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iDNO Transformer LV ACB Trip Unit

Steven Dwight

Hi,

I'm being asked by the iDNO whether we require a trip running from the transformer mounted ACB into our LV switch room, as the iDNO are providing a 2100A metering cubicle we are providing has no trip or isolation facility.

Our new main LV panel is located within a remote GRP enclosure adjacent a new ASHP compound. Within the GRP enclosure the iDNO will be providing the above 2100A Schneider link cubicle.

My query is that under emergency conditions, I.E. the fire officer needing to isolate the supply to site, is isolating the main incomer on our main panel sufficient to satisfy EWR with regards to cutting the supply to site? In this scenario the 2100A Schneider cubicle would be still live.

To isolate the supply to the 2100A Schneider cubicle, we would require the trip to isolate back at the TX LV ACB.

The only time I have experienced TX LV ACB trips is on privately owned HV networks, where onsite engineering team have specially trained operatives that hold HV working permits, therefore can access the TX and associated LV ACB to reset is required and when safe.

I've always understood that isolating the supply at source, essentially the supply side of the main incomer is sufficient to satisfy EWR. A trip to the DNO ACB would require the local network engineer to be called out to reset their ACB, which isn't ideal for the client.

We have specified the main LV panel incomer to have micrologic 5 intelligence, which I'm being advised could negate the need for the trip, though the ownness for the decision for omitting TX LV ACB trip is being pushed onto me, the LV designer.

In summary there are two questions:-

1.0 - Is isolating the panel at the incomer, leaving the 2100A cubicle live, safe isolation for emergency purposes under the electricity at work regulations.

2.0 - If the answer to 1.0 is 'No'; then surely the client needs to be part of this decision and made aware that under the emergency conditions, that to re-energise the supply to site, they will need to contact the DNO to visit site and reset the TX ACB.

Thoughts on this would be appreciated.

Steve

 

  

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    Hello Steve, I think you need a safe means of isolating the supply (so that the outgoing terminals of the metering equipment are dead) that can safely be operated locally under fault or emergency conditions.  In addition, if you have access to the 'cubicle' you would also need a means of isolating that.  These could be the same. The LV breaker trip is fine for emergency use but not really practical for maintainance or routine use as you would need IDNO to reset it.  You might well find that NGED have provided an emergency disconnection arrangement for their equipment that feeds the Idno.  Worth a look, if need be you may be able to negotiate use of that.

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    Hello Steve, I think you need a safe means of isolating the supply (so that the outgoing terminals of the metering equipment are dead) that can safely be operated locally under fault or emergency conditions.  In addition, if you have access to the 'cubicle' you would also need a means of isolating that.  These could be the same. The LV breaker trip is fine for emergency use but not really practical for maintainance or routine use as you would need IDNO to reset it.  You might well find that NGED have provided an emergency disconnection arrangement for their equipment that feeds the Idno.  Worth a look, if need be you may be able to negotiate use of that.

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