1. PV Array DC Isolator Rating
This presentation is about making sure you have the correct rated DC isolators for your PV system

2. 5033 has these requirements for switch disconnectors
Not polarity sensitive
1.25 × ISC ARRAY or the PCE backfeed current whichever is greater
Certified to IEC 60947
Interrupt all live conductors simultaneously
5033 has these requirements for switch disconnectors
polarised switchgear cannot be used
Be rated to 1.25 X Isc of the array
Look for IEC certification for the specific device. You need to ask your wholesaler or equipment supplier for this.
If you need to have two devices (one pos one neg) they need to mechanically linked to operate simultaneously
Clause (a) – Polarity
Clause IEC 60947
Clause (d) – Simultaneously

3. Transformer Based Isolator Voltage Rating
Array connected to isolated (Transformer Based) inverter
5033 now more specifically defines voltage ratings for switch gear. This is covered in appendix B.
Going to start with the easy one.
With transformer based inverters
When an earth fault occurs both poles of the isolator share the array voltage. Therefore both poles together must be rated to the PV array max voltage.
In this example <CLICK> this is equivalent to 2 poles in series.

4. Know Your Isolator Ratings
You can use the whole device rating for systems connected to a transformer based inverter
As you can see in this example the whole device is rated at its full current right up to 1200V.
Therefore if you are using this isolator with a transformer based inverter you could use it with an array of up to 25A remembering that we need the isolator to be rated to 1.25 X array current.(as 25 X 1.25= 31.25A)

5. Transformer Based Isolator Voltage Rating
4 pole device, one array to one inverter.
4 poles in series rating used
To expand on this further:
A lot of isolators have 4 pole (2 in positive and 2 in negative)
When a transformer based inverter is isolated with a 4 pole device then the 4 pole rating is to be used
Appendix B2 (a) – Isolated

6. Transformer Based Isolator Voltage Rating
4 pole device, two arrays to an inverter.
2 poles in series rating must be used
If a transformer based inverter with 2 arrays is being isolated by a 4 pole isolator then the 2 poles in series rating must be used. <CLICK>
Notice how the current handling capability of the isolator is reduced as the voltage goes up.
Appendix B2 (a) – Isolated

7. Transformer-less Based Isolator Voltage Rating
Array connected to non-isolated (Transformerless) inverter
Array connected to non-isolated (transformerless) inverter
This is a bit more complex. In this example one pole of the isolator may be required to break the whole array voltage and current.

8. Transformer-less Based Isolator Voltage Rating
Array connected to non-isolated (Transformerless) inverter
The reason that one pole may need to switch the full voltage and current is due to the fact that:
if there is an earth fault DC may flow <CLICK>
through the earth fault,
Back to the MEN point,
Then back trough the inverter.
I don’t know a lot about the technicalities of how a TL inverter works but some may have a connection from the DC to the neutral at some point.
Therefore as in this example one pole may be carrying the full array voltage and current.

9. Know Your Isolator Ratings
Must know the rating per pole (per side, per leg)
It is not as easy as a transformer based system,
you need to know what the rating is per pole or number of poles in the positive and negitive leg of the array.
This is sometimes call rating per side or per leg

10. Know Your Isolator Ratings
Cannot use the whole device rating
As per the example with a transformer based inverter where an array is connected to the inverter via a 4 pole isolator we need to use the 2 poles in series rating.
@ 600V the rating is the same. But:
As you can see in this example as the Voltage goes up the amount of current the device can handle is reduced.

11. Using one isolator for 2 arrays
500V = 13A
13A / 1.25 = 10.4A
In this example we have two arrays connected to one inverter.
Therefore we must use the 1 pole rating <CLICK>. As you can see from both these specs as the voltage increases there is a substantial drop in the amount of current the isolator is rated for.
So if you have two arrays with a PV array max voltage of 500Vdc the isolator is only rated at 13A <CLICK>
Remember that the current rating must be 1.25X Isc <CLICK>
So the array’s short circuit current cannot be greater than 10.4A

12. Arrays that are functionally earth
See AS/NZS 5033 Appendix B
Functionally earth system is different to the earthing of metal parts of the panels.
It is where one leg of the PV array is reference to earth:
for example some thin film modules need to have the negative of the array referenced to earth
If you are doing these types of system you need to look at 5033 appendix B as there are different ways that this earth referencing can be done

13. First you need to know whether your inverter has a transformer or not
Summary
Know the topology of the inverter (TL or not)
Know the PV Array Max Voltage of the array
Know the Short Circuit current of the array
Know the isolator ratings
In summary there are 4 things you need to know to ensure your isolator rating is suitable
First you need to know whether your inverter has a transformer or not
Next you need to know what the PV Array Max Voltage of the array
Also what the Short Circuit current of the array
Finally what the isolator ratings are at a per pole or leg level
At the end of the day, as is the case with any other electrical installation, it is the licenced person responsibility to ensure that all equipment is correctly rated.

14. Thank You
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Thanks.