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Author Topic: Distro Panel  (Read 5751 times)

George Dougherty

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Distro Panel
« on: August 15, 2014, 12:27:57 am »

What are my limits on breakers in a panel assuming the main breaker is 100A 120/240?  I currently have it setup with 60A 3x20A circuits on each leg for a total of 120A breaker capacity.  Obviously, I'd never be able to pull that from the panel, but I'll rarely have all the circuits utilized let alone tapped to capacity.  I've been pondering picking up some used PL380's for sub duty which have a 30A plug on them.  Ideally then I'd have them on a 30A breaker.

Would I be out of line in having 2x20A and 1x30A for 70A of load capacity on each leg?  I'm guessing the answer is yes as I've got a 200A main at the house with far more than 200A worth of breakers on the panel.  I'm really looking for rated capacity on a certain load with various connectors and cabling so the breaker trips before anything downstream is damaged, correct?  I still have 4 slots open on the panel  as well, could I leave the 3x20A circuits and add a 30A circuit since I may use different combinations depending on the gear at the gig?
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Jonathan Johnson

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Re: Distro Panel
« Reply #1 on: August 15, 2014, 12:49:10 am »

As I understand it, you aren't limited to a maximum total ampacity of branch circuit breakers (as long as there is upstream overcurrent protection sufficient for the rating of the panel and the supply wires; such protection could be a "main breaker" in that same panel). Instead, you are limited to the total number of breaker poles the panel is rated for. In larger panels, this will be either 40 or 42. Note that some positions on the busbar may be designed to handle only a single, full size breaker; other positions may be designed for either full-size or 1/2-size breakers.

For example, if you have a panel with 30 positions (there will be 15 positions on one pole, 15 on the other), you will see that it has 20 positions that accept only full-size breakers and 10 positions that accept either full-size or half-size (sometimes called "tandem") breakers. (In some brands of panels, the 2-for-1 spaces have a notch in the busbar. The tandem breakers will only fit in the space with the notch. In other brands of panels, different methods are used to control the type of breaker used.)

When you go to the home improvement center, you'll find that they have tandem breakers that fit both the busbars with the notches and busbars without the notches. The ones that fit the busbars without the notches may be a code violation, they are "for replacement use only."

Here's another sticky situation: there are several brands of breakers that seem interchangeable. There is probably no problem interchanging them. But if you look closely, each one has a "type" designation (i.e., Type BR or Type QP). Technically, you can only use a "type" of breaker in a panel that lists it as acceptable on the manufacturer's information sheet on the panel. And manufacturers typically don't certify other manufacturer's breakers in their own panels. So putting that Murray breaker in a Siemens panel is a code violation (even though Siemens owns the Murray brand and the breakers are identical. Go figure.).

One last point: if you do not have proper overcurrent protection for the whole panel, the total ampacity of the branch circuit breakers on each pole should not exceed the rating of the panel or the supply wires.

All that being said, I could be wrong. I will defer to any electricians that chime in here (and they will, I'm sure!).
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Mark Cadwallader

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Re: Distro Panel
« Reply #2 on: August 15, 2014, 01:08:27 am »

Am I correct in understanding that you have a 100A dual-pole main breaker, and that the other breakers are single pole?  If so, you should be able to pull 100A on each leg of the split-phase service. (100A on one leg of 120v, and 100A on the other leg of 120v.  I assume you are in North America, with your description of 120/240 volt service.)

You could have 3 x 20A and 1 x 30A breakers on EACH leg and not trip your main breaker, since that would still only be 90A per leg.

Please note that I am not a licensed electrician, merely a somewhat experienced layman.  I will be glad to be corrected by any of the real experts who hang out here. Mark C.
« Last Edit: August 15, 2014, 09:52:50 am by Mark Cadwallader »
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George Dougherty

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Re: Distro Panel
« Reply #3 on: August 15, 2014, 03:02:42 am »

Am I correct in understanding that you have a 100A dual-pole main breaker, and that the other breakers are single pole?  If so, you should be able to pull 100A on each leg of the split-phase service. (100A on one leg of 120v, and 100A on the other leg of 120v.  I assume you are in North America, with your description of 120/240 volt service.)

You could have 3 x 20A and 1 x 30A breakers on EACH leg and not trip your main breaker, since that would still only be 90A per leg.

Please note that I am not a licensed electrician, merely a somewhat experience layman.  I will be glad to be corrected by any of the real experts who hang out here. Mark C.
The main is 100A in total, taking up two spaces in the Distro panel, each labeled 50A and a bar tying the switches for the two together.  It's my understanding that those are properly sized for a Cali twist-lock connector being rated for 50A single phase or 100A 3-phase.  I had input on it from a friend who used to build distro panels but my terminology may not be correct.
« Last Edit: August 15, 2014, 03:06:26 am by George Dougherty »
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TJ (Tom) Cornish

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Re: Distro Panel
« Reply #4 on: August 15, 2014, 07:08:28 am »

The main is 100A in total, taking up two spaces in the Distro panel, each labeled 50A and a bar tying the switches for the two together.  It's my understanding that those are properly sized for a Cali twist-lock connector being rated for 50A single phase or 100A 3-phase.  I had input on it from a friend who used to build distro panels but my terminology may not be correct.
George, that is a 50A 2-pole breaker, not a 100A breaker. Calling it 100A will confuse anyone you talk to about your system.

The main breaker is sized to the supply tails, so for 50A you need #4 wire (#6 is commonly used but is technically illegal). You can have significantly more than 50A worth of breakers per leg and not have code problems, but at some point you will have operational problems depending on how much power you are pulling at any given time.

If it were me, I would not add any more breakers than your current 3x20A per leg. Get a current meter and figure out what your loads actually are. You may be able to combine some existing loads together, freeing up a circuit or two.
« Last Edit: August 15, 2014, 07:10:45 am by TJ (Tom) Cornish »
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George Dougherty

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Re: Distro Panel
« Reply #5 on: August 15, 2014, 09:30:29 am »

George, that is a 50A 2-pole breaker, not a 100A breaker. Calling it 100A will confuse anyone you talk to about your system.

The main breaker is sized to the supply tails, so for 50A you need #4 wire (#6 is commonly used but is technically illegal). You can have significantly more than 50A worth of breakers per leg and not have code problems, but at some point you will have operational problems depending on how much power you are pulling at any given time.

If it were me, I would not add any more breakers than your current 3x20A per leg. Get a current meter and figure out what your loads actually are. You may be able to combine some existing loads together, freeing up a circuit or two.
Thanks for the correction.  I have a 15' lead hard wired to the panel now with 6/4 but intended to size my eventual feeder cable at 4/4 with the Cali connectors. With that short of a lead to the plug, should I be on 4/4 now?

I actually only use the distro maybe once per year. I'd like to use it more frequently, but rarely have need or ability. I'm running a fully horn loaded rig good for 1000-1500 people and my monitor rig are medium sized powered monitors from db Tech.  I don't regularly do events that call for rock concert levels and often can run just fine off an EU3000i.  The subs may be a little hungry for more power if I push it, but nothing trips.  When I'm operating off wall power, I generally try to spread the load onto 3-4 15A circuits and I could run all 4 of my subs with headroom off just a single PL380.

The more I read about the 30A plug last night, the more I realized I don't need bigger than a 20A circuit to run it at the ~5ohm load I'd have with two subs per channel.  My subs will only take 800W RMS, so the 2000-2500W I could pull per side should be adequate for the style of music I play and the size of rig I have.

I really sized the distro panel based on other providers sized like me that also deal with Incandescent lighting rigs and figured I'd have plenty for growth plus LED lighting when I hire someone in to cover that portion of a gig.
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Mark Cadwallader

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Re: Distro Panel
« Reply #6 on: August 15, 2014, 10:02:16 am »

I believe that 6 AWG stranded is the largest size of conductor which can be fitted to a "California standard" 50A connector.  It is my understanding that because of de-rating called for by the NEC for a multi-conductor cable, the NEC (strictly applied) would require a 45A breaker to protect the 6/4 feeder cable.  Mark C.
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TJ (Tom) Cornish

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Re: Distro Panel
« Reply #7 on: August 15, 2014, 11:34:48 am »

The more I read about the 30A plug last night, the more I realized I don't need bigger than a 20A circuit to run it at the ~5ohm load I'd have with two subs per channel. 
30A circuits are a pain in the butt.  I agree that your PL380 will be fine on a 20A breaker if you don't spend all day with the clip light on.

[Rant]
Speaking especially to lounge-level folks:

Some folks (not implying you, George - just speaking generally) seem to think that having a rig that requires a power distro is some kind of a badge - "look how cool/big/awesome my system is - I need to take the panel cover off and use these gnarly jumper cable clip things to get the juice I need".  While there is no doubt that many folks do need a distro, I believe many people underestimate the value of being able to run on a couple Edison circuits.  All of the bizarre schemes of cables, adapters, and frequently incorrect panel devices people come up with just get in the way of the goal, and this energy would be better spent actually understanding their power draw, and then being realistic about the size show the venue can support. 

Any distro equipment should be made of standard components (ideally by a shop that does ETL work), and be modular enough so that you can run your show on Edison power without hours of re-wiring or illegal adapters.

This can have many positive outcomes - safety, cost savings, and simplicity.
[/Rant]
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Mike Sokol

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Re: Distro Panel
« Reply #8 on: August 15, 2014, 12:09:29 pm »

While there is no doubt that many folks do need a distro, I believe many people underestimate the value of being able to run on a couple Edison circuits.  All of the bizarre schemes of cables, adapters, and frequently incorrect panel devices people come up with just get in the way of the goal, and this energy would be better spent actually understanding their power draw, and then being realistic about the size show the venue can support. 

This is doubly true for LED lighting systems. While some of the little Chauvet (and similar) DJ lighting may not have the visual punch and sex appeal of a really large professional lighting system requiring a genny and big distro, I've got to admit that stringing 30 LED "PARs" together on a single 20-amp circuit is pretty cool. And the crowd in a smaller club or theater will be just as wowed by these baby systems. Plus the heat build up is much less with LEDs compared to old-school incandescent, and getting rid of the gels couldn't make me happier. Maybe I'm just getting older and crankier, but I really don't feel like lugging a ton of copper around for distro unless I really have to. Less is more..  8)
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Greg_Cameron

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Re: Distro Panel
« Reply #9 on: August 15, 2014, 02:01:52 pm »

I believe that 6 AWG stranded is the largest size of conductor which can be fitted to a "California standard" 50A connector.  It is my understanding that because of de-rating called for by the NEC for a multi-conductor cable, the NEC (strictly applied) would require a 45A breaker to protect the 6/4 feeder cable.  Mark C.

Technically as you've stated, 6AWG 4 wire cable isn't NEC compliant for a true 50A, you'd need 4AWG. I could have sworn Hubbell had rated their wire clamps for their CS connector to 4AWG, but the current spec shows only up to 6AWG. However, the Leviton version does specify wire sizes up to 4AWG: http://www.grainger.com/ec/pdf/50Amp-Wiring-Devices-Brochure.pdf . That's probably the way to go to get both NEC compliance and minimum voltage drop for a full 50A distro.
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Re: Distro Panel
« Reply #9 on: August 15, 2014, 02:01:52 pm »


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