How many moving lights on a soca ch?

[Elluc]

Hello blue room!

 

I have been wondering about this for a while.

 

Someone told me that you should only put 1 moving light on each soca channel so if it breaks you can kill the power with out taking out any more lights.Is this something people do? It seams that on a big gig you'd need loads of soca cable using this method!

 

Going the other way, If you have to fully load up a 16A feed with discharge lights what sort of head room do you need to leave? Is there an exact calculation you can do to see how much power is drawn when the lamps strike with out taking out the breaker?

 

Also what is the standard size of soca that companies stock? 1.5 mm or 2.5mm? or would it be normal to spec a gig with both?I assume if you're only putting one light on each channel then 2.5mm is going to be a bit overkill and add to the weight!What would you likely get if you just asked for 'soca'?

 

And finally 1.5mm soca is rated at 13A right? I've seen it used with 16A tails on 16A breakers so this is a bad idea right?

Thanks!

[csg]

19 pin soca connectors themselves are 10A / contact if my memory is correct? thats why most soca distros are tripped at 10A.

 

1 fixture per way is the best way, and unless the runs are silly long, I'd stick with 1.5mm all the way. sure. this can leave you with many runs, but many of us have done shows where the soca drop into dimmer world resembles a good size tree trunk!

 

I allow around 30% headroom to allow for run up current.

 

1.5mm will handle 16A just fine on modest runs in single / 3 core, 18 core will lead to some cumulative heating however.

[Alec97]

When I've used 1.5mm HO7 for discharge movers it gets quite warm this was running 8 martin mac 250 krypton's it was around 2700 watts power draw from them all which is about 12 amps at 230v

I would say 1.5mm cable is suitable for no more than 15 amps 230v :unsure:

[csg]

did you allow for harmonics or power factor in your calculations?

[themadhippy]

2700 watts power draw from them all which is about 12 amps at 230v

Argh but we be talking about discharge lights so that little bugger power factor comes into play,as a rough guide, unless youve got the exact figure , 0.8 is the normal assumed pf

[Elluc]

Ok cool,

 

I checked current rating for CEEP soca connectors (couldn't find definitive answer for amphenol) and they are rated at 25A!

Also, Avolites power cubes and art racks both protect socca outputs on 16A c breakers (except dim only op on power cube which are 10A)

 

 

So it seams the cable, if 1.5mm is the week point.

 

If 1.5mm cable is the norm does that mean a lot of protection is over rated and therefore needing extra care from techs not to over load?

 

So I need to read up on power factor to know how to correctly load a 16A. Will this explain how much current is drawn when the lamps strike?

[csg]

No, as stated above, a conventional inductive reactive load will present a power factor of roughly 0.8 if corrected reasonably, some older fixtures like clay paky miniscan hpe's are not corrected and are far worse ( 900VA for a 300w lamp...)

 

As discharge lamps run up, they will pull more current still.

 

The chance of a 1.5mm core burning out at a resistive load of 16A is very unlikely. As socas are generally soldered , loose connections are more unusual than for Ceeforms, where poor maintenance and loose contacts are a common failure mechanism.

 

Yes, 1.5mm soca is often warm at even 10A load per ch, but on the one fixture per circuit rule, this becomes a non issue, and even 16A protection will catch major faults. C type 10A MCB's are what I like to see on hot power racks.

[themadhippy]

The other thing to watch out for is the grouping factor,6 circuits in 1 cable will get hotter than 6 individual cables so the current carrying capacity of the cable is reduced by a factor found in the 17th big green book of rules