Page 67 - Uninterruptible Power Supplies

Interconnecting the Standby and Normal Supplies
Interconnecting the Standby and Normal Supplies 65

Generator Manual changeover or
circuit mechanically and electrically
Generator breaker interlocked devices

R
Y Normal
supply
B

N
E
(if provided)

Local
earth Essential Non-essential
electrode load load
Figure 2.8 Typical connections for alternative supplies when the normal supply
uses single point earthing (TN-S or TT).

Resistor
Neutral Earth busbar
busbar

Earth busbar

(a) (b)
Figure 2.9 Neutral earthing of a generator. (a) Low voltage. (b) High
voltage.

point will be connected to the earthing resistor which in turn will be con-
nected to the earth bar and on to the earth electrode (see Figure 2.9b).
High-voltage power is usually supplied from a three-wire system,
there being no neutral, an earth connection may not always be pro-
vided. For such installations triple pole electrically interlocked circuit
breakers will be required as illustrated by Fig. 2.10.

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