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Old 01-12-2009, 06:44 PM   #31
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Unfused connectors MELTED House wires WHAT TO DO???


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Originally Posted by AllanJ View Post
We would need the whole paragraph mentioning this impedance to understand the significance. For example if we are talking about voltage drop imposed by the panel, an impedance of one milliohm from the hot service feed for the main breaker through to the hot lead out of a branch circuit breaker would mean unmeasurable voltage drop.
In the same chapter he talks about the percent impedance method for determining short circuit current and mentions 20,800A, which would put the impedance at closer to 10 milliohms.

My dryer nameplate says 24A but I can check the 240v current draw with a clamp-on ammeter. I can use another unused 240v line to measure voltage drop at the panel without taking the cover off while having my wife switch the dryer on and off until I get some idea of the drop.

1 milliohm would give me a 24 mV drop, the other would give 240 mV. My meter may be able to resolve a change this small, otherwise I'll have to make a circuit that cancels out most of the 240v, kind of an expanded-scale meter.
If I can get off my butt I'll invest 15 minutes and check it for my house. Other houses drawing current from the same xformer will reduce this Thevenin equivalent impedance.

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Old 01-13-2009, 12:52 AM   #32
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Unfused connectors MELTED House wires WHAT TO DO???


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In the same chapter he talks about the percent impedance method for determining short circuit current and mentions 20,800A, which would put the impedance at closer to 10 milliohms.
That sounds unrealistic to me, why would we all use 10KA breakers if your home service could short 20KA?

2/0 copper is 0.08 milliohms per foot. 4/0 Al is about the same.

If your service drop is only 20 feet long, that's 40 feet of wire. So you got 3.2 milliohms just in the wire on a short service drop.

And that's not even talking about the impedance of the transformer, which is surely several times that.
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Old 01-13-2009, 12:55 AM   #33
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Unfused connectors MELTED House wires WHAT TO DO???


Well I wonder what the insurance company does about wiring that is so sub standard it doesn't even come close to any codes now or ever. I gutted all the EMT today. I found some really scary stuff. I forgot my camera over there.

The 1/2" emt run to the AC contained 2 #12 and a insulated ground wire, all THHN. It appears at one point the THHN was damaged due to a bad pull. That must have arced and about 20' of the run melted and fused together all 3 strands of the THHN. If it wasn't in EMT the house would have most certinly been on fire if that happened.

Some of the things I have found are too scarey to describe, will have to post photos.

The electrician that is going to megger the upstaris circuts didn't make it today, but hopefully tommrow.

If what happened in that conduit to the AC happened anywhere else in the house... Well it could have happened partially and just managed not to start a fire, but the wires could still be in very bad shape.

I found that all the Knob and tube is feed off of Romex. Atleast some of the junctions to romex are burried in the walls....

Don't if it I should laugh or cry.

Much of this was done by the previous owners, and has been this way for over 3 decades.

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Old 01-13-2009, 01:11 AM   #34
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Unfused connectors MELTED House wires WHAT TO DO???


Jamie.,

Thanks for letting us know up the speed with the damage ya got on your father's house.

Speaking of Megger I have Fluke Megger { yes there is serveal verison on market } and I got a simple megger which it will give me go or no go with the cables or conductors { It a Amtech but not sure if the company still in bussiness or not }

Merci,Marc
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Old 01-13-2009, 01:12 AM   #35
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I gutted all the EMT today.
I know you are anxious, but you might be hurting your ability to make a larger insurance claim here for bringing all the damaged circuits up to code.

Was there already a permit pulled for work at his house before the accident?

If so, the insurance company is going to be more likely to see your claim as a way to fund the work you were already planning on doing.
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Old 01-13-2009, 01:23 AM   #36
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Unfused connectors MELTED House wires WHAT TO DO???


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I know you are anxious, but you might be hurting your ability to make a larger insurance claim here for bringing all the damaged circuits up to code.

Was there already a permit pulled for work at his house before the accident?

If so, the insurance company is going to be more likely to see your claim as a way to fund the work you were already planning on doing.
NO permit was in place prior to the accident. Was just a simple repair. This all started because I discovered that a ground was energized. My mom complained, "when I touch that switch I get a little tingle". Then in the process of figuring out where that ground was being energized, I was tracing circuits to find out what goes where, with the goal being to find what is connected to the circuit that had the energize ground and to find the fault and repair it. Then my dad was in the panel and we had the accident.

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Old 01-13-2009, 09:00 AM   #37
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Unfused connectors MELTED House wires WHAT TO DO???


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That sounds unrealistic to me, why would we all use 10KA breakers if your home service could short 20KA?.
Just because the panel can short 10KA among bus bars, chassis, or whatever without melting does not mean you ever want to try it. So you want to keep the current limited using 100 amp or 200 amp breakers or whatever matches the kind of service you installed.

Ability "to short 20 KA" also needs a paragraph of explanation. Is it just theoretical given the resistance of the metal parts inside, or is it related to lightning arresting features?

When you get a tingle touching something that should be grounded, suggesting that a ground was energized, and a huge fault is not occurring, then you have an imperfect ground from that point back to the panel. Older systems including BX that rely on the cable sheath to serve as the ground are likely to have this kind of problem because the sheaths are screwed to junction boxes in the usual daisy chain from receptacle to receptacle. These screw joints oxidize.

If a properly grounded wire or object were to become energized by a branch circuit fault including from a pull-damaged wire in a conduit, that circuit's breaker will trip.

A long (single conductor 14 or smaller gauge) wire that can be stretched from room to room can come in handy. Once you suspect a "ground" is energized, you need another zero volt reference. The official zero volt reference is the panel ground/neutral bus bar. Use your voltmeter to measure from the suspected energized ground down to there*. Turn off breakers one at a time until this "ground to ground voltage" drops to zero. Now you found the circuit that is "energizing the ground".

Sometimes the continuity back to the panel ground is so imperfect that phantom voltages give you a tingling when you touch supposedly grounded equipment plugged in. Then establishing a proper ground back to the panel -- a new bare wire roughly following the route of the branch circuit will work -- will drain off the phantom voltage and not trip any breakers.

For curiosity's sake only. Downstream of the 20 foot melted together conduit wires find a metallic path between plumbing and that circuit's wiring (or the conduit itself) so as to cause the massive fault current in the pipes to choose that conduit as a route back to the panel ground.

* I will leave it as an academic exercise using the volt and ohm functions of a multimeter to find out when and where plumbing fixtures or radiators can be used as a zero volt reference so you don't need such a long wire to stretch all the way down to the panel. Or you can use a radiator anyway and jump to the conclusion you found the circuit that is energizing a suspected ground when you flipped off a breaker and the voltage between the suspected energized ground and the radiator dropped to zero. Do not touch the end of the long wire to things at random with the power on and without going through a voltmeter (not set to ohms). Turn off power before doing any ohms (resistance; impedance) measurements.

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Old 01-13-2009, 11:14 AM   #38
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Ability "to short 20 KA" also needs a paragraph of explanation. Is it just theoretical given the resistance of the metal parts inside, or is it related to lightning arresting features?
Lightning is irrelevant here. If you have 10 kiloamps of lightning, it's all over.

What we are talking about is the short circuit current of home service.
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Old 01-13-2009, 11:38 AM   #39
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Unfused connectors MELTED House wires WHAT TO DO???


Lightning is a whole other story. The strongest of lightning can be 100ka or more. It jumps anywhere it wants and does a "skin effect" of sorts on wiring.

I would not expect a tvss to even be intact after a direct lightning strike.
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Old 01-13-2009, 11:49 AM   #40
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Unfused connectors MELTED House wires WHAT TO DO???


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Lightning is irrelevant here. If you have 10 kiloamps of lightning, it's all over.

What we are talking about is the short circuit current of home service.
The series rating is what allows us to use 10 kAIC breakers. As long as the main is capable of interrupting the expected fault current, then we can use breakers downstream from that with a lower AIC. For example, if the main is 22 kAIC, then we should be able to use 10 kAIC breakers.
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Old 01-13-2009, 02:22 PM   #41
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The series rating is what allows us to use 10 kAIC breakers. As long as the main is capable of interrupting the expected fault current, then we can use breakers downstream from that with a lower AIC. For example, if the main is 22 kAIC, then we should be able to use 10 kAIC breakers.
So can we say with some certainty that the max current available at a resi. panel is <22kA, which implies a xformer impedance of >240/22kA = >11 milliohms?

For a house drawing 200A with a drop of 24v would give an upper limit of ~120 milliohms.

Turns out measuring this impedance with a DVM and a 24A load may be a bit messy.

Anybody have a link for Fusing Philosophy or rationale for resi. wiring that would explain why you can use 10k and 22k?
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Old 01-13-2009, 06:33 PM   #42
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Unfused connectors MELTED House wires WHAT TO DO???


Enjoy...


More scary "junction boxes" here...

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Old 01-13-2009, 06:34 PM   #43
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More scary junctions. Last one is a milk slot used as a junction box. Is that UL listed??? In the sleeves are junctions between knob and tube wire and thhn.

Other scary junction boxes shown here were photographed as found without changes.

Unfused connectors MELTED House wires  WHAT TO DO???-img_5172.jpg

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Unfused connectors MELTED House wires  WHAT TO DO???-img_5184.jpg
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Old 01-13-2009, 06:35 PM   #44
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Unfused connectors MELTED House wires WHAT TO DO???


I had to remove a couple wires that were damage... Yea, that was just about all of them.

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Old 01-13-2009, 06:37 PM   #45
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Unfused connectors MELTED House wires WHAT TO DO???


How would you like your THHN, well done or extra crispy?

See that last photo, Yes that is a junction to knob and tube, that was made with electrical tape to romex, than someone buried that in the ceiling and ran the power to the kitchen light.


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Unfused connectors MELTED House wires  WHAT TO DO???-img_5197.jpg

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Unfused connectors MELTED House wires  WHAT TO DO???-img_5205.jpg

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