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Old 01-28-2010, 09:18 PM   #1
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Ungrounded circuits


I have some ungrounded circuits in my house. Can I add a GFCI before the first outlet on the circuit and therefore protect all others down line and is this up to code. I live in Ontario Canada.

When replacing knob and tube is it acceptable to leave some that are only connected to a wall or ceiling fixture. If not would any of these be found on a home inspection.

Thanks for your help.
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Old 01-28-2010, 09:22 PM   #2
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GFCI is legal for ungrounded. You need to use the ungrounded stickers on the receptacles.

Home inspectors don't open things up so I don't how they would find K&T inside a wall.
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Old 01-29-2010, 08:48 AM   #3
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thanks joed
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Old 01-29-2010, 08:58 AM   #4
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Quote:
Originally Posted by beech View Post
When replacing knob and tube is it acceptable to leave some that are only connected to a wall or ceiling fixture. If not would any of these be found on a home inspection.

Thanks for your help.
I'm assuming that you mean leaving them powering a light or wall switch when you say this
IE you do not mean leaving live wires connected in the wall

Eaxample: If the K&T went from a ceiling fixture to an outlet & you rewired the outlet with a new circuit you could do one of 2 things:
#1 Leave the live K&T & wire nut them
#2 disconnect the K&T from the feed , cut the ends out of each box & push the dead wire out of the box

Only problem with K&T is that it can run everywhere
So killing only part of a circuit can be a PIA at times



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Old 01-29-2010, 11:37 AM   #5
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Thanks for all the advice, I appreciate it.

On that same note, can anyone tell me what the difference is between and outlet that is grounded as you would see in newer houses and one that is not grounded but is on a GFCI protected circuit. Is one safer than another? Thanks again.
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Old 01-29-2010, 11:51 AM   #6
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Although it would not matter on an appliance with only a 2 wire cord like a lamp, the newer circuit with the grounding conductor would be safer.
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Old 01-29-2010, 11:55 AM   #7
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thanks Jim
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Old 01-29-2010, 11:57 AM   #8
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Quote:
Originally Posted by beech View Post
Thanks for all the advice, I appreciate it.

On that same note, can anyone tell me what the difference is between and outlet that is grounded as you would see in newer houses and one that is not grounded but is on a GFCI protected circuit. Is one safer than another? Thanks again.
A properly installed equipment ground (grounded if you want to call it that) is protected from ground fault by the circuit breaker. The circuit breaker will open and clear the fault and deenergize the branch circuit it protects. Therefore you will be safe from shock and electrocution.

A gfci installed on a branch circuit with out an equipment ground protects you from electrocution but not shock. Meaning that if you have a ground fault .. good example of the worst screnario.. a bare part of a hot conductor touching a metal box that has a receptacle installed in it with a metal receptacle trim cover. Because there is no equipment ground and therefore no means for a fault current path back to the utility transformer a circuit breaker will not open and deenergize the circuit. The metal trim cover will be at line voltage due to the ground fault. You come along and plug your vacuum cleaner in and touch the metal cover. You will recieve a brief tingle type shock .. the gfci then opens when it detects the leak of current once it is around 5 ma and opens the circuit at the gfci. You get shocked but you don't get electrocuted.
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Old 01-29-2010, 12:02 PM   #9
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Thanks a lot. Would it make any difference if the GFCI protection was a GFCI breaker and not just a GFCI outlet?
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Old 01-29-2010, 12:29 PM   #10
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Quote:
Originally Posted by beech View Post
Thanks a lot. Would it make any difference if the GFCI protection was a GFCI breaker and not just a GFCI outlet?
The gfci breaker would offer protection against electrocution but not shock for everything on the branch circuit if the circuit does not have an equipment ground. You cannot protect for both without a equipment ground ran throughout the branch circuit. See the drawing below so you can see how the equipment ground provides this protection against both shock and electrocution. It provides a low impedance path back to the center tap of the utility transformer so that enough current passes through the circuit breaker to trip it and denergise the entire branch circuit before anybody touches anything.
A gfci breaker will trip under a couple circumstances ...current is leaking to a ground path and is actually flowing on that path so that the gfci can detect a difference between hot and neutral current. It trips. Or if a ground fault exists where current is not flowing until someone comes along and touches something or an event happens like dropping your hair dryer in the bathtub therefore giving the current some place to go it will then trip.

The use of both gfci protective devices and circuit breakers on grounded systems protect against both leakage current faults and overcurrent faults so this is far safer agaisnt all possible types of faults. Even though you have wiring that does not contain the equipment ground the use of gfci does increase safety .... some is better than none.


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Old 01-29-2010, 12:56 PM   #11
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thanks again for all your help
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Old 01-29-2010, 01:14 PM   #12
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I probably should expand on my last post as it may be confusing.

The gfci does not need the equipment ground to function as it is intended. It is meant to detect small milli-amps of current leakage by comparing the current in the neutral to the current in the hot wire. If they are not equal the gfci will trip.

The equipment ground is intended to facilitate the tripping of the circuit breaker if an overcurrent fault exists. It completes the fault circuit with the transformer. So if a hot wire touches a metal box it provides a completed circuit that current will flow on with enough amperage to open the magnetic trip part of a circuit breaker. If the equipment ground does not exist as in a non grounded system like yours then there is no protection from ground faults that would normally be an over current event. To see this look at the diagram. Now disconnect the equipment ground from that box. The fault path you see in red is now removed. Current cannot flow over the completed circuit and the metal box comes to line voltage and stays that way till someone gets shocked or worse to force an investigation as to why the metal is energized.

A gfci installed in that box with no equipment ground will protect you from electrocution if you touch the metal box because current will leak to you and trip the gfci. Just as current will leak to the water if you drop your hair dryer in the bathtub. It is important to note that the circuit breaker may not open during a leakage current event like the hair dryer dropped in the bath tub or you touching the energized metal box because there is a high resistance path current is using not allowing enough current to flow through the breaker to open it.

So to summarize you need both the equipment ground and gfci to protect agaisnt leakage and overcurrent type faults. A circuit breaker will not protect against low amperage faults that have the potential to electrocute you but gfci will. A 15 amp breaker needs considerable more than 15 amps going thru it to open quickly. A gfci does not need the equipment ground which is required by the circuit breaker for a ground fault in order to open and clear the fault. The circuit breaker cannot detect 5 amps flowing to your body but the gfci will so hope you see the comparison.
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