N pin on socket used for other means

[JamieP]

I have a site that has motors controlled via VFD.

The motors are run in suitable VFD cable.

The client wants the motors to connect via plug and socket arrangement. Rather than a 3+E socket they want to use a 3+N+E but want to use the N pin to continue the screen through.

I don't like this at all, I don't even like the use of the socket arrangement but I can't find anything to prevent or make this non-compliant.

I had suggested a 7 pin or similar and using one of the auxillary contacts for the screen or also thought the final part to the motor should probably be in a suitable flexible cable as I thought VFD cable was for fixed applications only. Other than that I assumed MIs would also prevent these arrangments but I just want something hard and fast around this because I can't find anything directly non-compliant other than it just seems wrong and just plain not acceptable.

Thoughts?

[AlecK]

However you 'continue" the screen it will actually be a break in the screening.
(unless you use metal-bodied plugs).
Which defeats the purpose of having the screen; which has to be continuous to be effective.

I agree a standard 5-pin socket should not have the N pin used for anything else but an N conductor.
Bit can't think of anything that makes this a compliance issue, other than MIs

[gregmcc]

I would imagine that the socket and plug both have clearly marked "N" on them. If some other device was plugged in, neutral return current would then flow through the PEC (via the screen connected to the 'N' pin on the socket), would the PEC be rated to carry the current?, quite common for the PEC to be smaller than the phase or neutral for that circuit.

Like AlecK said, a bad idea to use the N terminal for anything else other than the neutral, there will always be someone who will plug something else in and potentially cause a problem.

[MikeNZ]

I have a site that has motors controlled via VFD.

The motors are run in suitable VFD cable.

The client wants the motors to connect via plug and socket arrangement. Rather than a 3+E socket they want to use a 3+N+E but want to use the N pin to continue the screen through.

I don't like this at all, I don't even like the use of the socket arrangement but I can't find anything to prevent or make this non-compliant.

I had suggested a 7 pin or similar and using one of the auxillary contacts for the screen or also thought the final part to the motor should probably be in a suitable flexible cable as I thought VFD cable was for fixed applications only. Other than that I assumed MIs would also prevent these arrangments but I just want something hard and fast around this because I can't find anything directly non-compliant other than it just seems wrong and just plain not acceptable.

Thoughts?

Hi Jamie,
Is there a particular reason why they need to disconnect/reconnect these motors? And how often would this occur?
What sort of screen are we talking about here, is it stranded screening or some sort of copper tape, or a combination of the two?
I'm picking because there is no Neutral prevalent that this is a balanced load?
Not sure where you're based, but have a look at https://nz.rs-online.com/web/p/heavy-du ... rs/0448474, surely they might have something there.
They do have a wide range of industrial plugs and sockets that might help you out and to be fair, the people that own the place are
going to suck up the price of the conversion.

I don't like the idea of plugs and sockets on VSD's though and this strikes me as strange as to why they would need this.

Let us know how you get on.

Cheers,
Mike T.