Checking through 110v DC control supply
Checking through 110v DC control supply
(OP)
Is there an approved method of checking through a 110v DC control supply using a multi-meter?
I normally check with one lead of the meter connected to earth, and check for voltage at various points throughout the circuit, but an engineer at work says this is not the correct method.
Does anyone have any views on this?
clarkgrizwald
I normally check with one lead of the meter connected to earth, and check for voltage at various points throughout the circuit, but an engineer at work says this is not the correct method.
Does anyone have any views on this?
clarkgrizwald





RE: Checking through 110v DC control supply
The safety ground and the current carrying neutral. If you are checking the circuit/devices operation you should be checking from the neutral to the various points in the circuit. If you are checking safety aspects of the ground lead then use it(earth).
RE: Checking through 110v DC control supply
If you measure an ungrounded system relative to earth, the measurement is essentially meaningless because there is no other reference to earth - you should measure relative to one or other pole of the supply. Most people use the negative pole. If you do get any readings measuring to earth then you may have a ground fault. If your system is 'clean' the voltage you may measure will slowly fall to zero as the input resistance of the meter drains the stored charge from the system capacitance. So in essence, if your system is ungrounded then the other guy is right - sorry! - and if the system is intentionally grounded then your technique should work.
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One day my ship will come in.
But with my luck, I'll be at the airport!
RE: Checking through 110v DC control supply
Bottom line is, you should do both pole to pole and pole to ground.
RE: Checking through 110v DC control supply
Kinda depends on the fault detector - some inject low frequency AC onto the ungrounded supply, and that gives some wierd results. The Alstom MR625 (and MR627 I think) use this technique. My multimeter was not impressed!
If your system is clean, the 55V or whatever should gradually decay as the system capacitance drains through the meter impedance. If the voltage slowly decays all the way to zero, the chances are you have no ground faults.
----------------------------------
One day my ship will come in.
But with my luck, I'll be at the airport!
RE: Checking through 110v DC control supply
The circuit I was checking at the time was valve actuator limit switches, and the neutral conductor was not within reach for testing. That was why I was using the earth connection.
clarkgrizwald