Online assistance for electrical trade people in New Zealand and Australia Login  |  Register  |   Forgot Password
Assistance for electrical trade people




Click here to send Forum Admin a pdf document for publication on this Topic

Documents must be less than 200k in pdf format

Posted By Topic: Solar AC isolator

Aug 27 2019 07:00

Is it correct that you don't need an AC isolator for the inverter, if the inverter is mounted next to the switchboard? Within 3m?

Aug 27 2019 10:48

You alwsys need an AC isolator on the interface between the switchboard and the grid connect inverter, it provides an incoming supply (inverter input/output) isolation point.

In some cases the use of an MCB is required for overcurrent protection of the interface cabling. The MCB is capable of providing the isolation function required.

Figure 7.5 AS/NZS 3000:2007 is correct and is copied from AS/NZS 4777.1 which details the requirements of the inverter installation.

Aug 27 2019 17:48

Thanks Pluto for showing me where to look.
Would you agree then that the isolating switch alongside the inverter is not required if the following are meet.

-That the inverter is mounted directly along side the switchboard having a cable route not exceeding 3m (note 2).
-That the main switch isolator in the switchboard is visable from the inverter location (note 2), I am assuming that having to open the switchboard door is not considered a barrier.
-That the inverter supply main switch within the switchboard is an MCB rated to protect the current rating of the cable between switchboard and inverter (note 1).
-That the the main supply switch (MCB) is lockable (note 3)

I like the idea of a separate isolator and will always prefer this setup, but it is a question that has come up that I would like clarification on going forward.


Aug 27 2019 17:51

And to confirm also the last note. Is an MCB that can have a lock out tag attached considered the correct form of lockable?

Aug 27 2019 21:46

Many MCBs have available a locking device able to lock an MCB in the off position.

If the MCB installed has one of the matching MCB locking device available and correctly fitted, it can be considered to be lockable in the Off position when fitted with a small padlock to prevent easy removal of the device.

Aug 28 2019 09:33

Fig 7.5 in 3000 is "Typical" and therefore while a useful reference it does not - cannot - set any requirements.

Using the cited edition of 4777.1; clause 5.3.3 requires an isolator for the a.c. input from an inverter to an installation switchboard.This reflects "3000" clause which requires a "main switch" for EVERY supply into an installation.

There are NO exception in either document.
So Pluto's answer, that an isolator is always required, is correct.

The 3m you refer to presumably comes from 5.3.5 about overcurrent protection for inverter output not being required if inverter is in close proximity to the switchboard it supplies.

You can't apply an exception from one rule rules to a different rule. So the option of omitting overcurrent protection (available if certain conditions are net) can't be applied to the requirement for isolation.