Basic Solar Setup WIRING GRID TIE

quique · May 2009

Hi,

in Honduras we dont have credits for surplus energy produced, in other words we cannot sell in into the grid, so we use battery banks to store. Or basic setup is from PV array, to controller, to batteries, to inverter to ATS Switch which detects if there is solar power available from the battery bank. If there is, it runs solar, if there isnt, it reverts to grid power. My question is regarding the interconnection from inverter to main grid box to aux grid box.

The way we set it up is we took only the main lights lines coming from the house to the main breaker box and disconnected those breakers. Then we took those lines and ran them into an auxiliary breaker box next to the main box. And we feed that aux breaker box with the lines from the inverter.

The ATS is located between the inverter and the main breaker box and it determines whether there is enough power from inverter or not to make the switch. Then it outputs whoever wins to the aux breaker box.

But in a new installation the electrician simply ran a wire from the main breaker box to the aux breaker box. Like so.

losusa (dot) com/assets/wiring2.jpg [break link--looks like site has been hacked with trojan downloaders. -Bill B. Moderator]

So because the lights and tv still go thru the main breaker box, i was told to turn off the breakers in the main breaker box, otherwise the power will flow from main grid to main breaker box, push thru the aux breaker box, up the ATS (damaging it) and up to the inverter and damage it as well.

So ok, the breakers in the aux panel right now are off and the inverter is off. there is correctly now power from on the Aux Breaker Box's hot and neutral bars on top (SquareD). And I turned off the lights and tv breakers in the Main Breaker box so there should be no power running between the Main and Aux panels from he grid. But there is!! The ammeter placing the pos lead on the screw at the base of the breaker of the Aux Breaker Box and the neg lead placed on the neutral bar up top of the Aux Breaker Box reads 110V!?

Why if the breakers from the main panel are switched off?

BB. · May 2009

Re: Basic Solar Setup WIRING GRID TIE

Yes--the lousa site above has been compromised... It is has ~5 scripting sites listed such as:

%33%38%7a%75%2e%63%6e

which decode to things like:

38zu (dot) cn

Regarding your drawing posted on the link...

It looks like the electrician wired up a "bypass circuit" around the ATS (automatic AC transfer Switch). Those bypass breakers should be "locked off" so nobody ever turns them on--unless the ATS has been removed.

I am not quite sure of your question... The Aux Box should have AC power on the buses (hot/neutral) if:

A) the ATS is connecting that utility power to the Aux Box.
if the ATS is open, and the Inverter is turned on supplying power to the Aux Bus.

The Aux Bus will not have power if both the AC mains is down and the inverter is turned off.

The Inverter will blow up if there is AC mains power, the AC Bypass breaker is turned on and the inverter is turned on (or even turned off, but the AC Bypass breaker is on).

-Bill

quique · May 2009

Re: Basic Solar Setup WIRING GRID TIE

ok my question was indeed confusing. The ATS setup is one scenario. The interconnection between the AC Mains Box and the Aux Box is another and is a new setup which im trying to try out!

Forget the ATS setup, i was just using it as background info for you to to understand where i was coming from. The problem is that I had a new electrician set this up and he made this 'interconnection' which im worried about and ill tell you why.

The 'interconnection' i refer to is the cables running from the AC Main Box to the Aux Box. In the original-traditional ATS setup the wires from the lights to the AC Mains Box were disconnected from the breakers in the main box and physically transferred to the Aux Box. In the new 'interconnection' setup the wires from the lights that go to the AC Mains Box remain in place and a 'bridge interconnects' the AC Mains and Aux Box. This was cause of problem when someone connected turned on the breakers in the Aux Box. What happened was that the AC power from the main ran into the Aux Box and blew the breakers for some reason. So now im worried.

I replaced the fuse and was told that the breakers in the aux box must remain off until the inverter power is needed. At this point the breakers in the main must be switched off and only then can the aux breakers be switched on and the inverter powered up.

Ok, that made sense to me. But just to make sure i wanted to prove that when the main box breakers were turned off, no power ran from the main box to the aux box. But this is not the case. I took readings of 110V from the screw on the breakers of the aux box and the aux box neutral bar with the ac main box breakers turned off.

So my question is this:

1) should there be power readings of 110V (between the screw on the breakers of the aux box and the aux box's neutral bar) IF the AC main box breakers that are bridged or interconnected to the aux box are turned OFF?

2) if #1 turns out to be that yes, power will always flow into the aux box even if the ac main bridged breakers are turned off, then this is possibly not a good scenario, so it would probably just be best to take down that bridge, no?

mars

mike95490 · May 2009

Re: Basic Solar Setup WIRING GRID TIE

This is like trying to follow a convoluted math question. Can you sketch what the schematic is like? Red wire between the brass screw and the 4th terminal from the left (right), makes my brain hurt.

BB. · May 2009

Re: Basic Solar Setup WIRING GRID TIE

As always--the questions get a little bit deep when trying to answer "generic questions" when the specific hardware involved changes the "generic answers".

First--there the question of "stray 110 VAC"... How are your circuits wired in Honduras... I guess you have a "Hot and a Neutral" with ~110 VAC 60 Hz.

The hot lead will have a breaker/fuse for protection. The neutral will not. The neutral is normally connected to a cold water pipe and/or ground rod driven into the ground (ideally--real world, in other countries does not always match code).

So, the standard Breaker Box would look like:

[B]Your standard 110 VAC wiring?

[/B]                         Breaker[FONT=Fixedsys]s
Hot ==============+--/---- Load Hot
110 VAC  Bus Bars |
                  +[/FONT][FONT=Fixedsys]--/---- Load Hot[/FONT]
[FONT=Fixedsys]                  |[/FONT]
[FONT=Fixedsys]                  +[/FONT][FONT=Fixedsys]--/---- Load Hot

Neutral ==+=======[/FONT][FONT=Fixedsys]+------- Load Neutral
          |      [/FONT][FONT=Fixedsys] |
         ---      +[/FONT][FONT=Fixedsys]------- Load Neutral[/FONT]
[FONT=Fixedsys]         ///      |
     Earth Gnd    +[/FONT][FONT=Fixedsys]------- Load Neutral[/FONT]
[B]

The Transfer Switch (automatic or manual; Hot/Neutral switch together):[/B]

[FONT=Fixedsys]Hot ==============+--/---- Load Hot
110 VAC  Bus Bars |
                  +[/FONT][FONT=Fixedsys]--/---- Load Hot[/FONT]
[FONT=Fixedsys]                  |[/FONT]
[FONT=Fixedsys]                  |
                  +[/FONT][FONT=Fixedsys]--/-------o  /o---- Load Hot (or to aux beaker box)
                               / 
To   [Inverter]Hot-----------o/  [in Inverter On setting]
[/FONT][FONT=Fixedsys]Batt [        ]
VDC  [        ]Neutral[/FONT][FONT=Fixedsys]-------o  /o---- Load Neutral[/FONT][FONT=Fixedsys] (or to aux beaker box)[/FONT]
[FONT=Fixedsys]                               / 
 To Neutral Bus Bar----------o/  [in Inverter On setting][/FONT]

Now, I show the ATS/Transfer Switch as a DPDT (double pole, double throw) switch-- It switches your loads between the AC Mains and the Inverter output.

And--for the details... The Neutral Bus ATS/TS is needed for the typical MSW (Modified Square/Sine Wave) Inverter as they don't normally isolate between your Battery Ground and AC ground--if there was no ATS/TS on the Neutral, the inverter would short out. The inverter outputs are both "hot" with respect to safety ground (assuming your battery bank is negative ground to earth/water pipe).

However a TSW (True Sine Wave) Inverter does usually have isolation between the battery negative "-" terminal and the AC output (check manual or call Mfg.). So--you can use a SPDT (single pole, double throw) switch (similar to a 3-way light switch) and only switch the "hot lead".

Now, you can do the ATS/TS with a couple set of circuit breakers--but this is usually considered to be bad form (i.e., dangerous). If you always flip the breaker to "OFF", then flip the ones to Mains or Inveter to "ON" (two step process)--you are OK... However, if somebody makes a mistake and switches both sets of breaker to "ON" at the same time--at the very least--you probably have cooked your inverter.

Now, you can purchase a DPDT manual switch, or a DPDT Relay (typically connect the relay to the mains--Mains HOT, relay connects mains to Aux Box. Mains off, relay "fails over" to inverter).

Or, you can purchase relay systems designed for ATS.

Or, you can purchase Inverters that have the ATS built in (along with their own internal battery chargers).

Now, back to why you see 110 VAC in your Aux Box when you (think?) you have both sets of breakers/switches open.

There are different possibilities... Obviously, something may not be wired the way you think it is...

Or, your volt meter/DVM needs very little current to read 110 VAC. It is possible that there is a little capacitive or inductive coupling and it is just enough power to make your meter read 110 VAC. Typically, you take a 110 Volt 20-100 watt light bulb and clip it to the circuit--then measure the voltage (either the lamp will light, or it will "short out" the stray currents).

I am not sure what else to guess right now.

As always--it is dangerous to follow instructions from some guy on the Internet several thousand miles away who has never seen your setup or requirements. :roll:

-Bill

Basic Solar Setup WIRING GRID TIE

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