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Re wired GE relay box Low Voltage Transformer Transverter Converter
Install, troubleshoot, repair, replace LV transformers, converters, transverters

How to install, diagnose, and repair of low voltage transformers, transverters & converters used to power low voltage lighting systems, control systems & HVAC Equipment.

This article series discusses low voltage electrical wiring repair, parts substitution, parts replacement, and repair warnings. We describe the properties of low-voltage-controlled switches that operate 120V lights and receptacles in homes dating from the 1960's to the present.

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Guide to Low Voltage Building Wiring Transformers or Transverters

Low voltage transformer for heating or air conditioning (C) Daniel FriedmanPhoto: a low voltage transformer taking 120VAC input voltage and providing 24VAC output voltage commonly used to control heating or air conditioning thermostats or to supply low-voltage lighting relays in a building. - photo courtesy of professional home inspector David Goldstein cited at REVIEWERS

[Click to enlarge any image]

An electrical "transformer" converts voltage from one level to another, say from 120 Volts down to 28 Volts or to 24-Volts in order to supply the lower voltage to devices that are designed to operate at that level. A "converter" changes alternating current to direct current.

Electrical power entering buildings in the U.S. and in most of the world operates at 60-cycle alternating current (or 50 cycle AC).

Watch out: while low-voltage electrical wiring, typically in the 24VAC-28.5VAC range is safe and presents no risk of electric shock injury, the low voltage transformer or transverter is supplied with 120VAC or 220VAC as are line-voltage devices in most buildings.

If you are not trained in proper and safe electrical wiring you could cause a building fire or could be shocked or killed working on or installing a low voltage transformer.

In addition even low-voltage wiring, if improperly-installed, may make the equipment it is intended to operate unsafe.

Alternating current:

If you measured the voltage level on an AC circuit, you'd see the voltage level varying between +120V down through 0 volts and continuing down to -120V and then cycling back up again 60 times a second. That's what 60-cycle AC means.

Direct current:

if you measure the voltage level on a DC circuit, you'll see the level staying roughly constant at whatever voltage level the circuit is supplying. For example, most automobiles operate most of their electrical components at 12-volts direct current or 12-V DC.

The switches and the relays they control in a building low-voltage wiring system are designed to operate at 28-volts of direct current.

Definition: An electrical "transformer" converts voltage from one level to another, say from 120Volts down to 28Volts in order to supply the lower voltage to devices that are designed to operate at that level.

Definition: A current "converter" changes alternating current to direct current. Electrical power entering buildings in the U.S. and in most of the world operates at 60-cycle alternating current (or 50 cycle AC).

What's the difference between a "transformer" and a "transverter"? Not much.

Definition: A "transverter" combines transformi g 120VAC or 220VAC to 24VAC or some other low voltage, combined with changing alternating current to direct current.

For example, a 120 VAC input to the transferter may produce 28V DC output current.

So in building low-voltage wiring systems a "transverter" is used to transform 120V down to 28V and also to convert the voltage from alternating to direct current.

We only need one of these transverters. Old low-voltage wiring electrical systems use a single transverter to accept incoming 120V AC current and change it to 28V direct current.

The switching relays in older low-voltage wiring systems are operated individually, that is, one at a time.

For example, most automobiles operate most of their electrical components at 12-volts direct current or 12-V DC. The switches and the relays they control in a building low-voltage wiring system are designed to operate at 28-volts of direct current.

The switching relays in older low-voltage wiring systems are operated individually, that is, one at a time.

In a building using low voltage switches to operate lights, the transformer is supplied with 120VAC or in some countries 220 or 240 VAC or even 277 VAC as input voltage and it provides 24VAC output voltage that is sent through low-voltage wiring to power control relaysthat in turn are controlled by low voltage switches or other controls.

The transverter is step-down transformer which is itself powered by a 120V circuit in the building converts its incoming 120-volt alternating current (120 VAC) to a 28-volt direct current (28 VDC).

This is the operating voltage and current type used to power the switches and the relays that they turn on and off.

Diagnose, Repair or Replace Low Voltage Wiring Transformer or Transverter

Low voltage transformer for heating or air conditioning (C) Daniel FriedmanIntermittent Failure of Lights or other Relay-controlled Devices

Intermittent operation of lights or other relay-controlled devices in a home usually is due to a failing power supply transverter. The voltage output of the Transverter should be 28 - 31 VDC. If voltage is not in that range, the transverter should be replaced.

Low Voltage Output at the Transverter

Low voltage at a transformer/transverter may mean that it needs to be replaced, or it may simply mean that a switch in the home is stuck.

Check the Transverter voltage output. In a normal low-voltage electrical system the output voltage at the transverter should be 28 - 30 VDC if measured between the "switch" and the "relay" output wires on the Transverter with either one of these wires disconnected.

You don't need to disconnect both wires since disconnecting just one of them interrupts the circuit. But of course it's ok to disconnect both.

If the voltage is 0 VDC, or a really low 2 - 4 VDC, this is indicates of a stuck low-voltage switch. Touch-Plate Lighting informs us that the transverter drops in voltage output down to 3 volts after operating the relay coil in order to protect against burning up the coil.

If you read a voltage higher than 3 volts and lower than 26 VDC from the Transverter, then the transverter should be replaced.

If you are reading 28 - 30 VDC and still nothing is working then you have a wiring problem: something is not connected (as in a wire coming loose from under a wire nut) or something incorrectly wired (as in when changing a component in the system and not re-connecting to the proper wire).

See

Basics of Wiring Low Voltage Transformers

Honeywell 24VAC Low Voltage Transformer wiring details (C) InspectApedia.com

Shown here, a Honeywell 24VAC low voltage transformer marked NEMA type D, meets NEC class 2 not wet, class 3 web UL 1585 requirements.

The low-voltage wire screw terminals on the face of the transformer are marked "LOAD" and "C" or "Common"

For clarity we have over-written the text embossed in the tan plastic face of this transformer the letters R, Load, and C (for Common) using Red and Black in the another photo of the face of this transformer, given just below.

The high voltage wire connections to the transformer are made by using the black and white leads provided.

Standard line voltage wiring connections at the transformer - the "Primary" side

[Click to enlarge any image]

In typical HVACR control circuits and in building low-voltage lighting control systems, the low voltage transformer has AC input voltage and produces AC outpout voltage (typically at 24VAC or at 28.5 VAC though other output voltages are available

For equipment that needs a DC (Direct Current) electrical supply, other versions of these transformers can be fed 120VAC (or 220VAC) and can include an intrnal diode that will produce DC outpout on the secondary side.

Standard low-voltage wire connections at the transformer - the G99dja"Secondary" side

Honeywell 24VAC Low Voltage Transformer wiring details (C) InspectApedia.com

Other Low-Voltage (LB) Transformer, LV Device, LV WiringConnections

Details about thermostat wiring and low voltage control wiring for tranformers used on heating and air conditioning circuits are found

at THERMOSTAT WIRE CONNECTIONS

In low voltage lighting control systems, unlike a conventional 120-V electrical light circuit switch, the low voltage switch is talking not to the light, but to the relay. The low-voltage relay is also referred to as a "latching relay".

A "latching relay" is a switch that "latches" into whatever position it is told to enter.

So such a relay needs to receive a separate signal to tell to it to "Make" (turn on) or "Break" (turn off) the household current which the relay is passing on to the light or other device it controls.

If an older low voltage transverter still has the labels by the output wires, you may see labels reading "switch" and "relay". When wiring such a transverter, connect the wire from your low-voltage switch to the terminal marked "Switch". Similarly, connect the wire from the relay to the transverter terminal marked "Relay".

If the older Transverter connections are not labeled we're in more trouble but it's still simple to determine which wire to connect to which terminal.

Watch out: Before disconnecting the old transverter, follow the wires from the old Transverter to what it is connected to. Touch-Plate Lighting says the easiest way to do this is by locating the wire of the Transverter that connects to one wire of every relay inside the relay enclosure. This wire will be the "relay" wire. Therefore the other wire will be the "switch" wire.

Example of using a low voltage transformer to power an HVAC thermostat and showing the convention of Red = R = power and C = common terminals at the transformer (C) InspectApedia.com adapted from Scaringe cited & discussed at InspectApedia.comOur illustration, adapted from Scaringe (2011) illustrates the use of a 28.5 VAC low voltage transformer to power, through a room thermostat, relays controlling an HVAC system.

How to Choose the Right Transformer for Home Low Voltage Wiring Systems

Touch-Plate's TPS-0120 120V Transverter power supply operates relays from every Touch-Plate® system from 1946 to early 1980’s. It's input is 120 V A. C.

Its output: 28.5V D.C.

Other power supplies are used to transform 120V to 6.3 V A. C. offering from .150A (150 milliamps) up to 4 Amps (400 mva) depending on the application such as for pilot lights (incandescent lamps explained just above), or other power supplies.

Other power supplies may be found installed for for pilot lights.

These are simply little lights at switches that indicate if the device controlled by the switch has been turned "on" or "off". If you see a silver box labeled "PL-6" mounted above or below each relay this is a transformer for pilot lights.

Touch-Plate Lighting says that the the pilot light transformers for the master switch stations are usually located in the master bedroom and/or some other main living area.

Touch-Plate also points out that these transformers are not necessary to operate electrical lights or receptacles in the building. If the pilot lights were to malfunction or stop working, you would lose the indicator light for the specific relay it is connected to, nothing more.

That is, a PL-6 power supply has nothing to do with operating the relay itself, only the indicator light that shows if a relay (and the device it controls) is switched "on" or "off".

Low Voltage Transformer Wiring Instructions, Manuals

Goodman 208-240VAC to 24VAC transformer cited & discussed at InspectApedia.com

Photo: a Goodman 208/240VAC to 24VAC transformer as sold online, P/N Goodman 0130M00138S


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