E Loop and inverters

**Die sparky** · 15-Nov-23, 10:32 AM

I imagne the inverter he is testing is a 5kw?

**GCE** · 15-Nov-23, 11:19 AM

Originally Posted by Die sparky

The AC passthrough is 70 amps but can the inverter deliver 70 amps in island mode? Would have to be one hell of a inverter so perhaps 4.6 ohm is correct for the inverter?

Valid point

Think we are over thinking

Dylboy is taking readings in island mode which would mean sizing the output CB of the inverter but we have all been thinking back to incoming CB
The incoming readings under the incoming CB , being 70Amps, would need to be tested to determine the size for that CB

Will let Dylboy confirm my thought process .

**Justloadit** · 15-Nov-23, 12:17 PM

A point to remember here. All inverters have a built in Electronic over current detection. Trying to size a CB after the inverter in my opinion is fruitless, as it will trigger long before any circuit breaker will even experience an over current, and in my opinion is merely a circuit isolator more than a circuit breaker.
In the case that the electronics fails with in the inverter, it in most cases will be a short circuit.
2 things may happen, either the incoming supply circuit will trip due to the short within the inverter, or the ELU may trip due to their being an earth fault due to the failure.
In the case that there is a failure in the battery circuit, then the in line battery protection fuse nay blow, alternatively if it is a Lithium then the BMS will disconnect the battery from the battery line.

**Derlyn** · 15-Nov-23, 12:36 PM

Interesting thread, brothers.

So basically, it's pointless having a passthrough capability of 70A when the inverter can only deliver say 20A in islanding mode.

Am I correct in saying that the essential load must be selected so that it should not exceed the islanding mode capability of the inverter ?
ie. Forget about what the pass through capability is when deciding on the essential load.

**Justloadit** · 15-Nov-23, 02:40 PM

Originally Posted by Derlyn

Interesting thread, brothers.

So basically, it's pointless having a passthrough capability of 70A when the inverter can only deliver say 20A in islanding mode.

Am I correct in saying that the essential load must be selected so that it should not exceed the islanding mode capability of the inverter ?
ie. Forget about what the pass through capability is when deciding on the essential load.

I would say yes, as there is a relay in the unit which is probably the rating of the inverter. Exceeding the inverter current would probably trip the inverter even in pass through mode, as I have had my inverter bleeping when power through the inverter starts nearing the inverter capacity

**GCE** · 15-Nov-23, 02:53 PM

Originally Posted by Derlyn

Interesting thread, brothers.

So basically, it's pointless having a passthrough capability of 70A when the inverter can only deliver say 20A in islanding mode.

Am I correct in saying that the essential load must be selected so that it should not exceed the islanding mode capability of the inverter ?
ie. Forget about what the pass through capability is when deciding on the essential load.

Yip - I agree with Justloadit

Problem is contractors/installers are using bypss current in the design when placing complete houses on inverters and telling owners to switch appliances off and limit load just before loadshedding starts .

In the real world that is never really successful and they all forget the unknown power outage that happens , besides the fact that regulations do not allow it .

**Die sparky** · 15-Nov-23, 03:07 PM

Originally Posted by Justloadit

A point to remember here. All inverters have a built in Electronic over current detection. Trying to size a CB after the inverter in my opinion is fruitless, as it will trigger long before any circuit breaker will even experience an over current, and in my opinion is merely a circuit isolator more than a circuit breaker.
In the case that the electronics fails with in the inverter, it in most cases will be a short circuit.
2 things may happen, either the incoming supply circuit will trip due to the short within the inverter, or the ELU may trip due to their being an earth fault due to the failure.
In the case that there is a failure in the battery circuit, then the in line battery protection fuse nay blow, alternatively if it is a Lithium then the BMS will disconnect the battery from the battery line.

Would still be nice to see a circuit breaker and a fuse though.

**Die sparky** · 15-Nov-23, 03:15 PM

Wow pvc conduit bends so much nicer if you dont bend it over the knee. Just grab it like big motorcycle handles and bend it. Also nothing makes my loose my cool more than when the wires to a socket is way too short and when the back box is like 100mm away from the socket😡

**Derlyn** · 16-Nov-23, 02:05 PM

Originally Posted by GCE

Yip - I agree with Justloadit

Problem is contractors/installers are using bypss current in the design when placing complete houses on inverters and telling owners to switch appliances off and limit load just before loadshedding starts .

In the real world that is never really successful and they all forget the unknown power outage that happens , besides the fact that regulations do not allow it .

Just a question regarding your statement about regulations not allowing it.

All I can find is in 7.12.2.4 that states that there must be an automatic disconnecting device should the capacity of the alternate supply be exceeded.
I take it that the circuit breaker on the output of the inverter will suffice.
Am I missing something else in the regs ?

**GCE** · 17-Nov-23, 08:44 AM

In my opinion a circuit breaker installed after the inverter/alternative supply is already a given under 16.6.1 for isolation and also under 6.7 , protection

What I read in this particular reg is that the supply is not overloaded causing a change in voltage or frequency outside of normal.
That the parts of the installation that may cause an overload are automatically disconnected before any fault/tripping can occur - On bigger installations we use contactors or motorized CB to take out aircons , refrigeration so as not to overload the generator .

Coming back to a domestic install with an inverter you would need to ensure that either the essential D/Board is sized correctly for the inverter or if you feeding the complete installation that the higher loads are dropped out with a contactor automatically so that you are not relying on homeowner to run around and make sure heaters , dishwashers , geyser , stove etc are switched off before load shedding so as not to overload the inverter.
If you rely on homeowner to drop the loads , what happens in an unexpected power outage ? it will trip the unit and the chance of voltage dropping out of spec first is high.
Bear in mind that this reg also stands on 800Kva alternative supplies that could take awhile to trip the CB

In short - overload protection is a given this is on top of the overload protection.

7.12.2.4 Where the alternative supply is intended to provide a supply to an
installation that is not connected to the main supply, or to provide a supply as
a switched alternative to the main supply, the capacity and operating
characteristics of the alternative supply shall be such that danger or damage
to equipment does not arise after the connection or disconnection of any
intended load as a result of the deviation of the voltage or frequency from the
standard range. Means shall be provided to automatically disconnect such
parts of the installation, as may be necessary if the capacity of the alternative
supply is exceeded.