conduit ground

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mickeyrench

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edison, n.j.
i am install ing a 100amp. 480 volt feed for a piece of equipment with a few motors and controls rated at 90 amps.min. and 125 max. i plan on pulling 3 # 3 thwn and using the 1 1/4" emt with double set scews on connectors. will the emt be best as the equipment ground or is a #6 the way to go. thanks for any advice.
 
Assuming the EMT is installed properly, the steel EMT will provide a lower impedance fault current path then the copper EGC you might place inside.

However there is something to be said for redundancy.
 
Is it a really long run? will it kill your profit margine to pull a ground wire? I always pull a ground wire in everything, but thats just me, if you install your set screw connectors properly you will have no problems without the extra ground wire.
 
mickeyrench said:
i am install ing a 100amp. 480 volt feed for a piece of equipment with a few motors and controls rated at 90 amps.min. and 125 max. i plan on pulling 3 # 3 thwn and using the 1 1/4" emt with double set scews on connectors. will the emt be best as the equipment ground or is a #6 the way to go. thanks for any advice.
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Either or both will work fine as an EGC.

I am a little nervous about the sizing of the #3 conductors though.
 
petersonra said:
I am a little nervous about the sizing of the #3 conductors though.
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Me too. How did you arrive at a minimum and maximum figure? Load is load. If you calculated it properly their would only be one figure. In calculating load you must allow for the "maximum load to be served". See 430.24 for calculating the load on a circuit that serves motors and other loads.
 
As a "rule of thumb", any run over 300 feet should have a properly sized grounding conductor run with the circuit conductors. There are published tables that will show how far you can run a circuit ans still have adequate grounding but they are all over 300 feet (some more than others). Dick Loyd's book on metallic raceways has those tables. :)
 
mickeyrench said:
i am install ing a 100amp. 480 volt feed for a piece of equipment with a few motors and controls rated at 90 amps.min. and 125 max. i plan on pulling 3 # 3 thwn and using the 1 1/4" emt with double set scews on connectors. will the emt be best as the equipment ground or is a #6 the way to go. thanks for any advice.
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unit was label to use a min 90amp to 125 amp max cb. { i believe} i will find out exackly tonight.
 
mickeyrench said:
unit was label to use a min 90amp to 125 amp max cb. { i believe} i will find out exackly tonight.
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NO, NO, NO!!!!
What you are probably seeing is a MINIMUM CIRCUIT AMPACITY of 90 amps and a MAXIMUM FUSE SIZE of 125 amps. That is not a range, they are specific values to be used for specific portions of the installation. One is used to select the conductor, the other is used to select the fuse/circuit breaker. If that is so, your #3 conductors are OK, IF the conductors AND TERMINATIONS are all rated for at least 75 degrees C. If any of your terminations are not labeled, you must assume they are only suitable for 60 degrees. At 60 degrees #3 is only rated for 85 amps and would not meet the 90-amp minimum circuit ampacity. Either grounding method should be fine.
 
haskindm said:
NO, NO, NO!!!!
What you are probably seeing is a MINIMUM CIRCUIT AMPACITY of 90 amps and a MAXIMUM FUSE SIZE of 125 amps. That is not a range, they are specific values to be used for specific portions of the installation. One is used to select the conductor, the other is used to select the fuse/circuit breaker. If that is so, your #3 conductors are OK, IF the conductors AND TERMINATIONS are all rated for at least 75 degrees C. If any of your terminations are not labeled, you must assume they are only suitable for 60 degrees. At 60 degrees #3 is only rated for 85 amps and would not meet the 90-amp minimum circuit ampacity. Either grounding method should be fine.
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good answer, i like a straight, right answer, one who know's what he's talking about!:D
 
haskindm said:
NO, NO, NO!!!!
What you are probably seeing is a MINIMUM CIRCUIT AMPACITY of 90 amps and a MAXIMUM FUSE SIZE of 125 amps. That is not a range, they are specific values to be used for specific portions of the installation. One is used to select the conductor, the other is used to select the fuse/circuit breaker. If that is so, your #3 conductors are OK, IF the conductors AND TERMINATIONS are all rated for at least 75 degrees C. If any of your terminations are not labeled, you must assume they are only suitable for 60 degrees. At 60 degrees #3 is only rated for 85 amps and would not meet the 90-amp minimum circuit ampacity. Either grounding method should be fine.[/QUO





after checking again last night it is labeled exactly as you say, and i 'll be using a #2 thhn . i was wrong. thanks for the help .
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haskindm said:
NO, NO, NO!!!!
What you are probably seeing is a MINIMUM CIRCUIT AMPACITY of 90 amps and a MAXIMUM FUSE SIZE of 125 amps. That is not a range, they are specific values to be used for specific portions of the installation. One is used to select the conductor, the other is used to select the fuse/circuit breaker. If that is so, your #3 conductors are OK, IF the conductors AND TERMINATIONS are all rated for at least 75 degrees C. If any of your terminations are not labeled, you must assume they are only suitable for 60 degrees. At 60 degrees #3 is only rated for 85 amps and would not meet the 90-amp minimum circuit ampacity. Either grounding method should be fine.
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This is almost exaclty what I would have said.....good call....I would go with an EGC, since it is my experience that set screws loosen over time especially when they are install in an exterior location.....

Jim
 
charlie said:
As a "rule of thumb", any run over 300 feet should have a properly sized grounding conductor run with the circuit conductors. There are published tables that will show how far you can run a circuit ans still have adequate grounding but they are all over 300 feet (some more than others). Dick Loyd's book on metallic raceways has those tables. :)
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The information from the GEMI software program shows that the conduit is an effective fault clearing path over a longer distance than a code sized EGC installed within the conduit.
 
I have not seen the GEMI software or read Dick Loyd's book...but always pulled an EGC in conduit runs - even rigid. Very good reason: I've seen lots of damaged conduit, poorly installed rigid (i.e. loose threads), and joints pulled apart at couplings or boxes. This happens lots of times where the conductors are still intact, the load still energized, motors running, etc.

I don't remember where or when, but years ago attended some classes on grounding, a movie was shown on bolted faults to ground using various types of raceway and EGC. Raceway was made up tight, and in other instances some couplings were intentionally made slightly loose - exactly as found in investigating the conduit and raceways found in ALL typical installations.
I guarantee it was a sight to see! Sparks flying all around, and conduit ripping loose from its supports.

You can be certain I took extra care to make absolutely sure everything was tight after that, and in addition we ALWAYS installed an EGC.

I'm sure we all do quality work, but how often have you seen lesser quality work on the same job when you are not the only electrician?
 
For me it depends on the job, the environment, the specs, how tight the money is, my mood, what I have available and maybe the phase of the moon.

The NEC considers steel conduit as a reliable grounding path, who am I to argue?

Here is the most recent panel statement to explain the rejection of 3 proposals asking for a 'wire' EGC.

Panel Statement: Studies show that all steel conduit is a reliable equipment grounding conductor in high temperature situations. UL white book does not require a wire type equipment grounding conductor. The technical substantiation does not support the proposal
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Panel Statement: Studies show that all steel conduit is a reliable equipment grounding conductor in high temperature situations. UL white book does not require a wire type equipment grounding conductor. The technical substantiation does not support the proposal
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For what it is worth, I agree with the panel statement. :)
 
iwire said:
For me it depends on the job, the environment, the specs, how tight the money is, my mood, what I have available and maybe the phase of the moon.
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Couldn't have said it better myself. :)

I remember reading something a good while back about conduit fitting continuity and durability. It was related to a study of fittings following the SanFrancisco earthquake. Does that ring a bell for anyone?
 
mdshunk said:
I remember reading something a good while back about conduit fitting continuity and durability. It was related to a study of fittings following the SanFrancisco earthquake.
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So, which fared better, setscrews or compression fittings?
 
LarryFine said:
So, which fared better, setscrews or compression fittings?
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I don't know. I just vaguely remember reading the paper. It might have been geared more toward steel vs. die cast fittings. I was sorta hoping it might ring a bell for someone and they'd post a link to it so I (we) could read it again.
 
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