from a single source of electrical energy which also appears to include a three phase supply which I think in the context of "supply" also means a single source.


537.2.1.3 also seems to assert that a situation where you may have two sources of supply (mains & PV for example) entering a common enclosure (say a junction box) but not actually connected to the same conductors within that junction box would also require a "warning multiple source" label.

It seems that the grid switch "enclosing"multiple final circuits across multiple phases and the humble domestic hallway switch "enclosing" at least two different final circuits do not qualify.

 

[holmslaw]

..

 

[Paul_C]

I'm not sure that I understand their reasoning at all. The 'low impedance path to earth' from a TN-C-S installation's neutral is all due to the supply's neutral conductor itself, and the same is also at least partially (possibly largely) true with TN-S. So why is the same not also true with a TT supply, even if it only supplies TT installations?

So much of the network is PME now, but let's examine the various non-PME options with the neutral earthed only at the supply transformer:

There's the typical older urban distribution system with separate earth provided by way of the cable armor to allow for a TN-S arrangement. According to the current thinking, the neutral does not need to be disconnected at the installation. But of course, although it's normal to use the supplied earth connection, it's quite possible to employ a TT system by installing an entirely independent earth rod for the house and making no connection to the supplier's provided earth. According to the current regs., this then means that the supply neutral needs to be disconnected along with the live conductor. But in both cases the neutral coming into the house is exactly the same. The same situation applies in the much rarer cases where a separate earth conductor is provided on overhead supplies to permit either a TN-S or a TT arrangement.

There the possibility of no PME and all installations having to be TT, as was once common in rural areas. If the supply neutral is still earthed only at the transformer, then it's effectively little different (in terms of what could happen to the neutral due to faults etc.) from the previous case. Yet the current thinking treats these differently by requiring the neutral to be disconnected in one case but not other other.

Then there is PME. The house installation could be connected to the network as TN-C-S, in which case the rules say that the neutral doesn't need to be disconnected. But don't use the supplier's earth provision to the neutral and use a local rod instead to make it TT, and then the neutral does need to be disconnected, even though it's exactly the same neutral from the same supply cable as you'd be using if you'd opted to go with TN-C-S.

And of course that's all on top of that long-standing 2-wire versus other types of service. If it's acceptable for the main switch to open just the live conductors of a 3-wire or 3-phase supply, with provision to isolate neutral by way of a separable link, then why isn't that just as acceptable for a simple 2-wire supply? Again, whether the supplying network is PME or not, or whether the installation is arranged to result in a TN or a TT system makes no difference to the fact that the incoming neutral to a 2-wire 240V house service is from exactly the same neutral on the lines outside which can be feeding a 3-wire 240/480V or 3-phase 240/415V service next door.

None of this makes a whole lot of sense!

 

[JohnW2]

I'm not sure that I understand their reasoning at all. ...

.... Yet the current thinking treats these differently by requiring the neutral to be disconnected in one case but not other other. .... None of this makes a whole lot of sense!

Exactly. We seem to agree.

Kind Regards, John.