Bonding Junction Box

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Re: Bonding Junction Box

quote:
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Originally posted by Jhr:
metal 6x6x4 Nema 3 J-Boxes
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Underground?

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George, Residential
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Yea George Nema 3 boxes underground, with 900 tons of concrete on top and fourteen dancing bears eating tiny marshmellow volkswagons crawling up and down the concrete heap, what do you think I meant come on man be serious! :p
 
Re: Bonding Junction Box

jhr,
but if you feel the EGC dosent have to be bonded to the box fine, but where does it say in the code, 250.148 also says circuit conductors that are been supported by the box, what does that mean.
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It doesn't say that you bond the EGC to the box when the circuit conductors are supported by the box. It says you must bond the EGC if the circuit conductors are terminated to equipment within or supported by the box.
250.148(A)Where circuit conductors are spliced within a box, or terminated on equipment within or supported by a box, any equipment grounding conductor(s) associated with those circuit conductors shall be spliced or joined within the box or to the box with devices suitable for the use in accordance with 250.148(A) through (E).
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That being said, this is a poorly written section, as there is no direction to other code sections that require a metallic box to be bonded when the circuit conductors are in a nonmetallic wiring method. Also I think that the change made in the 2002 that eliminated the bonding requirement when metallic wiring methods are used was wrong. If a ground fault occurs in the run or the enclosure, the only fault clearing path is the conduit. In many cases, normally as a result of poor installation practices, the conduit is not a low impedance fault clearing path. I think that we should return the code to the pre-2002 wording.
Don
 
Re: Bonding Junction Box

I've got to agree that this section is poorly written. The 1999 Code required this bonding whether the circuit conductors were spliced or not. However, since we've never been required to bond the EGC within a conduit body, the intent here was to bring boxes and enclosures used only as pull boxes into line with what we've done with conduit bodies. Lot's of wasted ink in my opinion. I would much rather see the EGC bonded to pull boxes whether or not there are splices in it. If you've gone to the trouble of pulling an EGC in your metallic conduit (which, as Don pointed out, is a good idea since the conduit may not provide a low enough impedance path for fault current by itself), you may as well take the time to bond it to your pull boxes.
 
Re: Bonding Junction Box

Originally posted by don_resqcapt19:
If a ground fault occurs in the run or the enclosure, the only fault clearing path is the conduit.
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How would a fault in this enclosure be any different than a fault in the middle of the raceway?

Due to the fact an EGC is run from source to load the conduits bond the enclosure from both directions.

If the NEC allows metal raceway to be the only grounding means in almost any installation it would not make sense to say it is not sufficient to bond the can in the middle of the run.

JMO, Bob
 
Re: Bonding Junction Box

Originally posted by iwire:
If the NEC allows metal raceway to be the only grounding means in almost any installation it would not make sense to say it is not sufficient to bond the can in the middle of the run.

JMO, Bob
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Mine, too.
 
Re: Bonding Junction Box

The conduit should not be allowed to be the ECG regardless of all else said.

Too many times I have seen a conduit broken apart with no ground wire. This from many years doing repair work.

A full size ground should be required for every installation.

That ground wire should be bonded at every box.

If larger wires are pulled streight through, then we should use a split bolt and an downsized bonding jumper to bond the can.
 
Re: Bonding Junction Box

Originally posted by jbwhite:
The conduit should not be allowed to be the ECG regardless of all else said.
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But it is not.

And it is a safe bet that the NEC rejects that idea every code cycle. :)
 
Re: Bonding Junction Box

Originally posted by iwire:
Originally posted by jbwhite:
The conduit should not be allowed to be the ECG regardless of all else said.
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But it is not.

And it is a safe bet that the NEC rejects that idea every code cycle. :)
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And I am still doing spec work. :)
And I will keep putting in the full size ground :cool:
 
Re: Bonding Junction Box

Originally posted by ryan_618:
Metal conduit without an installed EGC is typically a better effective ground fault current path that non-metallic conduit WITH an EGC.
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Until several other trades have worked in the ceiling and the conduits are no longer attached :)
And what about metal conduit with an ECG bonded at boxes?
 
Re: Bonding Junction Box

Originally posted by jbwhite:
Until several other trades have worked in the ceiling and the conduits are no longer attached :)
And what about metal conduit with an ECG bonded at boxes?
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Here we disagree.

If the tubing is properly installed, as in secured, the couplings will stay tight.

For what it is worth all it takes is one bad wire nut and you can lose the ground on non-metallic wiring methods.

No matter which method we choose the quality of the installation comes down to the installer.

I have just started going over a new job, the engineer shows us tapping a 4000 amp bus to feed a 1,600 amp breaker in a separate enclosure. The tap will be four sets of 600 copper in four 4" EMTs. The EGC on the plans is a 4/0 which is correct for a 1,600 amp feeder but not a 4000 amp tap. I will be installing a 500 EGC in each EMT not because I think it is really adding much but only to comply with the NEC. :)
 
Re: Bonding Junction Box

iwire, where does it say that the tap EGC has to be sized to the original feeder?
 
Re: Bonding Junction Box

Originally posted by jbwhite:
iwire, where does it say that the tap EGC has to be sized to the original feeder?
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Glad someone asked. :)

First ask yourself if there is a ground fault on on the supply side of the 1,600 amp breaker which circuit breaker will the EGC have to open?

Now look at the wording in Table 250.122.

Rating or Setting of Automatic Overcurrent Device in Circuit Ahead of Equipment, Conduit, etc., Not Exceeding (Amperes)
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[ January 12, 2006, 08:09 PM: Message edited by: iwire ]
 
Re: Bonding Junction Box

That being said, this is a poorly written section, as there is no direction to other code sections that require a metallic box to be bonded when the circuit conductors are in a nonmetallic wiring method. Also I think that the change made in the 2002 that eliminated the bonding requirement when metallic wiring methods are used was wrong. If a ground fault occurs in the run or the enclosure, the only fault clearing path is the conduit. In many cases, normally as a result of poor installation practices, the conduit is not a low impedance fault clearing path. I think that we should return the code to the pre-2002 wording.
Don
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I totaly agree, very well put Don. :cool: :cool:
 
Re: Bonding Junction Box

By the way to be clear, once you are on the load side of the new breaker the EGC will be based on that.

So in my case the EGC between the 4000 and 1600 amp breakers will be 500, once past the 1600 amp breaker the EGC will reduce to 4/0.
 
Re: Bonding Junction Box

Originally posted by jbwhite:
iwire, where does it say that the tap EGC has to be sized to the original feeder?
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I just realized ny 2005 is at the office and not here at home, but I am pretty sure they addressed this in the 2005 very clearly. 250.122(G), perhaps? Maybe 250.122(F)? Can anyone verify that?
 
Re: Bonding Junction Box

Originally posted by iwire:
By the way to be clear, once you are on the load side of the new breaker the EGC will be based on that.

So in my case the EGC between the 4000 and 1600 amp breakers will be 500, once past the 1600 amp breaker the EGC will reduce to 4/0.
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Bob,

I remember a similar post on this subject several months ago. There was some debate as to whether or not the EGC had to be sized based on the tap or the feeder size. Although I agree with your logic, was there ever a consensus on this issue?
 
Re: Bonding Junction Box

Originally posted by ryan_618:
I just realized ny 2005 is at the office and not here at home, but I am pretty sure they addressed this in the 2005 very clearly. 250.122(G), perhaps? Maybe 250.122(F)? Can anyone verify that?
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Mines in my truck, and don't feel like grabbing it right now. :)
 
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