I don't understand how Chassis Ground works...
Discussion
Could someone who understands the actual physics behind it:
1) How exactly is the Chassis a ground? I don't understand this concept. It's not connected to the earth- how does it act as a ground?
2) I tried connecting one end of the multimeter to the chassis and the other end to a point 1cm away on the chassis too- yet it still shows OL infinite resistance
sorry for being thick- if electrons take the path of least resistance wouldn't electrons from the negative lead of multimeter not find it easier to flow across that 1cm piece of metal back to the multimeter via the positive terminal?
yet they prefer to flow through the neg lead through the rest of chassis and away?
1) How exactly is the Chassis a ground? I don't understand this concept. It's not connected to the earth- how does it act as a ground?
2) I tried connecting one end of the multimeter to the chassis and the other end to a point 1cm away on the chassis too- yet it still shows OL infinite resistance
sorry for being thick- if electrons take the path of least resistance wouldn't electrons from the negative lead of multimeter not find it easier to flow across that 1cm piece of metal back to the multimeter via the positive terminal?yet they prefer to flow through the neg lead through the rest of chassis and away?
1. It's the negative return, of a dc circuit, to the battery. Battery negative is connected to chassis, components connect to chassis for their negative return path to complete the circuit. Saves having hundreds of extra wires going back to battery negative
2. Sure you're testing unpainted good clean metal surfaces?
2. Sure you're testing unpainted good clean metal surfaces?
Ilovecbrs599999 said:
I was also told however that the even when the battery is disconnected the chassis is still a ground. This is so seriously confusing me.
Don't believe everything people tell you perhaps?! The chassis is the negative return side connection to the battery. If the battery is disconnected then the circuit is broken.
Do some reading on the difference between AC and DC circuits. They are very different.
Before I posted here I intitially believed what everbody here is saying:
What confused me was this:
this was on a website called Bikechatforums where I asked the same question:
https://www.bikechatforums.com/viewtopic.php?t=321...
With such little experience myself and plenty online who have plenty of experience it's hard to completely filter out what is sensible to believe and what isn't
I am the gentleman in the first post of that topic on that website. Please note we are talking motorcycles (not that it'd probably make much difference)
The experience gentleman (and nobody in the that thread contested it) in the second post said:
" In most cases, there is only a single cable/strap going between the battery negative and ground, all the other companants earth through the frame. So for a continuity test, the battery need not be connected.
The answer is in the question really. You are checking "continuity to ground" and the whole frame on a bike is "ground". So you are checking for continuity between the measuring point and any piece of bare metal on the engine or frame rather than the battery negative. (the metal facing of the ignition lock is a good one. I usually stick the negative terminal of my meter in the key "gate")"
Is the second post wrong then?
In that thread did I receive the wrong advice then?
And in answer to the question there :
"when I am checking CONTINUITY TO GROUND , if I want to connect the other lead to chassis instead of negative battery terminal then surely the battery must be connected?" The answer is actually yes? Can't be done without battery connected and just putting black lead of multimeter to the chassis?
What confused me was this:
this was on a website called Bikechatforums where I asked the same question:
https://www.bikechatforums.com/viewtopic.php?t=321...
With such little experience myself and plenty online who have plenty of experience it's hard to completely filter out what is sensible to believe and what isn't
I am the gentleman in the first post of that topic on that website. Please note we are talking motorcycles (not that it'd probably make much difference)
The experience gentleman (and nobody in the that thread contested it) in the second post said:
" In most cases, there is only a single cable/strap going between the battery negative and ground, all the other companants earth through the frame. So for a continuity test, the battery need not be connected.
The answer is in the question really. You are checking "continuity to ground" and the whole frame on a bike is "ground". So you are checking for continuity between the measuring point and any piece of bare metal on the engine or frame rather than the battery negative. (the metal facing of the ignition lock is a good one. I usually stick the negative terminal of my meter in the key "gate")"
Is the second post wrong then?
In that thread did I receive the wrong advice then?
And in answer to the question there :
"when I am checking CONTINUITY TO GROUND , if I want to connect the other lead to chassis instead of negative battery terminal then surely the battery must be connected?" The answer is actually yes? Can't be done without battery connected and just putting black lead of multimeter to the chassis?
Edited by Ilovecbrs599999 on Sunday 10th September 10:42
I think some are getting confused over the definition of parts of the circuit (none above by the way before anyone bites)
A DC circuit has a positive & a negative from its supply (battery/alternator) & when something is connected across these it completes the circuit.
It does not need an earth, it does not need a ground (which is an earth by another name) it is more accurately called a chassis in the case of something like a car/bike/lorry etc that is not earthed. It gets this negative (return path for current) connection by virtue of the battery being connected to the car steelwork/chassis/engine.
The chassis is the return path for the current in the circuit & this can be picked up anywhere with a good electrical connection to the chassis, this makes the wiring used in the manufacture of the vehicle much less, other wise every switch/lamp/sensor would need a wire from the fuse box & also to the battery, whereas with a chassis as the return path it can frequently make do with just the one wire, or only a short negative wire to the chassis.
A DC circuit has a positive & a negative from its supply (battery/alternator) & when something is connected across these it completes the circuit.
It does not need an earth, it does not need a ground (which is an earth by another name) it is more accurately called a chassis in the case of something like a car/bike/lorry etc that is not earthed. It gets this negative (return path for current) connection by virtue of the battery being connected to the car steelwork/chassis/engine.
The chassis is the return path for the current in the circuit & this can be picked up anywhere with a good electrical connection to the chassis, this makes the wiring used in the manufacture of the vehicle much less, other wise every switch/lamp/sensor would need a wire from the fuse box & also to the battery, whereas with a chassis as the return path it can frequently make do with just the one wire, or only a short negative wire to the chassis.
So in conclusion:
When we check connection to ground
All we want to test is connection to chassis is good.
By that visual check When we reconnect the negative terminal of battery to chassis (when we the battery in) - the chassis will be grounded like everyone has explained.
By transitivity the connection to ground of everything will be good.
If this is all correct- thank you so much everyone!- it finally makes sense
When we check connection to ground
All we want to test is connection to chassis is good.
By that visual check When we reconnect the negative terminal of battery to chassis (when we the battery in) - the chassis will be grounded like everyone has explained.
By transitivity the connection to ground of everything will be good.
If this is all correct- thank you so much everyone!- it finally makes sense
Just to add, ground/earth is a way to provide a path for a fault current should one occur.
If a fault develops in a certain component, it is safer to give that fault current a dedicated path to earth - than to leave it ungrounded and risk a human touching it and them providing the path to earth. If this were to happen the human would form part of the circuit and allow current to flow to earth (if conditions were right) putting them at risk of electrocution.
The ground/earth allows a fault current to flow into the earthed structure (such as the chassis in the car, or you will see for example in houses the yellow and green wiring earth to copper pipes). Providing a path to earth will exceed the rating of any protection device (either a fuse in a car, or for example the MCB in your domestic distribution board) which will blow (fuse) or trip (MCB) and break the circuit. This all happens in a very short time period and is intended to prevent harm to any human.
The above is different to using the chassis for negative return. With the negative return there is still a potential difference (i.e voltage) but the current is very low by the point it enters the chassis and returns back to the battery negative terminal (hence why you dont get electrocuted if you touch a car which has the engine running, for example).
If a fault develops in a certain component, it is safer to give that fault current a dedicated path to earth - than to leave it ungrounded and risk a human touching it and them providing the path to earth. If this were to happen the human would form part of the circuit and allow current to flow to earth (if conditions were right) putting them at risk of electrocution.
The ground/earth allows a fault current to flow into the earthed structure (such as the chassis in the car, or you will see for example in houses the yellow and green wiring earth to copper pipes). Providing a path to earth will exceed the rating of any protection device (either a fuse in a car, or for example the MCB in your domestic distribution board) which will blow (fuse) or trip (MCB) and break the circuit. This all happens in a very short time period and is intended to prevent harm to any human.
The above is different to using the chassis for negative return. With the negative return there is still a potential difference (i.e voltage) but the current is very low by the point it enters the chassis and returns back to the battery negative terminal (hence why you dont get electrocuted if you touch a car which has the engine running, for example).
Ground and earth on a car / motorcycle
It has been my bug bear for a number of year, as you cannot have an "earth" on a car as it is not connected to earth.
"Ground" is possibly a better name.
It should be called "chassis" or "-Vdcc" if you are an electrician ( not very catchy though)
Jack
It has been my bug bear for a number of year, as you cannot have an "earth" on a car as it is not connected to earth.
"Ground" is possibly a better name.
It should be called "chassis" or "-Vdcc" if you are an electrician ( not very catchy though)
Jack
sparks85 said:
Just to add, ground/earth is a way to provide a path for a fault current should one occur.
You are talking about a "protective ground/earth", which is designed as a fault current path. In terms electrical circuits the term "ground" can refer to a common return path or a reference point from which voltages are measured and most often these two points are the same. IOW "Ground" is perfectly correct terminology for a cars frame which is connected to one side of the battery.
Mr2Mike said:
You are talking about a "protective ground/earth", which is designed as a fault current path.
In terms electrical circuits the term "ground" can refer to a common return path or a reference point from which voltages are measured and most often these two points are the same. IOW "Ground" is perfectly correct terminology for a cars frame which is connected to one side of the battery.
I stand corrected! I deal with vaguely related stuff in my day job (electrical rail engineering) where we would use the terminology 'negative return's and 'earthing' in two very different contexts.In terms electrical circuits the term "ground" can refer to a common return path or a reference point from which voltages are measured and most often these two points are the same. IOW "Ground" is perfectly correct terminology for a cars frame which is connected to one side of the battery.
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