A new standard for dimmer 3 phase plugs

[Andy Ciddor]

GY has raised another issue which has been pretty much ignored by a lot of people who really do know better: cable derating.

A 1.0sqmm cable is only rated at 10 Amps when it's on its own. Stick it in a bundle of other cables where it can't dissipate all the heat produced by the passage of current, and its rating drops dramatically.
Every electrician and electronic engineer learns this about 10 minutes into their training and every student who ever passed through training with me at WAAPA had it hammered to them too. Despite this there is still a widely held belief that all of the 1.0 sqmm circuits in a 6 circuit multicore can safely and reliably carry 10 Amps. According to standards each circuit is actually only rated for 5.7 Amps (6.5 Amps for a 4 circuit multi). That's why 4 way and 6 way multicores need to be 2.5 sqmm, but all too frequently are not.

For anyone who doesn't have a derating table at hand, I have an Excel spreadsheet that does the calculations for you. I'll post it in the Members Only content section later in the day when I get back from my errands.

And just to make your day: let me point out that 500V rated multicores (as featured in an alarming number of cables) are only suitable for use where ALL circuits are running on the same phase. As soon as one circuit in the muticore is on another phase there is a requirement for insulation suitable for 660V / 1kV. If you have an electrical incident with your gear and there is a 500V multicore in use, you can say goodbye to your insurance protection and your loved ones and be prepared to spend a few years in a correctional establishment becoming good friends with your cellmate.
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Andy Ciddor

[GY]

Thanks Andy for getting slightly more technical and expanding more on this.
I dont have the facts and figures on all this - I just know the realitys of how it all works from doing it for many years.
To go slightly off tanget- cable issues are the BIGGEST cause of problems. Be it underesized mains or extensions, or small size multicable, or badly made and terminated, or badly maintained, this will give you problems.
Yesterday I had two examples:
- a crappy DMX cable causing my rig to wigout. I dont know if it was crap cable or it had malfunctioned. But it was a cable issue
-I rolled up the thinest piece of chain hoist cable I have ever seen. Thankfully it was only 20m long because the voltage drop over anything longer would not drive a hoist.

And if you want to hear my black and white people theory you will have to pay me, because it is very important, and has proved true countless times.

Cheers
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GY

You know all the other info about me
Or hunt me down on Facebook !

[David Ashton]

Andy, I was under the impression that the multicore as a whole was de-rated, so that you could run some circuits at 10A if others were off,if each individual wire is de-rated there is hardly a legal install in WA, and possibly the country, would you be kind enough to quote the reg. for 500volt cable not being legal, I see a situation where a huge number of installs are illegal.

[rossgo]

It's clear the entertainment industry needs it's own electrical standards
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ROSS CARDWELL
FREELANCE LIGHT & SOUND, SYSTEM TECH
SPARKY

[Andy Ciddor]

[Andy Ciddor]

Cable voltage first:

[David Ashton]

This use of peak voltage is new to me, how about using peak to peak ratings like the use to rate speakers, but seriously where can I find this interpretation in which standard? and you didn't answer the de-rating question.

[Jeff morgan]

GY broughtlup a good point( you are a good thinking man GY) ..you have to think about what you using on your supplies,which I have said before. Be careful on what you say about derating, basic pricipal you start to derate the cable after 25m. Also the new AS3000 but not yet AS3008 begins in a few months. As far as what a cable is rated if you wanted to run 35amps down a 2.5mm cable you can BUT! you have to work out the time that you will use that cable at that current and that may be only 4mins, I remember going to Standards brief for cable rating etc and the average electrician did not want to know about this sort of thing ...so rating a cable is not as easy as the old 2.5mm 20 amp theory. 30 years ago 2.5mm was 28amps on a wire fuse the in 80's they kneejerked and made it 16amps then back to amps then what ever you like dependant on time etc ..and etc etc ,then 3008 came out and cable ideas changed again, it does vary depending on what you are using it for.
IF you know that 3rd Harmonics are going to stuff your 3phase plug ....why are you pluging it in? If the producer wants it all up use two supplies/two outlets/two dimmers.

If the 40amp plug is burning I would hate to think what its doing to the cable as I would imgine the cross sectional area of a neutral pin in a plug is larger then the 6mm cable we use. I would also imagine that harmonics would change from make to make of dimmer due to components etc ..how do we work all that out.

We have a bad habbit in this indusrty to push the boundries of our equipment.
If we being the older of the industry are not teaching the younger
are we maybe the problem. And the last thing we should be doing is picking on the younger lighting industry because they dont know.

And good on you rossgo for for putting up with problems that we
have not tought you about. Your are always in these forums and your enthusiastic ideas and points of veiw are refreshing.
Sorry but I have spent more than my two cents worth.

[JBoer]

[Andy Ciddor]

Cable Derating:

[David Ashton]

Jeff said IF you know that 3rd Harmonics are going to stuff your 3phase plug ....why are you plugging it in? If the producer wants it all up use two supplies/two outlets/two dimmers
I know its stuffing up plugs and thats why I'm going to try and change it to a better quality plug, the logic that we keep using a dangerous and inferior plug and adjust the rest of the gear to compensate for a bad design when a safer and cheaper option is already used around the world is puzzling.

[Andy Ciddor]

There are derating factors for cable length, bundled cables and cables wound on drums. I've only been referring to the bundled cables derating factors, but the spreasheet I've put up includes the wrapping factor for use in cable reelers and with leads fed from spoolers, etc.
The tables I'm using have been around a long time. The ones I'm quoting came originally from my 1981 (metric) copy of AS 3000, but remain the same in current versions.
There is also a (slightly less aggressive) derating table in my 1961 SEC Vic Wiring Regulations.
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Andy Ciddor

[Jeff morgan]

I sent an email off to Standards about the Insulation /voltage rating of
the multi core cables we use etc. He was happy to say that cables are rated at RMS values and thus 400V on the on each conductor of the multi core cable is to be at least 400V. No mention about 600V etc. He did send me off into the world of many more standards,3008, 5000 etc.
So I would be great Andy, if you could find where the 600V come into play. As it may have a big impact on installations and production works.

Also interesting thing, AS3000 /2007 now talks about third harmonics and adding them to final neutral calcs. Third harmonics and higher Should be taken as 100% and added onto the maximum out of balance load to determine neutral size.
This may have an impact on Plugs etc.
Maybe its time to have a chat to Gerard industries.

[p_c]

Hey Rossgo,

Even though this thread is so totally out of my league.... i'll answer your question.

The way i normally approach this is: select all of one fixture type and then use MATricks to break the group up in to every third or fourth fixture. Then lamp on each group over about ten to fifteen seconds. This way i usually get a decent cross section of the system. If i'm feeling particularly pro-active and in the same place for a while i'll program a lamp on sequence that delays the lamp strike across the system.

I NEVER program a lamp off sequence... call me paranoid... but if your using non hot re-strike lamps...... you're asking for trouble.

I did once accidently lamp on 460 Mac 2000 washes in one go.... fortunately the world didn't end... although i wouldn't recommend this!!

P.C
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Paul Collison

[rossgo]

Thanks PC
wow 460 mac 2K's at once!!!, there would of been a massive voltage drop. and a coulple thousand Amps flowing in those few seconds.
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ROSS CARDWELL
FREELANCE LIGHT & SOUND, SYSTEM TECH
SPARKY