Why "critical load panel only" when grid is down?

[jflorey2]

I might have found my solution. This guy has three panels. Main, critical and "switchable". . . . Thoughts?

How is that any better than having a main and a critical panel?

[jflorey2]

[*]I'm sure some would argue that I'm relying on a setting in my inverter to prevent flow. The same could be said of trusting the islanding features of all hybrid inverters.

No, the two are nothing alike. If you rely on people making the right decisions to prevent power flow back to the grid, then you will put utility workers at risk, period.

That being said, in your case you are only putting yourself and your system at risk.

[gmanInPA]

No, the two are nothing alike. If you rely on people making the right decisions to prevent power flow back to the grid, then you will put utility workers at risk, period.

That being said, in your case you are only putting yourself and your system at risk.

I wasn't saying they were alike - only that I could imagine someone would argue that routing the generator back into the AC1 input on the inverter was some how anti-island - but indeed, it is NOT the same. There is no way I can back-feed the grid - period - not through a human decision. The only risk I incur is to my own equipment (and safety) as you speak of. In fairness, the moment you have any installed solar equipment, or electrical equipment installed, you're at equal risk - unless you are somehow prevented from changing any settings.

[ButchDeal]

I wasn't saying they were alike - only that I could imagine someone would argue that routing the generator back into the AC1 input on the inverter was some how anti-island - but indeed, it is NOT the same. There is no way I can back-feed the grid - period - not through a human decision. The only risk I incur is to my own equipment (and safety) as you speak of. In fairness, the moment you have any installed solar equipment, or electrical equipment installed, you're at equal risk - unless you are somehow prevented from changing any settings.

That is how you would deal with it using the non-radian inverters like mine if you wanted a generator. Connect it to AC1 with a disconnect on the Grid side.
The radian can deal with a generator on AC1 or AC2. AC2 just makes things simple as no other disconnect is needed.

[gmanInPA]

That is how you would deal with it using the non-radian inverters like mine if you wanted a generator. Connect it to AC1 with a disconnect on the Grid side.
The radian can deal with a generator on AC1 or AC2. AC2 just makes things simple as no other disconnect is needed.

Well my main reason for having it usually feed AC2 is so that it only feeds my critical loads typically and also freeing me of needing an ATS. It's main purpose is to recharge batteries based on SoC triggers - not to run the whole house. The Inverter and AGS turn on the generator. I suppose it could do that on either AC1 or AC2, but I want my grid and my generator to feed the inverter directly - though I know some people would rather have the genny feed the main. For my layout, that just didn't make sense. The other arrangement with the switches just gives me the freedom to run whatever I want off the generator(s) in un-forseen circumstances. Also, if I shut down my entire inverter system (using the DPDT bypass I have in place for such), I can still run the generator as a whole house-backup.

[inetdog]

... and also freeing me of needing an ATS..

Make that "needing an external ATS" and I will agree. There is an ATS which is integral to the hybrid inverter.

[gmanInPA]

Make that "needing an external ATS" and I will agree. There is an ATS which is integral to the hybrid inverter.

Agreed/understood

[kingofbanff]

Thanks to ButchDeal and gmanInPA for the time you are putting into this. I wish I had a level of expertise in any field so I could add value in a forum...
Using gmanInPA interlock I have adjusted my design. I originally got the interlock idea (not knowing what it was called) from here
So now I have three panels. The main panel will be fed by the grid. It will have circuits that will never be run off batteries or generator (fine I'll get a stinking generator you persistent b*******!)
The second panel will be the switchable loads. These are loads I may or may not want to run in a grid down situation. My washing machine for example. If the grid goes down mid cycle and I'm out of the house I don't want the machine to draw down my batteries. So by default when the grid goes down this panel goes down. I will manually need to switch the interlock at the critical load panel to get the inverter to feed this panel. Then I can shut down all loads on this panel until I want to use one if the sun is shining. The third panel will be the critical load panel.

[ButchDeal]

the connection from the CC / inverter/ battery is more of a T like this

inverter
|
|------------ Charge controller
|
Battery

If the sun is up you would have no problem running the washing machine
That is a very flexible configuration as well.

If you have the generator connected with auto start you likely could have quite a bit on the critical load panel without the need for the interlock and switchable loads unless you plan for it to be way over inverter breaker size. The outback will just start the generator to help it out, or to charge the batteries and help.
I wouldn't put things like electric water heater or electric dryer on the critical load but you could put them on your switchable load panel.

[kingofbanff]

If you have the generator connected with auto start you likely could have quite a bit on the critical load panel without the need for the interlock and switchable loads unless you plan for it to be way over inverter breaker size. l.

thanks again ButchDeal
Can you point to an article on how panels are sized? I have 200 AMP service currently. However, if I add up all the breakers they are way over 200A. Obv I don't run every single load at max Amps simeltaneously. So I figure there is some formula they use...that way I can figure how many circuits I can put on my critical load panel given the two outbacks have a combined max of 50Amps.
thanks

[inetdog]

thanks again ButchDeal
Can you point to an article on how panels are sized? I have 200 AMP service currently. However, if I add up all the breakers they are way over 200A. Obv I don't run every single load at max Amps simeltaneously. So I figure there is some formula they use...that way I can figure how many circuits I can put on my critical load panel given the two outbacks have a combined max of 50Amps.
thanks

The relevant article is called the National Electrical Code.
It has detailed guidelines for calculating the expected load on a feeder or service, and it does not involve adding up the breakers, not does it even involve adding up the actual current drawn by all connected loads. There are service factors which take into account that not everything will be running at once.

[gmanInPA]

I agree with @ButchDeal... If you have a generator backing up the inverter, and you have an auto start generator module, you can just have the generator start up to support the loads that the batteries would otherwise not support very long. Doing so you can avoid the whole switched panel idea and the manual process of switching it over. These hybrid inverters can be setup to be quite smart.

[Sunking]

I agree with @ButchDeal... If you have a generator backing up the inverter, and you have an auto start generator module, you can just have the generator start up to support the loads that the batteries would otherwise not support very long. Doing so you can avoid the whole switched panel idea and the manual process of switching it over. These hybrid inverters can be setup to be quite smart.

That is the way it is meant to work. Otherwise you spend a fortune on batteries and replacement cost. Small inexpensive batteries to carry a light load for a short time, and genny to do the real work. Much less expensive intially and long term with better reliability. If batteries were the right answer telecom, military, and mission critical applications would use it.

[kingofbanff]

Well I'm back again after some huddling with the designer/ installer. It was going to be prohibitively expensive to do the rewiring of panels that the previous iteration required. So the latest idea is much less elegant but appears to address my concerns.

For those who have just joined: I'm installing 13kw and want to be able to use all that power even if the grid is down which means I want to selectively turn on circuits when the sun is shining. I have 19kwh of batteries. I don't want them getting emptied running items like in floor heating or the oven if the grid goes down while I'm out of the house and just turned the oven on.

The designer proposes a 200 amp contact switch in between the meter and the main panel. When the grid goes down the switch prevents the back feeding of the grid. The batteries are feeding the main panel which will drain them quickly. We will set the controller on the Outback Radian to only allow a DoD of 20%. So then when I realize the grid is down it is up to me to manually trip all the breakers that I don't want drawing from the batteries. Then I reset the DoD to 50% to run my current critical loads. When the sun is shining I can run more of the house.

Thoughts?

[jflorey2]

The designer proposes a 200 amp contact switch in between the meter and the main panel.

What is a "contact switch?" Do you mean relay? If so then the relay needs to be a 200 amp 4PDT relay that does two things:

1) One gang switches between utility feed (when energized) and inverter feed (when de-energized.) The armature connects to the busbar in the load center. This prevents backfeeding.
2) Another gang switches between AC out from the panel (when energized) and open circuit (when de-energized.) The armature connects to inverter AC in. This prevents the inverter from trying to charge its batteries from its own AC output.

These can also be two separate relays as long as they are driven by a common source. That source should be a PROTECTED circuit on or near the meter.

Of course the above description is just a long-winded way of saying "automatic transfer switch" of which there are plenty on the market. You can get one for about $500.