E Loop and inverters

[Dylboy]

Hello

So I did an E loop of an inverter in island mode, got 2.60 ohms. So that means the current which will flow on an Earth fault is 88 amps.

The out out breaker of the inverter is a 50amp and wired 10mm.

But now this 2.60ohms and the current of 88A will not be enough to trip the output CB of the inverter....

But..... The pass through of the inverter is 50Amps... So if I de rate the output CB to a 40A (so double the rates current trips the main breaker ) we are now loosing 10Amps worth of pass through current...

So what can be done ? Sure the inverter has its own protection of short circuit and overload but the output CB is not good ?



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[Derlyn]

Hello

So I did an E loop of an inverter in island mode, got 2.60 ohms. So that means the current which will flow on an Earth fault is 88 amps.

The out out breaker of the inverter is a 50amp and wired 10mm.

But now this 2.60ohms and the current of 88A will not be enough to trip the output CB of the inverter....

But..... The pass through of the inverter is 50Amps... So if I de rate the output CB to a 40A (so double the rates current trips the main breaker ) we are now loosing 10Amps worth of pass through current...

So what can be done ? Sure the inverter has its own protection of short circuit and overload but the output CB is not good ?



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I don't think the problem lies with the breaker, so changing it is not solving the problem.
The problem is that the earth loop impedance is too high. That's the problem that needs sorting.
Maybe bigger earth cabling to bring down that reading.

Have a lekker weekend.

[Dylboy]

Yes ya I thought of that too but it's 6mm earth and the live conductors are 10mm and the neutral earth loop was at 2.30 (somewhere around there )

So it's the actual electronics of things I think dictating the ohms.

Often times I have the same earth loop as well as neutral loop and this is what is bringing up this post as I am at a loss and tried contacting others and their thoughts but to no real avail.

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[Dylboy]

Have a lekker weekend too! Already at the pub to catch up with some mates and then decided to braai some meat later as well. It's Friday nine the less haha.

Also looks like we doing ok in the cricket so that's great and also the Nedbank golf is on.

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[GCE]

I have had this discussion
We also get what we deem to be high but when we calculate it is within spec

Do you have a earth neutral bridge permanent , internal or external relay

Rmax = V /( 2 x rated circuit current )

R max = 230/(2 x 50Amp CB ) = 2.3ohm

This is what you are getting on neutral earth loop

This is where I have a difference of opinion and never quite got to finish the conversation
To do a neutral earth loop you place the earth and neutral lead on the neutral , so basically bridging out your earth neutral test leads .

When testing earth loop on an inverter you are basically at the earth neutral bridge point - Are you not then doing a neutral loop test ?

In my opinion the earth loop impedance should be zero as I am at the star point and I strongly believe that the results being shown by meters on in actual fact neutral earth loop tests

[ACElectric]

Hello

So I did an E loop of an inverter in island mode, got 2.60 ohms. So that means the current which will flow on an Earth fault is 88 amps.

The out out breaker of the inverter is a 50amp and wired 10mm.

But now this 2.60ohms and the current of 88A will not be enough to trip the output CB of the inverter....

But..... The pass through of the inverter is 50Amps... So if I de rate the output CB to a 40A (so double the rates current trips the main breaker ) we are now loosing 10Amps worth of pass through current...

So what can be done ? Sure the inverter has its own protection of short circuit and overload but the output CB is not good ?



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sorry i am with stupid but how will 88 amps NOT trip a 50 amp breaker, is the breaker faulty?

[Derlyn]

Good morning brother.
You are quite correct. 80 amps should trip a 50A breaker, however, when doing a loop test the resistance must be low enough that should an earth fault occur, at least TWICE the current of the protective breaker must flow, therefore ENSURING that the breaker will trip.

8.6.5.1 At the main switch, the impedance shall be such that an earth fault current double the rated current (or
higher) of the main protective device automatically disconnects the supply to the installation.

[ACElectric]

Thank you brothers, what device are these they are mentioning in the next reg?

Reg 8.6.5.2 If, for practical reasons, the requirement in 8.6.5.1 cannot be
complied with, as an alternative, an earth fault detection and disconnecting
device may be installed at the supply to the installation. The earth fault
detection and disconnecting device should be so installed that it operates at
a current related to the earth fault loop impedance which will limit touch
voltages to 25 V under short-circuit fault conditions for a period not
exceeding 5 s

[GCE]

It will be an Adit unit - Basically an overgrown earth leakage unit that works from a CT measuring earth current

Used to be a Bylaw in PE to have fitting on main incomers and then you would set to 10% of current - So a 800Amp supply when you leaked 80Amps to earth it would trip - There are various makes by most CB manufacturers , example link pasted below

https://strike.co.za/wp-content/uploads/sites/71/brochures/ADIT-ECOVER.pdf

[Dylboy]

I always understood it as an Earth leakage device but say rates at 100mA.

So a 100mA would be used if the Earth loop is less than 2300ohms. So that if there's is an Earth fault, i.e a kettle had the line or the neutral touch earth then with the Eloop being less than 2300ohm a current of 100mA will flow thus disconnecting the supply. Sure a kettle is on a 30mA but just an example if it was on a dedicated circuit.



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[Dylboy]

Another case, did the E loop and the N loop of a Victron.

E loop of 4.6ohms
N loop of 4.6 ohms.

This means the resistance of the earth wire was the same as the Neautral thus the same readings.

This gives a fault current of 49.3 Amps (the voltage was 227on the rest instrument)

So now that means the output CB needs to be at minimum a 25Amp CB to satisfy the double the current thing as that allows instant trip. (Depending on the type or curve of the breaker).

But the AC passthrough is 70Amps! So putting a 25A main CB basically renders the inverter useless.

So now what happens when it comes to the CoC when we test the inverter supply ?

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[Dylboy]

Not sure why the meter read 227volts as it is set to 230 output in island mode though. Maybe my meter is weird as often reads different to my other multimeter too

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[ACElectric]

I am not sure but, since it is not practical, as the reg states, it looks like reg 8.6.5.2 must be applied then? Since it is the only "other" alternative without dropping the breaker size.

[Dylboy]

Me too but that to me is neutral loop test. Also inverters have their own inbuilt protection so surely doing a CB for the conductor protection is satisfactory?

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[GCE]

Not sure why the meter read 227volts as it is set to 230 output in island mode though. Maybe my meter is weird as often reads different to my other multimeter too

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If the meter is not true RMS it can struggle to read a modified sine wave and you may find that the sine wave is a bit out -