Detecting 1/2 sized egc's

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Cletis

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I was using a http://www.testequipmentdepot.com/products.htm?item=CT80&ref=gbase&gclid=CLep8vyU08ECFUNp7Aod4A4Arg circuit analyzer today looking and some stuff along with other testers and was curious. Will the extech or any other analyzer detect and show egc size (impedance?). I was in a house with a bunch of knob and tube hacked into old bx hacked into old romex no ground, 1/2 sized grounds etc. On many of the circuits it showed an ok ground but I had to explain to customer that they are only 1/2 sized and the implications of this. It was hard to explain to the HO, I just got a black stare mostly.

Can the extech be used for this or any other testers to detect 1/2 sized egc's ?
 
Well, I decided to read the manual. Basically, if the ground impedance is between 0.25ohms (preferable) and 1ohm the egc is in the correct zone and will be able to clear a fault. Does this sound correct to you grounding experts out there??
 
Cletis said:
Well, I decided to read the manual. Basically, if the ground impedance is between 0.25ohms (preferable) and 1ohm the egc is in the correct zone and will be able to clear a fault. Does this sound correct to you grounding experts out there??
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That doesn't tell you that the EGC is sized per the code rules. A 100' of #18 would be that resistance range.
 
resistance of a conductor will depend on it's size and length, plus any weak points. Even a "good" splice will introduce a small amount of resistance.
 
I would think there should be some absolute number to go by for egc impedance (just like VD %) as a general rule of thumb ? Am I right or wrong?
 
Cletis said:
I would think there should be some absolute number to go by for egc impedance (just like VD %) as a general rule of thumb ? Am I right or wrong?
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Unless the circuit length is so great that you have to upsize the CCCs, the standard size EGC will work fine, and the resistance will vary with the circuit capacity.
And if you upsize the CCCs for VD, the code currently requires you to increase the EGC proportionally.
It is simpler for the NEC to regulate the size than to put in a performance test such as resistance or VD.
 
I have a question for you short circuit experts. If I have 3 branch circuits 10,12, and 14 and there is an identical ground fault, does the same amount of fault current flow back on the 10,12, and 14 egc if they all were hooked to the same load ??
 
Most EGC sized per NEC are likely larger then needed to carry enough current to operate overcurrent devices. NEC does want them to be large enough to be reliable and to remain intact after they have been called upon to clear a fault.

You still can run into situations especially with long circuit runs where the EGC or even the ungrounded conductor has enough resistance to cause slower response time from overcurrent devices. Source impedance does factor in some as well.

You may see circumstances where a fault occurs and a breaker trips very quickly - yet same breaker in another installation seemingly allows longer fault duration before tripping. Look around for things like long circuit length or smaller source transformer, and then it will make sense why same breaker has seemingly different performance in the two different locations.
 
Cletis said:
I have a question for you short circuit experts. If I have 3 branch circuits 10,12, and 14 and there is an identical ground fault, does the same amount of fault current flow back on the 10,12, and 14 egc if they all were hooked to the same load ??
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ActionDave said:
Then it would be a phase to phase fault. I should think the egc would not see any current.
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I think he was asking if he had three examples of the same thing other then conductor size was different in each example.

The example with larger conductor would have less resistance and is capable of carrying more current, but to know exactly how much current flows you need to take impedance of the source into consideration as well. If the source is relatively small and has a high enough impedance the source itself may be more current limiting then the conductors in question.
 
I'm simply trying to figure a way to "quantify" to the customer that a 1/2 sized egc on residential branch circuits is not a good thing and needs a new circuit ran (other than its now against code).
 
iwire said:
Sure would like to see a picture of you using this tool. I am fascinated with how you do so.
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Obviously I am not the OP. This caught my eye, also, and I just went through the Owners Manual. Found the image below while I was noodling around for info on the Extech CT80.

21Kp-AAXARL.jpg
 
Cletis said:
I would think there should be some absolute number to go by for egc impedance (just like VD %) as a general rule of thumb ? Am I right or wrong?
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The code does not work that way, buy you could make it so....public inputs (proposals) for the 2017 code are due no later than 5pm, November 7th.
 
Cletis said:
I have a question for you short circuit experts. If I have 3 branch circuits 10,12, and 14 and there is an identical ground fault, does the same amount of fault current flow back on the 10,12, and 14 egc if they all were hooked to the same load ??
Click to expand...
The amount of current flow on any circuit is a function of the voltage and impedance of the circuit, and in the case of a fault, also a function of the available fault current at the supply end of the circuit.
 
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