Transcript Principles of Electrical Safety

Electrical Safety
Mark Gough
Electrical Inspector
Northern Specialist Group
Topics Covered
Duties of Inspector
 Generation
 Distribution
 Case Studies

Duties

LEGAL prevent danger to your self and
others affected by your undertaking.
Recent case inspection company fined £200 000 and
possible manslaughter charge


Moral to ensure safety Fairground
Operators and members of public
Economic Comprehensive inspection and
testing is a skilled job and takes time.
FFI, loss business you and operator, PN’s IN’s Fines, court
costs etc all uninsurable
Fairground Generation
Brown Phase
Generator
or
transformer
400V
Black Phase
230V
400V
Star Point
400V
230V
Grey Phase
230V
Neutral
Earth (Circuit Protective Conductor)
Note 5 conductors
Essential
Generators with 4 conductors
Oooerr!
230 V
50 Hz
If you touch the ride with fault and adjacent metalwork what will
happen
Protection against Indirect Contact
Aaagghhh!
230 V
50 Hz
Current flows from the supply, through the fault, through her
and back to the supply via earth.
If you add an earth conductor 5 wire
system
Fuse
230 V
50 Hz
Protective Conductor
What happens when I introduce the same type of fault as before?
Protection against Indirect Contact
Fuse
230 V
50 Hz
Protective Conductor
It’s determined by the voltage and the ‘Earth Fault Loop Impedance’ –
a very important system parameter. If it’s too high not enough
current will flow to blow the fuse quickly enough to prevent danger.
Protection against Indirect Contact
Not Again!!
Fuse
230 V
50 Hz
Here the fairground owner has joined the neutral and earth.
What Would happen?
Protection against Indirect Contact
Fuse
Oh for
Goodness
Sake!!
230 V
50 Hz
Here the return is damaged The exposed metal work of the ride
could become live. If the return is damaged
Protection against Indirect Contact
Fuse
230 V
50 Hz
Protective Conductor
Now let’s introduce a ‘bonding’ conductor that connects the
exposed metalwork together.
Protection against Indirect Contact
This is clever
stuff. I wish
I could be an
Electrical
Engineer.
Fuse
230 V
50 Hz
Protective Conductor
We have here the concept of Earthed Equipotential and Automatic
Disconnection of Supply (EEBADS) – the fundamental safety system
in the UK for protection against indirect contact electric shock.
At Generators

Check 5 conductors (no more or less)

Do an earth loop impedance test or earth
to neutral continuity

Fused correctly working 100mA RCD?

Earth spike? Preferable not as important
as earth neutral continuity test
What can be done including 30mA RCD
Distribution
30mA RCD sockets and
lighting
 Suitable plugs
 Short runs
 Damaged Cables
 Overloaded Circuits

Recap
Generators 5 core AND earth
neutral continuity (ELI test)
 100mA RCD time delayed
 Final circuits 30mA RCD
 BSEN 603092 plugs / sockets
 Encourage use of plug in
testers

Competence Costs
BUT
Incompetence Costs
More