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[Jamin Lynch]

A local venue has a show coming up that needs some additional power to support a lighting package the band is bringing. There's no place to "easily" obtain any more house power. They want to bring in a 25K portable generator for their lighting package.

The house sound system runs off dedicated house power.

Refresh my memory on the potential problems/hazards of doing that

Thanks

[Steve-White]

Properly done, the risk would be very low.  Potential for issues is there for sure.  In the end the risk is directly proportional to the experience and skill level of the electrician overseeing the project.

Improperly wired power distribution or generator could be bad.  Improper grounding could be very bad.  Again, it rests on the shoulders of the electrician.

[Jamin Lynch]

Properly done, the risk would be very low.  Potential for issues is there for sure.  In the end the risk is directly proportional to the experience and skill level of the electrician overseeing the project.

Improperly wired power distribution or generator could be bad.  Improper grounding could be very bad.  Again, it rests on the shoulders of the electrician.

Can you expand on what "properly done" would look like?

***I got a blank stare from the electrician when I mentioned it.

[Steve-White]

Can you expand on what "properly done" would look like?

***I got a blank stare from the electrician when I mentioned it.

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.

[Brian Jojade]

+1 with Steve. 

Yes, it certainly can be done safely.  But it's imperative that it is done 100% correctly.  If the electrician on hand has no experience with this, you NEED another electrician involved.

Done incorrectly, people can DIE, so take this very very seriously.

[Tim McCulloch]

What I've done to mitigate *some* risk:  {edit} never mind.

What I will say - don't cross the streams.  Don't have fixtures from different power sources interconnected by ANYTHING that is not electrically isolated (including DMX and IP networking).  The band's LX package needs to be on it's own universes and you'll want an opto-isolator between the console outputs and both the venue and band LX.

This is where you find out what you don't know...

What we have done in one venue is to transfer all the venue LX to the genset, and it's still no guarantee that all components of the venue LX are part of the transfer.  We installed the LX originally but can't vouch for what was added later...

Edit ps:  note that none of this guarantees safety for either life or property.  You need an industrial electrician with background in multiple sources (think: back up power).  It might be worthwhile to call up your local AHJ and asking what considerations they have and if this requires permits and inspections.

[Stephen Swaffer]

As a licensed electrician let me point out this.  The definition of a separately derived system is, from Article 100 of the NEC An electrical source, other than a service having no direct connection(s) to circuit conductors of any other electrical source other than those established by grounding and bonding connections.

Given that definition, the building I currently sit in has at least 7 or 8 separately derived services-every transformer supplied subpanel is a separately derived service.  A generator is no different-the only real difference is that instead of a POCO source driving the primary of a transformer, a diesel or gasoline engine is driving the armature that services as the "primary of the transformer".  (Similarly, a motor functions as a transformer with the armature being the secondary)

From a technical standpoint it really is that simple.  The key in the definition is "other than those established by grounding and bonding".  There is a whole chapter in code (250) on grounding and bonding.  It is emphasized in code classes and by inspectors everywhere-so if the electrician is indeed qualified he should be able to figure out grounding and bonding of separately derived services.  Do that right and it should be no different than many of the venues you work at-I doubt most of you even realize when you are dealing with a separately derived service in any given venue?

[Jamin Lynch]

As a licensed electrician let me point out this.  The definition of a separately derived system is, from Article 100 of the NEC An electrical source, other than a service having no direct connection(s) to circuit conductors of any other electrical source other than those established by grounding and bonding connections.

Given that definition, the building I currently sit in has at least 7 or 8 separately derived services-every transformer supplied subpanel is a separately derived service.  A generator is no different-the only real difference is that instead of a POCO source driving the primary of a transformer, a diesel or gasoline engine is driving the armature that services as the "primary of the transformer".  (Similarly, a motor functions as a transformer with the armature being the secondary)

From a technical standpoint it really is that simple.  The key in the definition is "other than those established by grounding and bonding".  There is a whole chapter in code (250) on grounding and bonding.  It is emphasized in code classes and by inspectors everywhere-so if the electrician is indeed qualified he should be able to figure out grounding and bonding of separately derived services.  Do that right and it should be no different than many of the venues you work at-I doubt most of you even realize when you are dealing with a separately derived service in any given venue?

Thanks Stephen

That explanation makes some since to me. I'll mention "separately derived service" to the electrician and see if I get something more than a blank stare. If so, I'll walk away slowly. 

I've already sent the venue a disclaimer that I'm not qualified to give advice or make recommendations for electrical applications. 

We recently had the same issue come up with another band. At that time it was up to me. I just told the band we did not have adequate electrical service for their lighting package. They ended up not using it. Problem solved.

It think the venue is now talking about adding additional power just for this reason. Hopefully it can be done by Friday. I believe That would be the ultimate solution

[Dave Garoutte]

You could isolate the control from the lighting by using wireless DMX if you had to.

[Erik Jerde]

As a licensed electrician let me point out this.  The definition of a separately derived system is, from Article 100 of the NEC An electrical source, other than a service having no direct connection(s) to circuit conductors of any other electrical source other than those established by grounding and bonding connections.

Given that definition, the building I currently sit in has at least 7 or 8 separately derived services-every transformer supplied subpanel is a separately derived service.  A generator is no different-the only real difference is that instead of a POCO source driving the primary of a transformer, a diesel or gasoline engine is driving the armature that services as the "primary of the transformer".  (Similarly, a motor functions as a transformer with the armature being the secondary)

From a technical standpoint it really is that simple.  The key in the definition is "other than those established by grounding and bonding".  There is a whole chapter in code (250) on grounding and bonding.  It is emphasized in code classes and by inspectors everywhere-so if the electrician is indeed qualified he should be able to figure out grounding and bonding of separately derived services.  Do that right and it should be no different than many of the venues you work at-I doubt most of you even realize when you are dealing with a separately derived service in any given venue?

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

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