Non-metallic sealtite and grounding

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wireman

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Here's a the situation:
A rigid metal conduit is ran from a MCC to within 3 feet of a 480V-3ph motor. Non-metallic sealtite connects the conduit to the motor and a proper size ground wire is ran along with the motor leads.

The question: Is a grounding jumper wire required on the outside of the non-metallic sealtite, or is the ground wire inside the conduit sufficient (assuming the ground wire is connected properly on both ends)?
 

tom baker

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Re: Non-metallic sealtite and grounding

While the equipment may be properly bonded by the internal equipment ground, the raceway may not be. since its contains conductors over 250 V to ground, proper bonding is required on the raceway terminations. You may need bonding bushings on each end. I always used assured bonding on one end of a 277/480V raceway, due to the higher level of fault current with 480 V circuits.

[ March 25, 2003, 08:41 PM: Message edited by: tom baker ]
 

hornetd

Senior Member
Re: Non-metallic sealtite and grounding

I have to echo Tom Baker's concern on this one. You may need to install a box between the conduit and the sealtight so as to have a place to bond the EGC to the load end of the raceway or you could run a bonding jumper on the outside of the sealtight.
--
Tom
 

don_resqcapt19

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Re: Non-metallic sealtite and grounding

What code section can be cited to require that both ends of the raceway be bonded to the EGC?. I see no code rule that requires that this raceway be bonded at the load end.
Don
 

tom baker

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Re: Non-metallic sealtite and grounding

Don, I see your point. If the load end is bonded with an equipment grounding conductor, then that would bond the raceway, assuming no reducing washers are used at the load end. However I recommend assurred bonding with any raceway containing 277V conductors
 

don_resqcapt19

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Re: Non-metallic sealtite and grounding

Tom,
I agree that a bonding jumper at the load end would improve the fault clearing path, I just don't see a code rule that requires you to bond around the nonmetallic flexible conduit in this case. Where I'm at we pull an internal equipment grounding conductor and install an external bonding jumper around the liquidtight flexible metal conduit at all motors.
Don
 

hornetd

Senior Member
Re: Non-metallic sealtite and grounding

Originally posted by don_resqcapt19:
Tom,
I agree that a bonding jumper at the load end would improve the fault clearing path, I just don't see a code rule that requires you to bond around the nonmetallic flexible conduit in this case. Where I'm at we pull an internal equipment grounding conductor and install an external bonding jumper around the liquidtight flexible metal conduit at all motors.
Don
Don
I think both Tom Bakers reply and mine were based on best practice rather than code requirements but I guess I should have made that clear.

My consern is that unless the racewy is bonded to the EGC at both ends the resultant higher impedance might delay the operation of the Over Current Protective Device. Experience has shown that 480/277 volt circuits are particularly prone to destructive arcing.
--
Tom
 

don_resqcapt19

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Re: Non-metallic sealtite and grounding

Tom,
I don't think that there is any problem with increased impedance in the fault return path, when both the supply conductors and the EGC are in the same metallic raceway.
Don
 

hornetd

Senior Member
Re: Non-metallic sealtite and grounding

Originally posted by don_resqcapt19:
Tom,
I don't think that there is any problem with increased impedance in the fault return path, when both the supply conductors and the EGC are in the same metallic raceway.
Don
Would not the increassed impedance cause the arc to last longer and do more damage.
--
Tom
 

don_resqcapt19

Moderator
Staff member
Re: Non-metallic sealtite and grounding

Tom,
What I tried to say was, I don't think the lack of bonding on the load ends makes much of a change in the impedance of the fault return path via the internal EGC. Yes, there would be a lower impedance path if the raceway was bonded, because you now have a parallel path for the fault current. I think that I was reading your post as saying that the lack of bonding at the load end would increase the impedance of the internal EGC.
Don

[ April 01, 2003, 04:54 PM: Message edited by: don_resqcapt19 ]
 
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