ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
AreMetal Ladders Ever OK For Electrical Work?
by HotLine1. 01/22/18 07:31 PM
Photocell
by twh. 01/22/18 05:06 PM
VDE 0100 to introduce AFCIs
by sparky. 01/20/18 05:09 PM
MRI LED lights dimmer control replacement - wow!
by Potseal. 01/19/18 08:52 PM
New in the Gallery:
Housebilding DIY wiring
SE cable question
Who's Online Now
0 registered members (), 22 guests, and 7 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
480/277 volt service bonding #88770
07/21/04 07:51 PM
07/21/04 07:51 PM
S
shortcircuit  Offline OP
Member
Joined: Jun 2004
Posts: 608
massachusetts
What size bonding conductor is required to connect the bonding bushings installed on the steel conduit on the line side of a 200 amp 480/277 volt service disconnect with 3/0 copper service entrance conductors?
Also,the service will be fed with a underground latteral in 2" pvc with a section of 2" ridged conduit up the power company's pole. What is the method for bonding that ridged riser conduit.Is a ground clamp at the top of the conduit all that is needed for the poco to connect to?

2017 / 2014 NEC & Related Books and Study Guides
Re: 480/277 volt service bonding #88771
07/21/04 08:47 PM
07/21/04 08:47 PM
C
cpal  Offline
Member
Joined: May 2004
Posts: 162
Cohasset MA
Equipment Bonding Jumpers are sized per section 250.102 in this case 250.102 (C) Size — Equipment Bonding Jumper on Supply Side of Service. I would size the jumper per table 250.66 (#4CU or 2 AL).

The metal riser at the pole should be bonded in accordance with section 250.92 (A) using a method described in 250.92 (B). Part (A) requires that the metal raceway enclosing service conductors be bonded. And the method in part (B) States that electrical continuity at service equipment, service raceways, and service conductor enclosures, shall be ensured by one of the following methods, ( 1-4):
(1) Allows bonding to the grounded service conductor, (2) allows connections utilizing threaded couplings etc, made up wrench-tight. The third (3ed) provision recognizes threadless couplings and connectors, and the fourth (4th) requires approved devices, such as bonding-type locknuts and bushings
Bonding jumpers meeting the other requirements of this article shall be used around concentric or eccentric knockouts that are punched or otherwise formed so as to impair the electrical connection to ground. Standard locknuts or bushings shall not be the sole means for the bonding required by this section.

250.97 will require one of these four methods be employed where the voltage to ground exceeds 250V. (There is an exception)

I believe if you read the Code 250.102 (C) establishes the size of the bonding conductor on the line side of the service equipment, which would require a No. 4 CU or No. 2 AL to the metal raceway (yes a bonding bushing will work but so would a pipe clamp, etc.). I will stand by to read other opinions.
Charlie

Re: 480/277 volt service bonding #88772
07/21/04 09:09 PM
07/21/04 09:09 PM
S
shortcircuit  Offline OP
Member
Joined: Jun 2004
Posts: 608
massachusetts
thanx charlie...
OK...does the #4 copper bond to the metal riser pipe have to run out from the service equipment location to the riser or can the section of pipe be bonded out at the pole to the power companys grounded conductor or pole ground wire?

Re: 480/277 volt service bonding #88773
07/21/04 09:58 PM
07/21/04 09:58 PM
C
cpal  Offline
Member
Joined: May 2004
Posts: 162
Cohasset MA
250.92 (B) allows the raceway to be bonded to the grounded conductor (neutral)
250.142 allows the use of the gounded conductor (neutral) to ground on the supply side of the main disconnect. the connection from the raceway to a neutral is a bonding wire. I think Its ok touse a No. 4 Cu or 2 Al from , say a bonding bushing to the neutral at the pole.
In our area most leave a bonding bushing on the riser and the utility will catch it with their No. 6 that they run to the rod at the base of the pole. No one seems to argue with this. But I think the Code requires a full size bond wire per 250.66 to the neutral.

any way thats how I read it!!

Re: 480/277 volt service bonding #88774
07/22/04 05:48 PM
07/22/04 05:48 PM
S
shortcircuit  Offline OP
Member
Joined: Jun 2004
Posts: 608
massachusetts
An associate of mine told me that an inspector told him to drive a seperate ground rod at the pole to ground the steel riser pipe up the side of the POCO pole...this doesn't seem right though because there is no connection to the service grounded conductor?

Re: 480/277 volt service bonding #88775
07/22/04 06:04 PM
07/22/04 06:04 PM
I
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Shortcircuit you are correct this ground rod would be worthless.

The only way a fault to this raceway would clear is with a connection to the neutral in some way not through the earth.


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Re: 480/277 volt service bonding #88776
07/22/04 06:42 PM
07/22/04 06:42 PM
S
shortcircuit  Offline OP
Member
Joined: Jun 2004
Posts: 608
massachusetts
Thanx iwire...the groundrod didn't seem like the correct method for bondind the riser conduit...
Grounding and bonding is confusing even for some inspectors I guess.


Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
Attic Rat
Attic Rat
Bergen Co.,N.J. USA
Posts: 524
Joined: December 2003
Show All Member Profiles 
Top Posters(30 Days)
Admin 20
sparky 15
Potseal 12
Popular Topics(Views)
243,606 Are you busy
180,418 Re: Forum
170,875 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.030s Queries: 14 (0.013s) Memory: 0.9839 MB (Peak: 1.1367 MB) Zlib enabled. Server Time: 2018-01-24 05:48:02 UTC