garrisonm1
Member
- Location
- Maryland
Does a pull box have to be grounded at the box?
pull boxes
- Thread starter garrisonm1
- Start date
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goldstar
Senior Member
- Location
- New Jersey
- Occupation
- Electrical Contractor
Re: pull boxes
If it's metal, yes. If you're using EMT or rigid to connect the box to the breaker panel, the conduit serves as the ground.
If it's metal, yes. If you're using EMT or rigid to connect the box to the breaker panel, the conduit serves as the ground.
A
a.wayne3@verizon.net
Guest
Re: pull boxes
i`ve always thought that as long as there isn`t a splice in the pull box it doesn`t have to have a ground tap ????????????
i`ve always thought that as long as there isn`t a splice in the pull box it doesn`t have to have a ground tap ????????????
russ
Senior Member
- Location
- Burbank IL
Re: pull boxes
250.4 Yes!
250.4 Yes!
Re: pull boxes
250.148
Prior to the ?02 code it was a bit unclear. Most inspectors interpreted it like this:
If you pulled an equipment grounding conductor in with a metallic raceway, you must bond it to every pull box. This cost a large contractor in Los Angels a lot of money at a very large job when they had to go back and bond all of there large feeder pull boxes that they didn?t bond because there were no splices and EMT was the wiring method.
250.148 in the ?02 code makes it pretty clear that (as long as a raceway is used that is suitable for use as an equipment grounding conductor) if there are no splices or equipment utilized in or mounted to the box, bonding the equipment grounding conductor to the box is not required.
250.148
Prior to the ?02 code it was a bit unclear. Most inspectors interpreted it like this:
If you pulled an equipment grounding conductor in with a metallic raceway, you must bond it to every pull box. This cost a large contractor in Los Angels a lot of money at a very large job when they had to go back and bond all of there large feeder pull boxes that they didn?t bond because there were no splices and EMT was the wiring method.
250.148 in the ?02 code makes it pretty clear that (as long as a raceway is used that is suitable for use as an equipment grounding conductor) if there are no splices or equipment utilized in or mounted to the box, bonding the equipment grounding conductor to the box is not required.
goldstar
Senior Member
- Location
- New Jersey
- Occupation
- Electrical Contractor
Re: pull boxes
Nick & A.wayne3,
You're exactly right and I stand corrected. I was too quick to answer. I made an assumption that there was a device installed or a splice made in the JB.
[ March 28, 2003, 05:41 AM: Message edited by: goldstar ]
Nick & A.wayne3,
You're exactly right and I stand corrected. I was too quick to answer. I made an assumption that there was a device installed or a splice made in the JB.
[ March 28, 2003, 05:41 AM: Message edited by: goldstar ]
sparkmantoo
Member
- Location
- Virginia
Re: pull boxes
something about relying on fittings to ensure that you maintain that mechanical bond through the raceway system just seems to puzzle me. i know that it is okay to use the conduit as a grounding means, and using rigid, i definately don't have a problem with. but what would happen if someone whacked that conduit say with a fork lift and seperated those fitting to where they were not making contact. where would we be then? i guess my point is IMO the grounding of the electrical system is the most important part of what we do. without proper grounding we stand unprotected from any faults that may occur. am i wrong to be concerned about this scenario?
something about relying on fittings to ensure that you maintain that mechanical bond through the raceway system just seems to puzzle me. i know that it is okay to use the conduit as a grounding means, and using rigid, i definately don't have a problem with. but what would happen if someone whacked that conduit say with a fork lift and seperated those fitting to where they were not making contact. where would we be then? i guess my point is IMO the grounding of the electrical system is the most important part of what we do. without proper grounding we stand unprotected from any faults that may occur. am i wrong to be concerned about this scenario?
- Location
- Massachusetts
Re: pull boxes
sparkmantoo
The code address's this a couple of times that I can think of, 2002 NEC 250.92(B) bonding at services and 250.97 Bonding over 250 volts.
If the pull box was for a 480 volt branch circuit or feeder and you where coming in and out with metal raceway through concentric knock outs you would have to use bonding bushings with bonding jumpers to the box.
Most of the job specs we get require a grounding conductor, many times even though we put a pull box in to meet code we pull straight through it so we do not add a jumper there, but the ground conductor is terminated at the start and finish.
[ March 30, 2003, 08:17 AM: Message edited by: iwire ]
sparkmantoo
The code address's this a couple of times that I can think of, 2002 NEC 250.92(B) bonding at services and 250.97 Bonding over 250 volts.
If the pull box was for a 480 volt branch circuit or feeder and you where coming in and out with metal raceway through concentric knock outs you would have to use bonding bushings with bonding jumpers to the box.
Most of the job specs we get require a grounding conductor, many times even though we put a pull box in to meet code we pull straight through it so we do not add a jumper there, but the ground conductor is terminated at the start and finish.
[ March 30, 2003, 08:17 AM: Message edited by: iwire ]
Re: pull boxes
Straying from the NEC application of this and looking at the engineering aspect it gets a little more complicated. The Soares Book on Grounding has a section dedicated to the effectiveness of steel conduit as an equipment grounding conductor. Conduit is only effective for a certain distance. After that point, figured by calculating all the relevant parameters, there is too much impedance to clear a fault. This is remedied by adding an equipment grounding conductor to run in parallel to the conduit. There will be a slight but increasing impedance difference between the conduit and conductor the longer the run gets. It is therefore recommended that the equipment grounding conductor be bonded to the conduit system ,IE; in a j-box, at intervals of 100ft or less. For more info see the Soares Book on Grounding and check out the PDF file named Modeling and testing of steel EMT, IMC and rigid (GRC) conduit part 1 here.
Straying from the NEC application of this and looking at the engineering aspect it gets a little more complicated. The Soares Book on Grounding has a section dedicated to the effectiveness of steel conduit as an equipment grounding conductor. Conduit is only effective for a certain distance. After that point, figured by calculating all the relevant parameters, there is too much impedance to clear a fault. This is remedied by adding an equipment grounding conductor to run in parallel to the conduit. There will be a slight but increasing impedance difference between the conduit and conductor the longer the run gets. It is therefore recommended that the equipment grounding conductor be bonded to the conduit system ,IE; in a j-box, at intervals of 100ft or less. For more info see the Soares Book on Grounding and check out the PDF file named Modeling and testing of steel EMT, IMC and rigid (GRC) conduit part 1 here.
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