Consequences of Ground Fault on a Floating 24 VDC Power Supply (Fire Alarm Panels) 2

[DM2]

I'm trying to better understand the potential consequences of a ground fault on a 24 VDC floating power supply, similar to that used for a fire alarm panel.

In my mind I'm guessing that if the circuit is grounded (and lets say your ground fault detection isn't working) there is the potential that insufficient current (or voltage?) is available to a device (relay, light, solenoid, etc.).

I see all sorts of posts advising how to troubleshoot ground faults but I really haven't seen anything that tells me why you need to monitor for a ground fault on a floating DC system...can someone educate me?

Regards,
DM

"Real world Knowledge isn't dropped from a parachute in the sky but rather acquired in tiny increments from a variety of sources including panic and curiosity."

 

[stevenal]

You monitor so the first ground fault can be detected and repaired before the second occurs. If of the opposite polarity, the second will cause a short circuit disabling your alarm system.

 

[DM2]

Steve...that's not answering my question. I'm wanting to know what could happen if you didn't have the indication that the panel had a ground. As I understand it, a single ground may not be an issue, but multiple grounds could cause problem. Essentially...what's the justification for monitoring a ground fault?

Some older panels have the ability to bypass ground fault detection, System 3 Control panels as an example. Someone might remove the jumper than enables ground fault detection. The possible reason is that they have DC voltage connected to grounded equipment that causes the ground fault. When we have this issue, we use DC-DC converters.

Regards,
DM

"Real world Knowledge isn't dropped from a parachute in the sky but rather acquired in tiny increments from a variety of sources including panic and curiosity."

 

[Compositepro]

"In my mind I'm guessing that if the circuit is grounded (and lets say your ground fault detection isn't working) there is the potential that insufficient current (or voltage?) is available to a device (relay, light, solenoid, etc.)."

Why would you think that? Nothing will happen. The second ground fault will cause your system to fail. This is why you monitor for ground faults.

 

[itsmoked]

If you have a floating DC system you can have a ground fault anywhere and it will still work fine.
You can have five more and it will still be fine as long as they're all on the same side like the positive side only or the negative side only.

The problem comes when a second GF occurs on the other side shorting the supply.
OR
Occurs somewhere in the sensing side causing a false "fire" alarm or preventing ANY fire alarm.
Or
Having a particular side GF'd causing rapid galvanic corrosion to occur somewhere in the system wires, or piping.

Having a GF sensing scheme keeps things exceptionally "safe" because you need two GFs to manifest a serious immediate problem and catching the first of the two failures allows remedy repairs before the actual function is impaired while also removing the possibility of a galvanic event going on for an extended period.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[TugboatEng]

The consequence of the ground fault is that you'll have to bypass the fault alarm which means your system will have a yellow light and you will not pass your next inspection. These can be difficult to find so start now and save yourself the hassle of a deficiency at your next audit.

In my industry, ground faults are usually caused by water intrusion into a sensor/annunciator enclosure or a faulty detection panel.

 

[DM2]

Keith,
Thanks for your input...appreciated.

Regards,
DM

"Real world Knowledge isn't dropped from a parachute in the sky but rather acquired in tiny increments from a variety of sources including panic and curiosity."