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Looping Lighting feeds at switches in singles

Baldyhugh
Hi

A few months back I posted a question regarding different methods of connecting lighting feeds and switch feeds at switches in singles conduit cable. My question was more from an eddy current perspective. I’m currently working on a job with steel trunking where the drops to switches and sockets etc from the steel trunking are in plastic conduit and the switches / sockets are plastic. My previous post queried whether having just live / switch live and earth down through a single hole in the trunking to the switch or live/neutral/earth supply to switch and live/neutral/earth out to the light through a single hole in the steel trunking was acceptable. I opted for the latter. My question now is can I take a permanent feed to the next switch from the previous switch? In effect I’ll have l/n/e supply to switch and l/n/e to the light and l/n/e to the next switch, so 9 cables at the switch position all through a single hole in the steel trunking. I know this method is used in domestic settings with t&e cable but singles in conduit has the flexibility of running each single cable directly where it needs to go but from an eddy current perspective having all my single cables through the single hole in the metal trunking down to the switch gives me peace of mind. Thanks in advance
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    Having the live feed to a switch, and the switched live from the switch to the lamp passing through a single hole or conduit is fine.

    The current "goes" along one wire and "returns" along the other, thereby producing no significant magnetic fields or eddy currents.


    Slightly more complex arrangements with multiple switches are also fine provided that "go" and "return" currents are all passed through the same conduit or hole in metal trunking.


    What should be avoided is a SINGLE wire without the corresponding wire that carries current in the other direction. I doubt in practice that it matters much for the modest currents in a typical lighting circuit, but still poor practice and arguably prohibited.
  • 0
    There are those who would say that a smallish current in a single lighting conductor run through a steel plate will not create any dangerous heating rise.


    Z.
  • 0
    Zoomup:

    There are those who would say that a smallish current in a single lighting conductor run through a steel plate will not create any dangerous heating rise.


    Z.


    True, almost certainly too small to measure. Still best avoided though for two reasons, firstly the IET regulations would seem to prohibit this even if harmless, and secondly the electromagnetic fields are alleged to cause ill health.


  • 0
    Having the live feed to a switch, and the switched live from the switch to the lamp passing through a single hole or conduit is fine. The current "goes" along one wire and "returns" along the other, thereby producing no significant magnetic fields or eddy currents.

    And the same for N when it's looped at the light (the traditional way with conduit is to loop L at the switch and loop N at the light) - as long as all the wires to any accessory pass through the same hole/conduit, then the currents must balance - as there's nowhere else for any of it to go.

       - Andy.
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    These currents are part of a circuit. This is as Broadgauge says exactly the opposite so there is no significant field. His point about EM fields is nonsense, many of us would be severely damaged if this were true, particularly those having NMR scans, the danger is from heating if anything, and this needs very high frequencies and high field strengths. There are detectable effects on Haemoglobin (blood contains iron atoms) for example but have never been shown to be dangerous. A single cable with magnetic material does cause eddy currents, but the heating effect at low current is negligible at 50Hz. The regulations are rather vague about this, probably could do with clarification and revision.
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    AJJewsbury:
    Having the live feed to a switch, and the switched live from the switch to the lamp passing through a single hole or conduit is fine. The current "goes" along one wire and "returns" along the other, thereby producing no significant magnetic fields or eddy currents.

    And the same for N when it's looped at the light (the traditional way with conduit is to loop L at the switch and loop N at the light) - as long as all the wires to any accessory pass through the same hole/conduit, then the currents must balance - as there's nowhere else for any of it to go.

       - Andy.


    Andy

    I know the traditional method with conduit and singles is to loop the neutral at the light but my example of 9 wires ( l/n/e feed to switch position , joining neutrals and earths in the switch box, l/n/e switch feed to light and l/n/e loop feed to next switch through one hole in the metal trunking is also acceptable? Just to clarify the conduit and switch is plastic but the trunking is metal.


    Thanks


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    davezawadi (David Stone):

    These currents are part of a circuit. This is as Broadgauge says exactly the opposite so there is no significant field. His point about EM fields is nonsense, many of us would be severely damaged if this were true, particularly those having NMR scans, the danger is from heating if anything, and this needs very high frequencies and high field strengths. There are detectable effects on Haemoglobin (blood contains iron atoms) for example but have never been shown to be dangerous. A single cable with magnetic material does cause eddy currents, but the heating effect at low current is negligible at 50Hz. The regulations are rather vague about this, probably could do with clarification and revision.


    I agree that the alleged health effects are nonsense, and was therefore careful to use the word "alleged" in my post.

    However not everyone agrees and some allege all sorts of ill effects.


  • 0
    Baldyhugh:
    AJJewsbury:
    Having the live feed to a switch, and the switched live from the switch to the lamp passing through a single hole or conduit is fine. The current "goes" along one wire and "returns" along the other, thereby producing no significant magnetic fields or eddy currents.

    And the same for N when it's looped at the light (the traditional way with conduit is to loop L at the switch and loop N at the light) - as long as all the wires to any accessory pass through the same hole/conduit, then the currents must balance - as there's nowhere else for any of it to go.

       - Andy.


    Andy

    I know the traditional method with conduit and singles is to loop the neutral at the light but my example of 9 wires ( l/n/e feed to switch position , joining neutrals and earths in the switch box, l/n/e switch feed to light and l/n/e loop feed to next switch through one hole in the metal trunking is also acceptable? Just to clarify the conduit and switch is plastic but the trunking is metal.


    Thanks




    Yes, it's fine. Each group of L/N/PE will sum to zero, so three such groups must also sum to zero.

       - Andy.


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    Thanks for all your help. Much appreciated

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