Design 3 phase on one bar?

[Soundguy]

Greetings, crew. Electrical design experts out there?

I am preparing to mount 24 fixtures which draw 6 amps of 240v each (144A total). Our electrician is happily recommending that we use the incoming 3phase 125A service across the bar, but I seem to remember that lighting multiple phases across the same bar isn't safe.

He thinks I'm making this up to make his life difficult, and has told me that bringing in 144A of single phase is impossible, and having several phases lighting different fixtures on the same bar is safe.

After all, we have professional three-phase dimmers which light several lights on the same bar, where theoretically, fixtures hanging side by side could source their electricity from different phases.

Your two cents/pence?

 

[Chris15]

On what basis would there be a problem?

So long as you have the normal insulation requirements satisfied you should be fine. Absolutely would you normally have all three phases on a bar or truss...

 

[STEVETERRY]

Greetings, crew. Electrical design experts out there?

I am preparing to mount 24 fixtures which draw 6 amps of 240v each (144A total). Our electrician is happily recommending that we use the incoming 3phase 125A service across the bar, but I seem to remember that lighting multiple phases across the same bar isn't safe.

He thinks I'm making this up to make his life difficult, and has told me that bringing in 144A of single phase is impossible, and having several phases lighting different fixtures on the same bar is safe.

After all, we have professional three-phase dimmers which light several lights on the same bar, where theoretically, fixtures hanging side by side could source their electricity from different phases.

Your two cents/pence?

This is common practice and will be fine under current codes.

The is some lore that in the UK in the deep dark past, there was a rule that no two phases could be within arm's reach in order to prevent the possibility of a 400V shock. I have no details on this, but I often run into it with older consultants. Perhaps some of our UK colleagues can shed light on the origin of this "rule"?

ST

 

[derekleffew]

From a thread on the forum BlueRoom.org, Run animation motor from dimmer - Blue Room technical forum :

Why do you have to keep the phases apart? It's no longer a part of the regs...

Whilst I realise that IEE no longer consider this to be a problem, most of the venues that I have worked in in the last 20 years have had a geographical separation of the phases. When specifing, calculating and processing a lighting rig this natural separation has crept into my work. It is now second nature for me to separate phases in the old-school method of allowing 2m separation between bars/areas on differing phases.

Sorry if this annoys, but I am too long in the tooth to change now.

Reading between the lines a little in the on-site guide, where it says that if outlets on different phases cannot be seperated that a warning label about the prescencee of 400 volts should be fitted, I would have thought it is acceptable to call it best practice to seperate the phases.
I'll look up references once I've got round to knocking the snow off the van and dug out the books.

Oh, fer crying out LOUD!!
There USED to be a spec in the regs which stated phases had to be separated by 2m (6 ft in old money) BUT that was phased out AGES ago as being rather a) impractical to police and b) easy to circumvent, esp without realising.
In industrial situations there is an assumption that the majority of people likely to work on the wiring of installations using 3-ph outlets will have had the training and experience to treat it with the respect it deserves.
And 250v ALSO hurts and can kill just as easily as 440v!

 

[mrcog]

I really would'nt worry about having multiple phases on one bar, the very chances off have 2 different lanterns, on two different phases, both having a dodgy earth, and dodgy RCD on the dimmer channel, and have a fault that turns the body of the lantern live is VERY VERY slim and therefore the chances off getting a 415V shock is pretty **** slim...

I wouldn't worry in my opinion, however thats just my opinion and I'm sure many industry veterans will beg too differ and still abide by the old IEE rules

Just my 2p

James

 

[Soundguy]

Hmmm. Thanks crew (and thanks, Derek, for dredging that post up from Blueroom).

Seems that it used to be a reg, but not any more. While it makes sense from a safety perspective, our whole catwalk system is one piece of interconnected metal (and connected to our building earth), so any two phases anywhere in the whole lighting rig would make for a 400V problem, but be sure to blow a GFI/breaker before it set up two fixtures live and shockable at 240V.

Guess we were both right, but the electrician was correct that it can be done.

Hate being wrong on anal safety issues...I certainly get enough grief for enforcing them (like the director in our current show who can't understand why putting 130 5th grade students on and off risers in TOTAL BLACKOUT is a bad idea..."I don't want the audience to see them," he says. "Wouldn't matter," I said, "they'll hear the screams, groans, and thumps of falling bodies.")