ADB Stagelight EURODIM Twin Tech, Installation Manual

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EURODIM TWIN TECH
User Manual - page 58
Issue 2.1 www.adbstagelight.com
Rules No. 2 and No. 3 are NOT VALID for systems with phase-control dimmers! That is
because their currents are not sine wave.
12.4 Current in the Neutral – Dimmer Systems
The harmonics in each of the three phase currents add up in the Neutral. The current in
the Neutral can be higher (!) than the current in any Line.
Rule with phase-control dimmers
The max. current in the Neutral is 125% of the max. current in the Line.
Warning
Never use supply cables with a reduced-sized Neutral conductor. This is dangerous and
not compliant with standards / regulations.
125% in the Neutral – how can I see this for myself ?
You can see this with a simple set-up which requires only basic equipment:
-
any 3-phase dimmer, e.g. an ADB MEMOPACK or MICROPACK,
connected to a three- phase star supply (3P+N+E)
-
three identical lamp loads e.g. 1 kW luminaires
-
a true rms A-meter with 10 A range, or with a 10 A current clamp
-
a lighting control desk e.g. an ADB MIKADO or LIBERTY lighting control desk.
Connect the lamps to dimmers on three different phases; e.g. dimmers 1, 2, 3 for
MEMOPACK 15 or MICROPACK. Connect the A-meter to measure the current in the
supply Neutral.
Try out various combinations of level settings, including combinations of: one dimmer @
100%, one @ 70%, one @ 0%.
You’ll find that the Neutral current can reach 125% of the lamp current.
12.5 Practical implications
12.5.1 Example No. 1
If you want certainty for continuous duty and any combination of dimmer levels, then a
CEE63 (3P+N+E) plug is suitable for a dimmer unit of max. 34kW. Larger loads can
overload the N pin for some combinations of levels.
Formula: Watts = 3 x 230V x (63 / 1.25) A.
12.5.1 Example No. 2
A 3-phase dimmer cabinet rated for a Line current of 100A, will/should have Line busbars
rated for minimum 100 Arms and a Neutral busbar rated for minimum 125A rms.
12.5.2 Example No. 3
Existing installation, and the existing cable has a half-size N. The circuit-breaker which
feeds the cable is a type with four sensing devices: three in the Lines and one in the
Neutral (rated for half current). The sensitivity of the MCCB has been trimmed to e.g. 200A
for each Line, and consequently 100A for N.
-
if the load is a ‘balanced load’ without dimmers, then I
neutral
is approx. 0, and this
installation is suitable for 138kVA. Formula: 3 x 230V x 200A.
-
if the load is a dimmer system, with luminaires nicely distributed evenly over the three
phases, then you risk tripping for a power as low as 55kW. Indeed, for the most
unfavourable combination of dimmer level settings, a total load above 55 kW can result