What is the maximum control volts with isolation transformer?

What is the maximum control volts with isolation transformer?

• A. 100 volts
• B. 150 volts
• C. 200 volts
• D. 120 volts

Answer: (B)

Isolation of the control circuit from the line power is the key idea here. An isolation transformer keeps the control side electrically separate from the mains to reduce shock risk and limit fault energy. In HVAC controls, that isolation is paired with a safe voltage level for the control wiring. The highest voltage you normally use on a control circuit powered through an isolation transformer is 150 volts. That limit balances having enough voltage for practical control loads with staying within standard insulation and safety ratings for control equipment. So, while 120 V is a common nominal control voltage, the maximum allowed on such a isolated control path is 150 V. Values like 100 V are below the maximum, and 200 V would exceed typical safety limits for control circuitry.

Isolation of the control circuit from the line power is the key idea here. An isolation transformer keeps the control side electrically separate from the mains to reduce shock risk and limit fault energy. In HVAC controls, that isolation is paired with a safe voltage level for the control wiring. The highest voltage you normally use on a control circuit powered through an isolation transformer is 150 volts. That limit balances having enough voltage for practical control loads with staying within standard insulation and safety ratings for control equipment.

So, while 120 V is a common nominal control voltage, the maximum allowed on such a isolated control path is 150 V. Values like 100 V are below the maximum, and 200 V would exceed typical safety limits for control circuitry.