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[Tim McCulloch]

Stephen, thanks for the info, in the interest of learning more a couple questions that hopefully you can shed some light on.  With the primary power source being the POCO and the separately derived services coming from transformers wouldn't it all still be in sync at 60Hz?  Would there be additional potential problems/danger from a completely separately derived source like a generator that wouldn't be in sync phase-wise with the POCO derived services?  If you had a system to make sure the power coming off the generator was in-sync with the POCO then I would think (though I could absolutely be wrong) that the generator source would then be effectively no different than just another transformer derived service.

Continuing on that line of thought, what is the danger of say a mixer plugged into a service that is 45 degrees out of phase from another service that a second mixer is plugged into.  Those two mixers are then connected together with an XLR.  If they're well built the AC power supply should cleanly convert AC to DC and make power phase issues moot.  If the grounds are properly bonded there shouldn't be a ground differential to cause problems.  All is good?  Something goes boom?

Thanks!
Erik

You don't want to combine out-of-phase sources.  The local genset lacks the rotational inertia the PoCo grid has.  You'll be picking up pieces and parts of the local genset "if the streams cross".

The inadvertent combining of power sources is exactly why I said there can be NO connection between them - not a DMX cable, not a CATx, not a mic cable.

Note Stephen's comments about Code, and the only place a separately derived source can be interconnected is the grounding/bonding connection.  EVERYTHING is about keeping them otherwise separate.

Opto-isolation of the DMX is the key here.  If the same LX console is controlling the venue LX on PoCo, and band LX package on genset, you'd damn well better make sure they are isolated.

[Stephen Swaffer]

I don't want to start an argument-but I do have to respectfully disagree with Tim (who I respect greatly for his wisdom).  In addition to being an electrician in industrial facilities for a good chunk of my career, I have been interested in ham radio and electronic tinkering since high school.  I can only think of 5 types of equipment that have the phase relationship of a power source appear past the incoming power supply. The vintage tube audio amplifiers (really any tube equipment), welders, electric heat elements and lighting and motors.  Virtually everything else immediately converts AC to DC eliminating any phase/timing considerations.  Those loads that do see the AC on them are never interconnected downstream of the actual control device-contactor/scr or triac dimmer-or the like.  Most certainly phase conductors and neutrals should never be mixed between separately derived systems supplying a piece of equipment.  The greatest concern for that would be with any connections using tails/camlocks.

I have attached three (admittedly crude drawings).  The first shows correct bonding.  Done this way, there will never be any "objectionable current" on shields/equipment housings or any of the other wiring that actually gets physically interconnected.  If the yellow curved line interconnections exist, then there is the potential for voltages created by voltage drop to cause hum.  Mike Sokol had many posts regarding downstream ground/neutral connections.

In the drawing without a bonding jumper, the generator winding is shown floating.  This is a dangerous condition-especially in the case of a fault as there is no return path to cause a breaker to trip.  Putting a meter between ground and any of the genny leads-phase or neutral will give wildly erratic, meaningless readings.  This has the potential for damaging a power supply on connected equipment with voltage spike across an internal component and the housing.

The last one-separate grounds-is perhaps the most dangerous and probably most common mistake made.  Someone will drive a ground rod at a genny and say "it's grounded"-but there is a big question mark as to how much resistance is between the grounds-in a swamp on the edge of Orlando the connection is probably decent, in the desert in Vegas probably not so much.  In this situation, your equipment shields (mic/dmx cables) etc.  become the bonding jumper instead of piece of #4 or larger copper. Code requires any and all grounding electrodes in venue to be bonded, yet most people do not understand the difference between grounding and bonding (electricians should-but not all do). Overlooking the bonding can be very hazardous to personnel and equipment.  It is usually not an issue with "separately derived" sources like transformers in a venue-not because of phasing-but because bonding is usually inspected and maintained properly.  The definition of bonding is "an intentionally created metallic connection"-in installs that has to be done once.  With a genny someone has to make that conscience decision every time it is hooked up.

Having said that-optical isolation of dmx and other equipment is never a bad idea.  Mistakes can and do happen; however, in my opinion, optical isolation is never a pass to not get the electrical installation done in a manner that makes the isolation a redundant protection.

[Steve-White]

No.

Reason, liability pure and simple - I will in no way be associated with this adventure.  An online forum isn't the place to explain this - consult an electrician.  Getting a "Blank Stare" from "the" electrician isn't processing at this end.

If it's true, find another electrician.  Any qualified electrician can make this work.

Be safe sir.

I told ya so....   

[Jamin Lynch]

I'm happy to report that the venue has decided to install permanent power for visiting bands to use.

Thanks for all the replies and help

 

[Matthew Knischewsky]

I told ya so....   

"Any qualified electrician can make this work." Not so fast!

"A qualified electrician familiar with temporary power can make this work" would be the more accurate statement. 

I have worked along side many fine electricians who can bend conduit intuitively, employ the best techniques for fishing tricky wires, can rough in a residential unit to code without using a tape measure, etc etc. What many of them almost never encounter is temporary power, let alone for entertainment applications. For many electricians the items we use on a daily basis (twist locks, cam locks, portable distribution panels) are almost never encountered.

Just because they are qualified doesn't make them knowledgable about every situation. Hiring the person with the correct skillset is important- just like in sound reinforcement.

Suffering through years of blank stares,
Matt.

[Jamin Lynch]

"Any qualified electrician can make this work." Not so fast!

"A qualified electrician familiar with temporary power can make this work" would be the more accurate statement. 

I have worked along side many fine electricians who can bend conduit intuitively, employ the best techniques for fishing tricky wires, can rough in a residential unit to code without using a tape measure, etc etc. What many of them almost never encounter is temporary power, let alone for entertainment applications. For many electricians the items we use on a daily basis (twist locks, cam locks, portable distribution panels) are almost never encountered.

Just because they are qualified doesn't make them knowledgable about every situation. Hiring the person with the correct skillset is important- just like in sound reinforcement.

Suffering through years of blank stares,
Matt.

^^^
Agreed

[Steve-White]

"Any qualified electrician can make this work." Not so fast!

"A qualified electrician familiar with temporary power can make this work" would be the more accurate statement. 

I have worked along side many fine electricians who can bend conduit intuitively, employ the best techniques for fishing tricky wires, can rough in a residential unit to code without using a tape measure, etc etc. What many of them almost never encounter is temporary power, let alone for entertainment applications. For many electricians the items we use on a daily basis (twist locks, cam locks, portable distribution panels) are almost never encountered.

Just because they are qualified doesn't make them knowledgable about every situation. Hiring the person with the correct skillset is important- just like in sound reinforcement.

Suffering through years of blank stares,
Matt.

Like I said, here we are on the Merry Go Round.

Qualified for the task at hand.  What else would you seek qualification for?  What else would you consider as qualified?  Let's not play word games sir.

No, not every electrician has experience in entertainment system portable power and stage electric - that's a no-brainer.

One more time, this discussion isn't for an online forum - consult a qualified electrician - real simple answer.

[Stephen Swaffer]

I guess, in my opinion, hooking up "separately derived sources"-including temporary generators or permanently installed generators is a fundamental enough skill that I would not consider an electrician that can't figure it out qualified. Incidentally, electricians can be apprentices, journeyman or master's.  You don't want an apprentice or journeyman doing work "on the side"-a contractor would have at least one master on the payroll that can easily be consulted and they should know enough to get it right.  I wouldn't want a brain surgeon doing my knee replacement or my ortho surgeon doing brain surgery-but they both better be able to check my vitals or I'm looking elsewhere.

The main purpose of my posts is for the end user to understand that if an electrician/genny tech drives a ground rod and runs a feeder into a building and says "you're good" you need to find a different electrician or genny tech-or invite an AHD onsite to have a look see.  Some "electricians" aren't smart enough or are too embarrassed to give a blank stare.  A truly qualified electrician will know someone who knows.

Done right, I see no concerns from a different phasing or sync.  Done wrong?  I don't want to be involved even if I use optical or wireless isolation.  Making sure streams don't cross is OK for equipment, but streams not bonded and physically within 6 feet (arms reach) of each other are potentially lethal.  Maintaining that separation in a production environment is not feasible-getting it done right is feasible.  There isn't room for "good enough" on this-it is either right or unacceptable.

[Steve-White]

I guess, in my opinion, hooking up "separately derived sources"-including temporary generators or permanently installed generators is a fundamental enough skill that I would not consider an electrician that can't figure it out qualified. Incidentally, electricians can be apprentices, journeyman or master's.  You don't want an apprentice or journeyman doing work "on the side"-a contractor would have at least one master on the payroll that can easily be consulted and they should know enough to get it right.  I wouldn't want a brain surgeon doing my knee replacement-but they both better be able to check my vitals or I'm looking elsewhere.

The main purpose of my posts is for the end user to understand that if an electrician/genny tech drives a ground rod and runs a feeder into a building and says "you're good" you need to find a different electrician or genny tech-or invite an AHD onsite to have a look see.  Some "electricians" aren't smart enough or are too embarrassed to give a blank stare.  A truly qualified electrician will know someone who knows.

Done right, I see no concerns from a different phasing or sync.  Done wrong?  I don't want to be involved even if I use optical or wireless isolation.  Making sure streams don't cross is OK for equipment, but streams not bonded and physically within 6 feet (arms reach) of each other are potentially lethal.  Maintaining that separation in a production environment is not feasible-getting it done right is feasible.  There isn't room for "good enough" on this-it is either right or unacceptable.

Agreed Stephen.  This is a simple task for a properly qualified electrician.  Equally though, it's real easy to fry equipment or seriously injure or kill anyone within working proximity to the equipment.  Not to be taken lightly.

It needs consultation and on-site supervision of a qualified electrician.  An electrician qualified in both stage and temporary power systems.  Not some drooling idiot that does automotive electrical or wires houses for a living.

[Chris Hindle]

It needs consultation and on-site supervision of a qualified electrician.  An electrician qualified in both stage and temporary power systems.  Not some drooling idiot that does automotive electrical or wires houses for a living.

In the last 40 or so years, more than once I've gotten that "Who the hell are you?" look when I meter the distro before plugging in.
More than once I've had to say "Hey, Sparky, why is there 110 between neutral and ground?"
In 2 cases, the "answer" was "I've never hooked up 5 wires before"
An "electrician" that doesn't recognize / understand 3-phase is NOT the guy i want on my "team".
Chris.

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