# Question: What do the numbers on a transformer mean?

Contents

## How do I know what size transformer I need?

Calculate an example as follows. A 120-volt motor has a load amperage of 5 amps. Multiply 120 volts times 5 amps this equals 600VA now lets multiply the 125 percent start factor. Take 600 times 1.25 this equals 720VA and most transformers are sized by a factor of 25VA or 50VA.

## How do you identify a transformer?

The ratio between the number of actual turns of wire in each coil is the key in determining the type of transformer and what the output voltage will be. The ratio between output voltage and input voltage is the same as the ratio of the number of turns between the two windings.

## What is transformer nameplate rating?

Transformer Nameplate Rating – The voltage ratio is specified as V1 (rated)/V2 (rated). It means that when voltage V1 (rated) is applied to the primary, the secondary voltage on fullload at specified pf is V2 (rated).

## How much load can a 25 kVA transformer handle?

Three Phase Transformer

KVA 208V 2400V
20 56.6 4.82
25 69.5 6.02
30 83.4 7.23
37.5 104 9.03

## What size transformer do I need for a 100 amp service?

It’s very common to see a 100 amp breaker in a 480 panel feeding a 75 KVA transformer and a 225 amp main in the 120/208 panel. Just a short note here, the 480 side needs 3 wires and a ground, no neutral. The 120/208 side will need 4 wires and a ground. All grounds tie together.

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## How much can a transformer overload?

In distribution utility applications within a residential setting you can plan to overload transformers up to 200% or more of nameplate. This is depending of course on the coincidental loading of the services that are being served, the length of time the peak will be inplace, and the ambient air temperature.

## How can you tell which transformer is positive and negative?

Each terminal of the primary and secondary windings in a transformer are positive and negative as shown in the below circuit. The positive and negative terminals of the primary winding are A1, and A2, whereas the positive and negative terminals of the secondary winding are a1, and a2.

## How many ohms should a transformer read?

Look for a reading of somewhere between one and about 10 ohms. If any winding reads higher than 10 ohms you have probably found a bad transformer. Unless you didn’t get a good connection to the coil leads with your test leads. Always check at least 3 times before you draw a conclusion.

## How do I know what windings my transformer is?

In a step-down transformer, the primary winding will have a higher resistance.