Single phase transformer

[hp786d]

a single phase step down transformer from 230vac to 110vac, if i have ELCB to protect earth fault at primary side circuit, how can i protect earth fault at secondard side circuit without add on a ELCB

 

[TurbineGen]

I'm not sure what you're asking here. Are you asking what other device you can use? I think you are limited to fuses if you can't use a circuit breaker. Circuit breakers at 110VAC are inexpensive. Why can't you just use one of them?

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If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[PHovnanian]

It might be possible for a voltage sensing ELCB (as opposed to the GFI or RCB current sensing type) to sense a secondary ground fault. If the transformer secondary is grounded to the same system that the primary is and that the ELCB is sensing, a ground fault and subsequent voltage rise should be detectable regardless of whether it is on the primary or secondary system

Is this allowed per code? I don't know, as ELCBs were used in many different jurisdictions and I'm not sure what yours allows.

 

[jghrist]

In the USA, the NEC permits protecting secondary conductors with the primary overcurrent device for a single-phase transformer with a 2-wire secondary. If one end of the secondary winding is earthed, the earth current will be the same as the phase current, so the primary will see the same current (adjusted by the turns ratio). This won't provide sensitive earth fault protection. If the secondary is not earthed, there will be no earth current.

 

[ScottyUK]

Use an RCBO - a combined RCD and MCB in a standard module width. If you have a centre-tapped-earth transformer (55-0-55V) then use a double-pole RCD or RCBO.


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If we learn from our mistakes I'm getting a great education!

 

[waross]

As I read the question, he has ground fault protection on the circuit feeding the transformer secondary.
He wants ground fault protection on the transformer secondary without adding a ground fault p[rotection device on the secondary.
First answer; He can't.
Second answer, if he connects the transformer in a buck configuration the protection on the 230 V circuit will also protect the 110 V circuit.
The transformer must be 230:120 V to get 110 V output. That may be difficult to find, but no more difficult than a 230:110 V transformer. Both configurations can be made, it's just that no-one is making them.

Bill
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"Why not the best?"
Jimmy Carter