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Portable Power Cabling Size

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Kristian Stevenson:
I'm about to pull the trigger on some 5 conductor cabling to build L21-30 Amp Rack cables. We have one regular setup that dictates the racks be 100' from the PD. What size cable would be acceptable for this use case? I was considering 10/5 SOOW but the voltage drop is a little over 4%.

Would you consider this acceptable? I've read anywhere from 3 to 5% voltage drop is OK (depending on where you read it).

Tim McCulloch:
Back in the days of large frame analog consoles I used 8/5 for the 250' FOH run because of voltage drop.  We still use that cable and now I can power a small resistance heater for those OctoberFest gigs so my FOH guys don't freeze solid.

Matthew Knischewsky:

--- Quote from: Kristian Stevenson on May 20, 2019, 08:35:03 pm ---I'm about to pull the trigger on some 5 conductor cabling to build L21-30 Amp Rack cables. We have one regular setup that dictates the racks be 100' from the PD. What size cable would be acceptable for this use case? I was considering 10/5 SOOW but the voltage drop is a little over 4%.

Would you consider this acceptable? I've read anywhere from 3 to 5% voltage drop is OK (depending on where you read it).

--- End quote ---

10/5 is fairly standard for L21-30 cables. What's really going to make the difference is the amplifiers in the rack, their loading and how sensitive they are to voltage drop. For example, I've regularly used Crown V racks fed by 100' (and over) of 10/5, no problems with under voltage. Some earlier versions of lightweight amplifiers were not as forgiving.

Voltage drop is usually calculated with a fixed resistive load. Audio loads are not as simple to calculate.

Tim McCulloch:

--- Quote from: Matthew Knischewsky on May 20, 2019, 11:40:35 pm ---10/5 is fairly standard for L21-30 cables. What's really going to make the difference is the amplifiers in the rack, their loading and how sensitive they are to voltage drop. For example, I've regularly used Crown V racks fed by 100' (and over) of 10/5, no problems with under voltage. Some earlier versions of lightweight amplifiers were not as forgiving.

Voltage drop is usually calculated with a fixed resistive load. Audio loads are not as simple to calculate.

--- End quote ---

Back in the day of large filter capacitors it was easier to get a grip on current v/ duty cycle.  With Class D amps, not so convenient.

Since I also work as a stage hand I get to see what the big boys use; I haven't noticed anything that looked or felt unusual so haven't paid attention to the markings.  I'll start looking closer.

Brian Bolly:
I believe with 5 conductors in the jacket for 30A (L21-30) you need to be on 8/5, but I don't have my copy of the NEC handbook readily available.  Anybody have one handy?

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