How Much Ground Fault Is Too Much?
How Much Ground Fault Is Too Much?
(OP)
I have an ungrounded 125VDC diesel generator start system that indicates a positive ground via (1) ground detection light illumination on the battery charger and (2)voltage to ground measurement. (+) to grd reads 75.4VDC while (-) to grd reads 56.7VDC.
The criticality of this level of grd on the system is often second-guessed (some want to let it go because it is too small to find or too time consuming to find).
How much of a ground is too much?
Thanks in advance for your response!!
The criticality of this level of grd on the system is often second-guessed (some want to let it go because it is too small to find or too time consuming to find).
How much of a ground is too much?
Thanks in advance for your response!!





RE: How Much Ground Fault Is Too Much?
RE: How Much Ground Fault Is Too Much?
If the lamp lights you probably have a low resistance ground.
If you can't get the lamp to light, you have a high resistance ground.
Either can be an indication of a failing component. A very high resistance ground path may be an indication of surface contamination which will respond to a good cleaning.
respectfully
RE: How Much Ground Fault Is Too Much?
Waross' method is quite effective. A variation on the technique to prove a system is ground free is to connect a multimeter between one pole and ground. If there is very high resistance to ground the voltage measured by the multimeter should decay as system capacitance disharges through the multimeter. The effect should be similar on both poles. An old analogue multimeter like an AVO 8 is great for this because it has a relatively low input impedance compared to the modern digital types.
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I don't suffer from insanity. I enjoy it...
RE: How Much Ground Fault Is Too Much?
Your 125V DC system seems healthy, to me. The system is ungrounded - true but still can show voltage with reference to earth. It happens this way - In ungrounded DC systems, A high value resistance is connected between (+) & (-) poles and the centre point of the resistor is connected to earth through the earth fault detection relay. Thus, strictly speaking, the system is not ungrounded.
The voltage to earth of each of the poles during healthy conditions, is 125/2 = 62.5V. In case of grounding of (+) pole, for example, the (+) to earth voltage would read zero and that of (-) to earth 125V.
In your case, the slight difference in measured volts could suggest minor leakage due to moisture or any other in the terminal box etc. involving the (-) pole (as it shows lesser voltage to earth).
Trust the above is helpful.
RE: How Much Ground Fault Is Too Much?
This would indicate to me that the ground leakage is in excess of the level chosen by the original designer.
respectfully
RE: How Much Ground Fault Is Too Much?
Or the GF detection circuit is kaput.
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I don't suffer from insanity. I enjoy it...