I've been looking at at segregation requirements due to working a lot with instrument and instrumentation systems
At first I looked at the requirements of 3.9.8.3 so I made sure to follow either the instrument cables being rated for the highest voltage present or by keeping the low voltage cables DI. However there were certain situations that made this difficult such as certain parts inside switchboards but actually looking over this clause it sounds like it only applies to being "enclosed in the same wiring system". Am I right in thinking this actually only applies to things such as in conduit or trunking systems? Wiring systems that enclose the cables? So I would actually need to worry about these requirements in a switchboards for example because a switchboard isn't a wiring system? Or am I way off?
Is it still wise to keep things apart due to interference even if not a requirement electrically?
Curious of any input or thought
Segregation and interference
Re: Segregation and interference
"Wiring System" is not a defined term; but the meaning can be found by looking at the start of Section 34; where the fundamental requirements for wiring systems Are in 3.1.1 and the types of wiring systems are required by 3.2 to either comply with Table 3.1 or have an equivalent degree of safety and comply with the requirements of Section 3.
So "wiring system" includes both the conductors and any "wiring enclosure"; and when 3.9.8.3 sets the requirement s for segregation of different voltage levels within the same "wiring system" , it's talking about cables within the same conduit / duct /trunking / multicore cable.
Types if wiring systems are shown in RH column of Table 3.1; and are broadly classified on column 2 as "unenclosed", "in an enclosure" (meaning a "wiring enclosure"), "supported on catenary" , or "supported on insulators".
A switchboard isn't a "wiring system". It's a collection of fittings.
It will include wiring systems within it. Eg a standard LV switchboard will have at least one wiring system bringing the incoming supply, and several wiring systems for the departing circuits. There will also be wiring systems used within the switchboard, and these may be different iinside the switchboard and outside it, even for the came conductors. As example; a departing circuit may be insulated & sheathed cable (eg TPS), but within the switchboard we remove the sheathing so the conductors now are classed as "insulated, unsheathed".
So it's not that the rules of 3.9.8.3 don't apply within a switchboard; more that they apply differently.
Along a cable run, a TPS cable will mostly have DI; so it's not hard to apply 3.9.8.3 rule requiring DI between LV and ELV wiring.
If you put both into a trunking, eg for mechanical protection and/or cosmetic tidiness, with no terminations, DI is still maintained.
But if you then decide to mount an LV fitting (eg a socket outlet) on the trunking, you'll be removing the sheath and also will have uninsulated live parts. In effect, you've changed the wiring system; and since there's no longer DI on the LV at that point, other steps must be taken.
Similarly if you bring ELV conductors into a equipment enclosure such as a switchboard where there are insulated unsheathed LV cables, there can't be double insulation between them and the ELV conductors unless steps are taken to add some insulation or to effectively segregate the different voltage levels.
3.9.8.3 has nothing to do with interference; and everything to do with preventing hazardous voltages from getting onto the ELV system.
So "wiring system" includes both the conductors and any "wiring enclosure"; and when 3.9.8.3 sets the requirement s for segregation of different voltage levels within the same "wiring system" , it's talking about cables within the same conduit / duct /trunking / multicore cable.
Types if wiring systems are shown in RH column of Table 3.1; and are broadly classified on column 2 as "unenclosed", "in an enclosure" (meaning a "wiring enclosure"), "supported on catenary" , or "supported on insulators".
A switchboard isn't a "wiring system". It's a collection of fittings.
It will include wiring systems within it. Eg a standard LV switchboard will have at least one wiring system bringing the incoming supply, and several wiring systems for the departing circuits. There will also be wiring systems used within the switchboard, and these may be different iinside the switchboard and outside it, even for the came conductors. As example; a departing circuit may be insulated & sheathed cable (eg TPS), but within the switchboard we remove the sheathing so the conductors now are classed as "insulated, unsheathed".
So it's not that the rules of 3.9.8.3 don't apply within a switchboard; more that they apply differently.
Along a cable run, a TPS cable will mostly have DI; so it's not hard to apply 3.9.8.3 rule requiring DI between LV and ELV wiring.
If you put both into a trunking, eg for mechanical protection and/or cosmetic tidiness, with no terminations, DI is still maintained.
But if you then decide to mount an LV fitting (eg a socket outlet) on the trunking, you'll be removing the sheath and also will have uninsulated live parts. In effect, you've changed the wiring system; and since there's no longer DI on the LV at that point, other steps must be taken.
Similarly if you bring ELV conductors into a equipment enclosure such as a switchboard where there are insulated unsheathed LV cables, there can't be double insulation between them and the ELV conductors unless steps are taken to add some insulation or to effectively segregate the different voltage levels.
3.9.8.3 has nothing to do with interference; and everything to do with preventing hazardous voltages from getting onto the ELV system.
Re: Segregation and interference
So because 3.9.8.3 applies only to "enclosed in the same wiring systems" I could have primary insulation LV and ELV cables not rated to the highest voltage level within the switchboard and near each other? Because each is its own wiring system and they aren't enclosed in the same wiring systems because as you say a switchboard isn't a wiring system but it will contain wiring systems
Am I correct in thinking this?
Am I correct in thinking this?
Re: Segregation and interference
taking a simplistic-but pedantic approach, yes the insulated unsheathed conductors of the LV circuits are not the "same wiring system" as the ELV cabling. So that specific rule may not be enforceable.
I say "may not" because some would view the equipment enclosure as part of the wiring system. I don't believe that's valid.
But for switchboards and other equipment enclosures, we still have to take precautions to avoid getting LV onto the ELV. Other rules still apply; eg 1.5.11, 4.1.2.
We also have a specific rule (2018 edition) prohibiting comms gear from being on the same faceplate as a socket or switch ; so that TV or telecoms workers don't have to access LV gear when working on their ELV systems.
Remember too that comms people are NOT entitled to open a switchboard or other LV equipment enclosure; as the enclosing is part of meeting basic protection requirements, and opening it disables the protection-by-enclosure.
There isn't - can't be - a specific rule for every possible situation.
Often we have to just rely on the fundamentals rather than specific rules
I say "may not" because some would view the equipment enclosure as part of the wiring system. I don't believe that's valid.
But for switchboards and other equipment enclosures, we still have to take precautions to avoid getting LV onto the ELV. Other rules still apply; eg 1.5.11, 4.1.2.
We also have a specific rule (2018 edition) prohibiting comms gear from being on the same faceplate as a socket or switch ; so that TV or telecoms workers don't have to access LV gear when working on their ELV systems.
Remember too that comms people are NOT entitled to open a switchboard or other LV equipment enclosure; as the enclosing is part of meeting basic protection requirements, and opening it disables the protection-by-enclosure.
There isn't - can't be - a specific rule for every possible situation.
Often we have to just rely on the fundamentals rather than specific rules
Re: Segregation and interference
Understood, it's something I would usually take care to avoid but I was just curious around the legalities of it
Also understand this is different for telecommunication systems as well which need either 50mm segregation as minimum (300mm recommended), earthed metal or an insulating barrier (I think, that's just off the top of my head but you get the drift)
Most the instrument cable I'm using seems to be rated for 500V anyway so it's not really an issue for me, like I said was more just curious around the technical side of it
Also understand this is different for telecommunication systems as well which need either 50mm segregation as minimum (300mm recommended), earthed metal or an insulating barrier (I think, that's just off the top of my head but you get the drift)
Most the instrument cable I'm using seems to be rated for 500V anyway so it's not really an issue for me, like I said was more just curious around the technical side of it
Re: Segregation and interference
Hi all,
I want to switch 24vdc on one module, and 240vac on another in the same 2g switch plate. Both cables are double insulated and rated to 1000v.
Is this OK?
I want to switch 24vdc on one module, and 240vac on another in the same 2g switch plate. Both cables are double insulated and rated to 1000v.
Is this OK?
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Re: Segregation and interference
I would suggest that they are both not double insulated as the TPS would be removed somewhere inside the flush box before the cable is terminated in to the switch.
Good practice is to not have two different voltages present in the same switch plate.
Good practice is to not have two different voltages present in the same switch plate.
Re: Segregation and interference
Agree that neither cable can be considered to be double insulated; due to sheath of each being removed to expose basic insulation.
However 3.9.8.3 applies to "wiring systems" and not within equipment enclosures.
The clause I mentioned earlier is 4.4.1.1.3 of 2018 edition; which states:
"A low voltage fixed switch or socket outlet, or its faceplate, shall not incorporate a connecting device for telecommunications, data, television, radio or other similar wiring systems".
There's a Note that USB charging sockets are acceptable; which is because they may be ELV in the (accessible) front side, but are LV on the back.
Note that this restriction only applies to switches, sockets, and associated faceplates;
so it has no effect on other equipment enclosures such as switchboards or control panels.
In industrial wiring it's absolutely normal to have both LV & ELV wiring in same equipment enclosure.
Anyone accessing such an enclosure can be expected to be competent for accessing LV.
True that 2018 edition has not been cited in Schedule 2 of ESRs, so this is not an absolute requirement in NZ yet.
But it's still relevant guidance; and I would not want to try explaining to a Coroner why I hadn't followed it.
The only good time for not following latest edition is if doing so results in non-compliance with cited edition - not common, but can happen.
Also (unfortunately) true that this new requirement is hidden under 4.4 (heading: "socket outlets"); really should be at a higher level (4.1 - 4.3).
That's because the "driver" for introducing it was mainly sockets with provision for extra switch (or other module); that many people then used for ELV comms cabling.
The fundamental requirement it supports is 4.1.2 (d); prevention of shock in event of reasonably expected conditions;
'cos it's reasonable to expect that ELV service people, likely not qualified / competent/ licenced to access live LV conductors / terminations, will need access.
So the question needing an answer is: what is the 24 V d.c. for?
Is it within the description of " telecommunications, data, television, radio or other similar wiring systems"?
If not; then you may have a valid argument for ignoring the new clause.
However 3.9.8.3 applies to "wiring systems" and not within equipment enclosures.
The clause I mentioned earlier is 4.4.1.1.3 of 2018 edition; which states:
"A low voltage fixed switch or socket outlet, or its faceplate, shall not incorporate a connecting device for telecommunications, data, television, radio or other similar wiring systems".
There's a Note that USB charging sockets are acceptable; which is because they may be ELV in the (accessible) front side, but are LV on the back.
Note that this restriction only applies to switches, sockets, and associated faceplates;
so it has no effect on other equipment enclosures such as switchboards or control panels.
In industrial wiring it's absolutely normal to have both LV & ELV wiring in same equipment enclosure.
Anyone accessing such an enclosure can be expected to be competent for accessing LV.
True that 2018 edition has not been cited in Schedule 2 of ESRs, so this is not an absolute requirement in NZ yet.
But it's still relevant guidance; and I would not want to try explaining to a Coroner why I hadn't followed it.
The only good time for not following latest edition is if doing so results in non-compliance with cited edition - not common, but can happen.
Also (unfortunately) true that this new requirement is hidden under 4.4 (heading: "socket outlets"); really should be at a higher level (4.1 - 4.3).
That's because the "driver" for introducing it was mainly sockets with provision for extra switch (or other module); that many people then used for ELV comms cabling.
The fundamental requirement it supports is 4.1.2 (d); prevention of shock in event of reasonably expected conditions;
'cos it's reasonable to expect that ELV service people, likely not qualified / competent/ licenced to access live LV conductors / terminations, will need access.
So the question needing an answer is: what is the 24 V d.c. for?
Is it within the description of " telecommunications, data, television, radio or other similar wiring systems"?
If not; then you may have a valid argument for ignoring the new clause.