# Grounding & Bonding of 3 Wire Fed Subpanel



## funkking (May 27, 2020)

We have a 40 year old pole barn that has a sub panel that I upgraded several years ago. The sub panel has a 3 wire feed from the house, no EGC was originally run with the supply feeders. The sub panel is grounded via a ground rod at the pole barn. When I upgraded the panel, I separated the neutrals and grounds.

However, the more I think about this, and the more I learn about grounding and bonding, the more I question whether or not it should be this way.

My question is: since the subpanel has a grounding system different from the main panel at the house, should the neutrals and grounds be bonded or separated? I am having trouble making clear sense of 250.32(B)(1), Exceptions 1 & 2. (2017 NEC).

I understand that if it were a 4 wire feed from the house, the neutrals and grounds would be separated.

Thanks.


----------



## Bird dog (Oct 27, 2015)

Draw it out. Yes, the neutral needs to be bonded to the ground bar where all your EGCs run to or put in the bonding strap supplied with the panel. Right now, if a hot shorts to the EGC, the panel could have 120v on it & the breaker won't trip. Even if the ground rod was 25 ohms or less. The current wants to go back to its source-the POCO xfmr.


----------



## funkking (May 27, 2020)

Bird dog said:


> Draw it out. Yes, the neutral needs to be bonded to the ground bar where all your EGCs run to or put in the bonding strap supplied with the panel. Right now, if a hot shorts to the EGC, the panel could have 120v on it & the breaker won't trip. Even if the ground rod was 25 ohms or less. The current wants to go back to its source-the POCO xfmr.


Thanks for the quick answer and for verifying my worry. lol Sounds like I have some work to do in the barn this weekend. 

I've been studying for an electrical exam, and in the course of my study, I began to learn more about grounding and bonding. This is what prompted my worry.


----------



## Bird dog (Oct 27, 2015)

Well the good thing is you caught it. Now you also understand it's easier just to drive a ground rod or two for a service & skip the 25 ohm testing.


----------



## funkking (May 27, 2020)

Bird dog said:


> Well the good thing is you caught it. Now you also understand it's easier just to drive a ground rod or two for a service & skip the 25 ohm testing.


For my fix, I think I'll just put in the jumper, rather than deal with re-landing a bunch of wires.


----------



## rjniles (Aug 1, 2011)

funkking said:


> For my fix, I think I'll just put in the jumper, rather than deal with re-landing a bunch of wires.


Just install the green bonding screw in the neutral bar.

Sent from my Moto E (4) Plus using Tapatalk


----------



## Bird dog (Oct 27, 2015)

btw, if you ran all your EGCs to the neutral bar, you still need the bond strap or bond screw to bond the can to the neutral bar.


----------



## funkking (May 27, 2020)

Bird dog said:


> btw, if you ran all your EGCs to the neutral bar, you still need the bond strap or bond screw to bond the can to the neutral bar.


Yep.


----------



## VELOCI3 (Aug 15, 2019)

*Grounding &amp; Bonding of 3 Wire Fed Subpanel*

Auxiliary buildings should have the EGC extended from the main building. 

The barn panel neutral should not be bonded. 

It also needs a ground rod. 

Power supplied to detached buildings is considered a feeder when supplied from a main or sub panel. 


Sent from my iPad using Tapatalk


----------



## yy4u222 (Jul 8, 2021)

I have the same situation. Older poll barn with close to 200ft of #2 wire but they only put 3 wires No ground wire from main pan. Now to pull a new ground wire almost impossible. I have installed 2 ground rods 6ft apart. Do i separate the ground and neutrals or do i bond the sub. Seems to me bonding would still cause a loop back on the neutral.


----------



## SCR (Mar 24, 2019)

yy4u222 said:


> I have the same situation. Older poll barn with close to 200ft of #2 wire but they only put 3 wires No ground wire from main pan. Now to pull a new ground wire almost impossible. I have installed 2 ground rods 6ft apart. Do i separate the ground and neutrals or do i bond the sub. Seems to me bonding would still cause a loop back on the neutral.


Install the bonding jumper. If there is no incoming bond, the neutral needs to be bonded to ground at the sub-panel to make a safe installation.


----------



## cuba_pete (Dec 8, 2011)

SCR said:


> Install the bonding jumper. If there is no incoming bond, the neutral needs to be bonded to ground at the sub-panel to make a safe installation. No exceptions.


The exception is what allows one to do that.


----------



## yy4u222 (Jul 8, 2021)

cuba_pete said:


> The exception is what allows one to do that.


Very true Norm install would be no bond and separate grounds.


----------

