I have a tripplite iso box.
I got it for testing circuits.
From wiki
Isolation transformer - Wikipedia, the free encyclopedia
"An isolation transformer is a transformer, often with symmetrical windings, which is used to decouple two circuits. An isolation transformer allows an AC signal or power to be taken from one device and fed into another without electrically connecting the two circuits. Isolation transformers block transmission of DC signals from one circuit to the other, but allow AC signals to pass. They also block interference caused by ground loops. Isolation transformers with electrostatic shields are used for power supplies for sensitive equipment such as computers or laboratory instruments.
In electronics testing, troubleshooting and servicing, an isolation transformer is a 1:1 power transformer which is used for safety. Grounded objects (desk, lamp, concrete floor, oscilloscope ground lead, etc.) near a device under test which is not isolated may be at a hazardous potential difference with respect to that device. By using an isolation transformer, the bonding is eliminated, and the shock hazard is entirely contained within the device—there is no danger in touching a live part of the circuit while another part of the body is at earth potential.
Isolation transformers are also used for the power supply of devices not at ground potential. A well-known example is the Austin transformer for the power supply of air-traffic obstacle lamps on mast radiators insulated against ground.
Isolation transformers are commonly designed with careful attention to capacitive coupling between the two windings. This is necessary because excessive capacitance could also couple AC current from the primary to the secondary. A grounded shield is commonly interposed between the primary and the secondary. This greatly reduces the coupling of common-mode noise present on supply conductors.
Differential noise can magnetically couple from the primary to the secondary of an isolation transformer. This requires other measures, such as a filter, to block differential noise from the secondary of an isolation transformer.
Bare uncased isolation transformers have floating outputs (not tied to ground). Most commercial isolation transformer assemblies sold have one leg of the secondary tied to ground as a safety requirement. This forms a new neutral which eliminates common mode noise, and differential ground noise, prime functions when used to power equipment."