VFD cable article

[Voicecoil]

A link to this landed in my inbox this morning:

https://www.belden.com/blog/industri..._hsmi=77557346

There's some pricey bits of wire there, but I do like (and see the sense) of the 3 conductor + 3 earth arrangement to make it symmetrical and reduce interference.

[Kitwn]

Interestingly their cable selector says I need a 4 conductor cable of 14AWG (2 sq mm) per conductor with an outer shield. That's for a 5m (16ft) length. I'm using 1 sq mm but don't run the spindle up to anywhere near it's full 3HP.

I'm not sure how many MYCNCUK readers own a six-wire spindle. I think the 3+3 solution is for much bigger machines than we ever see.

Kit

[Doddy]

Full disclosure: I'm a cynical old git.

The article is... interesting a bit like some of the theory thrown about in the audio rags (at least back when I was a lad) - for me they moved the island (reference to when I stopped watching the TV series "Lost", akin to the "Jump the shark" on Happy Days) when promoting gold-plated mains sockets/plugs/wiring and wrapping paper-clips around the power pins of unused equipment.

Belden's claims of electrocution and 250% increase in spindle life need a little qualification - much depends on the quality of the original installation.

Anyhoo... perhaps I'll acknowledge that VFD cabling is a way to ensure that the cable is correctly rated to what is a fairly dirty electrical environment (the backside of a VFD), but I'm reasonably confident that my existing CY cable will outlive my interests. The same goes for every connector in the circuit and the termination with the VFD and spindle.

YMMV.

EDIT:

Dammit, Kit, stop replying just before I do whilst making the same point more clearly and succinctly.

[Voicecoil]

Interestingly their cable selector says I need a 4 conductor cable of 14AWG (2 sq mm) per conductor with an outer shield. That's for a 5m (16ft) length. I'm using 1 sq mm but don't run the spindle up to anywhere near it's full 3HP.
Kit

I noticed that too. The tables I have for CY cable give a 15A rating for 1mm2 which ought to be fine - or does the structure/extra insulation of the fancy cable mean it has to be run cooler I wonder? - they certainly are quite fat. Or is it simply that they don't make any smaller than 14AWG??

[AndyUK]

Belden's claims of electrocution and 250% increase in spindle life need a little qualification - much depends on the quality of the original installation.

The first issue I take with this claim is that its not a 250% increase. He says 2 years to 5 years, which in my book is an increase of 150%, as an increase of 100%. (i.e. doubling) is 4 years.

[Voicecoil]

The first issue I take with this claim is that its not a 250% increase. He says 2 years to 5 years, which in my book is an increase of 150%, as an increase of 100%. (i.e. doubling) is 4 years.

You have to remember that salespeople for big American corporations aren't always the best at maths! One of the failure mechanisms that I hadn't appreciated before was ground currents (due to cable asymmetry, hence the preferred 3+3E configuration) flowing through motor bearings which apparently shortens their life. I'll miss out on this one as my JK spindle has ceramic bearings, happy days

On another tack I did a bit of searching whilst nibbling at my spicy turkey bun this lunchtime, and quite a few people do these 3+3E VFD cables, however sadly no-one seems to make them in less than 1.5mm2, and they all seem to have a pretty massive minimum bending radius, typically 20x diameter, which given the large cable OD's (10...13mm for 1.5mm2) is not useful for the typically "small" machines the likes of us are making. Also a lot of the problems with voltage spikes/ringing are more likely with high voltage (380V+) systems with long cable lengths, again not a likely scenario for us.

[Kitwn]

EDIT: Dammit, Kit, stop replying just before I do whilst making the same point more clearly and succinctly.

Do you think we're evidence of pan-global telepathy?:

I also remember the fun and games about gold plated plugs and such. Funny thing is the pundits used to claim BBC R3 as a reference for good audio and I can confirm that neither the Broadcasting House turntables or the Holme Moss transmitters had gold plated plugs.

[Kitwn]

On another tack I did a bit of searching whilst nibbling at my spicy turkey bun this lunchtime, and quite a few people do these 3+3E VFD cables, however sadly no-one seems to make them in less than 1.5mm2, and they all seem to have a pretty massive minimum bending radius, typically 20x diameter, which given the large cable OD's (10...13mm for 1.5mm2) is not useful for the typically "small" machines the likes of us are making.

Plus the manufacturers of small machine spindles like ours would have to bring both ends of the three windings, plus a separate casing earth connection out to a seven pin plug.
Readers should also beware of some cable sizes quoted in diameter and others in cross-sectional area.

Kit

[Lee Roberts]

my spicy turkey bun this lunchtime

Bit early for Turkey isn't it, we've not even got Halloween out the way yet?

[Voicecoil]

Plus the manufacturers of small machine spindles like ours would have to bring both ends of the three windings, plus a separate casing earth connection out to a seven pin plug.
Readers should also beware of some cable sizes quoted in diameter and others in cross-sectional area.
Kit

I'm pretty sure there wouldn't be any problems with commoning up the 3 earth conductors to a single pin at the spindle, it's all about balancing inter-conductor capacitance along the length of the cable, a few cm at the far end is unlikely to upset things. And the outer screen would be best connected only at the VFD end to avoid HF earth currents, so likely you could do it with a standard 4 pin plug - if you could fit the rather fat cable into said plug of course.