Back feed thru a fusible disconnect

[SunEagle]

So you would take a metal object and start smashing live electrical parts? potentially exposing live electrical parts?
Letting the building burn is more like it. If the building is that engulfed it is pretty much too late anyway.

I think the FD (which I am not one of) would first try to kill all power to the burning building no matter what is it constructed of. If they can't guarantee that all power is off then they probably would just let it burn. It doesn't have to be fully engulfed but if they only have water as a suppressant they won't pour it on an energized circuit. It's too dangerous to them.

[Naptown]

If there is no way to disconnect the panels and isolate the power from them the FD is not going to risk the chance of electrocution to anyone using a hose to put out the fire. Trust me when I say the FD will find a way to make sure there is no live power cable anywhere they are working. I have seen the FD in action and they will find a way to de-energize all power feeds to a building before they will try to put it out with water. If that means tearing the panels off the roof using their ladder truck then so be it. If they can't find a way to kill all power then unless there is someone that needs to be rescued they will let the building burn. It is for their own safety.

People first, property second. I believe Sunking when he states they will use their axes on the panels.

So you would take a metal object and start smashing live electrical parts? potentially exposing live electrical parts?
Letting the building burn is more like it. If the building is that engulfed it is pretty much too late anyway.

[SunEagle]

The issue is the panels are on the roof. Disconnect must be accessible (near the meter)
Fire department shows up and turns off the disconnect. Now DC power is off to the inverter but is still alive and well on the roof from the panels to the disconnect. the only way to turn off the voltage would be to either cover them or short the entire array out which would drop the voltage to 0
However the fire department isn't going to do that.

If there is no way to disconnect the panels and isolate the power from them the FD is not going to risk the chance of electrocution to anyone using a hose to put out the fire. Trust me when I say the FD will find a way to make sure there is no live power cable anywhere they are working. I have seen the FD in action and they will find a way to de-energize all power feeds to a building before they will try to put it out with water. If that means tearing the panels off the roof using their ladder truck then so be it. If they can't find a way to kill all power then unless there is someone that needs to be rescued they will let the building burn. It is for their own safety.

People first, property second. I believe Sunking when he states they will use their axes on the panels.

[Naptown]

Well if have you have panels without a way to totally disconnect their power leads then set a fire and you will see for yourself. There has been more than one occasion that someone got shocked by solar panels due to the lack of a disconnecting means. It is now a code requirement.

The issue is the panels are on the roof. Disconnect must be accessible (near the meter)
Fire department shows up and turns off the disconnect. Now DC power is off to the inverter but is still alive and well on the roof from the panels to the disconnect. the only way to turn off the voltage would be to either cover them or short the entire array out which would drop the voltage to 0
However the fire department isn't going to do that.

[SunEagle]

I am trying to envision firefighters climbing onto two story snow and ice covered roof with fire coming out of it and fire axing up to 40 solar panels before the roof caves in and they all parish.

Well if have you have panels without a way to totally disconnect their power leads then set a fire and you will see for yourself. There has been more than one occasion that someone got shocked by solar panels due to the lack of a disconnecting means. It is now a code requirement.

[rick1]

No they do not. They have fire axes, and one of the first things they do when they pull up to a house fire with solar panels is smash every solar panel with a fire axe. It is the only way to turn them off.

I am trying to envision firefighters climbing onto two story snow and ice covered roof with fire coming out of it and fire axing up to 40 solar panels before the roof caves in and they all parish.

[Sunking]

The FD doesn't have bolt cutters on the truck?

No they do not. They have fire axes, and one of the first things they do when they pull up to a house fire with solar panels is smash every solar panel with a fire axe. It is the only way to turn them off.

[russ]

The FD doesn't have bolt cutters on the truck?

[Naptown]

Actually the FD pulls the meter. Most main disconnects are located inside.

[Dakota]

Yes, you could put a padalock on that, but I don't that would be a good idea.
That is the Main Breaker for all the power to the entire site. With a fire in the
home, the first thing the Fire Dept will want to do is close that Breaker and cut
all power so they can chop and saw without risk.

I agree that the Utility wanting another AC Disconnect for the inverter input
is some what redundant, but it does give them the option to lockout the inverter feed
without putting the entire site in the dark.

Yes that will work and since the breaker is next to the meter the backfed breaker should also serve as the utility disconnect. Question is about the panel is the cover lockable?
Remember to feed the solar into the panel at the opposite end of the panel from the main breaker and label accordingly.

[Naptown]

Yep, the label is still on the backside of the enclosure door and specs the
225 Amp bus bars. I also went to Siemens web site and printed out all
the specs on that model.
Good that will get passed the inspector

I'm not sure I am getting across how the power is coming in here.
I have an underground service that of course first feeds a meter on the back of
a detached garage. From the meter enclosure it feeds, right next to it, this
Siemens Outdoor Circuit panel which has only one the one 200 Amp breaker
in it.
This feeds, right next to it a large Midwest Terminal or junction box
and the main power lines to my house, over a 100 feet away, are
attached to the lugs in this enclosure and then go underground.

Seeing as I will have the AC disconnect right next to this terminal box,
the simplest way is to just feed directly out of the disconnect into
these same lugs which do have empty spots available.

Yes that will work and since the breaker is next to the meter the backfed breaker should also serve as the utility disconnect. Question is about the panel is the cover lockable?
Remember to feed the solar into the panel at the opposite end of the panel from the main breaker and label accordingly.

[Dakota]

Yep, the label is still on the backside of the enclosure door and specs the
225 Amp bus bars. I also went to Siemens web site and printed out all
the specs on that model.

I'm not sure I am getting across how the power is coming in here.
I have an underground service that of course first feeds a meter on the back of
a detached garage. From the meter enclosure it feeds, right next to it, this
Siemens Outdoor Circuit panel which has only one the one 200 Amp breaker
in it.
This feeds, right next to it a large Midwest Terminal or junction box
and the main power lines to my house, over a 100 feet away, are
attached to the lugs in this enclosure and then go underground.

Seeing as I will have the AC disconnect right next to this terminal box,
the simplest way is to just feed directly out of the disconnect into
these same lugs which do have empty spots available.

[Naptown]

No, that should meet the NEC 120% rule --- that Siemens #WB2225 Outdoor
Circuit Breaker Enclosure has a 225 AMP Bus rating, so 225A X 1.2 = 270 Amps
and with a 200 AMP breaker installed could go to a 70 A OCPD.

The inverter has a Max continuous rating of 47.5 Amps so should be OK with
60 amp fuses.

I'm still a little uncertain if it's kosher to back feed thru that fusible AC disconnect
because I can't find any examples of doing that. I can't see a problem with that
method as long as the Utility is on the Line input and the inverter on the Load terminal
so that when the AC Disconnect is in the OFF position the fuse terminals are not hot.

You are correct I forgot about the 200A breaker. Now the trick is to prove it to the AHJ who typically takes one look at the breaker label and goes from there. Are there markings on the panel that specify that the buss bars are rated for 225A?

[Zee]

oh, good you are diligent and checked: yes it is kosher to backfeed both fusible and non-fusible ac discos.
Like ya said: LINE side of disco= utility!
Breakers have rare but real issues with backfed currents as NAPTOWN said very well.

[inetdog]

I'm still a little uncertain if it's kosher to back feed thru that fusible AC disconnect
because I can't find any examples of doing that. I can't see a problem with that
method as long as the Utility is on the Line input and the inverter on the Load terminal
so that when the AC Disconnect is in the OFF position the fuse terminals are not hot.

Where in or outside the panel will you be connecting your fused disconnect? If it is not landing at a breaker in the main panel, then it is necessarily a line side tap.
As long as you follow the conductor size and other limitations for a line side tap, I do not see it being significant whether you use a fused disconnect or a subpanel with a main breaker.

A lot of standard illustrations and guides do not seem to get that when the disconnect is open there is no power on the GTI side.