SPD Location

[Seven-Delta-FortyOne]

Because I don’t understand completely how they work, I have this question

SPDs are wired in parallel, but is it required that power “pass” the SPD in order for it to function?

What got me thinking about this is an install on a system with an ATS that feeds several downstream panels.

If in place it at the main, obviously it will be offline when on gen power.

If I put it on the “load“ terminals of the ATS, will it protect the ATS itself, both on utility and gen power? Or would this require 2 SPDs, one on the main breaker, and one on the generator breaker?

Its a type 1 SPD any the way, so it can go on a 200A main.

 

[jim dungar]

Yes the SPD is in parallel, but anything upstream from it may not be protected.
Very, very, very simply; Surge currents do not appear at all parallel points simultaneously. The impedance of the conductive path to the SPD may slow down its response enough that a lower impedance parallel path see the surge first.

 

[Seven-Delta-FortyOne]

It seems an SPD installed on an ATS may or may not protect the internal components of the ATS.

 

[jim dungar]

It seems an SPD installed on an ATS may or may not protect the internal components of the ATS.

Unless there is a near lightning strike between the generator and the ATS, you may not need to worry about the generator side.
My preference is to put the SPD as close to the wire entrance to the building as possible. This might mean an SPD at the normal source panel and a separate SPD on the backup side of the ATS.

 

[hillbilly1]

Surges usually come through the poco side, but I actually had one on a brand new service I put in. Lightning hit an abandoned utility pole, (nothing at all on it other than the GEC) jumped to an outbuilding, popped through the concrete slab, hit a couple of extension cords laying on the slab, ran into the house disintegrating the gfi and box on the side of the house, blew the spd and the poco transformer. Only electrical damage at the house other than gfi, drop cords and the spd, was two mini splits. Don’t know if the spd reduced the amount of damage.

 

[Seven-Delta-FortyOne]

Around here, we get some nasty surges when the power fails. I’ve had the SPDs blow, and actually blow doors on panels open and the SPD pop off the bus bar, when a tree fell on the 12kV lines and caused a phase to phase fault.

When it goes back on, poco has recommended that people wait a few minutes before powering up their house, just to let the dirty power through.

I put the SPDs at the main panel, but I was thinking about the possibility of having a surge from the genset, when it powers on the house, and for example, the residents had been using large amounts of power when utility failed.

I admit that’s a rare scenario. But if one were to attempt to protect against that, I suppose a second SPD at the gen would be the solution.

 

[hillbilly1]

Sags are usually the biggest problem with generators, SPD’s don’t do anything for that. Surges are usually cut short by the over speed function of the generator, but a SPD on that side never hurts.