We received had a significant weather event here in Texas where I lost a AC Compressor control board, a landscape power supply (literally blew it apart), and some pool equipment. Not sure where the surge came from in this case.

To help avoid this in the future, I have installed a Siemens FS140 SPD in my Main Breaker Panel, which is about 175 ft of cable away from the Meter/service disconnect co-located with the transformer by the street. I have also installed a Intermatic PS3000 SPD at my pool equipment panel.

I have a few questions:

  1. Given the distance from my Main panel to the sub-panel (~75 FT cable), is there any benefit to installing a second SPD at the sub-panel, or should the FS140 provide adequate protection downstream?
  2. Further, is there benefit to adding SPD (AG3000 types) to my compressor cutouts, or does the FS140 protect me there as well?.
  3. Lastly, when the house was built, I have rough-in photos showing the Ufer (lots of rock here in Texas) earth ground line installed into the foundation, and up into the main power panel. Looking in the panel, it’s connected appropriately to the ground bar. There is also a bare copper wire going from the ground bar up into the attic through the framing and over and down to the the entry points for the propane line and the refrigerant lines for the AC compressors (on the outside of the foam insulation). The bare copper for the propane line indeed exists and is bonded to the pipe on the outside wall. For the AC units, on the other hand, I due to not see a bare copper line coming out of the outside wall along with the refrigerant lines. Although there is metal to metal connections of copper refrigerant lines hooked to the AC, wouldn’t this ground line be redundant to the ground wire coming from the power panel that is hooked to ground inside the power cutout and also bonded to the AC metal casing? Wondering if the bare wire is clamped to one of the pipes underneath the insulation, or cut off because it was considered redundant.

I have attached a diagram where I have tried to depict my configuration the best I can.

I’m fine paying more for some additional protection if it indeed has a chance of helping, but would rather save the cost if it not going to do anything.

SRMenter image description here

  • 1
    What is the 75' run from your main panel to the sub panel? Is it underground in conduit? Over the air with wires?
    – SteveSh
    Jun 4, 2023 at 1:07
  • 1
    And why would the main power panel have a floating neutral? I thought neutral and earth ground were supposed to be tied together in the main panel only.
    – SteveSh
    Jun 4, 2023 at 1:09
  • All the equipment you mentioned as being damaged was outside the house (AC compressor, pool equipment, landscape power supply), right? Was anything inside the house damaged, like a TV, refrigerator, computer?
    – SteveSh
    Jun 4, 2023 at 1:42
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    @SteveSh Once you get downstream from a main disconnect everything gets treated as a sub-panel with a floating neutral, even if it's the "main panel". Ground to neutral bonding occurs in the meter/service disconnect. Jun 4, 2023 at 2:25
  • @ George Anderson - Thanks for that clarification. I'm not sure my house with a less than 10 year old meter, disconnect,and main panel is wired that way. There's a 200 A disconnect just behind the meter, both of which are in an attached garage. The cable then runs 30 ft or so into the house and the main panel. I'm 99.9% certain that the neutral and grounds are tied together in that main panel (which I've had that open many times). I've never had the main disconnect opened to see what's behind the breaker.
    – SteveSh
    Jun 4, 2023 at 10:49

2 Answers 2


I lost a AC Compressor control board, a landscape power supply (literally blew it apart), and some pool equipment. Not sure where the surge came from in this case.

That sounds like a Fist Of God event. Given that you have a local transformer so 2400V crossing onto your 120V lines is unlikely,I'd say it was probably a lightning strike on your transformer or the distribution wires to it. Transformer insulation is only so good.

Sending an SPD to fight lightning is like sending Hawkeye to fight Thanos.

Slightly more useful is the modern Eaton multifunction xFCI breakers, which can detect overvoltage and undervoltage and trip for those. Far from a guarantee, though.

  • thanks. My power company's website says their protective measures (lightning arrestors and capacitors) and adherence to state regulations, makes damage to my house contents. That doesn't make me sleep better. They go on to say the only time I should see a surge is if lightning struck between the transformer and my house, but I don't see any physical indication of direct strike that would do this. This did have a Eaton GFCI breaker (White Label) in the panel that was also taken out. Jun 5, 2023 at 13:22

Why Whole Building Surge Protectors Don't Work


It is acknowledged that supplemental lower clamping level point-of-use products (SPDs) are still required to protect sensitive electronics

The Siemens FS1440 brochure states 600v VPR ... "whole house" and branch circuit protectors typically had a very high let-through voltage or VPR (Voltage Protection Rating) of 700 to 1,000V. A 700V VPR is too high to protect sensitive electronic equipment, requiring a lower 330 to 400V VPR point-of-use protection for optimum protection of these sensitive systems.

but for Long Distances- Would additional SPDs help me? yes if you use a type 3 point-of-use surge protection device. Would make sense for AC control board not so much for inexpensive landscape light box. SPD's do work, if installed properly at the proper locations.

your comment: My power company's website says their protective measures (lightning arrestors and capacitors) and adherence to state regulations, makes damage to my house contents.

if that wasn't a typo, and i interpret it correctly, that's largely correct the utility company cannot protect your home electronics from surge (to do so they would have to protect/prevent above ~300v. Not realistic, they protect the grid in the voltage neighborhood of 7200v and above (maybe 2400 idk). So do they "make damage to your house contents" no, better wording would be they cannot prevent [any] damage {down at your 240v level}. Post a link to that website if you can with that wording.

Intermatic AG3000: VPR = 700v. Not likely to save your AC control board, but I suppose it would work if you get them to honor their claimed Connected Equipment Warranty 3yr $7500 https://www.intermatic.com/Product/AG3000?setcontextlanguagecode=en

  • Here’s their condensed language: external power surge could cause damage to electronics, appliances, and even wiring, but are unlikely due to to precautions taken by PEC. We safeguard our voltage by adhering to statewide standards and installing protective equipment, such as lightning arresters and capacitors. The only time you would experience a power surge is if lightning struck between the transformer and your house. To protect from this, equip your home with a whole-house surge protector. Be sure to look for one with a low voltage protection rating (VPR), ideally no higher than 600-volts. Jul 6, 2023 at 17:54
  • that website wording I agree with and is worded well. Your wording of makes damage to my house contents is not present there, and the only place I see that is your comment below.
    – ron
    Jul 6, 2023 at 18:15

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