?need for identifiable bonding jumpers?

[dpaolini]

Good morning, this is my first post so please bear with me!


10,000 square-foot residence with 600 amp service. Four 150 amp subpanels scattered throughout house. Someone installed a 125 amp sub sub panel using one and a half inch rigid conduit.The conduit is connected to the subpanel and sub sub panel through concentric knockouts. Bonding bushings are installed on each end of the conduit.


Four wires connect the subpanel and sub sub panel. Two #2 hot, one # 2 neutral,and one # 4 green insulated equipment ground. The green # 4 is run through the bonding bushings (insulation removed where it passes through bonding bushing).

My concerns:

1. is this a 2014 NEC compliant bonding method? Or does the NEC require identifiable bonding jumpers between the ground bars in panels and bonding bushings?

2. Bonding bushings required in both the sub panel and sub-sub panel?

Thanks!!!

 

[kwired]

What is not "identifiable" about it?

FYI the RMC and locknuts would be acceptable without additional bonding bushings or a green wire within the conduit in most cases in a dwelling, over 250 volts to ground and you need to pay closer attention to this.

Though nothing wrong with the 4 AWG bonding jumper if it has 150 amp overcurrent protection it could have been 6 AWG.

 

[texie]

What is not "identifiable" about it?

FYI the RMC and locknuts would be acceptable without additional bonding bushings or a green wire within the conduit in most cases in a dwelling, over 250 volts to ground and you need to pay closer attention to this.

Though nothing wrong with the 4 AWG bonding jumper if it has 150 amp overcurrent protection it could have been 6 AWG.

Yep, there is nothing wrong with the installation the OP describes. It exceeds code. The guy that installed the sub-sub panel gets a gold star.

 

[dpaolini]

Thanks

Thanks

Thanks for the quick and informative replies. I always interpreted the Code to require separate bonding jumpers to bonding bushings. One of younger electricians proved me wrong!

 

[texie]

Thanks for the quick and informative replies. I always interpreted the Code to require separate bonding jumpers to bonding bushings. One of younger electricians proved me wrong!

I think I understand you to say that the EGC in the conduit and the bonding jumper should be 2 separate conductors-each brought to the equipment ground bar. That is also an OK way to do it, but not a required method.
But also, the point kwired was making is that the bonding bushings, while a good idea, are not required in this case at all as concentric/eccentric KOs are listed for bonding at less than 250 volts.

 

[fmtjfw]

Just got back from the Western Section IAEI symposium. UL guy said only listed concentric/eccentric KOs for bonding are found in "outlet boxes and 4x4s etc., not in cabinets like panelboards. Check the listing of a cabinet before believing KOs are acceptable.

 

[infinity]

Just got back from the Western Section IAEI symposium. UL guy said only listed concentric/eccentric KOs for bonding are found in "outlet boxes and 4x4s etc., not in cabinets like panelboards. Check the listing of a cabinet before believing KOs are acceptable.

That's true if the voltage is over 250 volts to ground.

 

[kwired]

Just got back from the Western Section IAEI symposium. UL guy said only listed concentric/eccentric KOs for bonding are found in "outlet boxes and 4x4s etc., not in cabinets like panelboards. Check the listing of a cabinet before believing KOs are acceptable.

That's true if the voltage is over 250 volts to ground.

Always been my understanding - over 250 volts to ground you better use additional bonding method unless you know the KO has been evaluated for the purpose.

Not so certain that I agree that it makes sense though, higher voltage should have more ability to push current through a questionable path.

 

[meternerd]

What is not "identifiable" about it?

FYI the RMC and locknuts would be acceptable without additional bonding bushings or a green wire within the conduit in most cases in a dwelling, over 250 volts to ground and you need to pay closer attention to this.

Though nothing wrong with the 4 AWG bonding jumper if it has 150 amp overcurrent protection it could have been 6 AWG.

I thought if it went through any concentric knockouts, it wasn't suitable as a ground. Don't guess I've ever seen listed knockouts. Are they built different than the standard ones you see on most service and breaker panels?

 

[fmtjfw]

I thought if it went through any concentric knockouts, it wasn't suitable as a ground. Don't guess I've ever seen listed knockouts. Are they built different than the standard ones you see on most service and breaker panels?

The explanation that we got was that if you look at the KOs in a 4x4 box for instance, the "ties' to the box or to the larger KO are heavier, and the punched out part is more substantial. The KO's in "sheet metal boxes' and panel boards have less substantial ties to box to larger KOs.

 

[texie]

I thought if it went through any concentric knockouts, it wasn't suitable as a ground. Don't guess I've ever seen listed knockouts. Are they built different than the standard ones you see on most service and breaker panels?

You may be thinking of concentrics on the line side of a service. Concentrics would need to be bonded around in all cases per 250.92. The OP situation is a feeder less than 250 V to ground which would make concentrics OK on their own.

 

[dpaolini]

make your own knockouts?

make your own knockouts?

sounds like it will be easier if panels were made thicker or if there were no more concentric knockouts?
speaking of knockouts has anyone tried the Milwaukee knockout tool?

 

[infinity]

sounds like it will be easier if panels were made thicker or if there were no more concentric knockouts?
speaking of knockouts has anyone tried the Milwaukee knockout tool?

Just got one a few weeks ago. Great tool, no more pumping until your arms fall off.

 

[tom baker]

Always been my understanding - over 250 volts to ground you better use additional bonding method unless you know the KO has been evaluated for the purpose.

Not so certain that I agree that it makes sense though, higher voltage should have more ability to push current through a questionable path.

With the higher voltage a 1 ohm ground fault at 480/277 creates 5X the heat than 120

 

[kwired]

With the higher voltage a 1 ohm ground fault at 480/277 creates 5X the heat than 120

Ok, that makes some sense, but what is not factored here is trip curve of overcurrent devices which will not necessarily be same from one install to the next even with many other similar characteristics. One could still have more heat from a slower responding device at lower voltage, then from a faster responding device at a higher voltage.

 

[electricalist]

Sometimes you may see reducing washers where con or ecc ko s are present to satisfy bonding. 250 v to ground that means the only place you need to see bonding bushings would be the probably gutter that fed more than one panel and in the first panel. If this makes sense with pipe . The pipe if the connections are legit and the entrance in and out of anything it goes through maintain continuity from begening to end. You are grounded. It has become the norm to put a ground in the pipe. Pull a ground landed in the panel a. If you do good work itll have continuity before u land it in panel b. 277 is when I first had to be aware of bonding in random settings. Also I think your gonna check isolated grounds and neutral in the sub panels. Check for continuity. . If you do dont stress they are and always will be bonded even though they are seperated. Isolating a grounded conductor thats bonded to a grounding conductor is not possible. Lol