Instruction: Evaluate the answerability of a question by analyzing the related document, outputting yes if the document contains information addressing the question, and no otherwise.

Input:
Question: do i need it for each panel or just the main panel?
Document: Easy to install. You must add a 20 amp double pole circuit breaker to you circuit breaker panel. If your panel is inclosed in a wall you may need to cut into the wall to install as it should be flush to the panel. Only 4 wires to connect. If main circuit breaker is in the same panel, ground and netural can be connected together.
You can find detailed installation instructions on the Leviton website if you need to assess the complexity of installing before buying.Just note that this protector does not come with the four wires required to connect it to the main panel. It needs two black wires (one for each of the two hot electric busses), one white one (for the neutral connection) and one green (for the ground connection). You can use any cable or wires with a minimum of 12 gauge if connected to a 20 amp breaker.
Do I wish i received 100% payment for my loss, of course! However, they could have easily tested the unit and denied any malfunction of the unit and paid me nothing. So in the end, I would have to say that I do recommend this unit and that is why i am changing my rating to 2 stars. I still stand by original recommendation, that even with this unit attached to your main service, you still need surge protectors for every single thing you plug into an outlet!
I would have given it 5 stars if there hadn't been a mistake in the instructions. (I know! I know! REAL men don't read instructions!! What could possibly have come over me?!!! Hopefully they won't revoke my guy card for that one minor infraction!) The instructions call for 3/4" conduit between the box and the main panel. In reality, the knockouts are sized for 1/2" conduit.
As beefy as this unit "appears" in the photo, it is clearly labeled INDOOR USE ONLY. I confirmed this with Leviton support. If you are unfamiliar with NEMA ratings (as I am) and you need an outdoor unit, this one is not for you. The description should clarify that this is for indoor use only.
Hopefully in the event of a surge, the Leviton 51120-1 Surge Protector breakers are among the first breakers to see the surge. I installed a total of three Leviton 51120-1 Surge Protectors, 2 for both main boxes on the house and 1 on the main box for our outbuilding. I ordered one additional Leviton 51120-1 Surge Protector for our Emergency Circuit Main Box which is powered (at times) by a standby emergency generator when we lose local service.
I won't actually know, of course, how well it works until we experience another voltage spike (our last one cost us over $2500 in damaged circuits) but I very much like the size of the unit and it's easy installation. The warranty that comes with this surge protector is comforting to have. Hopefully I'll not need it either.
The Leviton 51120-1 Surge Protector installation was fairly easy to install. Fortunately, there were additional empty spaces within each electrical main box to add two additional 20 amp breakers so the surge protectors could be on their own breakers. I did shuffle a few of the existing circuit breakers so the surge protector breakers were the top breakers on one side of each main. The basement is unfinished so installation was much easier for the first two surge protectors. The third was installed in an outbuilding with plywood interior walls.
I live in area with frequent power outages when the Thunderstorms roll in in the spring. After our last brown out followed by a power surge, I said enough already and purchased this item. This is a whole house surge protector (it will do nothing in a brown out) The item is well made of solid metal and has two green lights on the front to tell you its working. If these lights ever go out, it has taken a surge and will need to be completely replaced.
There are 5/8" knockouts on all sides of the box.Needless to say, if you are not comfortable messing around inside a breaker panel, hire a licensed electrician to install this.
Answer: yes