Does anyone know the preferred means of grounding light poles besides the grouding electrode?
There seems to be a big misconception that ground rods should be used to ground light poles. The fact is that connections to earth alone like that have too much resistance (impedance) to be of any use in a tripping a breaker if the pole was to become energized. The preferable method of grounding is by connection to a grounding conductor that is run with the supply wires.
Bill
thanks bill, how about bonding to the re-bar cage?
Mike Holt has been discussing this issue in this newsletter. You should be able to find the topic on his website.
http://mikeholt.com
This is the second attempt to post this reply. Hope is it not a duplicate
Try going to Mike Holt's website. He has been discussing it.
http://mikeholt.com
My experience has always been in low-isokeraunic areas, {5-10…not 100 like in central Florida} but the flat-coil-of-#6-solid-in-the-bottom-of-the-hole ground electrode is useless for clearing 60Hz faults. It is needed for the “lighting rod” characteristics of a lot full of aluminum light standards.
Bjarney,
Can you cite any document or source that says the coil of #6 at the bottom of the hole makes a better grounding electrode than the concrete base and its re-bar?
Don(resqcapt19)
No, I'm sorry I can't. I was taking for granted that a couple of acorn clamps on the #6 from the coil extension passing the rebar cage being a de facto practice—but shoulda’ figured it as a “regional variation." It would be a waste not to take every advantage of a ready-made attribute that comes with cages and concrete. In my experience, that detail seems to show up in a lot of municipal-specification boilerplate, but then again I've not worked in Detroit, Michigan or Muleshoe, Texas.
The ‘coil’ has probably been adapted from the long-standing utility practice for wood-pole butt grounding. The hippest in-the-know electrical experts call it a microUfer matrix. ;-)
ok guys, so should i rely on my grounding electrode in the conduit or should you also run a bonding jumper from the cage through the form of the base to the hand hole.... simplist explanations greatly appreciated...
The point is, there are reasons for both.
Thanks guys for the timely info. I have thirteen cast iron light poles to put up. The lights will be on three seperate controls. Can all the pole grounds be daisy chained together on one ground wire? Total amps of all thelights is approx. 15, and I will be pulling 10awg. Thanks
Trainwire
Menegt.....I don't know how your overhead layouts are going to be fed from, but if it's serving a private facility, it has been my experience that each one can be fused and depending on the voltage, I pull either a three or four conductor cable for each one, fed from an ac distribution box. That way each one gets its own EGC for the fixture itself. As far as the pole itself is concerned, I've always used 4/0 cadweld to the GEC whenever possible.....Burns
train--
Depends on voltage drop allowance and overcurrent device...99NEC250-122 could have a couple of applicable paragraphs.
your egc must be per code:
250-2. General Requirements for Grounding
(d) Performance of Fault Current Path. The fault current path shall be permanent and electrically continuous, shall be capable of safely carrying the maximum fault likely to be imposed on it, and shall have sufficiently low impedance to facilitate the operation of overcurrent devices under fault conditions.
The earth shall not be used as the sole equipment grounding conductor or fault current path.
250-122. Size of Equipment Grounding Conductors
(c) Multiple Circuits. Where a single equipment grounding conductor is run with multiple circuits in the same raceway or cable, it shall be sized for the largest overcurrent device protecting conductors in the raceway or cable.
Table 250-122. Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment
Rating or Setting of Automatic Overcurrent Device in Circuit Ahead of Equipment, Conduit, etc., Not Exceeding (Amperes)
Size (AWG or kcmil)
Copper Aluminum or Copper-Clad Aluminum*
15 14 12
20 12 10
30 10 8
40 10 8
60 10 8
100 8 6
200 6 4
300 4 2
400 3 1
500 2 1/0
600 1 2/0
800 1/0 3/0
1000 2/0 4/0
1200 3/0 250
1600 4/0 350
2000 250 400
2500 350 600
3000 400 600
4000 500 800
5000 700 1200
6000 800 1200
remember this egc has to be sized for voltage drop so keep it the same size as your largest wire