EMT grounding

[10Driver]

OK, just came across a situation that I think needs to be corrected. Have a solar system that is properly grounded from the PV's to the inverter (have two inverters). The Inverter case is plastic and the EMT has a grounding bushing connecting the EMT to a ground bus bar in the inverter. However, from the inverter a ground wire goes from the inverter through the FMC to a combiner MLO (connecting the two inverters) but there's no ground bushing on the FMC (leading from the plastic inverter case to the metal combiner) attached to the inverter bus bar on one end nor is there a grounding bushing at the combiner MLO to the combiner MLO ground bus bar (which has concentric knockouts). The ground IN the FMC does connect to the inverter ground bus bar at one end and the combiner bus bar at the other end BUT if I'm reading 250.64(E)(1), the FMC with a ground wire INSIDE needs to be grounded ON BOTH ENDS....

I think the FMC needs to be grounded on both ends through approved methods. Any thoughts????

 

[Steve16]

250.64 is specific to grounding electrode conductors, not equipment grounding conductors

 

[Jaybone812]

OK, just came across a situation that I think needs to be corrected. Have a solar system that is properly grounded from the PV's to the inverter (have two inverters). The Inverter case is plastic and the EMT has a grounding bushing connecting the EMT to a ground bus bar in the inverter. However, from the inverter a ground wire goes from the inverter through the FMC to a combiner MLO (connecting the two inverters) but there's no ground bushing on the FMC (leading from the plastic inverter case to the metal combiner) attached to the inverter bus bar on one end nor is there a grounding bushing at the combiner MLO to the combiner MLO ground bus bar (which has concentric knockouts). The ground IN the FMC does connect to the inverter ground bus bar at one end and the combiner bus bar at the other end BUT if I'm reading 250.64(E)(1), the FMC with a ground wire INSIDE needs to be grounded ON BOTH ENDS....

I think the FMC needs to be grounded on both ends through approved methods. Any thoughts????

250.64 has nothing to do with you’re egc , and a ferrous metal raceway that contains a gec needs to be bonded at both ends . You are referring to an equipment grounding conductor and they are applying one of the 314.3 exceptions to the install that permits the use of a non metallic box with a metal raceway and using a bonding bushing with a bonding jumper to satisfy the conditions in the exception




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[10Driver]

OK, let me retry...without the aforementioned grounding bushings, how is the conduit "continuously grounded" if there is a break in the grounding?

 

[10Driver]

250.64 has nothing to do with you’re egc , and a ferrous metal raceway that contains a gec needs to be bonded at both ends . You are referring to an equipment grounding conductor and they are applying one of the 314.3 exceptions to the install that permits the use of a non metallic box with a metal raceway and using a

250.64 has nothing to do with you’re egc , and a ferrous metal raceway that contains a gec needs to be bonded at both ends . You are referring to an equipment grounding conductor and they are applying one of the 314.3 exceptions to the install that permits the use of a non metallic box with a metal raceway and using a bonding bushing with a bonding jumper to satisfy the conditions in the exception




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OK, that makes sense but without the bonding bushings on both ends of the FMC and only one end secured to the combiner box (that has knockouts) with just conduit locknuts, how does that maintain continuous grounding of the conduit?




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[roger]

OK, let me retry...without the aforementioned grounding bushings, how is the conduit "continuously grounded" if there is a break in the grounding?

If something breaks in any type situation something will be compromised.

 

[Jaybone812]

OK, let me retry...without the aforementioned grounding bushings, how is the conduit "continuously grounded" if there is a break in the grounding?

If the metal conduit is internally bonded you’re fine . If the raceway comes from a bonded metal enclosure the emt already is bonded to the egc internally at the other end of the conduit assembly . The bonding bushing would only be required if nm enclosures were at both ends of the raceway


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[10Driver]

If the metal conduit is internally bonded you’re fine . If the raceway comes from a bonded metal enclosure the emt already is bonded to the egc internally at the other end of the conduit assembly . The bonding bushing would only be required if nm enclosures were at both ends of the raceway


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Which it is....the plastic inverter case is between the incoming EMT from the solar array to the outgoing FMC going to the metal combiner box (secured with only a conduit locknuts which does not qualify for grounding in a metal box with knockouts....). Or am I misreading the NEC?

 

[roger]

Which it is....the plastic inverter case is between the incoming EMT from the solar array to the outgoing FMC going to the metal combiner box (secured with only a conduit locknuts which does not qualify for grounding in a metal box with knockouts....). Or am I misreading the NEC?

The EMT fittings will be listed and recognized for bonding/grounding, double locknuts would be for threaded conduit, not tubing (EMT). In either case only one end needs to be bonded for your application.

 

[roger]

I should have said the same thing regarding the FMC.

 

[Jaybone812]

Which it is....the plastic inverter case is between the incoming EMT from the solar array to the outgoing FMC going to the metal combiner box (secured with only a conduit locknuts which does not qualify for grounding in a metal box with knockouts....). Or am I misreading the NEC?

690.43 is in reference to solar equipment grounding and bonding . 690.43 tells us that all non current carrying metal parts and enclosures shall be connected to a egc in accordance with 250.134 or 250.136 and 250.134 tells you that bonding the metal enclosure with a wire type egc is all you need . You are not using the locknuts to ensure electrical continuity or for “grounding “ you have a wire type egc . Factory kos or punched holes , doesn’t matter


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[Jaybone812]

The EMT fittings will be listed and recognized for bonding/grounding, double locknuts would be for threaded conduit, not tubing (EMT). In either case only one end needs to be bonded for your application.

Exactly as long as it’s bonded at one end he’s good


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[Jaybone812]

Which it is....the plastic inverter case is between the incoming EMT from the solar array to the outgoing FMC going to the metal combiner box (secured with only a conduit locknuts which does not qualify for grounding in a metal box with knockouts....). Or am I misreading the NEC?

in the situation you are describing there are not non metallic enclosures at both ends of the raceway, there’s one nm enclosure between two metallic enclosures. So both of the metal raceways are bonded at one end

 

[10Driver]

in the situation you are describing there are not non metallic enclosures at both ends of the raceway, there’s one nm enclosure between two metallic enclosures. So both of the metal raceways are bonded at one end

With the exception of the end of the FMC at the combiner....it's not properly grounded so in the event of a short in the FMC, a CB will not trip and the FMC could be energized. I don't have a problem with only one side being grounded but EMT on the solar array side IS grounded on both ends.

 

[roger]

With the exception of the end of the FMC at the combiner....it's not properly grounded so in the event of a short in the FMC, a CB will not trip and the FMC could be energized. I don't have a problem with only one side being grounded but EMT on the solar array side IS grounded on both ends.

So you have been given the correct code articles yet you want something else. FMC, FMT, LFMC, EMT, IMC, RMC only need one end bonded, go with it.

 

[Jaybone812]

With the exception of the end of the FMC at the combiner....it's not properly grounded so in the event of a short in the FMC, a CB will not trip and the FMC could be energized. I don't have a problem with only one side being grounded but EMT on the solar array side IS grounded on both ends.

250.118 permits the use of fmc as a egc if conditions are met and correct fittings are used . It is properly grounded . If the wire type egc bonds the metal enclosure it is properly grounded at the metal box, when you use a equipment bonding jumper(egc) from that fmc raceway to bond the metal enclosure the egc is bonded to the fmc and the wire type egc will clear the fault . You aren’t using the fmc as your egc here you have a wire type egc . The locknuts arent ensuring continuity the egc is by binding the enclosure . You don’t have to satisfy 250.80 or 250.92 because they are fused conductors and 250.97 doesn’t apply here . If it’s gonna keep you up at night get a bonding locknut if you don’t want to keep the bonding bushing


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[Jaybone812]

So you have been given the correct code articles yet you want something else. FMC, FMT, LFMC, EMT, IMC, RMC only need one end bonded, go with it.

I said throw a bonding locknut in at the metal enclosure it it’ll help him sleep at night lol. But he’s already compliant no need for anything additional bonding

 

[10Driver]

I said throw a bonding locknut in at the metal enclosure it it’ll help him sleep at night lol. But he’s already compliant no need for anything additional bonding

Thanks for the help. Going to install a ground bushing. I think it's an impaired connection (250.92 (B) considering the knockouts) but even if it isn't, like you said, it will help with the sleep going forward with the inspection....

 

[Jaybone812]

Thanks for the help. Going to install a ground bushing. I think it's an impaired connection (250.92 (B) considering the knockouts) but even if it isn't, like you said, it will help with the sleep going forward with the inspection....

250.92(b) does not apply here at all you are not bonding a metal raceway to service equipment . A feeder or branch circuit will never require additional bonding unless the voltage to ground is 250 or more with an impaired connection 250.97 . The conductors are fused here and there’s an egc . Doesn’t matter if it’s a punched hole or concentric KO additional bonding (bonding bushing ) is not required here or for any branch circuit or feeder less than 250 volts to ground


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[Jaybone812]

Thanks for the help. Going to install a ground bushing. I think it's an impaired connection (250.92 (B) considering the knockouts) but even if it isn't, like you said, it will help with the sleep going forward with the inspection....

And youre welcome glad I could help lol


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