Entrance cable size

Hi Folks,
I always enjoy reading the message board and I’m amazed at the knowledge here. I have a question in regards to an entrance cable size / breaker size.
The cable coming in said 2 awg and is approximately 3/8". There is a 200amp main disconnect at the bottom of the panel, with the neutral connected but the two hot cables are connected to a 100amp circuit breaker with a sticker stating main breaker. That’s due to the wire size that it can’t be in the 200amp main disconnect? How can I tell if the main service will accept a 200amp panel? The meter has 200CL but the cable size appears lacking.
Any help would be appreciated!
Thanks, Ralph



It appears they are back feeding this panel for use as a 100A panel. Your question is how can you tell if this service can be 200A…that depends on the factors involved.

You have to size based on the weakest link concept, if the conductors coming in are 2 AWG AL or ( even 2 AWG CU ) then based on 310.15(b)(6) of the NEC it can handle 100A…(P.S. # 2 CU can handle 125A respectfully )…but in this case because it is # 2 it can no way handle or be a 200A service and this is probably why they did not use the 200A main breaker in this enclosure.

Check out my video on sizing a service - www.theelectricalguru.com/video.html and it will help you I am sure.

Now on that backfed breaker…make sure it is supported in the box by something OTHER than the standard snap in of the device…it has to be retained by a clip or similar device.

Also…ignore the 200CL on the meter…does not play a role here.

SO…panel is probably rated for 200A, Meter outside is probably rated for 200A, BREAKER being used is rated for 100A and the conductors feeding the panel are rated for 100A…it is a 100A service.

Thanks Paul, That video and the answer to my question is very infomative.
This is an underground entrance cable that has the meter in the basement just above the panel. The disclosure called out a 200amp panel, which it is, but there is only wire service for a 100amp panel. That was my main concern that I wanted to be sure before I labeled it 100amp service in my report.
The 100amp breaker needs a “clip”? Why is that?
Thanks again, not only for the answer but answered in the real time that it was deleivered.

**(F) Back-Fed Devices.

Plug-in-type overcurrent protection
devices or plug-in type-main lug assemblies that are
backfed and used to terminate field-installed ungrounded
supply conductors shall be secured in place by an additional
fastener that requires other than a pull to release the
device from the mounting means on the panel.

There are many reasons for this…but I personally experience one reason alot…the conductors are generally larger like # 2 AWG and so on with these and the breakers snap in but don’t hold real tight sometimes and can pop out or pull loose, they can pull loose enough to offer a poor connection as well which could result in some impedance or resistance ( depending on how you want to look at…you DC Guys out there…:slight_smile: and well…thats one reason…reduce the likelyhood is one.

I guess another would be to reduce the “EASE” of someone removing a 100A and replaceing it with a 125A…BUT we know a screwdriver wont stop them from trying…but it is yet another reason…

Also since it is being used as the main OCPD of the enclosure it should to be fixed…so the retention clip helps handle that…and I am sure others will have many other reasons…and some will say because it is code…in the end all valid points.

however…this panel generally is not designed for being backfed…it has a main breaker provided…so will be interesting to see other comments on the subject.

Just not something i do…i dont mess with backfed options much…Marc might…

Paul, why is it called “back fed”?
Thanks, Ralph

Because generally a breaker is connected to the buss and it is being fed through the BUSS to the point where you make the connections with the conductors…

In a backfed breaker situation you are supplying the power to the termination points on the breaker and it is feeding the enture BUSS itself…turning it into the defacto main breaker…

What is important to note is generally panels should be listed for such use really and retention devices should be used on the backfed breaker…

Here ya go…this may be helpful as well.

**Backfed Breakers

The National Fire Protection Association (NFPA) has
issued an informal opinion (just as good as a formal
one, but you get it quicker and not in writing) that the
backfed circuit breakers used to connect a utilityinteractive
inverter to the load center must be clamped.
“Clamped” means that the individual circuit breaker
must be attached to the load center back plane with a
screw or other device specifically made for the purpose
of preventing the breaker from being inadvertently
pulled loose from the bus bars of the load center. The
screw or other device is supplied by the manufacturer of
the load center. Many load centers have no provisions
for clamping, and therefore are not suitable for


**• Determine whether the existing load center has a kit
that can be used to clamp breakers into position, and
use that kit.

In PV Systems…there are exceptions and so on…but thats a little beyond this subject.

That was my first thought. I would be checking the panel label.

Also, it appears to be a GFCI breaker, which is not too common, but not a problem that I’m aware of. . .

Any panel may be compliantly backfed, as long as there is a hold down accessory or clip used. The lugs on that 200 amp breaker will make real nice “feed through lugs” for a future outbuilding, a subpanel, etc. No UL or NEC or manufacturer prohibition against backfeeding any panel, whether it already has a factory main or not.

From time to time, I’ll backfeed a 200 amp panel on a 100 amp service for the express reason that I want a generously sized panel with lots of “slots”. The “main breaker” or “service disconnect” sticker must absolutely be used on, or very near the backfed main to avoid confusion.

You will notice the only real difference in backfeeding is when this is the service disconnect. You should see a breaker “suitable as service equipment” (or words to that effect) and not a regular branch circuit/feeder breaker. The service rated “disconnect” will usually be twice as big as the branch breaker for a given amp rating. This gives them more rail stabs and a better chance of dealing with available fault current from the utility.
It is probably something you should look at when a a backfed main in a panel is the service disconnect. In a sub panel, even feeding the whole house, you can use a branch/feeder breaker because you are behind the service disconnect.
Example is a service rated 100a SqD breaker is usually 2 wide, 2 high and eats the top 4 slots. The branch circit style in 100a looks like the one for the water heater. (1 wide 2 high)

Not so. For instance, CH 100 amp panels use a regular back fed 100 amp breaker, right from the factory. The Square D catalog table note lists any of their thermal-magnetic breakers as acceptable for use as service disconnecting means when used with hold down kit part number blah, blah, blah. The UL only listed panelboards as being suitable for use as service equipment, and not breakers. The UL White Book has about 6 pages near the end dedicated to the qualifications of a panelboard to be marked as suitable for use as a service disconnect. There are no UL listed breakers that are alone marked as being suitable for use as a service disconnect. When you buy a Square D 100 amp weatherproof outdoor service disconnect can, for instance, you use a regular QO breaker in it with a hold down. The label inside that service disconnect can says “suitable for use as service equipment when used with hold down kit…”.

I suppose I over simplified the question, what is the available fault current from the utility and what is the breaker rating?
Residential 200a drops usually get called 22ka here.
I know I see the bigger breakers around here. Maybe it is because they use the same triplex for 100a as they do 200a and transformers are sized for all electric houses. It could be simply that nobody wants to sign off on <10ka AFC without an engineer.