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Author Topic: L-Acoustics LA12x - Powering Amp Racks with 208v/3Phase  (Read 2827 times)

Peter Carpentier

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L-Acoustics LA12x - Powering Amp Racks with 208v/3Phase
« on: August 01, 2023, 04:43:56 PM »

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.   
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Jonathan Johnson

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Re: L-Acoustics LA12x - Powering Amp Racks with 208v/3Phase
« Reply #1 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.
« Last Edit: August 03, 2023, 03:07:41 PM by Jonathan Johnson »
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Re: L-Acoustics LA12x - Powering Amp Racks with 208v/3Phase
« Reply #2 on: August 03, 2023, 03:41:12 PM »

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.

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.
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Andre Vare

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Re: L-Acoustics LA12x - Powering Amp Racks with 208v/3Phase
« Reply #3 on: August 03, 2023, 09:26:06 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.
It is fair warning.  There are too many people who do not know what they are doing playing with electricity.
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Russell Ault

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Re: L-Acoustics LA12x - Powering Amp Racks with 208v/3Phase
« Reply #4 on: August 05, 2023, 02:48:56 PM »

{...} Is there a reason for this requirement from L-Acoustics, {...}

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
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Tim McCulloch

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Re: L-Acoustics LA12x - Powering Amp Racks with 208v/3Phase
« Reply #5 on: August 05, 2023, 05:07:45 PM »

I'm following because I've got a rack of LA12x and I'd love to get it off 120V to 240.

Anyone from l'Acoustic USA on the forum?
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Ross Goldman (2)

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Re: L-Acoustics LA12x - Powering Amp Racks with 208v/3Phase
« Reply #6 on: August 08, 2023, 08:24:45 PM »

I asked the Senior Application Project Engineer for L-Acoustics USA and he replied:

"You absolutely CANíT use 208volts for our controllers
 
You need for each controller, 1 x ground, 1 x neutral and 1 x hot at 110vots.
 
Each controller need to have his own breaker."
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Russell Ault

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Re: L-Acoustics LA12x - Powering Amp Racks with 208v/3Phase
« Reply #7 on: August 08, 2023, 09:41:36 PM »

I asked the Senior Application Project Engineer for L-Acoustics USA and he replied:

"You absolutely CANíT use 208volts for our controllers
 
You need for each controller, 1 x ground, 1 x neutral and 1 x hot at 110vots.
 
Each controller need to have his own breaker."

That's...bizarre. Did he mention why they need a neutral?

-Russ
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Stephen Swaffer

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Re: L-Acoustics LA12x - Powering Amp Racks with 208v/3Phase
« Reply #8 on: August 11, 2023, 12:30:30 PM »

Not intending to throw shade on L-Acoustics engineers but I have dealt with way too many issues created by product engineers that did not understand power distribution or how to properly size wire taking in to account derating, etc.

That said, it makes sense from a lawyer/liability standpoint.  Too many people don't understand how to check for voltage without a neutral present and if you derive 208/220/230/240 from two 110 circuits, if a breaker trips on one it will look there is no power there when in fact there still is.
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Steve Swaffer

Tim McCulloch

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Re: L-Acoustics LA12x - Powering Amp Racks with 208v/3Phase
« Reply #9 on: August 11, 2023, 01:22:18 PM »

I asked the Senior Application Project Engineer for L-Acoustics USA and he replied:

"You absolutely CANíT use 208volts for our controllers
 
You need for each controller, 1 x ground, 1 x neutral and 1 x hot at 110vots.
 
Each controller need to have his own breaker."

Yeah, I'd want to hear the ENGINEERING explanation as to how the amp knows the difference and why it will go full "Joan of Arc" if it doesn't get what it wants.

« Last Edit: August 11, 2023, 07:34:49 PM by Tim McCulloch »
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Re: L-Acoustics LA12x - Powering Amp Racks with 208v/3Phase
¬ę Reply #9 on: August 11, 2023, 01:22:18 PM ¬Ľ


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