Floating DC system and fuse usage

Hi,

I am working on a project where the entire system uses a floating ground philosophy on the 24VDC side.
We have used fuse terminal blocks for distribution of 24VDC to the external termination panels.
When we tried to test for fuse breakage by removing a fuse on the distribution Terminal blocks, we found that we do not get a fuse breakage LED indication.
Moreover, the voltage measured in the system does not hold steady at +12VDC & -12VDC but keeps fluctuating.

I need advice on why the fuse removal is not being picked up and also whether there are any other methods of testing the same.
Also information whether the fluctuation i have mentioned here is normal to a floating system.

Which leg do you have the fuse in? Normally its in the +24VDC leg, check the polarity thru your fuse block.

If you are measuring from ground to one side of your 24VDC power supply then you will get some floating. It will not always be a perfect split.

Or do you actually have a +12DC to -12VDC power supply?

When measuring voltage on a floating system always use the common of the power supply as your reference point.

That's the way I do it.

the fuse is in the +ve side.
the power supply unit on the DC side is not connected to any ground and now we are receiving +12 & -12 or close this value when measured.
The problem is that when we remove the fuse or install a blown fuse, the meter shows reversed polarity when measured between +VE and Ground reference. Also this condition does not generate a LED indication.
Does all floating system have voltage in the circuit irrespective of an open circuit condition.

A blown fuse indicator will only work if an actual load is attached to the circuit. This is true whether you have a grounded or ungrounded system. I've seen people attempt to place two BFI fuse blocks in series. If both fuses open on a short circuit (as they should), then neither indicator will illuminate. The BFI relies upon a parallel circuit to the fuse element in order to become energized.

rikku9791 said:

the fuse is in the +ve side.
the power supply unit on the DC side is not connected to any ground and now we are receiving +12 & -12 or close this value when measured.
The problem is that when we remove the fuse or install a blown fuse, the meter shows reversed polarity when measured between +VE and Ground reference. Also this condition does not generate a LED indication.
Does all floating system have voltage in the circuit irrespective of an open circuit condition.

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Using ground as a reference is meaningless ( except telling you that your system is not grounded) in a floating system. Use the common of your power supply.

ungrounded is meaning that the voltage can be anywhere, so i would not recommend it, it can even have 400 volts when there is a small leakage somewhere in a PTC of a motor for example.
that said you will need a reference to put your meter on and do not rely on this + and - as the meter is influencing this voltage.
try it by having your meter on the circuit and just touch any cable (it is only 24 volt so no problem, you will see you meter going crazy.