Non Earthed DC systems funny thought

[Dylboy]

Hello

So the boss and I awhile ago had a discussion about DC system mostly from panels.

So it came when he said he hates stripping DC cables or touching them before the islaotor due to shock and it being DC. Then I said but if you hold the positive only you are fine. You may be at a potential but no return path through you as the panels are not earthed. I.E. the negative earthed like in A.C systems. So it will not go from positive into you while standing on the earth.

Now am I completely wrong ?

Just a bit of a Friday message of thought that I have had for awhile

Also this "live work" is very rare and when testing other installs etc so please don't say " always work dead" as it is not always possible. The world ain't perfect



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[Justloadit]

Hello

So the boss and I awhile ago had a discussion about DC system mostly from panels.

So it came when he said he hates stripping DC cables or touching them before the islaotor due to shock and it being DC. Then I said but if you hold the positive only you are fine. You may be at a potential but no return path through you as the panels are not earthed. I.E. the negative earthed like in A.C systems. So it will not go from positive into you while standing on the earth.

Now am I completely wrong ?

Just a bit of a Friday message of thought that I have had for awhile

Also this "live work" is very rare and when testing other installs etc so please don't say " always work dead" as it is not always possible. The world ain't perfect



Sent from my SM-N960F using Tapatalk

A proper installation is supposed to have a disconnect switch next to the panels, and one before the device that the panels are connected to.

Now back to your point, will depend where your negative of the cable is connect to.
If it is a hybrid inverter or any other inverter depend on design, then effectively the Negative of the panel is effectively connected to the mains Neutral via the sine wave bridge switching devices, so it is quite possible, depending on the PV voltage to have a voltage flowing between PV positive and earth..

[AndyD]

DC systems are the same as AC systems when it comes to the earth arrangement and how it has an effect on the way you can get a shock. If the supply is allowed to float ie neither leg of the supply is referenced (connected) to earth then, in theory you can make contact with either of the supply wires and you won't get a shock. Think about a high impedance or IT earthing arrangement often used in hospitals for example where the neutral is not earthed at source and all exposed conductive parts are bonded to earth.

[Justloadit]

The only concern I have with floating supplies, and there are high frequency switching devices in the load, is the build up of static voltage in the load, which at some stage will be high enough to discharge to earth. The point of break down could be an enameled wire as found in motors, transformers and inductors, or it could be between a semiconductor and earth.

In both cases this is catastrophic to the equipment, or a user who may have contacted the floating equipment, and has a low impedance to earth.