2 - 10
Supply-on-Test wiring - general points
•
It is good practice to route the three phase conductors in a close tre-foil layout, held
together with cable-ties. This minimises stray magnetic fields from the cable array, and
reduces inductive losses in the cables. In the event of a high fault current flowing this
arrangement minimises the risk of sudden and violent cable movements.
•
If the connections are made using more than one conductor for each phase connection
all the cables on any one phase should be of exactly the same length, and laid along
a similar route. Ensure that the three phase conductors are equally shared between
multiple cable entry openings, to minimise eddy current losses.
•
The load bank supply cables must be protected by the short circuit protective device
(SCPD) which is suitably rated to the capacity of the supply cables.
Is a local isolator required?
When planning the installation consider if a local isolator switch is required. If the output
circuit breaker of the Supply-on-Test is easily accessible, then this can perform the
isolating function.
Protective earth connection
An earth conductor must always be bonded to the frame of the Supply-on-Test and
connected to the grounding terminal of the load bank (marked PE).
Making connections for single-phase operation
3-phase load banks can be used for testing single-phase supplies. The method of
connection (and the load available) will vary depending on the rating of the load bank, the
supply voltage and frequency. Refer to chapter 4 for more information about changing
between single and three phase testing.
Single phase wiring
Single-phase operation is achieved by connection between two phase terminals, one of
which is used as neutral.
A-C connection mode.
The A-C connection mode shown in Figure 2-6 will give
approximately 50% loading capacity when the nominal load bank supply voltage is
connected or 17% loading capacity when a single-phase (
√
3
) equivalent supply is used.
Figure 2-6
A-C connection for a single phase supply
Note:
If the load bank
is fitted with a 3-phase
fan motor, an external
3-phase mains input will
be required for the con-
trols and fan supply.
L1
L3
L (Live)
N (Neutral)
L1
L2
L (Live)
N (Neutral)
L3
2 - 11
The maximum permissible single-phase supply voltage for this connection is 100% of the
3-phase load bank rated voltage.
AB-C connection mode.
The AB-C connection mode shown in Figure 2-7 will give
approximately 66% loading capacity when the nominal load bank supply voltage is
connected or 22% loading capacity when a single-phase (
√
3
) equivalent supply is used.
Figure 2-7
AB-C connection for a single phase supply
The maximum permissible single-phase supply voltage for this connection is 86% of the
3-phase load bank rated voltage.
Control System Connections
Sigma LT load banks all have digital toggle local controls on the load bank. Alternatively
connect the hand-held to the upper connection socket for remote control of the load bank
and to control multiple load banks in a network.
Figure 2-8
The Sigma LT control cable connector.
Sigma LT hand-held
connection socket
Chapter Two
Load Bank Setup
