Surge Protection for Solar and Heat Pumps
Surge Protection for Solar and Heat Pumps
Solar inverters and heat pumps are among the most expensive fixed equipment in a modern home, and both are built around sensitive control electronics.
Quick answer
Solar PV needs protection on both sides: an AC Type 2 SPD at the inverter output or consumer unit, and a DC-rated SPD on the string side. Heat pumps are covered by a Type 2 SPD at the consumer unit feeding them. An AC SPD must never be used on a DC circuit.
Solar PV: two sides, two products
| Side | Where | SPD needed |
|---|---|---|
| AC | Inverter output / consumer unit | AC Type 2 SPD |
| DC | String combiner or inverter DC input | DC-rated SPD, tested to BS EN 61643-31 |
DC and AC surge protection are different product families because DC has no zero crossing to help extinguish the SPD after a surge. That is why DC SPDs are designed and tested separately. See DC surge protection for solar (1000V).
Heat pumps
A heat pump’s control board and inverter are what a surge damages. A Type 2 SPD at the consumer unit feeding the heat pump circuit is the normal arrangement, alongside the RCD type the manufacturer specifies. See heat pump tripping: electrical or heating fault? for how the protective devices interact.
Frequently asked questions
Can I use a normal consumer unit SPD on the DC side of a solar array?
No. AC SPDs are not designed for DC and can fail unsafely. Use a DC-rated SPD tested to the DC standard, rated for the string voltage.
Do I need surge protection on both sides of the inverter?
Both sides are exposed: the AC side to grid surges and the DC side to surges induced in the array and its cabling. Protecting only one leaves the inverter exposed through the other.
Does a heat pump need its own SPD?
It is normally covered by the Type 2 SPD at the consumer unit feeding it. A dedicated protection unit that bundles the SPD with the correct RCD is a convenient way to do this.
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