After reading multiple posts and the Victron Manual on the MP2 of the importance of checking the ground relay box in the MP2 configuration I did so.
Upon powering up the MP2, my 20a house breaker tripped immediately. I wasn’t sure why this was happening so I adjusted my ac in current limit from 20a down to 15a thinking I might have exceeded the current limit.
Powered on again only to have the breaker trip instantly again. I knew I probably had some wiring issues at that point so I throughly checked all my connections and found all okay. After thinking about it I wondered why there was an option to uncheck the ground relay box and did some more research.
I wish Victron and the numerous other posts I’ve read on this would have just included a simple sentence explaining that when connected to a home power source that is already bonded to earth ground, the relay box should be unchecked in the MP2 config. That also means that the ac input to the MP2 should REMAIN connected to the home AC outlet when tesing the inverter for a power outage (open the breaker instead of unplugging from home ac to maintain the physical ground conx).
By unchecking the relay box, one relies on the home wiring to supply the bonded ground and by then unplugging the MP2 from the home ac opens up the possibility of dangerous shock by an ungrounded system (which has been so emphasized for boat and off-grid folks). Bottom line is that I unchecked the box in the MP2 config and the MP2 has been working great without tripping the breaker in the home distribution box (but thankfully it did previously).
Lesson learned: If you’re plugged into a home ac connection, uncheck the MP2 config box unless you want to create problems with a ground loop issue - then don’t operate unplugged after that.
Thanks for your response and yes it could be dangerous, as I described, with an ungrounded MP2 but it is wired to the main distribution box and grounded there with a bonded earth ground. All junction boxes are also grounded and all operational measurements are well within spec. It seems happy and I’ll be doing further testing to make sure it can the loads.
The activation of the protective automation indicates that you have errors in the connection. For stationary installations operating with a connection to GRID, the grounding relay MP2 must not be disconnected. In the inverting mode, MP2 must ground the neutral.
If you have own grounding rod (TT system), you need to make the correct connection.
So lo and behold, after further checking I do have a floating ground but when I enable the MP2 ground relay it immediately trips the main distribution box breaker - I’m thinking due to a ground loop. Several articles I’ve read on the MP2 being fed by residential A/C require it to have the ground relay disabled for just this reason. However that leaves the neutral floating out of AC 1 Out even though the source neutral and ground are still connected back at the distribution panel. So cabinet ground is maintained via the distribution box neutral/ground bonding. I’m wondering if a GFIC outlet for AC 1 out might be in order to protect from shock while keeping the ground relay open? AC 1 is already fused with 30a breaker but won’t protect from shock obviously. The fact that the distribution box breaker trips immediately when the MP2 goes into inverter mode when the ground relay is enabled, but doesn’t trip it when it’s open, seems apparent that it is a ground loop problem that several of these articles have discussed. Any other thoughts on a possible solution? The system is in a closet in the basement and I’m the only one with access. The only device to be powered by it is a 1/2 HP sump pump (10a continous/29a momentary surge).
Stop these experiments and invite a competent specialist. He will check your grounding rod and also make the correct connection. I won’t teach you and tell you what to do. You don’t have the necessary measuring equipment and knowledge for this anyway.
Besides, it’s a big responsibility!
UPD: You are so careless and completely unaware of the dire consequences that could result.
UPD2: I think and insist that this issue should be closed.
This is such a tricky area to provide information about. It is almost in all areas where Victron is sold that this kind of AC work is legally the responsibility of a licensed electrician, and it is illegal for unqualified persons to undertake it.
The extent that Victron has gone to explain how our AC equipment is working in relation to earth fault protection is covered here - 7. Ground, earth and electrical safety
Beyond that there is no scope for discussion on this community. To everyone, if you are in doubt regarding AC wiring please use qualified licensed electrical trades people to test everything is safe.