Okay, let's analyze the best options for installing a Ditek 120/240 SPD to protect both your heat pump and hot tub, given your panel configuration and limitations.

Understanding the Goal

The goal of an SPD is to divert surge current away from sensitive equipment. Ideally, you want to install it as close to the protected equipment as possible, but also at a point where it can effectively protect both the hot tub and heat pump. The lower the impedance between the SPD and the equipment it's protecting, the better it can do its job.

Analysis of Options (in order of best to worst viable)


1) On the 80A Circuit Breaker at the Main Panel



(Best Overall and Viable) Why it's good

This is the best approach if technically feasible. By placing the SPD at the main panel, you're providing surge protection for the entire subpanel. This inherently protects both the hot tub and heat pump.

Considerations



Space

Make absolutely certain there's physical space in the main panel to install the SPD, its wiring, and to connect it to the 80A breaker terminals. Crowding can lead to overheating and safety hazards.

Wiring Run

Keep the wiring between the SPD and the breaker as short as possible. Longer wires add impedance, reducing the effectiveness of the SPD. Use the recommended wire gauge for the SPD.

Grounding

A good, low-impedance ground is crucial. Make sure the SPD is properly grounded to the main panel's ground bus.

Assuming feasibility, this is the recommended option. It provides the widest protection.2. 2) Directly on the Hot Tub



(Viable) Why it's potentially okay

Installing the SPD directly on the hot tub offers the best protection for the hot tub and likely will protect the heat pump to some extent.

Considerations



Code Compliance

Make sure you meet all electrical code requirements for installing the SPD within or near the hot tub.

Physical Space

Ensure there's adequate space within the hot tub's control panel or near it to accommodate the SPD.

Environmental Considerations

Hot tubs can be a humid and corrosive environment. Choose an SPD rated for outdoor use and ensure its connections are well-protected.

Wiring

Keep wiring runs short.

Grounding

The hot tub's grounding is critical. Make sure the SPD is securely connected to the hot tub's grounding system. This is a good option if putting it at the main panel is not feasible.3.

3) On the 50A GFCI Breaker in the Subpanel



(Viable, but Less Ideal) Why it's not as good as #1

While it's convenient (since the hot tub is already on a GFCI), it only directly protects the hot tub. The heat pump's protection relies on the subpanel's wiring and any potential let-through voltage of the 50A breaker on the heat pump.

Why it's not as good as #2

SPD may not be installed correctly within the subpanel

Considerations



GFCI Compatibility

Ensure the SPD is compatible with GFCI breakers. Some SPDs can cause nuisance tripping of GFCIs. The SPD should be connected downstream of the GFCI.4.

4) On the 50A Heat Pump Breaker in the Subpanel



(Less Ideal) Why it's not ideal

Similar to option #3, this only directly protects the heat pump. The hot tub's protection relies on the subpanel wiring.

Considerations

All the same considerations as #3 apply, just with the hot tub being the less-protected device.5.

5) Directly on the Heat Pump



(Least Desirable) Why it's the least desirable

You only protect the heat pump, and the hot tub is relying on the subpanel wiring to mitigate surges.

Considerations

All the same considerations as #2 apply, with the heat pump in place of the hot tub.

Important Considerations for ALL Options



Professional Installation

Have a qualified electrician install the SPD. Electrical work involving panels and breakers can be dangerous and must be done to code.

SPD Specifications

Ensure the SPD's specifications (voltage rating, surge current capacity, etc.) are appropriate for your electrical system and the types of surges you might experience. A higher surge current rating is generally better.

SPD Monitoring

Consider an SPD with status indication (lights or remote monitoring) so you can tell if it's still functioning properly.

Coordination

Consult with a qualified electrician or electrical engineer to ensure the chosen SPD is properly coordinated with your existing electrical system and grounding.

In summary


Best (and Recommended if Feasible)

Install the SPD at the main panel, feeding off the 80A breaker.2.

Second Best

Install the SPD directly on the hot tub.3.

Viable

Install the SPD at the 50A GFCI breaker in the subpanel (only protects hot tub) or the 50A heat pump breaker (only protects heat pump).4.

Least Desirable: Install the SPD directly on the heat pump.The best decision depends on the physical constraints of your panels, your budget, and the risk tolerance for each piece of equipment. A professional assessment is highly recommended. Good luck! Flag for review