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3.2 Electrical
The power distribution system used must provide adequate protection against excess line current and
leakage currents to earth.
Electrical Characteristics for ONE M8
For large installations, a three-phase supply is recommended and the power from each phase should
be distributed evenly to the single-phase appliance coupler on each panel. The screen may be
conveniently split into sections (e.g. rows or columns), each powered from a single phase.
3.2.1 Circuit Protection
Each section of the screen should be protected by a Circuit Breaker to protect against high fault
currents, and a Residual Current Device (RCD) to detect earth leakage currents.
3.2.2 Earth Leakage Considerations
To reliably operate a LED video screen, the leakage value figure per panel must be known, or if the
leakage value is close to the breaker trip value, the breaker may trip at a very inopportune time.
Ensure that the total leakage current value per earth leakage breaker is at least 10% (preferably 20%)
below the value earth leakage breaker trip point to ensure that nuisance tripping does not occur. Earth
leakage current is normally a constant value, but can increase in wet or humid weather, so this margin
is suggested.
Each panel of the system has earth leakage current contributions from two switched-mode power
supplies and one RFI filter. The total earth leakage current per panel can be up to 3mA at 240V. If a
24mA RCD is used, then the maximum number of panels per section should be safely limited to 8.
3.2.3 Inrush-current and over-current considerations
Video screen panels draw a very high in-rush or surge current at the moment of switch-on. This
current can be twenty times the maximum operating current of the panel, but occurs only for a very
short time
–
typically less than half an AC power cycle
–
less than 10 ms.
On each M8 panel the in-rush current is 180A at 230V. However, maximum current in the steady-state
for a panel is considerably less: 2 A at 240 volts. This high in-rush current needs to be considered when
selecting a suitable circuit breaker to feed the panels. In choosing the circuit breaker, both the
maximum operating current and the in-rush (surge) current need to be considered.