I'm hooking up a small whole house SPD in a full panel. (SquareD SDSA1175) I figured, throw in a 15A or 20A 2-pole breaker, tighten the clamps, done! Unfortunately, the last spare spaces in this panel were used to install a sub-panel that's about 75' of cable away. Plenty of room on the sub-panel, but I'd prefer to hook up the SPD as close to the service entry point as possible.

SquareD doesn't specify OCP for this unit on their instructions- in fact, they're showing it hardwired to the busses. I'm tempted to just piggy-back it off the 30A 2P dryer breaker. What are the rules for SPDs like this? The breakers are UL E80615, does that allow for 2 wires under the screw?

Steve,
The dryer breaker is an excellent choice. The closer the SPD is to the incoming power and ground connection, the better job it does. Also, a 30 amp breaker tends not to trip as fast if a utility or lightning event happens. All of Square D branch circuit breakers are rated for two wires.

On another note, Hubbell makes an SPD that installs under the electrical meter. The device installs just like the meter, then the meter plugs into it. I have both devices, because the Hubbell has a higher surge and voltage rating, while the panel mounted unit then can handle the rest of the surge that comes through. An SPD is an excellent insurance policy when considering the cost of the newer ranges, microwaves, flat screens etc.

Another good thing to do is to add new copper plated ground rods, if the existing ones are galvanized and are old. Over the years I have replaced rods when people have complained about their well pump or water heater elements burning out prematurely. This tends to happen more often in lightning prone areas.

GE makes one that looks like a two pole breaker just pop it in and go.

That's like $200, though. I picked up this one for $33

Also, it's a Murray panel.

I thought the SDSA series were for branch circuit protection you might want to check your data sheet.

As you are not in Florida, The SDSA is a good choice and to place it with the dryer breaker (or another 2 pole breaker near the incoming leads sounds good to me). I have often seen these right in the lugs with the service conductor which does not appear to be allowed anymore. There are many far better devices, but for more money than I have for such, that have disconnect and overcurrent protection devices built in. The SDSA is not rated for whole house, but is good for this type of application if your lightning exposure level is low.

I have installed a number of these panel protectors and the instructions always say it must be protected by a breaker.
The ones FPL put in the meter base are utility equipment, covered by the NESC but I bet there is some kind of overcurrent protection built into them.
My lightning protection scheme is basically a couple panel protectors, one in the main panel in the garage, one on the house sub panel and point of use protectors on critical equipment.
So far so good and I have had lots of close in strikes including two directly into my weather station mast.
<firmly knocking on wood>

I would go with the others, and connect the SPD to the 30/2.

Square D's type QO and HOM 15 - 30 Amp 2 Pole devices - when used with Copper Conductors, have a rating for (2) #14 - 10 per Lug.

Scott