Ground Fault Protection

Thread Starter

Shashwat97

Joined Apr 15, 2019
18
What exactly is ground fault protection ckt. When and how do one decide to incorporate it in the design? I'm developing an ECU for automatic HVAC system, would I need it?
 

vu2nan

Joined Sep 11, 2014
345
In an electrical system, a ground fault is an unintended contact between a supply and common/chassis/ground that could cause a fire or result in electrocution of personnel. Ground fault protection is a tripping mechanism that would clear the fault and render it safe. It is a mandatory safety requirement, for any electrical system, that could be met using fuses, circuit breakers, residual current devices etc.

- Nandu.
 

Thread Starter

Shashwat97

Joined Apr 15, 2019
18
In an electrical system, a ground fault is an unintended contact between a supply and common/chassis/ground that could cause a fire or result in electrocution of personnel. Ground fault protection is a tripping mechanism that would clear the fault and render it safe. It is a mandatory safety requirement, for any electrical system, that could be met using fuses, circuit breakers, residual current devices etc.

- Nandu.
In most of the ECUs i've not seen ground fault protection neither people add in their requirement, in this case how would you decide if you actually need it. Is there any parameter or factor that i should be looking
 

ronsimpson

Joined Oct 7, 2019
2,988
You need ground fault protection when some one could get shocked.
-If something is wired in you don't need it. (light, air conditioner, etc)
-Need it for outside plugins, in the garage where you stand on concrete or dirt. (not needed for inside plugs)
-Need it for around water, sink, tubs. Kitchen, Bath.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
If this is a ECU as in automotive application, then typically just fusing is required for protection.
In the general sense, a GFI etc is a stipulation for H.V. circuits, i.e. any voltage that exceeds 60v.
Personally I do not recall ever seeing one used in an automotive environment.
Max.
 

crutschow

Joined Mar 14, 2008
34,283
The primary use of a GFCI is to protect a person from a lethal electrical shock.
That's not considered likely with any voltage below 60V.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
Another feature of automotive wiring that generally makes the use of a GFI redundant is the fact the return path or "Gnd" is the chassis body/frame.
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
Just to make it clear, what environment are you using the term ECU? In the accepted automotive sense?
Or some other definition.
Max.
 

Tonyr1084

Joined Sep 24, 2015
7,853
[HOW] are you using the term ECU?
I was wondering the same thing. ECU to me means Engine Control Unit, as used in car engines. It could also mean Electronic Control Unit. How is the TS (Thread Starter) using the term ECU?

Other terms
PCM Power Control Module
ATC Automatic Transmission Control
BCM Body Control Module
GFCI Ground Fault Circuit Interrupter
AFCB Arc Fault Circuit Breaker
ICU Intensive Care Unit (where a person who's received a near lethal shocking may end up)

To get a good answer the TS needs to give a definitive explanation of what he/she is doing.
 

Thread Starter

Shashwat97

Joined Apr 15, 2019
18
Just to make it clear, what environment are you using the term ECU? In the accepted automotive sense?
Or some other definition.
Max.
Automotive domain, yes even i have not seen ground protection in any ECUs till now, let's say i'm sinking from a load inside my board not 60V, lower voltage, would i need it then?
 

Thread Starter

Shashwat97

Joined Apr 15, 2019
18
I was wondering the same thing. ECU to me means Engine Control Unit, as used in car engines. It could also mean Electronic Control Unit. How is the TS (Thread Starter) using the term ECU?

Other terms
PCM Power Control Module
ATC Automatic Transmission Control
BCM Body Control Module
GFCI Ground Fault Circuit Interrupter
AFCB Arc Fault Circuit Breaker
ICU Intensive Care Unit (where a person who's received a near lethal shocking may end up)

To get a good answer the TS needs to give a definitive explanation of what he/she is doing.
yes, you're right generally I work with BCM, currently I'm working on Climate Control Module.
 

marcf

Joined Dec 29, 2014
288
There is one application for ground fault Protection (probably best called detection) and this in fire alarm circuits. It is essential that the voltages involved (24vdc) are never in contact with the ac power ground. A ground fault condition can mean a crushed cable, or a disabled detection device or entire circuit.

I suppose that this would be a protection against the building occupants from a non operating fire alarm system.
 
Last edited:

MisterBill2

Joined Jan 23, 2018
18,176
The description in post#1 is not very clear, as many have commented.
If it is a control computer package for a typical home HVAC system then it would probably use the 24 volts AC transformer supply used with most HVAC systems in homes and buildings. That voltage is not considered a shock hazard voltage, and also it is usually isolated from ground, in which case there will not be even a potential shock hazard. A correctly sized fuse in the 24 volt supply line should be adequate.
 

MisterBill2

Joined Jan 23, 2018
18,176
The OP has already declared it is the automotive domain!
OK, It is mentioned somewhat in post #10, and slightly more in post #11.
GFCI is not an automotive thing. I am not even sure why the question arose.
NowEV batteries at 600 or more volts will be a serious shock hazard but for thosea GFCI will not be useful.
 
OK, It is mentioned somewhat in post #10, and slightly more in post #11.
GFCI is not an automotive thing. I am not even sure why the question arose.
NowEV batteries at 600 or more volts will be a serious shock hazard but for thosea GFCI will not be useful.
Ground fault protection typically applies to the differential sensing of the current flowing between the two conductors intended for the load. This would be the "hot" and neutral in US systems, but could be used in other situations as well. Deviations as small as 30 or 40 milliamps from the 15 or 20 amp circuit will trip the GFI. The term has also been used in isolated systems such as hospital operating rooms where both conductors are "floating" from ground and any connection beyond small capacitive leakage currents will trigger alarms or even shut-down. Certainly could apply to the case where alarm systems are supposed to be "floating" but somehow are now connected to ground as well; indicating either a fault or tampering.
 

ChasNC

Joined Jul 14, 2020
4
Yes, I would agree that it is always important to be descriptive when explaining your problem and make no assumptions. When I first read this post, I assumed it was a typical AC system. You can easily cause others to make assumptions by leaving out key data. For instance: this is a DC application. Any time you are working on something new like this, take the time to learn what exists out there first. GFCI protection is very common and there are many sources of information on the web. I always like to check Wikipedia first when diving into new waters. And for this topic: look for what level of current flow is risky for humans. Most standards require tripping at only 5mA. Very low.

I have worked with GFCI protection for along time and know the problems and pitfalls associated with it. GF protection is usually used in AC voltage systems due to typically higher voltages, and with plugged appliances, there is a high chance of contact or conduction with water ingress. AC is also dangerous not only due to any resistive path through the body but also the capacitive paths, like through your shoes to earth. Your shoes can have a very high DC resistance and protect you that way, but they could also easily have a low capacitive AC impedance still causing risk.

But a person can be badly shocked even with as low as 12VDC if they come into contact and their skin is sweaty and conductive with sweat salts. Telecom workers can be badly hurt if they touch the -48VDC rails with sweaty skin.

AC Voltage GFCI:
https://www.powerelectronictips.com/basics-ground-fault-interruptors-faq/

Detecting GF with pure AC systems is not difficult as long as ther is no DC. The present implementations GF protection is very problematic since they performed "typical" field testing and not a broad field test before launching. In most GFCI plugs and protective breakers, a current sense transformer is used to sense the "common mode" current flowing out of the hot and neutral wires. Literally think of a common mode inductor but being used to sense the common mode current. If the current leaving the hot completely returns through the neutral, the flux from both wires cancels and there is a net zero flux in the core. If there is a difference, the net flux is not zero and the sensor triggers a trip if enough current is sensed. The biggest problems here are (1) it assumes the current is line frequency and only a few line harmonics (i.e., no PWM or SCR triggered waveforms), and (2) there can be no DC offsets in the load. Yes, you can have significant DC in a load on an AC line! This is a common problem with microgrid inverters, which also cause problems backfeeding a distribution transformer with a DC offset and heating it up due to flux offset. The goof here is that the energy loss from the utility side into the transformer with DC flux completely wipes out the energy returned by the microinverter. The utility looses badly here and the market has not realized or corrected this yet.

SCR triggered loads also create tons of conducted EMI which will trigger a GFCI plug, as well as motor drive loads such as HVAC blower controllers and compressor drives. So building codes that require GFCI plugs on residential HVAC systems (most of the US) are going to cause people to have to suffer through nuisance tripping. If you do a search for the latter, the you will find the Internet is flooded with people trying to solve this. And the same for tripping GFCI plugs with SCR loads like variable speed saw and drills.

DC Voltage GF
In an automotive system with DC rails, it is going to be difficult to design a useful solution. I am curious as to what market spec required this? What DC voltage and what is the normal load current range? If it is to protect from a higher voltage DC rail for an inverter that makes sense to me but you are going to have problems from the inverter switching noise also, and any bulk SMPS noise for distribution and charging. If the user touches the PWM out wiring, the noise is going to be immense with PWM artifacts. In a typical automotive DC battery rail there is a tremendous amount of noise, so you getting a definition as to what frequency range is needed is going to be critical to complete this task. A fast trip is not wise since you will have nuisance trips due to the system noise. This is the reason why I explained the AC voltage GF solution. It has similar issues with noise.

I would also suggest doing an informal FMEA on what points can the user come into contact. Don't do a real FMEA, but think about what can be done wrong and how to detect it. Even user abuse. If they can - they will. Engineers are often tasked with protecting the user from immense stupidity, which if you think about it is keeping the gene pool dirty. But that is our job as well, and it is great to sometimes see the humor in things.

Hope this helps some. My biggest suggestion: do some research on the web.
 
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