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Posted By Topic: Generator

Grant777
Apr 13 2018 22:25

Hi guys
I went to connect a generator to a fixed installation today
After doing tests on the generator my results were
228 v between P+E . 120 v between P+E And 120v between N+E with load test between N+E It had a RCBO on generator and 2 pole 16 amp circuit breaker the generator is from the USA am I right in believing they have made this a two phase supply with actually no neutral or am I missing something

   

Grant777
Apr 13 2018 22:55

Sorry 228 between phase and Neutral
   

ppaw1965
Apr 14 2018 00:53

Its configured as a 220V single phase center tapped Earth for operation the fault protection. It's a generic setup that can also be used for 110V by changing the internal wiring configuration.
In the USA could also be used for 220V 2 Phase if reconfigured.
look for a thread.
Jonobang74
Feb 14 2017 19:07
This covers what your asking about
The link may work

https://www.electricalforum.co.nz/index.php?action=more_detais&id=1487052429
   

AlecK
Apr 14 2018 07:14

While commonly called single phase, this centre-tapped configuration is actually 2 phase with the phases at 180 degrees.
Very common for small portable gensets.
Connecting one to an installation will, not end well; as the MEN link will effectively short pone half of the winding. In many cases there is no overcurrent protection on the 2nd phase, and the result can be a fire. But in your case the RCBO should avoid that outcome.

You won't be able to test that RCBO with your RCD tester, because of the lower voltage between phase & earth.

What you need for supply to an installation is a genset with an "isolated" (from earth) output.
   

evanh
Apr 14 2018 12:46

Disconnecting the centre tap from the earth wire, allowing the generator windings to float, would make it work on NZ single-phase circuit.


   

Sarmajor
Apr 14 2018 16:53

That would work but the RCBO wouldn’t work unless you earthed one of the winding ends (N by definition) because without an earth reference leakage current has no where to go. It will be hard to achieve sufficient imbalance to make the RCBO operate.

Depending on the generator the over current section of the RCBO may not operate.
This is because in the event of a fault of negligible impedance between Phase and Neutral the output of the generator may be insufficient to cause enough current to flow to get the magnetic trip to operate.
The generator motor may stall in this case.
Don’t ask me how I know this🤓🤓 but it is fairly dramatic when it happens.

Better to get a more suitable generator.
   

pluto
Apr 14 2018 19:57

Sarmajor Apr 14 2018 16:53

Your comment 1
That would work but the RCBO wouldn’t work unless you earthed one of the winding ends (N by definition) because without an earth reference leakage current has no where to go. It will be hard to achieve sufficient imbalance to make the RCBO operate.

Depending on the generator the over current section of the RCBO may not operate.
This is because in the event of a fault of negligible impedance between Phase and Neutral the output of the generator may be insufficient to cause enough current to flow to get the magnetic trip to operate.
The generator motor may stall in this case.
Don’t ask me how I know this🤓🤓 but it is fairly dramatic when it happens.

My comment 1

If an RCBO is fitted and used to supply an electrical instalation as an alternative supply, the RCBO would trip and be unable to be reset due to MEN link in the electrical installation, so that is why you find the reference to isolated output when connected to an electrical installation in AS/NZS 3010.

If you use a type B MCB there is a higher chance of the MCB tripping under short circuit conditions.

AS/NZS 3010 allows for gensets up to 15 kVA to be stalled under overload conditions. In many cases the output voltage also drops under short circuit conditions which results in NO usable power output being available.