Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums > AC Power and Grounding

L-Acoustics LA12x - Powering Amp Racks with 208v/3Phase

(1/3) > >>

Peter Carpentier:
I recently noticed a paragraph in the LA12x manual that says the following:


When the product is used in a three-phase circuit, verify the electrical conformity and compatibility of the three-phase circuit.
Verify that the three phases work, and balance the loads between the three phases.
Verify that the neutral and earth work.
Never try to emulate a 230 V circuit connecting an apparatus to two live wires of a 120 V three-phase circuit. Never try to emulate a 200 V circuit connecting an apparatus to two live wires of a 100 V three-phase circuit.


This would imply that the standard practice of deriving a 208v circuit from a 3phase/208 service is not advised by L-Acoustics.  In our case we use L21-30 connectors drive a rack of three LA12x's from a 3phase/208v 30amp outlet.  Since these amps are 100v-230v, we could wire the distro to provide either 120v or 208v.  We have several racks that have been wired for 208v and have worked fine for years. 

Is there a reason for this requirement from L-Acoustics, or are they just literally saying "you can't get 230v from two 120v hot legs"?   Which of course is true.   

Jonathan Johnson:
I may be barking up the wrong tree, here, but I would assume that means "don't try to hack a 230-volt circuit by tapping into the hot legs of two different 120V circuits."

For example, you want to feed your amp 208 or 240 volts, but the venue has only 120V receptacles available. Some people have been known to identify two receptacles on different phases (poles) and tap off the hots of those receptacles into a 240V receptacle. It's not a wise life choice.

I don't see a problem with building a 208V circuit from two breakers on a 120/208V three phase panel, like any qualified electrician would do -- or plugging into your properly built distro that is fed from a 120/208V three phase circuit.

[email protected]:
It seems like it would work, logically, but, as the OP noted, L'Acoustics says "Never try to emulate a 230 V circuit connecting an apparatus to two live wires of a 120 V three-phase circuit."
So, even though we know that two legs 110V-to-neutral of a 3-phase will give us 208V and we do it all the time, what is LA actually telling us?  Is it that 208V is not good for the amps?  Is it that two hots, rather than a hot and neutral is bad?  I think that's the heart of the question.


--- Quote from: Jonathan Johnson on August 03, 2023, 03:04:55 PM ---I may be barking up the wrong tree, here, but I would assume that means "don't try to hack a 230-volt circuit by tapping into the hot legs of two different 120V circuits."

For example, you want to feed your amp 208 or 240 volts, but the venue has only 120V receptacles available. Some people have been known to identify two receptacles on different phases (poles) and tap off the hots of those receptacles into a 240V receptacle. It's not a wise life choice.

I don't see a problem with building a 208V circuit from two breakers on a 120/208V three phase panel, like any qualified electrician would do -- or plugging into your properly built distro that is fed from a 120/208V three phase circuit.

--- End quote ---

Andre Vare:

--- Quote from: Peter Carpentier on August 01, 2023, 04:43:56 PM ---Never try to emulate a 230 V circuit connecting an apparatus to two live wires of a 120 V three-phase circuit. Never try to emulate a 200 V circuit connecting an apparatus to two live wires of a 100 V three-phase circuit.

--- End quote ---
It is fair warning.  There are too many people who do not know what they are doing playing with electricity.

Russell Ault:

--- Quote from: Peter Carpentier on August 01, 2023, 04:43:56 PM ---{...} Is there a reason for this requirement from L-Acoustics, {...}

--- End quote ---

It's entirely speculative, but I wonder if having access to a neutral as well as a ground might be some kind of European regulatory/certification requirement? (I don't know of any electrical reason why a universal SMPS would care about having access to a neutral, although I'm hardly an expert.)

What I do know is that L'Acoustics' own LA-RAKs are only configured to feed their amplifiers hot-neutral regardless of whether the L21 or pin-and-sleeve supply connector is in use (unlike e.g. JBL's VRack, which can switch between hot-neutral and hot-hot configurations for both its L21 and pin-and-sleeve inputs with the flip a switch).

-Russ

Navigation

[0] Message Index

[#] Next page

Go to full version