Which ground?

[zoneblue]

I know that the better and more direct the ground path the better. But Im wanting to mount a SPD on an AC distributon box. Does the SPD ground wire need to connect to the main DC disconnect ground bus, or can i connect it to the AC distribution ground bus. The former would mean extending the green wire. The manual says something to the effect of in some systems the green wire is connected to the neutral in AC systems.

[niel]

if you are talking of the main ac distribution panel and not a sub box, the neutral and ground are bonded together internally there and both are technically going to the main service entrance ground rod. a picky inspector will insist on the ground bus though. the other 2 wires of course are going to the 2 hots. an spd in the main service breaker box is a very good idea to do as it gives some protection from the grid sending surges into the house. now how well the wire lengths fit in your box is a different problem. splicing i wouldn't recommend, but it shouldn't violate any nec rules as this is designed for surges only and not anything to do with normal power distributions. when in doubt you could ask your local inspectors if you have any.

hmmm reading your post again i have to ask, isn't your dc also grounded to the same rod as the ac? they should be intertied even if separate rods so as to make it 1 single grounding point for both. as for the purpose of grounding the spd it doesn't care which ground path it goes through as long as it goes to ground.

[zoneblue]

if you are talking of the main ac distribution panel and not a sub box, the neutral and ground are bonded together internally there and both are technically going to the main service entrance ground rod.

The SPD is to protect the inverter AC out. As i see it i have two choices, i can mount it in the main AC distribution breaker box, between its ground bus and hot. Its ground bus is bonded to neutral, and then runs to the main DC disconnect ground bus, which then runs to the earth stake.

a picky inspector will insist on the ground bus though. the other 2 wires of course are going to the 2 hots. an spd in the main service breaker box is a very good idea to do as it gives some protection from the grid sending surges into the house. now how well the wire lengths fit in your box is a different problem. splicing i wouldn't recommend, but it shouldn't violate any nec rules as this is designed for surges only and not anything to do with normal power distributions. when in doubt you could ask your local inspectors if you have any.

The alternative would be to mount it right on top of the VFX. But that would mean connecting to the inverters AC earth terminal (or its neutral), which ought to be connected to the inverters DC erath terminal,  which is then connected to the DC ground bus.

hmmm reading your post again i have to ask, isn't your dc also grounded to the same rod as the ac? they should be intertied even if separate rods so as to make it 1 single grounding point for both. as for the purpose of grounding the spd it doesn't care which ground path it goes through as long as it goes to ground.

Yes DC neg also ground bonded in the disconnect.  An epanel would make this a heck of a lot more straightforward! Eiither of my proposed solutions involves a daisy chain.