Cummins/Onan OT-A-4060A / OT-C-10050C — ATS Sizing for Fire Pump Motors (Supplement 962-1026)
Installation · Transfer switch in fire pump circuit applications
For the Cummins/Onan OT-A-4060A / OT-C-10050C, from the Cummins/Onan service manual.
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Procedure
- Rate the transfer switch for at least 115% of the pump motor full load amperes (FLA), using the motor nameplate FLA if available.
- Verify the upstream overcurrent protective device on the utility source side is within the maximum ampere rating allowed for the withstand and closing rating (WCR) of the ATS.
- Oversize the ATS as necessary if the upstream OCD exceeds the WCR.
- Locate the ATS and emergency side isolating switch in the fire pump room.
- Furnish and install a lockable isolating switch with auxiliary contacts on the generator side of the ATS.
- Connect the isolating switch auxiliary contacts to the ATS controls to prevent generator set starting when the isolating switch is open.
- Mark the generator side isolating switch with a caution that both the generator side isolating switch and the fire pump controller isolating switch must be opened before servicing.
- Supply all pump room auxiliaries from a separate ATS.
Specs & values
- ATS rated for at least 115% of the pump motor FLA
- 15 HP fire pump motor at 208 V: 70 A ATS, at 480 V: 40 A ATS
- 20 HP: 208 V 70 A, 480 V 40 A
- 25 HP: 208 V 125 A, 480 V 40 A
- 30 HP: 208 V 125 A, 480 V 70 A
- 40 HP: 208 V 150 A, 480 V 70 A
- 50 HP: 208 V 225 A, 480 V 125 A
- 60 HP: 208 V 225 A, 480 V 125 A
- 75 HP: 208 V 260 A, 480 V 125 A
- 100 HP: 208 V 400 A, 480 V 150 A
- 125 HP: 208 V 400 A, 480 V 225 A
- 150 HP: 208 V 600 A, 480 V 225 A
- 200 HP: 208 V 800 A, 480 V 300 A
Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.