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Cable routing/eddy currentso

Hi

I have a query regarding a cable route for a job I’m currently on (when lockdown rules allow me back to it!). I have to supply a feed motor on a farm, the contactor feeding it is at one end of the building in a plant room. There is an existing steel trunking running the length of the building and I plan to come out of this close to the motor with pvc conduit. However there is a paddle switch in the meal hopper beside the motor that will control the contactor. This needs a simple two wire connection. My question is can I run these two cables out of the trunking in the same conduit as the cables to the motor. I plan to put a wiska box or similar at the other end of the conduit so that I can split off to the motor and paddle switch separately, and there will be an isolator before the motor.

The question however remains regarding the ‘control cables’ in the same conduit as the motor supply. They are from the same circuit and the same voltage but was concerned about eddy currents.

Thanks in advance

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0 Zoomup over 5 years ago

AJJewsbury:

So in my example of plastic conduit and plastic switch and box coming from a steel trunking, it is actually a two gang switch on two different circuits, it is acceptable to have (in this example) just a live and switch live for each circuit down to the switch but an earth isn’t required as regards eddy current considerations as there can be no possibility of an earth fault at the switch due to its plastic construction?

That's about the size of it!

Please see 411.3.1.1

I'd suggest otherwise.

If it's an all-insulated switch then protection against electric shock is by double or reinforced insulation rather than ADS (how could ADS operate without any earthed metalwork?) Thus it's not section 411 that applies but 412. It's therefore the (not greatly dissimilar) regulation 412.2.3.2 we should be looking at. 412.2.3.2 does have a get-out though (via 412.1.2) where the system is controlled so that unauthorised changes (such as the introduction of class I accessories) can't be made.

- Andy.

The O.P said........ "Reason I ask is that I have seen different methods of only lives to the switch and then some as L/N/E. Obviously a metal switch would require an earth cable ran to it and in domestic settings it is becoming more common to have a neutral in the switch box for a variety of reasons, but in my example of trunking/conduit coming out of a metal trunking to a plastic switch I was curious to other peoples methods"

The O.P. refers to light switches in "domestic settings" and I replied with reference to domestic settings saying that a C.P.C. will be required at all electrical "points". Why wouldn't they? I think that you are muddying the water unnecessarily saying that a C.P.C. is not required. This could cause confusion. 411.3.1.1 is a coverall requirement in most domestic and many other cases. Running a C.P.C. to a plastic box is no great difficulty and will cause no harm. In fact it will be good to have if needed in the future. In a domestic situation the householder may change a plastic light switch for a metal plated switch that requires earthing. A readily available C.P.C. will make this upgrade easy and safe.

I would not rely upon the 412.1.2 requirement that effective measures such as by adequate supervision will be reliably in place here at the farm, so that no change can be made that would impair the effectiveness of the protective measure of Double or Reinforced insulation. Any old body could alter the installation. "Oh, I'll put a metal switch here as the old plastic one is cracked. A metal one will be stronger safer. Oh, there is no earth. I'll just have leave the earthing then."

Can we really be sure that changes won't be made by a user without authorisation? 412.1.2.

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0 Zoomup over 5 years ago

AJJewsbury:

So in my example of plastic conduit and plastic switch and box coming from a steel trunking, it is actually a two gang switch on two different circuits, it is acceptable to have (in this example) just a live and switch live for each circuit down to the switch but an earth isn’t required as regards eddy current considerations as there can be no possibility of an earth fault at the switch due to its plastic construction?

That's about the size of it!

Please see 411.3.1.1

I'd suggest otherwise.

If it's an all-insulated switch then protection against electric shock is by double or reinforced insulation rather than ADS (how could ADS operate without any earthed metalwork?) Thus it's not section 411 that applies but 412. It's therefore the (not greatly dissimilar) regulation 412.2.3.2 we should be looking at. 412.2.3.2 does have a get-out though (via 412.1.2) where the system is controlled so that unauthorised changes (such as the introduction of class I accessories) can't be made.

- Andy.

The O.P said........ "Reason I ask is that I have seen different methods of only lives to the switch and then some as L/N/E. Obviously a metal switch would require an earth cable ran to it and in domestic settings it is becoming more common to have a neutral in the switch box for a variety of reasons, but in my example of trunking/conduit coming out of a metal trunking to a plastic switch I was curious to other peoples methods"

The O.P. refers to light switches in "domestic settings" and I replied with reference to domestic settings saying that a C.P.C. will be required at all electrical "points". Why wouldn't they? I think that you are muddying the water unnecessarily saying that a C.P.C. is not required. This could cause confusion. 411.3.1.1 is a coverall requirement in most domestic and many other cases. Running a C.P.C. to a plastic box is no great difficulty and will cause no harm. In fact it will be good to have if needed in the future. In a domestic situation the householder may change a plastic light switch for a metal plated switch that requires earthing. A readily available C.P.C. will make this upgrade easy and safe.

I would not rely upon the 412.1.2 requirement that effective measures such as by adequate supervision will be reliably in place here at the farm, so that no change can be made that would impair the effectiveness of the protective measure of Double or Reinforced insulation. Any old body could alter the installation. "Oh, I'll put a metal switch here as the old plastic one is cracked. A metal one will be stronger safer. Oh, there is no earth. I'll just have leave the earthing then."

Can we really be sure that changes won't be made by a user without authorisation? 412.1.2.

Z.
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Cable routing/eddy currentso

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