Pick the smallest standard series isolating transformer for each fixture line, check lamp current and loading, and total the order.
List the transformers you need with lamp load, lamps per transformer, lamp current and transformer type. The tool picks the smallest standard series isolating transformer for each line, checks that the lamp current suits a 6.6 A secondary, checks loading, and totals what you need to order.
Comma separated. The 30/45 W size is entered as 45. FAA also lists 10/15 W and 20/25 W types (enter 15 and 25). Edit to match your supplier's range.
Added to the lamp load before choosing a size. Usual practice is to match the rating to the lamp load, so the default is 0. Enter a margin only if your specification requires one.
Placeholder. FAA AC 150/5345-47 minimums are 80 % for 30/45 W and 65 W, 85 % for 100 W and 150 W, and 90 % for 200 W and above, so 90 % is optimistic for the small sizes. Use the datasheet value.
Placeholder, used only for the kVA estimate. FAA requires at least 0.95 at rated load, and a lightly loaded transformer is lower. Use the datasheet value at your loading.
Each row is a group of identical transformers. Enter the number of transformers, not the number of lamps. The values below are examples only; replace them with your fixture datasheet figures. Lamp current is the secondary (lamp) current, normally 6.6 A; the 20 A figure is the primary circuit current of the 20/6.6 A type and must not be entered here. For halogen lamps enter watts. For LED fixtures enter the apparent power (VA) at 6.6 A from the fixture datasheet, because LED drivers are not resistive loads.
| Fixture | Transformers (qty) | Load per lamp (W / VA) | Lamps per transformer | Lamp current (A) | Transformer type | Status | Remove |
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| Fixture | Type | Qty | Load (W / VA) | Required (W / VA) | Selected | Loading | Status |
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Every step is shown so the result can be checked by hand.
The standard range of 30/45, 65, 100, 150, 200, 300 and 500 W follows common series isolating transformer practice (IEC 61823, FAA AC 150/5345-47). Confirm the current edition and your project specification.
The 6.6/6.6 A type has a 6.6 A primary and the 20/6.6 A type a 20 A primary. The type must match the current of the series circuit it sits on. Do not mix the two types on one circuit.
FAA lists no 65 W type with a 20 A primary, so for the 20/6.6 A type the tool skips 65 W and uses the next size. FAA AC 150/5345-47 also requires a transformer to have enough capacity for lamp ageing, secondary lead losses and contact losses, so check the lamp load you enter includes them.
Loading under 50% is flagged because a lightly loaded transformer has a lower power factor, which loads the series circuit and the CCR with more reactive current.
FAA minimum efficiency is 80 % for 30/45 W and 65 W, 85 % for 100 W and 150 W, and 90 % for 200 W and above, with a minimum power factor of 0.95 at rated load. One efficiency is applied to every line here, so the kW total is approximate.
If LED loads are entered in VA, the kW figure is a conservative upper estimate, because VA is not watts. Use fixture datasheet real power for a true kW figure.
The kW and kVA totals are an estimate of transformer input only. CCR sizing must also include cable losses, any other loads on the circuit and spare capacity.
Always confirm the final rating, lamp current and transformer type against the fixture and transformer datasheets. For a project report with design margin, power factor and loading window, use Calculator #49 Transformer VA Selection.
This tool is for planning and education and does not replace the project specification. See the Legal Notice.
Quick answers on picking the smallest standard series isolating transformer for each fixture line.
It picks the smallest standard series isolating transformer for each fixture line, checks that the lamp current suits a 6.6 A secondary, checks the loading, and totals what you need to order. You list the transformers you need with the lamp load, lamps per transformer, lamp current and transformer type.
The load is the load per lamp times the lamps per transformer. The required rating is the load times one plus the design margin, and the tool selects the smallest standard rating at or above it. The loading is the load divided by the selected rating. The default margin is 0, because usual practice is to match the rating to the lamp load, so enter a margin only if your specification requires one.
The standard range is 30/45, 65, 100, 150, 200, 300 and 500 W, following common series isolating transformer practice (IEC 61823 and FAA AC 150/5345-47). Enter the ratings comma separated, with the 30/45 W size entered as 45. FAA also lists 10/15 W and 20/25 W types, which you enter as 15 and 25. Edit the list to match your supplier's range.
Lamp current is the secondary current, normally 6.6 A. The 20 A figure is the primary circuit current of the 20/6.6 A type and must not be entered as the lamp current. The 6.6/6.6 A type has a 6.6 A primary and the 20/6.6 A type a 20 A primary, so the type must match the series circuit it sits on, and the two types must not be mixed on one circuit. FAA lists no 65 W type with a 20 A primary, so for the 20/6.6 A type the tool skips 65 W and uses the next size.
For halogen lamps enter watts. For LED fixtures enter the apparent power in VA at 6.6 A from the fixture datasheet, because LED drivers are not resistive loads. If LED loads are entered in VA, the kW figure is a conservative upper estimate, because VA is not watts.
Loading under 50 percent is flagged, because a lightly loaded transformer has a lower power factor, which loads the series circuit and the CCR with more reactive current.
Input power is the sum of the quantity times the load, divided by the efficiency, and input apparent power is that divided by the power factor. FAA minimum efficiency is 80 percent for 30/45 W and 65 W, 85 percent for 100 W and 150 W, and 90 percent for 200 W and above, with a minimum power factor of 0.95 at rated load. One efficiency is applied to every line, so the kW total is approximate, and 90 percent is optimistic for the small sizes.
No. The kW and kVA totals are an estimate of transformer input only, and CCR sizing must also include cable losses, any other loads on the circuit and spare capacity. Always confirm the final rating, lamp current and transformer type against the fixture and transformer datasheets. For a project report with design margin, power factor and loading window, use Calculator #49 Transformer VA Selection. This tool is for planning and education and does not replace the project specification.
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