Owner`s manual
161
2008 knight
elecTrical sysTem - house — 8
If the current remains above the service limit,
the system will turn off the next load in the
shedding table, again calculating the amount of
current that was removed and placing this value,
which is the value of that load, in memory.
The system continues to turn off loads until
the total current falls below the service limit or
all of the six controlled loads have been shed.
Through this process the system has “learned”
the amount of current each particular load draws.
This feature compensates for the differences in
current draw over a range of line voltage and
ambient temperature, by re-learning the load
each time it is turned off or “shed.”
The 50 Amp Smart EMS now waits until the
total current is lower than the service limit and
enough current is available (as compared with
the amount in memory for the last load shed)
before turning that load back on. This assures
that there is sufcient current to operate the load.
NOTE
There is a two minute minimum delay
period after a load is shed before the
load will be turned on again to prevent
air conditioners from turning on with a
head pressure.
Three Hour Averaging:
The RVIA (Recreational Vehicle Industry
Association) in conjunction with the NEC
(National Electrical Council) have established
rules regarding the rating of electrical systems
and the use of energy management systems.
One of these rules requires that, if any energy
management system is used, the average total
load current for the system over a three hour
period be limited to 80% of the service rating.
For that reason the 50 Amp EMS calculates the
average running current for the system and, if
it exceeds 80% of the service rating, the EMS
sheds loads to reduce the average current below
that limit.
For example, if a system operating under 120
Volt AC, 30 Amp service has been running at
the 30 Amp limit for three hours, the EMS will
change its shedding threshold to 24 Amps and
turn off loads until the 24 Amp limit is attained.
If the user selects the 20 Amp service mode
this limit translates to 16 Amps. Because the
EMS calculates a running three hour average, if
the average load current drops below the limit
the system restores power to loads based on
their impact on the limit. If the system is in the
averaging mode the decimal point at the lower
right corner of the load meter display on the
display panel illuminates.
Display Panel: The display panel connects to
the distribution panel located in the bedroom.
Six power status LED’s indicate power is
applied to those loads. These LED’s are on when
the power is applied. The load meter has a two
digit display to indicate the amount of current
actually being drawn by all the appliances in the
motorhome.
Four service type LED’s indicate the source for
120/240 Volt AC power. Three of these sources
are automatically detected and indicated by the
EMS, namely: Gen Set Service, 50 Amp Service
and 30 Amp Service.
The 20 Amp service mode is not automatically
detected and the operator must manually select
the 20 Amp mode when 20 Amp service is
available. The service select button allows the
current threshold to be set to either 30 Amps or
20 Amps, to match the incoming service.
Circuit Breaker
The internal conguration of the circuit
breaker is designed to trip when excess current
causes the breaker to heat up. The trip action of
the circuit breaker can occur within milliseconds
due to the speed at which electricity can travel.
Breakers are designed to operate at a continuous
load of 80% of the breaker’s rated capacity.
For example: A breaker with a 20 Amp
rating will operate a continuous 16 Amp load.
This design leaves a small amount of working
capacity within the breaker. When an inductive
load is applied, such as when an electric motor
turns on, the motor starts to spin and current
consumption may momentarily exceed the
rated capacity of the breaker. As the electric
motor comes up to operating speed, the electric
motor’s current consumption will decrease.
The AC current load then falls back into the
breaker’s rated 80% set point. This electric
principle should be kept in mind when using
anything other than 50 Amp shore service and
using appliances with electric motors, such as air
conditioners.
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