Dimmers
- Thread starterStageTech620
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Dionysus
Well-Known Member
Indeed, that would need to be a HARDWIRE installation. Which is why I said three different times that you would need an electrician.
I don't know if anyone mentioned this (I'll admit I skimmed through this thread), but...
A common misconception I've run into regarding "turning single-phase power into three-phase" is that you can just take 3 separate power feeds and make an "adapter cord" with 3 plugs and 1 socket to combine them.
Is it possible? Yes and no.
Is it safe? Only if you are absolutely 100% sure the building (and the adapter) is wired properly, and you can be absolutely 100% sure that one of the feed plugs will never ever ever become disconnected while a load (that uses said plug's "virtual phase") is plugged into the socket, and if you are absolutely 100% sure the total of the phase loads does not exceed any one of your single-phase feeds...
...and only if the previous "is it possible?" answer is "yes".
(In other words, with so much variance and potential dangers, no electrical authority would ever approve such an adapter.)
To answer the "Is it possible", question, the answer is only "yes" if the 3-phase load does not care about the relative phase angles (so automatically that excludes things like 3-phase motors and Delta loads), and, it can only be possible if it's a Y load with the sum of the phase currents being no greater than 1/3 of a single-phase feed.
The reason is, in a proper multi-phase system, the Neutral conductor only carries the "difference current" between imbalanced phases. But if the phases are not equally angled, the Neutral conductor then carries current sums. And if all the phases are at the same angle (ie. single phase), the Neutral conductor ends up carrying the total sum.
(I should also mention here that, should you make a bootleg "phase combiner" adapter, it will absolutely not work at all if plugged into circuit branches that have a GFI/GFCB/RCD, since such safety devices compare the Live current with the Neutral current and disconnect power if they mismatch by >5mA.)
So for example, if a balanced 3-phase lighting rig has a NEMA L21-30P plug (5-wire, 30 amp, 120/208 volt, 3-phase Y, grounded), and draws 25 amps from each phase... and you power it from a bootleg "phase combiner" adapter made with three NEMA L5-30P plugs (3-wire, 30 amp, 120 volt, single-phase, grounded) coming together to a NEMA L21-30R receptacle for the rig... and the adapter is plugged into 3 receptacles all on the same phase...
...you're going to melt the L21-30R receptacle's neutral conductor with 75 amps of current!
Furthermore, if you leave the Neutrals floating on two of the adapter's three plugs (as a safety measure so the adapter won't short-circuit a power line if plugged into incorrectly-wired buildings with Live and Neutral swapped), you're going to be running 75 amps of current through the Neutral conductor of the building's wiring branch that's feeding your Neutral-connected plug! And the really dangerous aspect of this is, the building's circuit breakers only detect current on the Live, not the Neutral wires! ...So the branch breakers will never trip! (Instead, you'll probably end up setting the building on fire.)
So long story short:
You can *sometimes* make a 3-phase load run on single-phase, but you absolutely must know what you're doing, you must know precisely what kind of load you're powering, you must be sure the building is wired properly, you must understand phasors and correctly calculate all the loads, you must make sure no unauthorized people disconnect or tamper with your setup in any way, and you must put appropriately-rated fuses or circuit breakers in your phase-combiner adapter, "de-rated" for single-phase feeding, if you want it to be safe.
If any of this seems new to you, I strongly recommend you do not attempt this on your own.
A common misconception I've run into regarding "turning single-phase power into three-phase" is that you can just take 3 separate power feeds and make an "adapter cord" with 3 plugs and 1 socket to combine them.
Is it possible? Yes and no.
Is it safe? Only if you are absolutely 100% sure the building (and the adapter) is wired properly, and you can be absolutely 100% sure that one of the feed plugs will never ever ever become disconnected while a load (that uses said plug's "virtual phase") is plugged into the socket, and if you are absolutely 100% sure the total of the phase loads does not exceed any one of your single-phase feeds...
...and only if the previous "is it possible?" answer is "yes".
(In other words, with so much variance and potential dangers, no electrical authority would ever approve such an adapter.)
To answer the "Is it possible", question, the answer is only "yes" if the 3-phase load does not care about the relative phase angles (so automatically that excludes things like 3-phase motors and Delta loads), and, it can only be possible if it's a Y load with the sum of the phase currents being no greater than 1/3 of a single-phase feed.
The reason is, in a proper multi-phase system, the Neutral conductor only carries the "difference current" between imbalanced phases. But if the phases are not equally angled, the Neutral conductor then carries current sums. And if all the phases are at the same angle (ie. single phase), the Neutral conductor ends up carrying the total sum.
(I should also mention here that, should you make a bootleg "phase combiner" adapter, it will absolutely not work at all if plugged into circuit branches that have a GFI/GFCB/RCD, since such safety devices compare the Live current with the Neutral current and disconnect power if they mismatch by >5mA.)
So for example, if a balanced 3-phase lighting rig has a NEMA L21-30P plug (5-wire, 30 amp, 120/208 volt, 3-phase Y, grounded), and draws 25 amps from each phase... and you power it from a bootleg "phase combiner" adapter made with three NEMA L5-30P plugs (3-wire, 30 amp, 120 volt, single-phase, grounded) coming together to a NEMA L21-30R receptacle for the rig... and the adapter is plugged into 3 receptacles all on the same phase...
...you're going to melt the L21-30R receptacle's neutral conductor with 75 amps of current!
Furthermore, if you leave the Neutrals floating on two of the adapter's three plugs (as a safety measure so the adapter won't short-circuit a power line if plugged into incorrectly-wired buildings with Live and Neutral swapped), you're going to be running 75 amps of current through the Neutral conductor of the building's wiring branch that's feeding your Neutral-connected plug! And the really dangerous aspect of this is, the building's circuit breakers only detect current on the Live, not the Neutral wires! ...So the branch breakers will never trip! (Instead, you'll probably end up setting the building on fire.)
So long story short:
You can *sometimes* make a 3-phase load run on single-phase, but you absolutely must know what you're doing, you must know precisely what kind of load you're powering, you must be sure the building is wired properly, you must understand phasors and correctly calculate all the loads, you must make sure no unauthorized people disconnect or tamper with your setup in any way, and you must put appropriately-rated fuses or circuit breakers in your phase-combiner adapter, "de-rated" for single-phase feeding, if you want it to be safe.
If any of this seems new to you, I strongly recommend you do not attempt this on your own.
Last edited:
BillConnerFASTC
Well-Known Member
Corrections:
"...if you are absolutely 100% sure the total of the phase loads does not exceed any one of your single-phase feeds..."
should have been:
"...if you are absolutely 100% sure the total of the phasor loads does not exceed any one of your single-phase feeds..."
"...if the phases are not equally angled, the Neutral conductor then carries current sums."
should have been:
"...if the phases are not equally angled relative to each other, the Neutral conductor then carries current sums."
"...if you are absolutely 100% sure the total of the phase loads does not exceed any one of your single-phase feeds..."
should have been:
"...if you are absolutely 100% sure the total of the phasor loads does not exceed any one of your single-phase feeds..."
"...if the phases are not equally angled, the Neutral conductor then carries current sums."
should have been:
"...if the phases are not equally angled relative to each other, the Neutral conductor then carries current sums."
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