AC Load Distribution Boxes

[idylldon]

Now that our band is playing out regularly, I'd like to tighten up our setup by making an AC distribution box. I plan to make my own, but before I do I thought I'd ask to see if anyone out there has a design they're happy with. What features would an ideal distribution box have?

 

Cheers,

--

Don

[rickkreuzer]

Most excellent topic, dude!

 

Are you looking to hardwire directly into a panel or just combine several circuits via regular ole plugs into a distro?

 

Rick

[idylldon]

ideas on any combination. We'd most likely be looking to combine several circuits into a dist. box. Also, most places seem to have a 220 outlet and making that into two 110 legs would be of interest.

 

Cheers,

--

Don

[idylldon]

ideas on any combination. We'd most likely be looking to combine several circuits into a dist. box. Also, most places seem to have a 220 outlet and making that into two 110 legs would be of interest.

 

Cheers,

--

Don

[Drumtech]

IMHO, it is very hard to find an unused breaker at a bar / club.

 

You should consider a hardwired unit which can always be connected to a breaker or a series of breakers...

[rickkreuzer]

 

Originally posted by Drumtech IMHO, it is very hard to find an unused breaker at a bar / club. You should consider a hardwired unit which can always be connected to a breaker or a series of breakers...

 

 

 

I agree, HOWEVER, most of us are just not experienced with hardwiring to a power supply which could quite easily kill us. Plus, most clubs would make you hire an electrician to come in and wire it up for you to be sure there isn't any liability on their part.

 

I've thought long and hard about this mysef. Currently we have some stupidly heavy thick and long extension cords. I'd love a distro...

 

Rick

[J Kylez]

 

Originally posted by rickkreuzer I agree, HOWEVER, most of us are just not experienced with hardwiring to a power supply which could quite easily kill us. Plus, most clubs would make you hire an electrician to come in and wire it up for you to be sure there isn't any liability on their part. I've thought long and hard about this mysef. Currently we have some stupidly heavy thick and long extension cords. I'd love a distro... Rick

 

 

I agree with this. If you are an electrician or know one that can help you do the project then go ahead. Otherwise, don't risk it. It's too dangerous and risky.

 

I do tie in with my own distro often but I had certified electrician check over the equipment after he helped me fabricate it.

 

I know you're pain though, it's almost impossible to utilize a larger PA with a nice light show without a tie in.

[Craig Vecchione]

 

Originally posted by idylldon ideas on any combination. We'd most likely be looking to combine several circuits into a dist. box. Also, most places seem to have a 220 outlet and making that into two 110 legs would be of interest. Cheers, -- Don

 

 

Before we go any further, just a note of caution: Any sceme utilizing both legs of a 240 circuit will result in the 120 circuits having opposite phases. Although almost unavoidable, this can cause dangerous situations when "iffy" vintage amps are used.

 

Also, it's very often a local fire & safety code violation for anyone to open a power distribution panelboard while a public venue is open for business. Always check with authorities (building department) and get ownership permission before attempting a hardwire. In many cities such a modification is strictly prohibited by code.

[Black Frog]

What do your tie-in's use for getting into the circuit panel?

 

We had one years ago that used some mombo-sized jumper-cable-type clamps. Grabbed both legs and ground of the panel and ran it to our own 8-circuit box with breakers.

 

We had an adapter that would go into a 220v wall receptacle as well....

[idylldon]

and I think these are valid points to present to the local club owners to convince them that perhaps separate "stage" power outlets are needed.

 

None of the "clubs" (I use that term loosely) we play have dedicated circuits to power the stage, and trying to identify separate circuits and their loads before hooking our stuff up is often problematic. Current draw hasn't been an issue in the past, but we're planning to add more PA gear and the power it requires has made a consistent and safe power hookup essential. Frankly, most of the club owners I've encountered can't be bothered with trying to make the band's job easier, though, as I said above, approaching them from the standpoint of safety issues might get some results. It'd be great to have all the necessary power hardwired right on the stage.

 

Thanks,

--

Don

[flanc]

I debated this long and hard as well. I opted to carry an assorment of extention cords. Beer + limited electrical knowlege + More beer + crappy wiring + rush to get things moving = toasted band guy acting like electrician

[J Kylez]

 

Originally posted by idylldon and I think these are valid points to present to the local club owners to convince them that perhaps separate "stage" power outlets are needed. -- Don

 

 

Half the time when this is done. There is:

 

1. Not enough power anyway

2. Tired breakers due to consistent overload and misuse

3. Broken hardware you are afraid to plug into in case of shorts

 

Just side note:

I always test wall outlets with a voltmeter for proper phasing, actual voltage, and ground leakage before I plug anything in. Even if I am familiar with the venue.

[J Kylez]

 

Originally posted by Black Frog What do your tie-in's use for getting into the circuit panel? We had one years ago that used some mombo-sized jumper-cable-type clamps. Grabbed both legs and ground of the panel and ran it to our own 8-circuit box with breakers. We had an adapter that would go into a 220v wall receptacle as well....

 

 

I'll use clamps as a last resort. This really isn't a good idea.

 

A lot regular venue's in my area have a dedicated subpanel with it's own 100 or 200A feed. This will usually have lugs to connect your wires. In this case you just need the pigtails. This is the best and easiest way really. Although the lugs always seem to get stripped out due to idiots who don't carry the right tools. Or they are missing. That's even worse.

 

I also have an assortment of 220 plugs. For smaller places these outlets are sometimes convenient. This isn't that bad for hookup either.

 

I have installed temporary breakers in panels and screwed lugs into the neutral bar a couple of times as well.

 

There are others here who can give better information than me though.

[agedhorse]

 

Originally posted by Craigv Before we go any further, just a note of caution: Any sceme utilizing both legs of a 240 circuit will result in the 120 circuits having opposite phases. Although almost unavoidable, this can cause dangerous situations when "iffy" vintage amps are used.

 

All building distribution that you are currently using consists of either two hot legs (120/240 volt single phase) or three legs (120/208 volt three phase) or some variation of this depending on the distribution type in your locale.

 

Using a (properly built) portable distro will cause no additional problems that would otherwise be encountered in a venue or building. Just because the term 240 volts is used does not mean that 240 volts is present in the connection, it means that the ditribution scheme is based on voltages that include 240 volts as one of the possible connections.

 

Iffy amps (vintage or otherwise) can not generate 240 volts from a 120 volt source, nor can it deliver more than 120 volts through a fault to ground. The only possibility is for 2 failed amps, plugged into different phase legs, to have leakage to chassis in the opposite direction which could deliver a higher potential between the chassis but not referenced to ground. This is the same no matter what type of distro (permenant or portable) is installed.

[J the D]

It is my understanding a 12 ga extension cord will deliver all the juice a 15 amp circuit is able to produce. I determine the total amperage draw of the rig, divide it by 12 (not a misprint), and look for that many separate circuits. Has worked without any problems so far.

[Drumtech]

I agree, HOWEVER, most of us are just not experienced with hardwiring to a power supply which could quite easily kill us.

 

So will driving a car with one hand if you don't know how... Certainly do not attempt to do something you are not either trained or feel comfortable doing. That said, the most fundamental part of a PA is POWER... I don't know what type of PA the original poster is using but if he / she is considering a distro, then a "tap in" distro may be an option. Of course, I DO NOT RECOMEND ANYONE TAPPING IN THAT DOES NOT HAVE THE EXPERIENCE DOING IT. I have several distros that use different methods of connecting to main power sources which include "tap in", twistlock and European 63 and 128 amp four or five pin connectors.

 

What I've done in clubs / bars that I do sound regularly for is install (at my cost most of the time) a quicker and safer method of connection. I purchase the tubing, conductors, breaker, and wall receptacle required for the PA and have it available when I'm contracted to do the sound. Normally, I'll contract the electrician that works for the club to install everthing as they know the ins and outs of the electrical system. I'll do this in clubs / bars that I work as little as two or three times a month. In the US, you should stick with Twistlock which is probably the most common type of connector. As for using the separate legs of the 220 to get two 110 circuits, you need to make sure you have a balance load or you run the chance of tripping a 220 breaker.

 

A great source for power distros is Motion Laboratoires (www.motionlabs.com). They make among other things, great 4 space rack mountable units and practical stage / drop boxes...

[agedhorse]

 

Originally posted by J the D It is my understanding a 12 ga extension cord will deliver all the juice a 15 amp circuit is able to produce. I determine the total amperage draw of the rig, divide it by 12 (not a misprint), and look for that many separate circuits. Has worked without any problems so far.

 

How do you calculate amperage draw?

 

a) 1/8 power spec?

b) measured under load?

c) The labels on the backs of equipment?

 

This can lead to massive over-specing of electrical source, as the numbers can be very mis-leading unless you know how they are derived. Asking for a seperate circuit for each amp would also work without problems, but just adds unnecessary cost and weight to the solution.

[Craig Vecchione]

 

Originally posted by agedhorse All building distribution that you are currently using consists of either two hot legs (120/240 volt single phase) or three legs (120/208 volt three phase) or some variation of this depending on the distribution type in your locale. Using a (properly built) portable distro will cause no additional problems that would otherwise be encountered in a venue or building. Just because the term 240 volts is used does not mean that 240 volts is present in the connection, it means that the ditribution scheme is based on voltages that include 240 volts as one of the possible connections. Iffy amps (vintage or otherwise) can not generate 240 volts from a 120 volt source, nor can it deliver more than 120 volts through a fault to ground. The only possibility is for 2 failed amps, plugged into different phase legs, to have leakage to chassis in the opposite direction which could deliver a higher potential between the chassis but not referenced to ground. This is the same no matter what type of distro (permenant or portable) is installed.

 

 

Hang on a sec....

 

I never said the use of a portable distro was any different. I specifically stated that any 120v derivation of a 240 branch would result in out-of-phase branches.

 

I also didn't state or imply that amps would 'generate 240 volts...'. However, a pair of vintage chassis-common amps, if plugged to out-of-phase circuits, will have a 240v potential between them. They don't have to be defective, only have to have the original wiring design. But none of this is really relevant to my point, which was just to be aware of the phase relationship issue when using 240v multiwire circuits.

[Craig Vecchione]

 

Originally posted by agedhorse How do you calculate amperage draw? a) 1/8 power spec? b) measured under load? c) The labels on the backs of equipment? This can lead to massive over-specing of electrical source, as the numbers can be very mis-leading unless you know how they are derived. Asking for a seperate circuit for each amp would also work without problems, but just adds unnecessary cost and weight to the solution.

 

 

I'll go out on a limb and assume JtheD is using the NEC spec that calls for a branch to have a load no greater than 80% of the overcurrent protection, hence "12" for a 15a branch, and that he's using the nameplate current draw for the device. While decidedly overkill in practice, it never hurts to start off with what NEC suggests and work downward as needed.

[J the D]

 

Originally posted by agedhorse How do you calculate amperage draw? a) 1/8 power spec? b) measured under load? c) The labels on the backs of equipment? This can lead to massive over-specing of electrical source, as the numbers can be very mis-leading unless you know how they are derived. Asking for a seperate circuit for each amp would also work without problems, but just adds unnecessary cost and weight to the solution.

 

 

Look at (or try and estimate) the average draw in watts and convert to amperes. This is why I give myself a 20% safety margin. I also turn things on in a sequential fashion.

 

I don't know if this is actually workable but it is the best I've been able to come up with considering mylack of electrical hookup skills. Have not lost anything yet.

 

But Andy, I would welcome any comments or recommendations you could give us weekend warriors in this area. I have been more concerned about not having enough amperage

[agedhorse]

Generally, choosing the AC draw measured based on something between 1/8 and 1/4 rated maximum (at clipping power into the actual load impedence. (see QSC website for a discussion of this). Otherwise, how would you plug in and operate a PLX-3402 off of a standard 20 amp which draws close to 50 amps steady state maximum power at 2 ohms. (this approximates about 12 amps average input curent at 1/8 power) This amp can be operated with music input at 2 ohms to clip on a 20 amp circuit with no problem at all. It's due to the crest factor (peak to average ratio) that averages out AC draw over a longer period of time rather than looking at an instantaneous slice of time. Since thermal and thermal/magnetic circuit breakers have trip delay, this also adds to your safety factor on a properly designed system.

 

I toured a system for years that had 15kW on the mains, 12kW of bi-amped monitors, plus stage and FOH power. I did this using a 30 amp 3 phase (120/208v) distro and NEVER had problems, but I both calculated the average line current, balanced the loads between all the phases and then verified the currents were in fact within safe ratings.

 

In actual operation, the system would peak at about 25 amps per leg driven pretty hard into limiting. This allowed me to carry a relatively small distro for the system size. It also pays to have efficient amps (Class H, PLX, PL, K2 etc) to minimize input power demand.

[Scodiddly]

Electrians usually carry a pretty handy device called a "clamp-on ammeter", which inductively measures the power being sucked through a wire. I bought one for under $40 (slightly on sale) a few years back.

 

What you do is make a special extension cable with the wires separated for a few inches. Those flat "airconditioner" extension cables are great for this. Then you get all/most of your rig set up, sucking power through this cable. Clamp the ammeter around the "hot" wire and read off the amps being drawn. Have a friend take a reading while you're all blasting away, since amps draw less current when not putting out a big loud signal.