Buck Boost Transformers

Why it is so much smaller

A buck boost unit is connected as an autotransformer, so the windings share a common connection and only the voltage difference passes through the transformer itself. Correcting 208 volts up to 230 means handling about 22 volts of difference, not the full 230. That is why a buck boost rated for a given load is a fraction of the size, weight and price of an isolation transformer doing the same job.

What you give up

Isolation. Because the windings are connected rather than separate, there is a direct electrical path from input to output. You cannot use a buck boost to create a separately derived system, to establish a new neutral to ground bond, or to break a ground loop. If any of those are the reason you are buying, you need a full two winding transformer.

Where it fits

Small voltage corrections, typically 5 to 20 percent. Running 230 volt equipment on a 208 volt supply, or trimming a 480 volt feed that runs persistently high. Beyond about 20 percent the economics stop favouring it and a standard transformer is the better answer.

What is a buck boost transformer

A small autotransformer that raises or lowers voltage by a modest amount, typically 5 to 20 percent. Because it only handles the voltage difference rather than the full load voltage, it is far smaller and cheaper than a two winding transformer of the same capacity.

Does a buck boost transformer provide isolation

No. The windings are electrically connected, so there is a direct path from input to output. If you need galvanic isolation or a separately derived system, you need a two winding transformer instead.

Can a buck boost transformer run 230 volt equipment on 208 volts

Yes, that is one of its most common uses. It handles only the roughly 22 volt difference, which is why it can be small and inexpensive for the load it supports.