9.5 Electrical installation
Requirements
The electrical installation should be carried out in accordance with
the wiring diagram. In the vicinity of hot parts (flue gas fan, flue
pipe), cables must be routed in steel pipes and with appropriate
clearances for temperature protection.
The cable entries for motors and appliances must be dust-proof and
provided with strain relief.
Note
The regulations of the local power supply utility must be observed.
Positioning the control panel
Optimal positioning of the control panel can minimise cable lengths
and therefore reduce costs. The location of the control panel must
be selected so that negative influence caused by thermal radiation
(boiler front panel, boiler back panel with flue gas collector and flue
gas fan, as well as flue pipe) and exposure to dust during cleaning is
minimised.
The ambient temperature of the control panel (approx. 10 cm away
from the control panel) must not exceed 40 °C. In case of doubt,
locating the control panel outside the boiler room near the boiler
room door is preferred.
Note
The regulations of the local power supply utility must be observed.
9.6 Safety equipment to EN 12828
The safety equipment for the heating system must be installed by
the authorised heating contractor.
EN 12828 applies to the design of hot water heating systems with
safety temperatures up to 105 °C and a maximum rated output of
1 MW.
In the case of sealed unvented hot water heating systems, boilers
with a rated heating output of up to 300 kW must be fitted with the
following safety equipment:
■ Diaphragm expansion vessel
■ Safety valve
■ Drain & fill facility
■ High limit safety cut-out
■ Thermometer
■ Pressure gauge
■ Low water indicator
Expansion
In a sealed unvented system, the pre-charge pressure of the expan-
sion vessel must be equal to the maximum system height plus
0.2 bar (0.02 MPa). For sizing the expansion vessel, see chapter
"Expansion vessel sizing".
Safety valve
Equip the boilers with a type-tested safety valve. For all other operat-
ing conditions, this must be identified in accordance with TRD 721
with "D/G/H". Install the safety valve at an easily accessible location
at the highest point of the boiler or in the immediate vicinity of the
flow line. It must not be possible to shut off the line between the
boiler and the safety valve. Pumps, fittings or constrictions must not
be present in the line. The discharge pipe must be designed in such
a way that no pressure increase is possible. Any expelled heating
water must be drained off safely. The outlet point of the discharge
pipe must be arranged in such a way that any water expelled from
the safety valve can be drained off safely and visibly.
Note
The safety valve is not part of the standard delivery of the boiler.
High limit safety cut-out
Equip each directly heated boiler with a high limit safety cut-out that
will shut down the combustion system when the permissible flow
temperature is exceeded and prevent automatic restarting. A reset
can only be performed manually by specialist personnel.
Thermometer
The flow temperature of the boiler must be indicated by a thermome-
ter.
Pressure gauge
Every sealed unvented heating system must be equipped with at
least one pressure gauge that indicates positive pressure in bar.
Low water indicator
Boilers must be protected against water shortage to ensure that the
combustion system is shut down and locked out if necessary. Install
this in the flow line close to the boiler.
■ With boilers up to a rated output of 300 kW, a low water indicator
can be omitted as long as heating can be reliably prevented when
the water level is low, e.g. by installing a minimum pressure limiter.
■ In attic heating centres a low water indicator or other suitable
device is required for every boiler to protect it against overheating
in case of water shortage.
Minimum pressure limiter
Recommended for flow temperatures in excess of 100 °C. One
required per multi boiler system.
Maximum pressure limiter
Every heat generator with a rated heating output in excess
of 300 kW must be equipped with a pressure limiter to prevent the
pressure from exceeding the maximum set pressure (see EN 12828,
Point 4.6.2.2.2).
Design information
(cont.)
VITOFLEX 300-UF
Viesmann
91
5682428
9
