DIY Doctor

Earth leakage trips when the power restores

Postby russell-sa » Sun Oct 19, 2008 8:00 am

I have a 3 phase residential installation with 9 DB boards. Each DB is fed from a central bus-bar and the earth is ankored thoughout.

Each time the utility supply company fails the power, on restoring, nearly all the DB boards earth leakages trip? This requires a manual restore for each DB board.

I suspect that the surge of power on restoring the supply causes the earth leakages to register the required 30mA to fail, so I was wondering if anyone had any ideas on what can be done to avoid this.

I had considered finding a product to delay the power restore to each DB, and rather have them restore at uneven intervals. This would avoid a sudden power draw to all the DB's at the same time which may be affecting the inbalance being detected by the earth leakages on each DB.

- The phases are generally balanced, but it does depend on what is
operating at the time of the failures / restore of power.
- The earth is bonded as required by the utility
- All the DB's are extremely stable outside of this one issue
- Lightning / surge protection has been installed - test has been conducted
without the surge protection with same results

Does anyone know of a DIN mountable product that can be added to assist / avoid this problem, or any other possible fix from this trying anomily.
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Simply Build It

Postby ericmark » Sun Oct 19, 2008 1:33 pm

I did have a similar fault on a couple of sites. Our cure was molded breakers and external current transformers with a little unit where both trip current and time could be set on two pots.
With construction sites and 30ma, 100ma, 300ma, and 500ma trips even with the S type delayed trips it would not trip in right order and only molded breakers seemed to work.
Last site we used Vigi units which added on to a MCB and converted them into RCBO these seemed to work well.
I think there are different methods used to measure the earth leakage I know some will work with DC injection and others will not. Also some makes seem better than others there are even auto reset types now.
I would invite one of the suppliers to site and ask for their recommendations I would think Teleme. etc will have something to do the job.

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