Type B Vital Relays - Alstom

Theory of Operation
2.2.2.3. Heavy-Duty Contacts
Heavy-duty contacts, shown in Figure 2–6, are commonly used in circuits of the first and
second voltage ranges where the continuous resistive load current is more than four
amperes. The first voltage range is 30 volts or less; the second voltage range is over 30
volts to 175 volts inclusive. Front contacts are usually Silver-Impregnated-Carbon to
Silver; back contacts are Silver to Silver.
For the rating of contacts on relays containing heavy-duty (HD) contacts consult the
specific relay's Engineering Data (ED) sheet.
Figure 2–6. 2 Front-Back (FB) Dependent Heavy-Duty Contacts
P1457, Rev. Nov/07 2–7 Alstom Signaling Inc.