Cessna 170, Руководство по обслуживанию

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Cessna 170 Service Manual
Electrical System
18
a. Bonding Connections . To assure a low resistance connection, remove nonconducting finishes; such as
paint and anodizing films, from the attachment surface to be contacted by the bonding terminal. Do not
ground electric wiring directly to magnesium parts.
b.
Corrosion Prevention . Electrolytic action may rapidly corrode a bonding connection if suitable
precautions are not taken. Aluminum alloy jumpers are recommended for most cases; however, use copper
jumpers to bond together parts made of stainless steel, cadmium plated steel, copper, brass, or bronze.
Where contact between dissimilar metals cannot be avoided, the choice of jumper and hardware should be
such that corrosion is minimized, and the part likely to corrode would be the jumper or associated hardware.
At locations where finishes are removed, apply a protective finish to the completed connection to prevent
subsequent corrosion.
c. Bonding Jumper Attachment. Avoid the use of solder to attach bonding jumpers. Bond tubular
members by means of clamps to which the jumper is attached. Proper choice of clamp material will
minimize the probability of corrosion.
d.
Ground Return Connection . IMPORTANT: When bonding jumpers carry substantial ground return
current, determine that the current rating of the jumper is adequate, and that a negligible voltage drop is
produced. This condition is frequently found at engine-to-airframe or firewall jumpers where substantial
return current is found during starting.
Current Limiters
The Cessna 170 was originally equipped with fuses which protect each electrical circuit.
These fuses are usually located in the lower instrument fuse-panel and are size AGS glass-tube fuses
measuring 9/32” X 1 1/4”. AGS is a size no longer used by manufacturers and sometimes difficult to find
therefore many owners substitute AGC fuses in similar amperages. The AGC series is not an exact fit (due
to ¼” diameter) and their performance is sometimes intermittent due to reduced contact area within the
holder.
The original Cessna part number (0411023) is the AGS series fuse with a following “dash” number indicating
the amperage. If this PN is searched for results may be frustrating. The modern equivalent Cessna part
number is: S1091 followed by the appropriate dash number.
(Example S1091-2 is a 10 Amp fuse. S1091–3 is a 15A fuse, S1091-4 is 25A, S1091-6 is 20A and so on as
indicated in the Illustrated Parts Catalog) Your Cessna distributor should have them in stock. Some large
fuse supply companies also carry the AGS fuses.
Many aircraft have been modified to utilize circuit breakers of the “pull” type. Examples are the 7277 and
7271 series of “Klixon” brand devices or the W23 series of Potter and Brumfield brand. Circuit breakers
have the advantage of being quickly re-settable, an especially useful feature at night.
Caution: Resetting
circuit breakers in flight should be done with care. Most guidelines either suggest or require that a circuit
breaker be re-set only ONCE while inflight. Similar procedures should be used for fuses. Never substitute a
larger capacity fuse for a failed fuse.
Note: Current limiters are not intended to protect devices such as radios, lighting, etc. Current limiters are
intended to protect the wiring from damage or fire due to excessive load demand such as may occur during
shorts or failed equipment. A current limiters size is determined by the wire gauge and its intended purpose.
A 10% over-size is usually specified for current limiters in order to accommodate power surge requirements.
Replace current limiters only with approved, aircraft quality units of similar capacity.