Sub Panel Predicament

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Old 08-16-18, 07:27 PM
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Sub Panel Predicament

Hello everyone.

I have an interesting situation that I'm not sure how to address.

Move into this house a year ago, and inherited many issues. The house was built in 86, but the 2 outbuildings were built in the early 70's.
One building (shed) in particular has a sub panel with glass fuses.
This shed has only one purpose, stores "stuff" and on the back side are a couple covered animal pens. The only thing we used for power last year were about 6 fluorescent lights, a couple of heat lamps in the winter, and some fans.

Recently, I am trying to improve some things and thought I would tackle this old panel.
What I found out is that I only have 2 wires coming to this panel. Both are 6 AWG, but there is NO ground wire coming from the main house panel that is 50ft away. The main house panel has a 20amp breaker controlling this sub panel.

I would like to replace this breaker with a 50 amp breaker and then install a 70 amp sub panel. I would not use all spaces, as I really just want to isolate the heat lamps, lights, the remaining outlets (total of 4) and the ability to add something in the future.

My question is whether I can install this sub panel and install a separate ground wire to a ground rod just outside of the shed. Or MUST I also run a ground back to the main panel?

I would obviously prefer to not trench this, and I thought about pulling new wire, however, the conduit used is 1" PVC pipe with 90-degree elbows........probably not very possible to pull the old out and pull new through this.

Thoughts?
 
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Old 08-16-18, 07:37 PM
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Welcome to the forums.

A two wire sub panel is not code current today. The best you'd have is 120v with no ground.
Unfortunately you will need to replace your two wire service with a four wire cable.

A 50' PVC run should be upgradeable to four wires.
 
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Old 08-16-18, 10:21 PM
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Iím not trying to bunk code. But throw a question out there to understand implications.
lets say I keep the wiring as is......with no ground back to the main panel.
If thats done, what is an option for installing.....maybe from a previous code.
Bond the neitralmand ground together?

Aside from code, what is the rreal risk at this point? I
 
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Old 08-17-18, 10:56 AM
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Having no ground from the sub panel to the main panel is dangerous. This is the connection that supplies the path in case of a short to ground. A ground rod is not a substitute for a proper panel ground connection.

The neutral and ground can ONLY be connected at the main panel. From that point forward..... neutrals and ground must remain separated.
 
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Old 08-17-18, 01:11 PM
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The neutral and ground used to be bonded in outbuildings back in the old days, but that method has been shown to be dangerous due to high likelyhood of failure of the shared ground/neutral wire and potential shock risk of ungrounded surfaces in the outbuilding. For example you can search this forum for how often broken neutral threads come up. The ground wire is a backup for the neutral so that the breaker trips if there is a fault. When the ground and neutral is the same wire, there is no backup and if there's a fault in a hot wire you have shock potential on any exposed metal surface in the outbuilding.

The only safe way to do this is to upgrade to a four wire feed, which should be OK in 1" pipe. For a 60A feed, you need #6 copper for the two hots and neutral and #10 copper for the ground. You also need a ground rod at the outbuilding which is primarily for lightning protection and not really related to the equipment ground wire despite the similar name.
 
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Old 08-17-18, 09:05 PM
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the conduit used is 1" PVC pipe with 90-degree elbows
Depending on the pipe that was used it is possible to pull the old wire out, especially with 1" pipe. If you can, pull both at a time and tie on a string or thin rope (para cord) when you pull them out. You can replace the wire with 3 #8 and 1 #10 for the ground and still have 50 amps, plus you will now have 120/240 volts.
 
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Old 08-20-18, 09:19 AM
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@ibpooks:
Thank you for the explanation. That makes sense now.
I was removing the old sub panel this weekend and noticed that the ground wire was tied into the neutral..........but nothing was obviously going back to the main panel or even going to a ground rod. It's funny that this has been used in this method for over 40 years......... lucky I guess.

@Ironhand:
Made an attempt pull a wire this weekend. No way. I dug down to the first 90-degree turn to cut it. When I did, I noticed that the pipe was filled with with insect debris. But so much that the wires were packed in there. Looks like it might not be completely encased in pipe back to the main. So new wire is obviously in my future.
 
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Old 08-20-18, 12:52 PM
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You can try to blow the old pipe out with compressed air. Sometimes that works, but beware when it cuts loose it makes a big mess. Staple some plastic up.
 
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Old 08-21-18, 07:52 PM
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6 lights, two heaters, and some fans...seems like a lot for a 20 amp breaker. Surprised it even worked without tripping???
I ran 10g 2 plus g wire uf from an afci gfci combo breaker ( inside house subpanel) for my shed and a second line for deck outlets on another breaker. I did not run ground rod on shed but there is no sub panel i used in shed,i ran right into box and fed from there. Where would i put ground rod?
 
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Old 08-22-18, 09:26 PM
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@ibpooks
Question for you. It didnít snap until you posted about the 4 wire feed. My main house panel only has a single pole breaker and Iím replacing it with a 50 amp single pole breaker that does fit. There is no room for a double pole breaker on this panel.
So a 4 wire feed will not work. Is my only option a new 3 wire feed? Or, is supplying 120 volt power an issue?
Itís been functioning well for us (with zero issues) for the year that we have lived here. I have only swapped out the glass fuse two times in the last year during the winter when we were running 3-4 heat lamps for the animals (we had abnormal temps in the low 20s for multiple days).

And based on how it is currently wired, Iím amazed myself that it worked at all or that we never had any serious issues. So I know code is code......but at the end of the day, this crappy electrical system has worked aside from loads that were too much but the breakers performed their job as designed. So are there any other solutions out there that might work in this regard? I know an answer could technically make someone ďliableĒ........and Iím not asking for that.......just throwing out questions to look outside of the box.
This conversation is better had over a couple of beers.
 
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Old 08-23-18, 09:04 AM
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You can run 120V to the outbuilding utilizing 3 wires. It's not the standard way of doing it, but it's possible. The catch is that you will only be able to put breakers in every other row in the subpanel as only half of it will be powered. Can you make room in the house panel by moving another circuit to a tandem breaker?
 
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Old 08-23-18, 08:55 PM
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That panel is jammed full. Itís located in the center of the back yard and supplies power to this shed, our pool equipment, another outbuilding, and to our house breaker panel.....I guess our home is also a subpanel to this.
I believe this property has some history.
 
 

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