Ground in residential system?

I understand the protection that a ground conductor provides a user that may come in contact with the appliance if it becomes hot. But I'm not clear on the purpose of a ground conductor re. its roll in circuit overload protection.

Say a 15A breaker in a breaker panel experiences an overload. The increase in current causes a mechanism (electromagnetic?) internal to the breaker to open the contacts.

How is this process (tripping of the breaker) different in a grounded system compared to an ungrounded one?

Thanks, BG

Reply to
BasicGuy
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There is no difference, as long as the circuit does not include the case of the device. But if the hot wire happens to com,e in electrical contact with the metal case, then the ground conductor carries the current from the case, back to the panel, that will trip the breaker. If the case had not been grounded through that conductor, the breaker would not have popped, and the device would just sit there with full line voltage on its case, waiting for an accidentally grounded person to touch it and complete the circuit.

Reply to
John Popelish

Great question, great answer ?

Reply to
Linux

On Sat, 1 Dec 2007 10:37:45 -0700, John Popelish wrote (in article ):

Thank you, John. Very concise. All is clear now.

BG

Reply to
BasicGuy

The current over load part of it has nothing to do with the additional ground wire. excessive current will cause the breaker to open.

Of course, if your L1 wire (High side) should happen to come in contact with your ground or L2 wire (low side), it'll also generate the over loaded current. the L2 wire and ground are joined in the distribution panel in the US, I don't know about any where else.

Now, the last one is where a ground system is used in circuit protect where is, the current may not and many times does not reach the over current point of a standard breaker. In cases like this we have what is called Arc Breakers and GFCI (Ground fault Circuit Interrupter) outlets.

GFCI work with even balance loads on the L1 and L2 wires, that would be the black and white wire in the US. The internals of the GFCI use the currents in both legs to oppose each other so that a null balance is created how ever, if for some reason the L1 line should momentarily come in contact with the ground some how at levels of like 10 ma's, it will cause current that normally flows through the L2 wire to be redirect to the case/ground and thus, the null circuit in side of the GFCI now has sufficient current to pull a mini current actuator that unlatches the mechanical catch.

Arc breakers are another story and can cause more head aches than the good they were designed to serve.

The idea behind the arc breaker is to detect the noise generated on the line when things like a plug is being slid into the outlet. If there is to much of those those little arcs you see if the appliance happens to be on as you're plugging it in. the arc breaker in the panel will trip. Arc breakers also serve the usual over load current protection and cost more than a non arc breaker.

Now on a side note, Arc breakers are known to false trip especially when high levels of noise maybe on the lines for examples, bad insulators on your service coming in at the pole on a rainy day! Some one driving by with a high powered low freq. transmitter in the car.. :)

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Reply to
Jamie

Jamie wrote: (snip)

I had not heard of arc breakers till reading this. very interesting. Thanks.

I found this tutorial:

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John Popelish
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Reply to
John Popelish

let me see if I understand your question correctly. you are inquiring why a ground is different than a neutral in an electrical panel or in circuitry?

The Ground is a direct path to ground and enters the ground as for a safety.

And as to the neutral to ground should be a value of point one% resistance or less to make proper for phasing concerns unless it is a bonded B phase which Ground and Neutral are bonded together such as for Industrial applications and for a desired voltage or other requirement of equipment or device.

Ground should never be switched or controlled the ground should always be continuous circuit this also includes neutral.

I hope this helps if you have further questions please feel open to contact me here.

Jeff,

Reply to
effectsunlimited

Other AFCI (US) info:

AFCIs (arc fault circuit interrupters) currently on the market only detect arcs at about about 60A level (requirement 75A). This will only detect parallel arcs - hot-to-neutral or hot-to-ground.

They also detect ground faults at a required level of 50mA (but commonly

30mA). (This is higher than the 5mA level for GFCIs.) The idea seems to be that an arc in a cable (romex, extension cord) with a ground wire present will soon produce a ground fault.

Starting 1-1-08 the NEC requires that "Combination" AFCIs be used. These detect arcs at a level of 5A and will detect series arcs (like loose connections). A minor problem is that as far as I know these devices are not currently on the market. SquareD says they will have them out by

1-1. But that gives no time for field experience before they are required to be used.

AFCIs detect current. They will not detect noise on the line unless that results in a current through the device that looks like a 'bad' arc. They are designed not to detect 'normal' arcs - switches opening, brush motors, light bulb burning out. Separating 'bad' 5A arcs from 'normal' arcs sounds like a challenge.

The NEC now requires AFCIs on bedroom circuits. Starting in the 2008 NEC they will more or less be required everywhere a GFCI is not required.

An interesting paper from the Consumer Product Safety Commission

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explains the rationale for using AFCIs, why normal circuit breakers aren't adequate, where the 75A level came from, normal and bad arcs.

Another good source is::

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from IAEI News, January/February 2003,The Truth About AFCIs (Part 1) (part 2 is at
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------------- The overload trip mechanism in residential breakers is thermal, which gives a time delay characteristic.

Probably in a couple other posts - when a circuit breaker trips on a 'ground fault' the current path does not involve the earth.

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