Surge protector

Thanks for the info.  That makes sense.  I'm running my T1's as rear surrounds and have them on a small APC surge protector.  My front end electronics are on a Furman Elite 20, but my front T Ref's and power amps are just into the wall.  Maybe I need to rethink things.  I'm in Vegas.  We don't get many thunder storms, but do get a few.  I've never had a destructive power surge so far, but......

Sense about the function of fuses.

Sounds like a cord and plug Type 3 SPD will do little, if anything, for protecting audio equipment from a high voltage transient event if the branch circuit wiring is less than 30ft long.

Well, that sure explains why Wirecutter’s testing with 5kV is useless... (not).

Based on other readings in the NEC, my understanding is that when the NEC includes minimum wiring distance as important they are considering the total amp interrupt rating. That is, if a short should occur, will it cause too much current for the upstream breakers. They are not making a statement about the effectiveness of the surge protector. They are saying you should keep it far enough away to ensure when the protector does work it won’t overload the breakers.

In the case of SMP devices, this is not an issue as they block current instead of encouraging it as MOV’s do.

Again, if you are questioning the effectiveness of Furman devices, I encourage you to read the full Wirecutter article and their testing methods. There’s no bone in that soup to pick.

So, I asked Pi.ai for a little help in reading, and Pi brought up 3 points worth discussing:

Type 3 Surge Protection Devices (SPDs) are typically installed at a distance of at least 10 meters (33 feet) from the main electrical panel or power distribution board for a few reasons:

1. To allow for proper voltage clamping: Installing the SPD at a certain distance from the panel allows it to effectively clamp down the overvoltage surge before it reaches the equipment being protected. This distance ensures that the SPD has enough time to react to the surge and divert it to ground safely.
2. To avoid potential damage to the electrical panel: If an SPD is installed too close to the electrical panel, there’s a risk that the surge energy diverted to ground by the SPD could damage the panel itself or the wiring connected to it.
3. To reduce the risk of interference: By keeping the SPD at a safe distance from the electrical panel, it minimizes the potential for electromagnetic interference (EMI) or other types of interference that could negatively impact the performance of nearby electrical equipment.

It’s been a really confusing read since some type 3 devices are permanently installed, and others are plug and cord.

If you use any series mode protection (Furman SMP, Brickwall or Zerosurge) these three points are moot. The low pass filter they incorporate (aka wave shaping filter) slows the super-fast rise time of a surge and reduces current flow due to the surge, and gives the surge protector enough time to disconnect if needed.

In essence the 10m requirement uses the wiring in the building as a RL low pass filter to ensure MOV’s downstream have time to react and won’t actually stress the AIR (Amp Interrupt Rating) of upstream breakers (kind of what I mentioned). However, series mode protective devices ARE RL filters (more L than R).

Other devices which are not strictly series mode like older Panamax may also include enough wave shaping to let the MOVs do their job.  It's not exactly guaranteed, but you can't really get to very low let through voltages without some sort of wave shaping/filtering in place because MOVs alone can't clamp low enough and fast enough to keep the let through voltages down.