Selector Switch in Voltmeter Wiring
Learn how to wire a voltmeter with a 2-position selector switch to measure voltage from two sources or points safely and accurately.
voltmeter selector switch wiring
Wiring a 2-position selector switch to a voltmeter will connect the input on the voltmeter to either of 2 measurement points through a common junction point. Toggle the switch to measure source A or source B; unused input (in the other circuit) will be electrically isolated so that no coupling may occur between circuits and so that voltage monitoring can be performed conveniently and safely, using just one of the instruments.
Formula & Table Summary:
Basic relationship:V = Vmeas (meter reads selected point voltage)
Series protection fuse (recommended): choose fuse rated for meter input current (If) and system voltage.
Input impedance effect: negligible if voltmeter input impedance (Zin) ≫ source impedance (Rs): Vread ≈ Vsource.
Selector wiring: Common → Voltmeter (+), Input A → Selector position 1, Input B → Selector position 2, Voltmeter (−) → Common return (N/ground).
| Item | Input | Connection | Notes |
|---|---|---|---|
| Voltmeter + | Common (COM) | Wired to selector common terminal | Meter positive/input terminal |
| Selector Pos 1 | Source A | Selector connects Source A to COM when on Pos1 | e.g., Phase L1 |
| Selector Pos 2 | Source B | Selector connects Source B to COM when on Pos2 | e.g., Phase L2 or phase-neutral |
| Voltmeter − | Common return | Connected to neutral/ground as required | Observe correct reference |
| Protection | Inline fuse / resistor | Optional on each input | Prevents meter damage on faults |
dual source voltmeter wiring
A single voltmeter can be set to measure voltages on two different sources, or measurement points (such as phase to phase, phase to neutral, or even two different circuits), other than by rewiring, with a 2-position selector switch on the voltmeter. The selector switch diverts the selected point of measurement to the input of voltmeter and isolates other source, avoiding cross-feed and also safeguarding meter. They are normally installed as a three terminal selector: common (to meter) and two selectable inputs. In the name of safety and accuracy, one should make sure there is a match between the voltmeter range and category rating of the application, proper fusing or isolating resistors as deemed necessary by meter maker and correct wiring polarity. The selector switch needs to handle the system voltage and with enough insulation between positions. Such combination is frequently applied in panels and switchboards as well as testing benches makes monitoring much easier and minimizes the number of meters on the installation.
selector switch voltmeter
| Selector | Measured Point | Expected Reading (V) | Remarks |
|---|---|---|---|
| Pos 1 | Phase L1 | 230 V | Nominal line-to-neutral |
| Pos 2 | Phase L2 | 230 V | Alternate phase check |
| Pos 1 | Phase L1-N | 230 V | Phase to neutral |
| Pos 2 | Phase L2-N | 230 V | Phase to neutral |
Frequently Asked Questions - Selector Switch in Voltmeter Wiring:
What does a 2-position selector switch do for a voltmeter?
It connects the voltmeter input to one of two measurement points, allowing selection without rewiring.
How many terminals does a typical 2-position selector have?
Usually three: common (to meter) and two inputs (Pos1, Pos2).
Do I need fuses on the selector inputs?
Fuses or input protection are recommended to prevent meter damage on faults.
Can I measure two phases with one selector and meter?
Yes — wire each phase to an input and the meter common to neutral/return as appropriate.
What rating should the selector switch have?
Switch must be rated for the system voltage and expected current/insulation category.
Is polarity important when wiring the voltmeter?
Yes — observe meter + and − terminals and connect returns to the correct reference (neutral/ground).
Can the selector isolate sources to prevent cross-feed?
A correctly rated break-before-make selector isolates the unused input to avoid cross-connection.
What happens if I select while measuring live sources?
Use a break-before-make switch to avoid momentary bridging; follow safe measurement practices.
Can I use this setup for DC and AC?
Yes, but ensure the voltmeter and selector are specified for AC or DC as required.
Who should install a voltmeter selector switch?
A qualified electrician or technician should install it to ensure safety and compliance.
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