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Re: Bonding and grounding [Re: lite bulb] #214364 11/20/14 03:10 AM
Joined: Jul 2004
Posts: 9,499
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gfretwell Online Content
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The OP said his only electrode was 2 rods.


Greg Fretwell
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Re: Bonding and grounding [Re: lite bulb] #214369 11/21/14 04:47 AM
Joined: Feb 2006
Posts: 78
L
lite bulb Offline OP
Member
Thanks for all the input and your help Guys. It just gets confusing on what to do when you have no building steel to use as a grid. Still not 100% on what to do.

Last edited by lite bulb; 11/21/14 04:49 AM.
Re: Bonding and grounding [Re: lite bulb] #214378 11/21/14 09:48 PM
Joined: Jan 2005
Posts: 5,316
renosteinke Offline
Cat Servant
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You've got two grounding issues to contend with- fault clearing and bonding to the building ground.

Faults are cleared by current flowing through that fat green wire you pull in with your feed. At the service, the ground buss is bonded to the neutral buss, to return 'utility' fault current to the utility's transformer over their neutral.

What about transformers? Well, the ground /neutral bond you make at your first overcurrent device after the transformer performs the same function for any 'lost' transformer secondary current.

Yet, the all of your services need to also be tied into the building's ground system. This system- the Ufer, ground rod, whatever - is best thought of as being there for lightning, though that's a bit overly simplified. What matters is that you don't want one end of the building to be at a different ground potential than the other end.

We keep this from happening by tying all our ground rods, Ufers, etc., together. If you do not have serious building steel - not even bar joists holding up the roof or a concrete slab - then you're stuck with running a ground wire back all the way to the existing ground rods.

Re: Bonding and grounding [Re: lite bulb] #214379 11/22/14 02:14 AM
Joined: Jul 2004
Posts: 9,499
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gfretwell Online Content
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If you want to look just like the handbook, connect a 250.66 sized jumper from each transformer to the 2/0 grounding electrode conductor and connect them with split bolts.

[Linked Image from gfretwell.com]


Greg Fretwell
Re: Bonding and grounding [Re: lite bulb] #214391 11/24/14 10:08 PM
Joined: Feb 2006
Posts: 78
L
lite bulb Offline OP
Member
The 5 kva control transformer is being fed from the mcc panel with two #12 and a ground on a 10 amp fuse, its leaving the mcc with grounding type sealtight, and returning to the mcc with the same type sealtight supping one 20 amp fuse to fed the computer,and one 20 amp fuse for printers. Do I still need grounding bushing if so what size wire, and do I need a ground back from xo to the main ground bar in the mcc, bonding xo in the transformer with #8. Also the main bonding will be done on a 2"x1/4 buss bar, can the buss be mounted with spacers on 3/4 plywood.

Last edited by lite bulb; 11/24/14 10:20 PM.
Re: Bonding and grounding [Re: lite bulb] #214401 12/01/14 03:13 AM
Joined: Feb 2006
Posts: 78
L
lite bulb Offline OP
Member
What is the smallest neutral I can use on this service, no 277 volt load just useing the neutral up to the first disconnect.

Re: Bonding and grounding [Re: lite bulb] #214402 12/01/14 11:58 PM
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Posts: 613
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shortcircuit Offline
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Can't be smaller than the required GEC...

Re: Bonding and grounding [Re: lite bulb] #214403 12/02/14 10:00 AM
Joined: Feb 2006
Posts: 78
L
lite bulb Offline OP
Member
The 5 kva control transformer is being fed from the mcc panel with two #12 and a ground on a 10 amp fuse, its leaving the mcc with grounding type sealtight, and returning to the mcc with the same type sealtight supplying one 20 amp fuse to fed the computer,and one 20 amp fuse for printers. Do I still need grounding bushing if so what size wire, and do I need a ground back from xo to the main ground bar in the mcc that is grounded back to the main panel, bonding xo in the transformer with #8 back to the gec.

Re: Bonding and grounding [Re: gfretwell] #214404 12/02/14 12:24 PM
Joined: Dec 2000
Posts: 4,283
electure Offline
Member
Originally Posted by gfretwell
If you want to look just like the handbook, connect a 250.66 sized jumper from each transformer to the 2/0 grounding electrode conductor and connect them with split bolts.


Isn't an exothermic weld or a non-reversible crimp required instead of split bolts?

Re: Bonding and grounding [Re: lite bulb] #214405 12/02/14 01:55 PM
Joined: Jul 2004
Posts: 9,499
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gfretwell Online Content
Member
250.30(A)(4)(c) says

Quote
(c) Connections. All tap connections to the common grounding electrode conductor shall be made at an accessible location by one of the following methods:
(1) A listed connector.


Greg Fretwell
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