551 

Federal Aviation Administration, DOT 

§ 27.1357 

(3) Each generator must have a re-

verse current cutout designed to dis-
connect the generator from the battery 
and from the other generators when 
enough reverse current exists to dam-
age that generator; and 

(4) Each generator must have an 

overvoltage control designed and in-
stalled to prevent damage to the elec-
trical system, or to equipment supplied 
by the electrical system, that could re-
sult if that generator were to develop 
an overvoltage condition. 

(d) 

Instruments. 

There must be means 

to indicate to appropriate crew-
members the electric power system 
quantities essential for safe operation 
of the system. In addition— 

(1) For direct current systems, an 

ammeter that can be switched into 
each generator feeder may be used; and 

(2) If there is only one generator, the 

ammeter may be in the battery feeder. 

(e) 

External power. 

If provisions are 

made for connecting external power to 
the rotorcraft, and that external power 
can be electrically connected to equip-
ment other than that used for engine 
starting, means must be provided to 
ensure that no external power supply 
having a reverse polarity, or a reverse 
phase sequence, can supply power to 
the rotorcraft’s electrical system. 

(Secs. 313(a), 601, 603, 604, and 605 of the Fed-
eral Aviation Act of 1958 (49 U.S.C. 1354(a), 
1421, 1423, 1424, and 1425); and sec. 6(c) of the 
Dept. of Transportation Act (49 U.S.C. 
1655(c))) 

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as 
amended by Amdt. 27–11, 41 FR 55470, Dec. 20, 
1976; Amdt. 27–13, 42 FR 36972, July 18, 1977] 

§ 27.1353

Storage battery design and 

installation. 

(a) Each storage battery must be de-

signed and installed as prescribed in 
this section. 

(b) Safe cell temperatures and pres-

sures must be maintained during any 
probable charging and discharging con-
dition. No uncontrolled increase in cell 
temperature may result when the bat-
tery is recharged (after previous com-
plete discharge)— 

(1) At maximum regulated voltage or 

power; 

(2) During a flight of maximum dura-

tion; and 

(3) Under the most adverse cooling 

condition likely to occur in service. 

(c) Compliance with paragraph (b) of 

this section must be shown by test un-
less experience with similar batteries 
and installations has shown that main-
taining safe cell temperatures and 
pressures presents no problem. 

(d) No explosive or toxic gases emit-

ted by any battery in normal oper-
ation, or as the result of any probable 
malfunction in the charging system or 
battery installation, may accumulate 
in hazardous quantities within the 
rotorcraft. 

(e) No corrosive fluids or gases that 

may escape from the battery may dam-
age surrounding structures or adjacent 
essential equipment. 

(f) Each nickel cadmium battery in-

stallation capable of being used to 
start an engine or auxiliary power unit 
must have provisions to prevent any 
hazardous effect on structure or essen-
tial systems that may be caused by the 
maximum amount of heat the battery 
can generate during a short circuit of 
the battery or of its individual cells. 

(g) Nickel cadmium battery installa-

tions capable of being used to start an 
engine or auxiliary power unit must 
have— 

(1) A system to control the charging 

rate of the battery automatically so as 
to prevent battery overheating; 

(2) A battery temperature sensing 

and over-temperature warning system 
with a means for disconnecting the 
battery from its charging source in the 
event of an over-temperature condi-
tion; or 

(3) A battery failure sensing and 

warning system with a means for dis-
connecting the battery from its charg-
ing source in the event of battery fail-
ure. 

(Secs. 313(a), 601, 603, 604, and 605 of the Fed-
eral Aviation Act of 1958 (49 U.S.C. 1354(a), 
1421, 1423, 1424, and 1425); and sec. 6(c) of the 
Dept. of Transportation Act (49 U.S.C. 
1655(c))) 

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as 
amended by Amdt. 27–13, 42 FR 36972, July 18, 
1977; Amdt. 27–14, 43 FR 2325, Jan. 16, 1978] 

§ 27.1357

Circuit protective devices. 

(a) Protective devices, such as fuses 

or circuit breakers, must be installed 
in each electrical circuit other than— 

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