Ah, bonding - my favorite topic. Here's my situation:
I have an outdoor run of RNC (PVC) which is interrupted at one point with a 6x6x4 metal raintight box, installed to accomodate the number of bends in the run and for ease of pulling. There will be no equipment or devices in this box; the conductors will merely be spliced together.
My question is this: What do I need to do to insure proper bonding/grounding of this box?
NEC 250.4 (A)(2)-(4) requires that (2)"Non-current-carrying conductive materials eclosing electrical conductors...shall be connected to earth..." [grounding] and that (3) "Non-current-carrying conductive materials enclosing electrical conductors...shall be connected together and to the electrical supply source..." [bonding].
Furthermore, 250.86 requires grounding (and bonding, according to editorial notes in the 2005 Handbook) of all metal enclosures.
My intent is to install a lug in the back of the box and attach the grounds there. But how does this satisfy the "shall be connected to earth" portion of the above-mentioned 250.4(3)? Furthermore, do I need to install a bonding bushing where each conduit enters the box? (remember: metal box, but NON-metallic conduit.)
By bonding the box to your EGC, you are bonding it to earth. Remember that your EGC is connected to your Grounding Electrode at your service through your main bonding jumper. So, by bonding your box to the EGC, you are also tying it to your Grounding Electrode system.
The method you are planning on using should be fine. Don't forget to scrape the paint off under your lug to ensure a good connection! Sometimes I will use a small bus bar kit meant for a panel when I have a couple larger wires coming in. Don't have to use a split bolt, and you use less pieces = less labor.
Re: Bonding a pullbox#97843 04/05/0604:13 PM04/05/0604:13 PM
The lug needs to be either in a machine screw threaded hole, (ya sure) or use a nut and bolt to fasten the lug, sheet metal screws are not acceptable. Size the bond to the largest conductor or overcurrent device depending on tables 250.66 or 250.122 and if you increased the wires for voltage drop you must adjust the bonding conductor. Bonding bushings on the conduits might look nice but will serve no practical purpose on PVC. Alan--
Alan-- If it was easy, anyone could do it.
Re: Bonding a pullbox#97844 04/05/0606:37 PM04/05/0606:37 PM
You could use a lay in lug and just strip a short section of the EGC without cutting it. 10-32 self tapping screws will work too. It is just the course thread "sheet metal" screw that is prohibited. If the wire is #10 or smaller you could just use a green S/T screw without a lug.
Re: Bonding a pullbox#97846 04/06/0608:49 AM04/06/0608:49 AM
Most weather proof boxes have that raised spot in them and include a ground screw, I usally do what gfretwell does and use a lay in lug with the supplied screw. By using a lay in lug you can pull the wiring straight through without cutting it.
Re: Bonding a pullbox#97847 04/06/0605:14 PM04/06/0605:14 PM
One point about drilling/tapping a hole in the box. When you scrape off the paint to ensure adequate bonding, you also destroy the corrosion resistance of the box! Be sure to apply a dab of oxide inhibiting compound beneath the lug, and after the lug is installed, and the wire attached, paint the box on both sides where the lug is installed with a corrosion type paint (galvanize).
Re: Bonding a pullbox#97848 04/06/0607:34 PM04/06/0607:34 PM
Be sure to apply a dab of oxide inhibiting compound beneath the lug, and after the lug is installed, and the wire attached, paint the box on both sides where the lug is installed with a corrosion type paint (galvanize).
That's a great idea, and fine workmanship. I'll keep this in mind next time I'm installing a lug in a metal box. Thanks for the tip!