5 KVA inverters in parallel

[ians]

Thanks to the half job of the solar installer (still waiting for his COC ... I doubt that I will ever see one) ... no indicator lights for the inverter output part of the DB and no labelling ... you can buy a indicator light which is a volt meter ... so rather than installing indicator lights ... the plan is to install round panel volt meter ... which will not only indicate that the inverter is on ... it will also indicate the voltage.

[Justloadit]

Thanks to the half job of the solar installer (still waiting for his COC ... I doubt that I will ever see one) ... no indicator lights for the inverter output part of the DB and no labelling ... you can buy a indicator light which is a volt meter ... so rather than installing indicator lights ... the plan is to install round panel volt meter ... which will not only indicate that the inverter is on ... it will also indicate the voltage.

You can even get one which shows Volts and Amps. Note this only works for AC.

I have made for DC PV measurement, but requires a switch mode PSU, which can work from 20V to 160V DC to be able to handle all types of installations, and also have the capability to measure up to 100Amps.
It is also nice to know what your panels are doing. It has MC4 in and out to make installation a lot easier. However I see many of the installations, there are no MC4 terminations into the inverters. I could make a modification and use terminals for connections, but now need a larger enclosure.

Sure many of the inverters have displays for all this, but you require to scroll through menus. I have found that after a few days the users forget the manner to scroll and find the info they want.
Sometimes a good old fashioned Volt/Ammeter is much easier.

[ians]

Time to start installing isolators ... mcb's and wiring.

So no earth leakage protection on the supply side.

3 x 5 kva off grid (using as a UPS for load shedding ...no solar panels)

The question:

From the meter 80 amps (25 mm wire) to an 80 amp double pole isolator ... 16 mm wire from the bottom of the isolator to the top of 3 x 25 amp single pole mcbs (bridged with a bussbar at the top) and a neutral bar.

From the bottom of the 25 amp sinlge pole mcb's ... 4 or 6 mm wire (all the ame length) to each the inverter input.

Option 1

From each inverter output using 4 or 6 mm wire to a bussbar ... then to a douple pole isolator (this step might not be required because of the changeover switch being an isolator) ... then to the changeover switch ? or

Option 2

From each inverter output to the top of 3 x single pole 25 amp breakers ... bridged with a bussbar at the bottom of each breaker ... to the changeover switch

Out the changeover smitch to the main DB using 25 mm wire (its a long run ... hence the 25 mm wire)

[Justloadit]

I would feel that option 2 is the better bet.
In the case that any servicing is required on one Inverter, you can safely isolate it from the system while working, no output - in feed from the bus bar.

[ians]

I Found this in a document from Victron.

"To safeguard against this issue, it is recommended to use long AC, cables of similar length. Always follow the
recommended cable lengths and thicknesses as listed in the product manual. Do not increase the cross-section
of the AC cabling more than is recommended in the manual!"


"AC fusing parallel strings
For units in parallel it is advised to use one AC fuse for all units on that phase. Both on the input, and on the
output. Multiple fuses which are mechanically connected are okay to be used, this is counted as one fuse"

[ians]

"AC fusing parallel strings
For units in parallel it is advised to use one AC fuse for all units on that phase. Both on the input, and on the
output. Multiple fuses which are mechanically connected are okay to be used, this is counted as one fuse"

If 3 x 5 kva units in parallel are used ... consideration if the units are 4000w (17 amps) or 5000w (21 amps) units

If I understand this correctly ...

Either 1 x single 50(4000 w) /60 (5000w) amp circuit breaker must be used wired from the breaker to the first unit looped to the second and then the third.

or

1 x triple pole 32/40 circuit breaker ... wired using 4mm or 6 mm wire ...each wire from the breaker to the inverter.

The apext installer manual (5 kva) recommends using 10 mm square wire (but that would be if you use 1 x circuit breaker.)

[ians]

"To safeguard against this issue, it is recommended to use long AC, cables of similar length. Always follow the
recommended cable lengths and thicknesses as listed in the product manual. Do not increase the cross-section
of the AC cabling more than is recommended in the manual!"

Taking this information into consideration ...

I would think going with a 32 amp triple pole mcb using 4 mm wire ... 3 wires from the bottom of the triple pole breaker to each inverter ... would be a better option due to a higher wire resistance.

[GCE]

"Multiple fuses which are mechanically connected are okay to be used, this is counted as one fuse"

)

I read it as meaning a T/Pole circuit breaker would be seen as one unit as you can isolate the output /input with one switch .
At least that way you prevent any back feed if one unit goes faulty
With fuses you would pop the one on the fault and the other 2 inverters would still supply power

[ians]

This happened many years ago when I started installing generators ... just not enough valauable information ... a few calls to the technical department ... a few visits to various sites and a new chapter in the SANS book was created ... maybe it is that time again or I should just buy the new ed 3 and all the information and drawings required to create a legal installation with a bunch of inverters in parallel.

[ians]

Looking at some skteches ... the inverter output to a triple pole breaker with a bridge piece at the bottom seems pointless.

It would be better to take the 3 wires from the inverter output to a bussbar (or just connect all three wires into the top of the breaker ...then a 16 mm wire from the bussbar to the top of a 60 amp D curve breaker ... from there to the DB main switch.