Question on Conductor Grounding on EG4 8k Solar Mini Split

[TricityWuf]

I've been running our EG4 solar mini split for a couple weeks now on temporary solar power, (+ and - ungrounded)
But the PV system im designing will have a grounded conductor (negative grounded).
I've tried looking through the manual but haven't found anything relateing to that.
Anyone know if it will work fine on a grounded negative system?

 

[timselectric]

I've been running our EG4 solar mini split for a couple weeks now on temporary solar power, (+ and - ungrounded)
But the PV system im designing will have a grounded conductor (negative grounded).
I've tried looking through the manual but haven't found anything relateing to that.
Anyone know if it will work fine on a grounded negative system?

I wouldn't recommend it.
I'm sure that it wasn't designed for it.
It should be grounded to the existing grounding system.
Why do you want to ground your DC negative?

 

[TricityWuf]

I wouldn't recommend it.
I'm sure that it wasn't designed for it.
It should be grounded to the existing grounding system.
Why do you want to ground your DC negative?

Mainly the MPPT I've got has a common negative. And also it's not a big system, 150~voc and about 10a at mpp. Very limited amount of roof space so the batteries and mini split have to be on the one same PV string.

 

[TricityWuf]

I wouldn't recommend it.
I'm sure that it wasn't designed for it.
It should be grounded to the existing grounding system.
Why do you want to ground your DC negative?

Also to clarify im not talking grounded like a vehicle 12v system.
The wires would be the ungrounded live conductor (positive), a grounded neutral conductor (negative), and then the equipment ground conductor. Just like a regular AC system or older PV systems.

 

[timselectric]

so the batteries and mini split have to be on the one same PV string.

That won't work. The two MPPT's will fight for control over the circuit.
And neither will produce very well.

Also to clarify im not talking grounded like a vehicle 12v system.

That is exactly what you are describing.

Just like a regular AC system

Not quite.

or older PV systems.

Newer systems are not designed this way.

Mainly the MPPT I've got has a common negative.

This is normal. But has nothing to do with grounding.
Unless you are building a mobile application. And connecting to the existing DC system. Then it's hard to avoid.
I assume that your mini split also has an AC feed. And this is the only grounding that should be connected to it.

 

[TricityWuf]

That won't work. The two MPPT's will fight for control over the circuit.
And neither will produce very well.

I was wanting to try, since it's two unalike mppts one with an operating voltage a lot lower than the mini split mppt. Figured it might reach a equilibrium around the min volt of the mini split mppt since the battery mppt can pull lower than the mini split. And I would rather the batteries have priority over the mini split anyways.
Not sure if it'll work but I'll find out lol

That is exactly what you are describing.

Its not what I mean, in the NEC a grounded conductor is any current carrying conductor that has a bond to the grounding conductor. Eg a neutral in a normal AC system.
There will be no current flowing through grounding conductor. I just don't want my batteries and 48v equipment that are somewhat in the open to have a negative connected to a 150v system without any ground bond on that negative. If there was a L-G fault on the PV side that would energize the negative of the batteries and other 48v equipment to the negative PV voltage without causing any fault current to shunt the voltage/trip a breaker, the only notice of the fault would be if you probed from the negative to ground.

A summery of the wires going to the mini split:
Green, grounding conductor.
White, 120vac grounded conductor.
Black, 120vac ungrounded conductor.
White marked with black, PV grounded conductor (negative).
Red, PV ungrounded conductor (positive).

I also mesured voltages on the PV input to the mini split while it was running, and I didn't see any voltage to anywhere. Unlike my EG4 48-3000 that has a transient voltage around 300vdc from either + or - terminal to a ground refrence.

 

[timselectric]

If there was a L-G fault on the PV side that would energize the negative of the batteries and other 48v equipment to the negative PV voltage without causing any fault current to shunt the voltage/trip a breaker,

It won't trip any breaker. PV panels are current limiting.
Connecting one side to ground just increases your chances of getting shocked. By exposing half of the circuit to everything that you can touch.

I also mesured voltages on the PV input to the mini split while it was running, and I didn't see any voltage to anywhere.

You will if you bond the negative.
Which could damage the mini splits MPPT.

 

[timselectric]

Not sure if it'll work but I'll find out lol

Hopefully it doesn't cost you much.

 

[zanydroid]

I’m not going to touch the mixing of grounded and ungrounded PV ?

What is the min operating voltage of the Minisplit MPPT? If they fight down to something below the voltage where the mini split’s DC DC converter can do useful work then the minisplit will get nothing.

My guess is the minisplit has to have a buck/boost MPPT to be able to convert to the inverter drive’s voltage so there’s a good chance for an overlap band between the two.