Hi.
I'm Amy Beaudet from the altE Store.
Thank you for watching our video series, we've broken it down into multiple parts to keep
it manageable.
This video is called "Solar Electric Components, Over Current Protection".
If you missed our earlier videos, I recommend you go back and watch the previous ones in
the series to get a good foundation.
We've gone over some more of the main components in a solar electric system; now let's talk
about some of the less glamorous devices, the ones that make everything work together
smoothly.
In this video we'll cover breakers and fuses, and some of the enclosures they go into.
Let's start with Over Current Protection, or OCP, One of the most important components
in a solar system is the Over Current Protection, the fuses and the breakers.
The key to a safely installed system is to plan for the unexpected, and have the system
automatically turn itself off if something goes wrong.
A fuse or breaker is required on every segment of the system, protecting the wire between
devices.
A breaker has several advantages over a fuse; the breaker can also be used as a disconnect
to turn off that segment.
A fuse cannot be inserted or removed under load, so you need a way to turn off the current
before removing or installing a fuse.
And, as you know, a fuse is a one time use device, once it blows, you need to replace
it, whereas a breaker can just be reset once the problem has been resolved.
However, fuses are usually less expensive than breakers, and generally available in
higher voltage ranges, which make them common in Grid tied systems.
But remember the fuse also needs a fuse holder, which can add to the expense.
In this battery based schematic, you see the DC breakers in the combiner box where multiple
strings are being wired in parallel, the breakers at the input and output of the charge controller,
and at the input of the inverter.
The are then AC breakers at the AC input and output of the inverter, and generator, if
used.
When selecting the breakers or fuses for your system, in addition to selecting the right
amps, be sure to check the maximum voltage they are rated for, and if they are for AC,
DC, or both.
Most DC breakers are rated for up to 150VDC, so grid tied systems that have the DC input
up to 600V, or even 1000VDC, need to use fuses, or specialty high voltage breakers.
The National Electric Code requires you oversize any OCP by 25% if it will be running for more
than 3 hours, which the solar system will.
Also, the breakers before the charge controller need to be oversized an additional 25% for
instances when the sun is shining brighter than the standard test condition, called over-irradiance.
So if your string is outputting 10 amps, you would need a breaker that can handle 15.6A,
so probably round up to a 20A breaker.
A ground fault is when there is current flowing through the grounding wire of a system, which
is a bad thing.
This is usually the result of the positive wire accidentally shorting with a grounded
component.
This is commonly caused during installation, when pulling the wire through the conduit
and accidentally scraping off the insulation, causing the positive wire to touch the grounded
metal conduit.
Believe it or not, another common cause can be from squirrels chewing on the delicious
insulation on the wires on the back of the panels, causing the positive wire to touch
the grounded frame or racking.
The National Electric Code requires that any PV system, with 2 exceptions, is required
to have a Ground fault protection device, or GFPD.
The 2 exceptions are off-grid instances where chances of fire are low.
1st, a ground or pole mounted system that is isolated from any building, and has up
to two parallel strings, for instance a stand alone water pumping system.
2nd, installs for "non-dwellings", where the grounding wire is doubled in size to handle
any extra current.
So as you can see, most installs require GFP.
The good news is that all grid-tied inverters and some MPPT charge controllers, such as
Midnite's Classic and Schneider's XW, have GFP built in.
So you only need to have a separate GFP device if you are using a PWM charge controller,
or an MPPT that doesn't have it built in, like Outback's or Blue Sky's.
Check your charge controller manual to determine if a GFP Device is needed.
Note that if you have a charge controller that has it built in, when you are using multiple
charge controllers in your system, you need to disable all but one of them, only 1 GFP
can be used per system.
Check the manual on how to disable the GFP on your device.
The GFP works by having multiple breakers combined.
One is between ground and negative, and the other is in the positive line of the circuit.
If more than � an amp is detected between negative and ground, the small breaker trips
and also trips the larger breaker that is in the positive line.
If you have multiple devices in the system that require GFP, for instance if you have
2 charge controllers that do not have integrated GFP, you would use a dual GFP that has one
ground/negative connection, but multiple positive connections, one for each charge controller.
Now let's go over the different breaker boxes commonly used in a PV system.
The combiner box is generally installed outside, near the solar panels.
They provide a way to bring each string to its own breaker or fuse, and then combine
the outputs of the strings in parallel.
You can then exit the combiner box with wire in conduit, protecting the wire as it travels
back to inside the building to the grid-tied inverter or charge controller.
An additional feature is available that allows you to throw a switch at the array, turning
off the DC power coming out of the panels.
Also, some have the ability to have a remote switch that is installed at the service entry
point of the building, allowing firefighters to turn off the power from the array at the
same location that they are turning off the grid power to the house.
States enforcing NEC 2014's Rapid Shutdown are requiring this capability to protect firefighters.
The combiner box is also a nice place to put a lightning arrestor, as it is generally at
the location in the system that would be most susceptible to lightning strikes.
The DC Load Center is generally installed in a battery based system inside near the
batteries, charge controller, and inverter.
There are several different models available from different manufacturers, but they all
usually contain the breakers from the PV array, the GFPD, if needed, the breakers between
the charge controller and battery bank, and the big breaker between the inverter and the
battery bank.
The AC Load Center provides a place to put your AC breakers in a battery based system.
You can't just use your Mains breaker box for the output of a battery based inverter,
as anything in the main box will be shut off when the grid is down.
Having a separate AC breaker box allows you to isolate the AC output and power your critical
AC loads from the batteries through your inverter.
It also provides a location to wire in an optional generator, if it is needed to supplement
your solar when there is not enough sunshine.
Bypass breakers allow you to remove the inverter from your system and power your loads from
an alternate AC source, like the grid or a generator.
This is useful if you need to take the inverter out for maintenance.
If you are doing a straight grid-tied system, a separate AC breaker box is not usually needed,
you would just add a 2-pole AC breaker for the inverter output to your Mains breaker
box.
To determine the size of that breaker, divide the wattage output of the inverter by the
AC voltage, generally 240V in North America, and multiply by 1.25 to oversize by 25% as
required by NEC.
For instance, a 5000W 240V inverter would need at least a 26A breaker, rounded up to
30A.
A Critical loads panel is used in a grid-tied battery backup system.
It's just a regular AC breaker box that is separate from the mains breaker box.
When the grid is up, the inverter is connected to both the mains box and the critical loads
panel, power is going to both.
But when the grid goes out, the inverter disconnects from the mains box, and only powers items
wired to the critical loads panel, like your fridge and well pump, getting its power from
the batteries.
Items not considered critical, and therefore not connected to the critical load panel,
like your hot tub, will be off until the grid comes back.
An ePanel or Power Distribution Panel holds both the DC and AC breakers in one box.
It makes for a clean install with all of the breakers in one place, and some of the sections
may be prewired from the manufacturer, saving time during the install.
It is usually one ePanel per inverter.
A battery based Inverter Power Panel is a prewired system complete with inverter, charge
controller, and breaker boxes, with all of the required breakers installed.
They make installing the system a snap, just hang it on a wall and connect it to the solar
input, battery bank, and AC input and output.
Hopefully this helped clear up some of the different over current protection requirements
and enclosures.
Check out our website for a great selection of breakers and load centers, as well as most
of the other BoS equipment needed to install your solar system.
Also watch more of our Video Series on our web site.
We've got a team of highly trained Technical Sales Reps available to help you plan your
system, give us a call.
And don't forget to check out the rest of our site at altestore.com, where we are making
renewable, doable.