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SAFE DEAD WORK

• “SAFE DEAD WORK”………….. What is this?

• There are two practical options…..

• NRS 097-2-1 compliance (switch off and break before you make)

• What is the Dead Grid Safety Lock?

• How does the Dead Grid Safety Lock work?

• Is installation net-energy throttling functions as a safety feature?

Electrical Installation Regulations

Point of

Supply

Point of

Control

Two Points of Supply

Utility

Point of

Supply

EG

Point of

Supply

LV Dead - Safe Work Practice

• Identify circuit

• Open circuit

• Isolate circuit

• Tag circuit

• Lock out circuit

• ( DO NOT USE EARTHING & BONDING )

• Test at location

• Work

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Locked Out and Tagged

Typical LV Locking and Tagging Equipment

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Test to Proof Voltage = 0 Volt = Safe

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Single Customers per MV-LV Transformer

• Employ standard LV safe procedure as given above:

• I.e. Isolation of the installation

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Multi-Customer LV Networks

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Complex and Impossible to

Employ the normal safe work

procedure

Typical Over Head LV Networks

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Where are the EG ?

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The only feasible Approach:

Secure - Automated

Safety Systems

How do we automate this?

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Contactor

C

NO

With the Utility side dead, a live EG cannot feed

power back

Simple example of one embodiment of the

principle.

UTILITY

NETWORK

CUSTOMER

INSTALLATION

Automated LV Safe Work Practice

• Normal upstream safety procedure

• Test at location + Automated Dead-Grid Lock

• Work

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Dead-Grid Lock

The Purpose of the DEAD-GRID LOCK is to ensure that power cannot flow back from a EG once a utility worker has proofed that this part of the LV network is safe to work on.

It relies on the EG to power down automatically when the utility power fails. ( Anti-islanding and out of bounds requirements)

Dead-Grid Lock

If this does not happen, the safe work procedure will detect the condition and further steps is to be taken to make the installation safe.

The sole purpose of this device is to secure that once the network is proven to be safe to work on- that it remains so, regardless of any actions or failure of equipment during this time on the EG’s side.

Test to Proof Voltage = 0 Volt

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The Critical Step : Test – once dead AND Utility supply locked

out –The automatic Dead Grid Safety Lock

ensures safety from the EG’s side.

Cable to EG

On / Off

AC

Disconnector

Dead-Grid Safety-Lock

Dead-Grid Safety-Lock

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8.9 kVA

On

PF .98

DC side

Arresters

PV

Str

ing

In

sta

llati

on

Main DB

Connection

Inverter

DGSL Installation on a PV Inverter

Safe Even when it is DEAD

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LV Live - Safe Work Practice

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Multi customer feeder -Minimum Safety Requirements

MAIN DB

POS

POC

Locked in

Grid-Tied-Mode

EG - DB

PE PE

Structural lighting

protection and

bonding of PV

panels