using conduit as EGC - getting 30 ohms

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art

art

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We have 450' of conduit feeding a load and using the conduit as the ECG. trying to install a ground wire and can not get the wire through the last 150'. We measured the resistance of the entire path and got about 30 ohms. will this be enough to trip the breaker? And, does the resistance have to be 25 ohms anyway? If I divide 240 V by 30 ohms I get 8 Amps which will not work but I'm not sure is this is the right approach.

also, how do I compare if we use the wire ECG?
 
art said:
We have 450' of conduit feeding a load and using the conduit as the ECG. trying to install a ground wire and can not get the wire through the last 150'. We measured the resistance of the entire path and got about 30 ohms. will this be enough to trip the breaker? And, does the resistance have to be 25 ohms anyway? If I divide 240 V by 30 ohms I get 8 Amps which will not work but I'm not sure is this is the right approach.

also, how do I compare if we use the wire ECG?
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A 30 ohm resistance is far too high to be an effective fault clearing path at 240V, as your calculation shows.
The 25 ohm figure for a rod-type ground electrode is pretty much an arbitrary figure and in any case has not relevance for EGC or GEC resistance.

I would measure the resistance of just the 150' section that you cannot pull through. If there is a high resistance there, you are SOL. If the high resistance is elsewhere in the path you could put in a box at each end of the 150' segment and bond the wire EGC to the raceway in each box. That would give you a code compliant EGC. I do not think that there is any code language the requires the entire EGC run to be only wire or only raceway.
 
art said:
We have 450' of conduit feeding a load and using the conduit as the ECG. trying to install a ground wire and can not get the wire through the last 150'. We measured the resistance of the entire path and got about 30 ohms. will this be enough to trip the breaker? And, does the resistance have to be 25 ohms anyway? If I divide 240 V by 30 ohms I get 8 Amps which will not work but I'm not sure is this is the right approach.

also, how do I compare if we use the wire ECG?
Click to expand...

Hi,


It will never trip the OCPD, because that is not his purpose.


The most important thing is to have a low impedance path to the source to clear the fault, in this case you get it with the EGC, so what you really need is continuity in this path.

Regards,
 
What is the load current, and what is the conductor resistance?

Could fault detection be an alternative?
 
art said:
We have 450' of conduit feeding a load and using the conduit as the ECG. trying to install a ground wire and can not get the wire through the last 150'. We measured the resistance of the entire path and got about 30 ohms. will this be enough to trip the breaker? And, does the resistance have to be 25 ohms anyway? If I divide 240 V by 30 ohms I get 8 Amps which will not work but I'm not sure is this is the right approach.

also, how do I compare if we use the wire ECG?
Click to expand...

if you have 450 feet of conduit the resistance should be a lot less than 30 Ohms. How are you measuring the resistance.
 
petersonra said:
if you have 450 feet of conduit the resistance should be a lot less than 30 Ohms. How are you measuring the resistance.
Click to expand...
:thumbsup:
In particular, if there is an imposed AC or DC voltage on the conduit (from leakage/fault current) most ohmmeters will not read correctly.
 
Thanks for the replies. I didn't do the measurement. I'll find out.

Sent from my LG-TP260 using Tapatalk
 
ptonsparky said:
I’m interested in why you can’t get a wire through that 150’. Is that section buried?
Why are you pulling an EG conductor? What circumstances brought about that need and, yes, how are you measuring that 30 ohms?
Click to expand...

it's underground and pretty old. Most likely collapsed somewhere along the way
 
petersonra said:
if you have 450 feet of conduit the resistance should be a lot less than 30 Ohms. How are you measuring the resistance.
Click to expand...

They connected a #8 wire from one end of the conduit to the meter and then the meter to the other end of the conduit. Measured the total resistance and subtracted the calculated resistance of the wire. I didn't do the calculation. I need help with that too...
 
art said:
it's underground and pretty old. Most likely collapsed somewhere along the way
Click to expand...

If that is in fact the case, you probably have a collection of bits of conduit flying in loose formation, hence the very high resistance.
 
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