Securitron MCL-24 - Manual (Page 6)

PN# 500-19100
Page 6 Rev. C, 04/11
occur at the point where the wire cable leaves the Magnalock case and enters the door
frame. Another area is via an improper splice on wiring in conduit. Either a metal door frame
or the metal conduit is capable of leaking power between multiple devices with abraded
wires, thereby bypassing switches. A good way to check this electrically (as opposed to
visually removing and inspecting the wires) is to use a meter and check for leakage between
the power supply positive or negative and the door frame and conduit. Magnalocks should be
powered by isolated DC voltage without any earth ground reference to positive or negative.
PROBLEM: The lock rusts.
Both the magnet core and armature are plated and sealed following a military specification. If
rusting appears, the most common cause is that improper cleaning (with steel wool for
instance) has occurred and this has stripped off the relatively soft plating. Once the plating
has been removed, it cannot be restored in the field, so the lock will have to be periodically
cleaned and coated with oil or other rust inhibitor. A rusty Magnalock will still function but at
reduced holding force. If the product is installed in a heavily corrosive atmosphere, such as
near the ocean, it will eventually rust even with non-abrasive cleaning. The only answer then
becomes continued periodic removal of the rust.
9. APPENDICES
A.
CALCULATING WIRE GAUGE SIZING
The general practice of wire sizing in a DC circuit is to avoid causing voltage drops in
connecting wires that reduce the voltage available to operate the device. As Magnalocks are
very low power devices, they can be operated long distances from their power source. For
any job that includes long wire runs, the installer must be able to calculate the correct gauge
of wire to avoid excessive voltage drops.
This is done by taking the current draw of the lock and multiplying by the resistance of the
wire I x R = Voltage drop (i.e. 0.100A x 10.1 Ohms = 1.01 Volts dropped across the wire).
For all intents and purposes it can be said that a 5% drop in voltage is acceptable so if this
were a 24 Volt system (24 Volts x .05 = 1.2 Volts) a 1.01 Volt drop would be within
tolerance.
To calculate the wire resistance, you need to know the distance from the power supply to the
Magnalock and the gauge (thickness) of the wire. The following chart shows wire resistance
per 1000 ft (305 meters):
Wire Gauge Resistance/1,000 ft Wire Gauge Resistance/1,000 ft
8 Gauge .6 Ohms 16 Gauge 4.1 Ohms
10 Gauge 1.0 Ohms 18 Gauge 6.4 Ohms
12 Gauge 1.6 Ohms 20 Gauge 10.1 Ohms
14 Gauge 2.5 Ohms 22 Gauge 16.0 Ohms