# Ideas on how to comply with Ground Fault detection



## albo2 (Oct 4, 2011)

does anyone know how to comply with this.


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## Plymouth60 (Sep 4, 2012)

I haven't been through it yet, but was considering a device like this:

http://www.bender.org/products/ground-fault-ungrounded-systems.aspx

Applications: IR425

Single-phase AC/DC systems up to 300 V
Systems with variable frequency drives (VFDs)
Control circuits
Portable generators
General low-voltage, ungrounded circuits
Large industrial systems

Cheers
John


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## CrunchTime (Feb 13, 2009)

I haven't been though this yet either, but note that the regs say "where the components are suitable", and there's a strong case to be made that series DC/brushed motors are not suitable since there's always some leakage current. Check with your certifier before spending too much effort on it (and report back here please )


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## albo2 (Oct 4, 2011)

CrunchTime said:


> I haven't been though this yet either, but note that the regs say "where the components are suitable", and there's a strong case to be made that series DC/brushed motors are not suitable since there's always some leakage current. Check with your certifier before spending too much effort on it (and report back here please )


Yep I read that however my conversion is AC induction I don't think I'll be able to get away with that, I have found a kit on jaycar electrical that measures voltage and can be set to switch a relay, if I connect that to the 12v system and set it to run an alarm if it sees say 20 volts wouldn't that work?


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## CrunchTime (Feb 13, 2009)

albo2 said:


> Yep I read that however my conversion is AC induction I don't think I'll be able to get away with that, I have found a kit on jaycar electrical that measures voltage and can be set to switch a relay, if I connect that to the 12v system and set it to run an alarm if it sees say 20 volts wouldn't that work?


I don't think it's the 12V circuit you need to worry about - it's the high voltage circuit. Also, running an alarm isn't good enough - it has to actually break the circuit. If the battery is sending 200A output one side, and only getting 100A back on the other, the other 100A is going somewhere it shouldn't (i.e. through you) this is a bad thing that needs to be stopped, and soon  

My understanding is that ground fault detection works by looking at the current (NOT voltage) going out from the power source i.e. battery, and compares it to the current returning - they of course should be equal. If there is a ground fault, it will cause the return current to be less than it should (since by definition some of the current is following another path), which then trips a relay to disconnect the power.

I understand the actual current difference that trips the relay is usually in the mA range, and triggers the relay in milliseconds, so the actual current going through the wrong path is very short duration.

But this is all just from researching it when I first saw the requirement, and I didn't get to a solution then, nor do I claim to be an expert...


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## albo2 (Oct 4, 2011)

CrunchTime said:


> I don't think it's the 12V circuit you need to worry about - it's the high voltage circuit. Also, running an alarm isn't good enough - it has to actually break the circuit. If the battery is sending 200A output one side, and only getting 100A back on the other, the other 100A is going somewhere it shouldn't (i.e. through you) this is a bad thing that needs to be stopped, and soon
> 
> My understanding is that ground fault detection works by looking at the current (NOT voltage) going out from the power source i.e. battery, and compares it to the current returning - they of course should be equal. If there is a ground fault, it will cause the return current to be less than it should (since by definition some of the current is following another path), which then trips a relay to disconnect the power.
> 
> ...


I guess if we used amps it would have to be done with hall effect sensors as I don't think you can put a shunt in the positive leg.

Just read through the bender site above and they have a DC detector that measures resistance to ground on both the positive and negative legs that would be the way to go, hmm I wonder how much they are, only one way to find out.


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## albo2 (Oct 4, 2011)

Could any of you smart people tell me what if any would be the effect of the main pack leaking to ground on the 12V system, wouldn't that see a negative voltage ie the ground having a higher potential than the positive terminal of the 12v battery


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## Tesseract (Sep 27, 2008)

CrunchTime said:


> ...My understanding is that ground fault detection works by looking at the current (NOT voltage) going out from the power source i.e. battery, and compares it to the current returning - they of course should be equal. If there is a ground fault, it will cause the return current to be less than it should (since by definition some of the current is following another path), which then trips a relay to disconnect the power.
> 
> I understand the actual current difference that trips the relay is usually in the mA range, and triggers the relay in milliseconds, so the actual current going through the wrong path is very short duration....


You are correct. The difficulty with complying with rules like this is that it is totally impractical to resolve milliamps of difference between the forward and return current out of, e.g., 1000A. A typical leakage current trip spec in the US is 5mA; that's 5 millionths of the output of a 1000A controller. Needless to say, a current measurement circuit with 0.0005% accuracy is going to be *expensive*... 

So the way this is typically done in traction circuits is to periodically measure the resistance between the two supposedly isolated systems. Note that the act of making this measurement creates a ground fault in itself, so the usual approach is to use a relay to connect the measuring circuit to the two isolated systems just long enough to take a measurement, then default to being disconnected so that isolation is maintained.

It's a laudable goal to look for current leaks like this, but it's an incredibly thorny problem to solve.


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## Coulomb (Apr 22, 2009)

albo2 said:


> Could any of you smart people tell me what if any would be the effect of the main pack leaking to ground on the 12V system, wouldn't that see a negative voltage ie the ground having a higher potential than the positive terminal of the 12v battery


Errr, no. Leakage from the traction pack to ground will have no effect on the 12 V system.

It won't have any effect on the high voltage system, either, unless there is a second fault. But the Encyclopedia Galactica notes the effect of even small currents on certain carbon based bipeds, if they come in contact with the traction pack when there is a leakage to ground elsewhere.

[ Cultural reference to the original Hitchhiker's Guide to the Galaxy TV series (well, the radio series was the real original, but I mean not the Hollywood movie.) ]


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## KiwiCatherineJemma (Sep 5, 2012)

Well if you are using a 3 phase AC motor, would a possible fix be to use 3 of those RCD/ELCBs as sold by various hardware and electrical stores for about $15 each. Plugged into a standard wall outlet the appliance, or extension lead, plugs into it's controlled output. I use mine for using an electric lawnmower outside, or for if I have an appliance in bits for repair, and want to power it up temporarily. Wire up normal type household 10 amp sockets and install 3 of these as required, running plugs to your motor. But does your motor draw more than 10 amps each across all 3 phases ? The household models available everywhere are limited to 10 amps each phase obviously, however a wholesale/trade supplier like Radcliffe might have a 3 phase model that could handle 32 amps per phase as a similar plug-in unit. Try asking around.


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## carrott (Aug 19, 2008)

There is a little bit of confusion here. The ground fault detection requirement in 2.4(1)(f) of Electric & Hybrid Vehicles 75-00(00) is intended to detect a connection between the battery and the frame of the car. It does not need to detect an imbalance between the current leaving the battery and returning the to the battery, so you don't have to look for mA's in 100's of amps.

The reasons for this requirement are fairly simple. If you have a connection from the battery to the frame of the vehicle (say from a wire that rubbed somewhere) then whenever you touch the battery and the frame you are likely to get an electric shock. Worse than this, when another wire rubs through and touches the frame of the vehicle, you are likely to get a short circuit and potentially a very big fire. I say likely because it depends on where the ground faults are introduced.

The easiest way to check if you have a ground fault is to take a multimeter and measure the voltage between several places on the battery and the frame of the vehicle. When you do this you may see some strange effects. My car has a high voltage which slowly falls to zero after you connect the meter because there is a parasitic capacitor formed between the battery and the body. A friend's car reads about half the pack voltage between his battery +ve and the frame because there is a 10Mohm connection inside his motor controller and my meter has 10Mohm input impedance. Both of these vehicles are safe.

Do not use the resistance scale on your multimeter, if there is a low impedance ground fault you will likely destroy the meter!

I haven't thought about how to build a detector which satisfies the requirements. You can't use an household DIN rail RCD as these are designed to compare two currents. The first ground fault doesn't cause any current to flow so these devices will not detect it.


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## albo2 (Oct 4, 2011)

Don't think there is any confusion on what this is for however it is a confusing issue on how to comply as there are contradictory requirements:

Is it possible to send a digital signal down the high voltage line and listen for it on the chassis?

2.2(3) The high voltage (exceeding 60V DC or 25V AC) electrical wiring within an
electrically‐powered low volume vehicle must:



(b) not be electrically connected to the vehicle’s chassis or body;


Instrumentation
2.4(1) The instrumentation of an electrically‐powered low volume vehicle must provide
to the driver, a clear visual indication of:


(f) where the components are suitable, the occurrence of a ground fault
(isolation failure), accompanied by an audible warning (see note 3).


NOTE 3: A ground fault detection system may not be compatible with some components. Brushed DC systems
will always have some earth leakage due to conductive dust from the motor brushes, and flooded
batteries will also inevitably cause some earth leakage due to conductive mist vented during charging. A
ground fault detection system as specified in 2.4(1)(f) should take account of the motor and battery
type. The aim is to detect a ground between the battery voltage and the vehicle structure or body (if
made of conductive material). To test (as part of the LVV certification process), a suitable resistor can
be connected between several electrical positions within the battery group, and several places on the
vehicle structure/body (including the structure near the battery), and check that the leakage detector
detects it.


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## Nick Smith (Oct 26, 2007)

I had an interesting conversation with the EV guy at Bender US head office this morning. Although he was not able to give me US pricing information, he did imply that the price break on multiples was worth pursuing. I will be following up with the NZ distributor... 

Additionally, he suggested that the EV spec boards can and should be used on the lead acid and brushed DC as the fault level settings can be varied. What this does for the brushed DC guys is give an indication that the carbon dust build up is getting to be a problem and it will tell the lead acid guys to clean up their batteries.

All round it is a good idea, but it is simply a bit expensive to comply with at the moment. The LVVTA spec was written with good intentions but in some cases with no immediate answer on how to comply.


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## Nathan219 (May 18, 2010)

Bender units work very well in this application, and they are able to be powered by many different sources. I have personally used them and seen them detect the slightest faults in the Mega ohms range, very good stuff and unbelievable customer support, truly a first class company and product. I NHTSA 500 ohms per volt isolation in the event of a crash. Benders units have no trouble detecting insulation integrity well beyond this standard.


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## albo2 (Oct 4, 2011)

Have just ordered an IR125 from Bender.


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## Duncan (Dec 8, 2008)

albo2 said:


> Have just ordered an IR125 from Bender.


Hi
did you mean an IR425?
And how much did it cost?


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## albo2 (Oct 4, 2011)

I only have a 100 volt system so this should do the trick, should work for anyone using the AC50 HPEV system, this is not specifically designed for automotive use but should work OK will report once I have it, the IR155 series is around 700 - 800 plus fitting kit but is a very nice automotive designed unit

Bender IR125Y-426 Insulation Monitor
1 B91023012; IR125Y-426 Insulation Monitoring Device AC
9,6-138V 50/60Hz DC9,6-138V 10...200 kOhm
402 $410.00 $410.00 S
402 1 B990056; Mounting Plate for IR 125Y $7.00 $7.00 S


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## Nick Smith (Oct 26, 2007)

Hi all. I would just like to point out that the new AC controller from Curtis (1239) has ground fault detection built in. You DC guys will just have to spend the money on a Bender relay still.

There was some interesting stuff going on with charlie Rickmans opel with the twin controller setup with it detecting intermittent ground faults. Turns out BOTH controllers were checking and when both happened to check at the same time each found the ground fault that the other had temporarily created. Turn it off in one controller and all good.


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## Duncan (Dec 8, 2008)

Nick Smith said:


> Hi all. I would just like to point out that the new AC controller from Curtis (1239) has ground fault detection built in. You DC guys will just have to spend the money on a Bender relay still.


No we won't

The rules for ground fault detection say "where the components are suitable"

And a bit later - "may not be compatible with some motor and battery types. Brushed DC systems will always have some earth leakage...."

So we don't need no stinking Bender thingy!

My device got through cert without as did EVNZ's pickup


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## Nick Smith (Oct 26, 2007)

Duncan said:


> No we won't
> 
> The rules for ground fault detection say "where the components are suitable"
> 
> ...


 I did not imply you HAD to have one - but if you did want one, you don't have many options...


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