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-   -   subpanel grounding 3-wire (http://www.diychatroom.com/f18/subpanel-grounding-3-wire-159930/)

jeffrey mays 10-13-2012 11:12 AM

subpanel grounding 3-wire
 
Hi I am new here and need some help with my sub panel, I've had an older retired electrician run a line to my garage and I have questions about the setup.

what he added was a 50 amp 240 breaker to the main panel in house and exiting the main is 1 inch conduit to a weather head and 3, 8 gauge copper separately sheathed cables running to my detached garage to a sub panel that has its bonding strap attached to the ground neutral bar ( only one ground/neutral bar in this box).

when I started to do research on adding circuits to this sub panel I have read that I need to add an additional wire to seperate the ground and neutral back to the main panel, so now I am asking what should I do to this setup and how I can add the 4th wire to this box.

can I just run a green sheathed wire to the main from the sub and be all set and tape or tie wrap this wire to the three wires already ran or runa ground between the attached to the conduit weather heads to each other and use the conduit to the boxes as the connection, to a second bar that I will have to add to the sub panel.

thanks
jeff

k_buz 10-13-2012 11:14 AM

How long ago was this done?

jeffrey mays 10-13-2012 11:36 AM

Last week

k_buz 10-13-2012 11:40 AM

I would tell him to come back and do it right. He also seems to have forgotten the ground rods at the sub panel.

The reason I'm not answering your direct question is specifics are needed. How was the pipe run? Is there a J-Box before the weather head? How do the wires enter the panel?

jeffrey mays 10-13-2012 11:57 AM

no j-box, should there be?
there is 1" conduit exiting the sub panel and the conduit is attached with a conduit connector, exits the wall of the shop and is attached to a weather head then to a ceramic knob and then the span to the house,

this house was built in the 30's and I dont really care about code, if I ever sell it I will just disconnect the garage line, I just need it to be safe so that I dont get shocked ect and do I need to add a copper rod at the panel...
thanks for the help
jeff

stickboy1375 10-13-2012 12:02 PM

Quote:

Originally Posted by jeffrey mays (Post 1030044)

this house was built in the 30's and I dont really care about code, if I ever sell it I will just disconnect the garage line, I just need it to be safe so that I dont get shocked ect and do I need to add a copper rod at the panel...
thanks for the help
jeff

See, we have codes to keep things safe...

k_buz 10-13-2012 12:02 PM

A ground needs to be run from the existing main panel (in the conduit) to the sub. I have no idea what size ground needs to be run because you haven't stated how large the sub is.

You will need two ground rods unless you can prove less than 25 ohms to ground.

jeffrey mays 10-13-2012 12:31 PM

the sub panel is Ge Industrial Systems TL412CP Indoor Main Lug Load Center 125 Amp the breaker is in the main panel and is a 50 amp, the line to the shop is aerial 3, 8 gauge sheathed copper bundled together straight to the sub thru the weather head and conduit.

I am thinking that I need to add an additional bar in the sub panel and run a 4th wire to the main panel....

the reason I am asking is that I have already invested 150.00 on the 8 gauge cables that are ran out there and now I have read that I need to have a 4th wire to seperate the ground and neutral wires at the subpanel, would it be ok to get a 12 gauge green sheathed copper wire and run this thru the conduit and attache the new ground bar?

k_buz 10-13-2012 12:36 PM

Nope...you would need a #10 THHW CU. You would need a minimum #8 CU for the ground rods.

jeffrey mays 10-13-2012 01:02 PM

thanks for the help , so I will need to add the #10 THHW for the ground, I have about 15 feet of the #10 THHW but will need to get to lowes and buy more to finish that and the additional ground bar kit in the sub panel I hope that I can get that at lowes to.

You say I need to add a ground rod and it is needed for lightening strikes, can I use just one bar?

what color wire should I buy for the ground

mpoulton 10-13-2012 01:39 PM

The 3-wire installation was code compliant up until a few years ago. The requirement to run 4-wire feeders is fairly new and if he's an old-school electrician who hasn't been keeping up with changes he may not have known about it - although he certainly should. The requirement for additional ground rods at the detached structure is not new and there's no way he should have missed that. The 3-wire feeder is not inherently unsafe, it is only slightly less safe than a 4-wire feeder. But it is not code compliant. As long as you have a 3-wire feeder, it is critically important that the neutral-ground bond in the subpanel be present. That's what protects you from shocks. If you remove the N-G bond in the subpanel, you will have a big problem. That can only be removed if you run the fourth wire back to the main panel, in which case that separate grounding conductor takes the place of the N-G bond in the subpanel.

jeffrey mays 10-13-2012 02:05 PM

Quote:

Originally Posted by mpoulton (Post 1030101)
The 3-wire installation was code compliant up until a few years ago. The requirement to run 4-wire feeders is fairly new and if he's an old-school electrician who hasn't been keeping up with changes he may not have known about it - although he certainly should. The requirement for additional ground rods at the detached structure is not new and there's no way he should have missed that. The 3-wire feeder is not inherently unsafe, it is only slightly less safe than a 4-wire feeder. But it is not code compliant. As long as you have a 3-wire feeder, it is critically important that the neutral-ground bond in the subpanel be present. That's what protects you from shocks. If you remove the N-G bond in the subpanel, you will have a big problem. That can only be removed if you run the fourth wire back to the main panel, in which case that separate grounding conductor takes the place of the N-G bond in the subpanel.

I dont understand as I am no electrician, are you saying that I need the fourth wire and what do I do with the ground strap in the sub panel/

mpoulton 10-13-2012 02:43 PM

Quote:

Originally Posted by jeffrey mays (Post 1030114)
I dont understand as I am no electrician, are you saying that I need the fourth wire and what do I do with the ground strap in the sub panel/

If you add a fourth wire, then you should add an isolated neutral bar in the subpanel. If you don't add the fourth wire, then you MUST NOT separate the neutrals and grounds in the subpanel.

jeffrey mays 10-13-2012 03:11 PM

I have 3 wire service and the wires are all black sheathed 8 gauge copper and I need the 4th wire to be 10 gauge and I will run it thru the conduit with the other wires but what color wire should I buy and does the wire need to be copper or can it be aluminum or something else , this wire will only be a ground any help is appreciated.

can I get a 10 gauge black sheathed wire and code it green with electrical tape and can this wire be aluminum...

mpoulton 10-13-2012 04:34 PM

The ground wire must be either green or bare. It cannot be black or any other color. If it's 10 gauge, then it must be copper. You could use aluminum but it would need to be larger, and it's weird to mix copper and aluminum in the same run. I would use solid bare copper.


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