Electromagnetic effects , star / delta motor wiring ?

[JD6400]

I occasionally come across reasonably sized ( not for some of you , I know ! ) star delta motors that have been run in 2 x 3core swa .
Now after looking in to this in the past , it has been suggested that as they tend to be only on motors up to 30kw or so , and as the loading per phase will be near on equal the effects are not worth even considering !?

That said , it is just wrong to do this , is it not ?

What do others think .

 

[netblindpaul]

Define 'machine' lol.

I have always favoured flexible conduit for final connection, but I guess it always depends on the application of the motor and any requirements the customer may have. I personally can't see the vibration of any decent motor being bad enough to work loose a decently glanded connection, if the vibration is that bad I would say there is a mechanical issue that needs addressing!

It feels wrong because you would always install using a 7 core cable! lol

Ok, the definition of "machinery" electrical equipment is easy, covered by BS EN 60204-1, and not BS7671.

If it is an assembly of linked components and is not part of the fixed electrical installation then it's machinery.

I do sometimes use flexible conduit.
However, what do, you, put "inside" the flexible conduit?
6491 type wire?
If so, again not suitable for connection to vibrating equipment.

Any rotating device vibrates.

Oh & I think it was me who said 7 core not the OP.

 

[D Skelton]

More to the point , why do it this way in the first place ?
I mean it is twice the work over just one 7 core !?

This is the obvious issue that you can't get your head around. I'd like to think that any decent spark would use one cable or one method of containment over two cables, still, I can't see an issue regs wise or principle wise with the latter of those two options.

 

[netblindpaul]

Not even the unsuitability of the wiring materials chosen?

 

[JD6400]

Ok, the definition of "machinery" electrical equipment is easy, covered by BS EN 60204-1, and not BS7671.

If it is an assembly of linked components and is not part of the fixed electrical installation then it's machinery.

I do sometimes use flexible conduit.
However, what do, you, put "inside" the flexible conduit?
6491 type wire?
If so, again not suitable for connection to vibrating equipment.

Any rotating device vibrates.

Oh & I think it was me who said 7 core not the OP.

Our standard set up on a dryer would be to come from the control panel in 7c swa (with a 2c controls swa for the isolator indicator switch if applicable with the control panel spec) on tray up to a 6 pole isolator then out in to the dryer in armoured flexible conduit on swivel top hats with what I call controls cable ( fine AWG ) in that with all terminations crimped with which ever one is appropriate for the motor .

 

[netblindpaul]

Sounds nearer the mark than SWA TBH.

The twin x 3C swa still may well (probably) need a local isolator, so it is a tonne of extra work.

 

[D Skelton]

Ok, the definition of "machinery" electrical equipment is easy, covered by BS EN 60204-1, and not BS7671.

If it is an assembly of linked components and is not part of the fixed electrical installation then it's machinery.

There are bound to be grey areas here surely between machine and fixed wiring!

I do sometimes use flexible conduit.
However, what do, you, put "inside" the flexible conduit?
6491 type wire?

6231 obviously

Oh & I think it was me who said 7 core not the OP.

huh?

Edit: Just thought I'd better point out that I'm not condoning the practice of using two seperate SWA cables to feed a motor, I'm just saying that there isn't anything technically wrong with it IMHO.

 

[netblindpaul]

Well D Skelton I disagree, & I bet you I can find regs in BS7671 & other standards that say that it is unacceptable, however, I can't be bothered to waste my time in proving something so obvious as to use fixed wiring materials on a vibrating machine.

You have obviously never been involved with vibration analysis and studied rotating machines.

 

[D Skelton]

Well D Skelton I disagree, & I bet you I can find regs in BS7671 & other standards that say that it is unacceptable, however, I can't be bothered to waste my time in proving something so obvious as to use fixed wiring materials on a vibrating machine.

Fair enough, nothing crystal clear in BS 7671 as far as I'm aware, 522.7 goes on about cables/wiring being 'secure' when connected to vibrating equipment, nothing about exactly what types are suitable. You don't have to prove anything to me mate, I don't doubt your credentials which is why I find your slightly haughty tone a little confusing :s I'm here for a discussion, not an argument and I'm more than happy to learn from those who are more experienced than I am.

You have obviously never been involved with vibration analysis and studied rotating machines.

I know a little but no, I haven't been involved with vibration analysis.

I never said it was a good idea, I just couldn't see anything technically wrong with it. As I said previously, it all depends on the application. If a motor has been in service for 20 years and the SWA glands connected to it are as secure as when they were first fitted then what's the bother, same as if the final terminations are still secure? You'd expect regular maintenance on motors and machinery anyway so the risk of connections coming loose are slim and bad vibration issues would surely be picked up and addressed before they became too much of an issue.

Like I said, I wouldn't choose to wire a motor in this this way, ever, but would I condemn one if I found it wired using 2 x SWA cables and everything was still secure? No, probably not. However, if you could find me some regulation that says otherwise or describe to me with my limited knowledge of vibration analysis exactly why a secure SWA connection is still a problem then I will obviously have to take this into account and reform my opinion/knowledge on the subject.