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Author Topic: Pulling power for ONE PA, from two different sources?  (Read 20052 times)

Jonathan Johnson

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Re: Pulling power for ONE PA, from two different sources?
« Reply #50 on: June 23, 2014, 01:37:02 am »

You're missing the OP's situation. It's not that the house only has one circuit (that'd be stupid. I can't believe you suggested that was the case.) - it's just that the two houses only are willing to provide him with one each.

Probably because each house has only ONE exterior receptacle circuit on the back deck. I'm guessing the owners aren't willing to have an extension cord going in the kitchen window.

Everyone.... Time to put this subject to bed.

Thx

Mike Sokol

Yes, I think this horse is dead. I'll stop beating it now.
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Kevin Graf

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Re: Pulling power for ONE PA, from two different sources?
« Reply #51 on: June 23, 2014, 09:01:43 am »

Now that it's to late to save the horse.  Why not just use a wireless audio link to the remote speaker system?
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Speedskater

jasonfinnigan

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Re: Pulling power for ONE PA, from two different sources?
« Reply #52 on: June 23, 2014, 05:06:53 pm »

I really don't get why there is so much discussion about this. I don't think it's a good idea to pull from two homes. I can get a 30Kw diesel Genny for $100-140 a day. and that includes them delivering it and driving the ground rods in (Yes, you do need ground rods for a Generator).
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Rob Spence

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Re: Pulling power for ONE PA, from two different sources?
« Reply #53 on: June 24, 2014, 12:00:51 am »

Heck, see if there is an electrician in the area that could put a 30 amp dryer outlet in the close house basement. Plenty of power, no ground issues. $25 in parts.


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Tim McCulloch

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Re: Pulling power for ONE PA, from two different sources?
« Reply #54 on: June 24, 2014, 12:15:01 am »

I really don't get why there is so much discussion about this. I don't think it's a good idea to pull from two homes. I can get a 30Kw diesel Genny for $100-140 a day. and that includes them delivering it and driving the ground rods in (Yes, you do need ground rods for a Generator).

Yeah.  I don't see why (other than the HOA proclaiming poverty) this is an issue.  Good generators don't have to be expensive unless you want holiday delivery and fuel service from the rental shop on that holiday.  The costs of delivery, fuel and return will be 3x the cost of the genset rental.

I can get a 25-40kW genset for about $125/day if we pick it up and return it.  The shop includes a ground rod and wire, and our preferred vendor will tech it in their shop before we pick it up.
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Stephen Swaffer

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Re: Pulling power for ONE PA, from two different sources?
« Reply #55 on: June 24, 2014, 12:27:46 am »

I really don't get why there is so much discussion about this.

2 reasons:

1.  Sometimes arguing is more fun than coming up with a simple solution.
2.  To check and see if Mike is doing is job. :)
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Steve Swaffer

Mike Sokol

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Re: Pulling power for ONE PA, from two different sources?
« Reply #56 on: June 24, 2014, 06:53:43 am »

2 reasons:

1.  Sometimes arguing is more fun than coming up with a simple solution.
2.  To check and see if Mike is doing is job. :)

Yeah, yeah, yeah...  :o
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Mike Sokol
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Stephen Swaffer

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Re: Pulling power for ONE PA, from two different sources?
« Reply #57 on: June 24, 2014, 11:27:13 pm »

I am actually working on a project right now where a customer wants to use an installed backup genny to provide emergency power for small crucial loads in 2 different buildings supplied by services on separate transformers.  This obviously requires me to connect the neutrals from each service.  No objections raised by the electrical inspector, but I will update this after I talk to the POCO this week.

At the risk of raising a dead horse, I got my answer today.

One genny can serve 2 separate services.  Grounds would be bonded together.  One of the transfer switches would be a normal 2 pole switch.  The second must be a 3 pole switch-the neutral on one of the services must be switched so that the neutrals from the 2 services are never connected.  Also, the second service must be wired with grounds and neutrals separated to have the proper configuration (one ground/neutral bond,period) when running off genny.

Too much of a headache IMO for the benefits to my customer at this point, but I suppose if the check is big enough?

For purposes of this thread, the POCO is obviously against using two services in a cooperative manner.  Though the have no problem bonding the grounds together.   
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Steve Swaffer

Steve M Smith

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Re: Pulling power for ONE PA, from two different sources?
« Reply #58 on: June 25, 2014, 01:36:40 am »

2 reasons:

1.  Sometimes arguing is more fun than coming up with a simple solution.
2.  To check and see if Mike is doing is job. :)

Or to quote something I read a few days ago:

"I'm not arguing with you, I'm explaining why you're wrong!".


Steve.
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David Buckley

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Re: Pulling power for ONE PA, from two different sources?
« Reply #59 on: July 30, 2015, 11:40:50 pm »

(Late response to a old thread)

There's some hints in the thread about high voltage bad things happening, but no clear explanations as to why.

The USA has adopted a system of distribution called Multi Grounded neutral  -MGN.  This is a system very different to that used over most of the rest of the world, and brings its own issues.  In theory, it is a superior system, saving money, and providing better lightning protection for distribution assets.  In practice, however, it provides a mechanism of fault current propagation, and has its own set of special dangers.

The big difference between what everyone else uses (which has no name) and MGN is to do with the way that single phase transformers are wired, the type of transformers that serve homes and smaller businesses.  Ordinarily, the final, single phase transformer serving a home(s) or building has its primary connected between two high voltage phase lines, but under MGN the transformer is connected between one phase line and a neutral cable, often called the messenger wire.  So a transformer here in New Zealand, typical of the rest of the world, has two high voltage terminals on it.  A USA transformer has one.

So in the USA, neutral is distributed via a wire.  And... the neutral to your home is also connected to that same neutral wire, so your home neutral is connected to the high voltage distribution network.  And that neutral distribution network is deliberately connected as far and as wide as possible.  It is also connected to the ground through plates and rods, at a substation, at the pole where the transformer is, and at your home.  The idea is that it is one big equipotential zone.

Having introduced all that, there are two problems that are seen with MGN.

The first is that there will be potential differences between the neutral "points" of each home, caused by voltage drop in the neutral wiring.  This is not just from the neutral current between the service entrance and the pole, but from current flowing along the messenger neutral from out-of-balance (and harmonic!) neutral return currents along the messenger back to the substation.  This can vary between millivolts and quite a lot of volts, depending on loads and distance.  At the service entrance of each house, neutral and ground are joined to form the earth point of the home.  Thus it follows that ordinarily, normally, and expectedly, there will be potential difference between the ground points of different homes.

If audio stuff is plugged in this situation, coming between two different ground potentials, then there will be circulating currents, which could potentially cause hum like a ground loop.  The current flowing could be quite significant, if the impedance of the system between different points is low, and this could leac to heating effects across audio cabling, and potentially across the PCBs of electronics.  Not good.

The more terrible situation is that of faults.

One fault mode is that many houses have poor - or missing - neutral connections, and thus their local ground potential is way out.  A house can function with a missing neutral using the water pipes as a neutral return circuit, or even sometimes a ground rod.  This can cause significant voltage difference between a house with a fault and other houses.

A bigger problem is a fault in the neutral messenger wire.  If this wire has an imperfect connection somewhere along its length then a voltage will appear across that imperfection, and that voltage will be reflected through the messenger neutrals to all the grounds of all the hoses, and the potential difference here could be quite large.  The edge case is total failure of the messenger neutral at some point.  The power system will continue to operate as the return currents will make their way through the ground system (including water pipes), but the potential difference between houses on either side of the fault could be hundreds or even thousands of volts.

Finally, if a transient event occurs, such as a lighting hit, or a fault such as a line touching another line (wind, car crash into pole) then there can be thousands of volts transiently across the messenger neutral.  This normally isn't an issue because nothing is connected "along" the messenger to be hit by that voltage potential, but if one has a audio rig plugged into two homes a distance apart, then these hundreds or thousands of volts could transiently appear across audio equipment, with bad effect.  Or it could appear across someone holding a microphone.

So, in summary, MGN brings a whole class of dangers associated with violating individual equipotenital zones, which could lead to damage and injury.  Just don't do it.

(Note to electrically savvy people - I have chosen to misuse the term "high voltage")
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Re: Pulling power for ONE PA, from two different sources?
« Reply #59 on: July 30, 2015, 11:40:50 pm »


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