has anybody here installed a TVSS?

[kwilcox]

I just finished installing a TVSS (whole house surge protector) in my electrical panel and have been researching these on some of the electrical contractor forums. Mine is an APC PMP1X. here's a shot of this device in my panel:

(the TVSS is the white box on the right side).

Anyway, there are many posts on the contractor forums which state that these devices are pretty much useless unless the lead length is kept to 6" or less. I've shortened mine up as much as possible, but I still have a 9" lead length. APC states that the leads should be kept "as short as possible" and that the device should be connected to a 30Amp double pole breaker "as close to the main disconnect as possible". However, the device also has a green ground connected wire which means that my combined lead length has to be longer than 12" (since this device protects L-L and L-G) simply because my ground bus is on the opposite side of the panel from my line entry point.

Has anybody here either installed or had one of these devices installed? Because we run lots of expensive HA gear I would assume these devices are pretty familiar to posters here. How have you set up yours? Is my installation useless because my L-L leads are 9" long?

 

[Digger]

I can understand keeping the lead length to a minimum and having the 30 A breaker closest to the main breaker so the TVSS has time to react BEFORE damage is done. I have one installed outside of my CB Box (it was provided with a nipple to attach to a conduit knockout). My lead length is also greater than 6 inches. I think that would be more of a concern for the Neutral and hot leads than the gnd. Since once the transient hits the TVSS unit it will send it to gnd.

It looks like you have some rust on the bottom of your CB Box. Is that corrected now? Thats one of the last things you wat is moisture in a box.

 

[upstatemike]

I have a square-D whole house surge protector that replaces a double breaker so the only lead is the neutral. I put it in the bottom slot next to the neutral/ground bus so the lead is only about 4 inches long.

It looks like you have a Square-D panel, is there some reason you didn't use their surge unit?

 

[Smarty]

UpstateMike,

I was looking at the Square-D products page
Square-D

and didn't find what you were referring to. Since I an just starting to build, I was hoping to borrow a good idea.

 

[upstatemike]

UpstateMike,

I was looking at the Square-D products page
Square-D

and didn't find what you were referring to. Since I an just starting to build, I was hoping to borrow a good idea.

Got mine at a local home store. The manual says it is a QO2175SB SURGEBREAKER Surge Protective Device.

***EDIT***

Looks like the 6th item down on your square-d page.

 

[Smarty]

Super...Thanks!

 

[kwilcox]

...It looks like you have some rust on the bottom of your CB Box. Is that corrected now? Thats one of the last things you wat is moisture in a box.

Yeah, the basement wall leaked badly before I bought the house. Its repair was a sale contingency. The entire foundation on three sides was dug up, drain tiles repaired and the walls straightened and re-sealed. The box along with the rest of the basement is dry now but it must've been quite the concern when the wall leaked

One of these days I'll clean it up with some naval jelly...

 

[kwilcox]

I have a square-D whole house surge protector that replaces a double breaker so the only lead is the neutral. I put it in the bottom slot next to the neutral/ground bus so the lead is only about 4 inches long.

It looks like you have a Square-D panel, is there some reason you didn't use their surge unit?

Well, I've always used APC for UPS applications and to tell the truth, I didn't even know that Square D even made such a device. The APC PMP1X is pretty nice though. It has a reaction time of 1ns and a UL 1449 SVR rating of 400V. Here's a quote from the electrican gurus on what this rating means:

"The Suppressed Voltage Rating (SVR) is a value that is assigned to an SPD by UL to indicate its protective characteristics. Each mode of the SPD is subjected to three impulses of a 1.2/50ms, 6kV voltage waveform and an 8/20ms, 500A current waveform. The resultant “measured limiting voltage†is measured at the ends of 6†leads extending from the terminals of an integrated product or 6†extending from the enclosure of a wall-mounted SPD." (how 'bout that for gobbledy-gook eh? :blink

Supposedly 320V is optimum and 400V is about as good as a MOV only TVSS can do. Like the Square D device, it can handle 600 Joules of surge energy.

That square D device looks pretty nice though. It's reaction time is somewhat slower and I couldn't find its SVR rating in the literature anywhere but it should be quite good given its L-L lead length which is essentially zero. Installation is a "snap" too I'll bet... (pun intended).

Edit: something else I wanted to mention. My panel is a split-bus design with circuits 1-12 on the supply side and circuits 13-20 on the load side of a 50A cutoff breaker which itself resides in slots 1&3. What this means is that there is no "main breaker" in my panel. Slots 1-12 are always energized (yikes!). Back in the day, this POS design was intended to allow major appliances to be placed on the top part and branch lighting circuits on the bottom. My panel is compliant due to the "6 disconnect" rule which allows mains disconnection with "6 hand movements".

Now since the NEC states that a TVSS must be installed on the load side of a panel mounted OCPD then I don't think I'd be compliant installing the Square D device in positions 1-12 even though it has its own internal protection fuses.

As you can see from the pic, its pretty crowded in slots 13-20 with split single pole 15A breakers being pretty much the norm. I'd have never been able to make 2 slots available on the "load" side of this panel and besides, putting it down there would lower its effectiveness for the circuits connected in the first 12 slots. Therefore, the TVSS I installed is on the supply side, but is compliant because the 30A double pole breaker it's connected to is actually one of the 6 disconnects required to de-energize the panel.