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14 CFR Ch. I (1–1–24 Edition) 

§ 25.1355 

(4) No corrosive fluids or gases that 

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

(5) Each nickel cadmium battery in-

stallation must have provisions to pre-
vent any hazardous effect on structure 
or essential systems that may be 
caused by the maximum amount of 
heat the battery can generate during a 
short circuit of the battery or of indi-
vidual cells. 

(6) Nickel cadmium battery installa-

tions must have— 

(i) A system to control the charging 

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

(ii) 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 

(iii) 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. 

(c) Electrical bonding must provide 

an adequate electrical return path 
under both normal and fault condi-
tions, on airplanes having grounded 
electrical systems. 

[Amdt. 25–123, 72 FR 63405, Nov. 8, 2007] 

§ 25.1355

Distribution system. 

(a) The distribution system includes 

the distribution busses, their associ-
ated feeders, and each control and pro-
tective device. 

(b) [Reserved] 
(c) If two independent sources of elec-

trical power for particular equipment 
or systems are required by this chap-
ter, in the event of the failure of one 
power source for such equipment or 
system, another power source (includ-
ing its separate feeder) must be auto-
matically provided or be manually se-
lectable to maintain equipment or sys-
tem operation. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–23, 35 FR 5679, Apr. 8, 
1970; Amdt. 25–38, 41 FR 55468, Dec. 20, 1976] 

§ 25.1357

Circuit protective devices. 

(a) Automatic protective devices 

must be used to minimize distress to 

the electrical system and hazard to the 
airplane in the event of wiring faults or 
serious malfunction of the system or 
connected equipment. 

(b) The protective and control de-

vices in the generating system must be 
designed to de-energize and disconnect 
faulty power sources and power trans-
mission equipment from their associ-
ated busses with sufficient rapidity to 
provide protection from hazardous 
over-voltage and other malfunctioning. 

(c) Each resettable circuit protective 

device must be designed so that, when 
an overload or circuit fault exists, it 
will open the circuit irrespective of the 
position of the operating control. 

(d) If the ability to reset a circuit 

breaker or replace a fuse is essential to 
safety in flight, that circuit breaker or 
fuse must be located and identified so 
that it can be readily reset or replaced 
in flight. Where fuses are used, there 
must be spare fuses for use in flight 
equal to at least 50% of the number of 
fuses of each rating required for com-
plete circuit protection. 

(e) Each circuit for essential loads 

must have individual circuit protec-
tion. However, individual protection 
for each circuit in an essential load 
system (such as each position light cir-
cuit in a system) is not required. 

(f) For airplane systems for which 

the ability to remove or reset power 
during normal operations is necessary, 
the system must be designed so that 
circuit breakers are not the primary 
means to remove or reset system power 
unless specifically designed for use as a 
switch. 

(g) Automatic reset circuit breakers 

may be used as integral protectors for 
electrical equipment (such as thermal 
cut-outs) if there is circuit protection 
to protect the cable to the equipment. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–123, 72 FR 63405, Nov. 8, 
2007] 

§ 25.1360

Precautions against injury. 

(a) Shock. The electrical system 

must be designed to minimize risk of 
electric shock to crew, passengers, and 
servicing personnel and to mainte-
nance personnel using normal pre-
cautions. 

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