Bringing a sub panel up to code

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Old 11-19-17, 04:21 PM
J
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Bringing a sub panel up to code

I have a detatched garage with a 3 wire subpanel off of a 90 Amp circuit in the mail panel. The conduit is not metal and is run under ground. I believe the 2 phases and neutral are #3 or #4 gauge but I haven’t measured them yet. I have done some research and have identified some problems with the sub panel.

1. There are 4 wire circuits connected and the sub panel has circuit grounds and nuetrals connected at the neutral bar.

2. There is no ground bar installed in the sub panel.

3. There is no ground from the main panel to the sub panel.

Other info: there is metal water pipes connected to the garage. It is not connected to the sub panel.

The 3 wires to the sub panel are run through a 1” conduit.

There is a seperate 240v circuit ran to the garage through a parallel conduit that is 2in diameter. I do not need to keep this circuit. Possible route for ground?

The garage had many 240v circuits that can be disconnected from the sub panel. The actual load would be a 240v 50 Amp GFCI protected spa and 3- 20Amp 120v circuits. So I could reduce the size of the breaker in the main box feeding the sub panel.

My goals are to connect a grounded bus in the sub panel. Separate grounds and neutrals for all circuits down the road. Be sure the neutral bar in the sub is floating. Run a 50amp 240v to GFCI disconnect for spa.

Questions: Does the ground for the sub panel have to be run to the main panel? Would a grounding rod suffice? Is it possible to run a heavy guage ground through the existing 2 in conduit that is buried under the drivway if I empty it? Since the ground and phase and neutral would be roughly the same length would that meet code? Do I need to dig up each end of the conduit to push the wire through? If I were to lower the load on the sub panel could thinner wires be used thus making it possible yo push through the existing conduit? Thank you!

Any advice is greatly appreciate!
 
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Old 11-19-17, 05:50 PM
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Does the ground for the sub panel have to be run to the main panel?
Yes. You need a low resistance path for the EGC to ensure a trip in case of a fault.

Would a grounding rod suffice
No. The resistance is too unreliable but it is required to minimize atmospheric charges.

Reducing the breaker would allow smaller wires. How big is the conduit?
 
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Old 11-19-17, 08:06 PM
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Hi Ray, there are two conduits. One is 1” diameter is it supplies the sub panel. There are 3 wires that are #3 or #4 gauge. They are about a 1/4” thick each. There is a seperate conduit that runs from the main to the garage that is 2” diameter. It supplies a 240v circuit that I assume existed prior to the installation of the sub panel. I am thinking I would remove the 240v circuit in the 2” conduit and run EGC from the main panel through to the sub panel through it. They are separate conduits but the are going to be very close to the same length.

The NEC calls for a #8 ecg on a 100 amp panel. So ai would need to run #8 stranded correct? That would allow me to keep the existing phase and Neutral.

Thanks for your help!
 
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Old 11-19-17, 08:48 PM
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Ground does not need to be in the same conduit as the current carrying wires. 8 copper is adequate for ground.

Three #3 ia max for 1" so you should be okay with the existing feed.
 
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Old 11-19-17, 09:16 PM
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You can only have one feed to a detached garage.

You could pull a grounding conductor into the conduit and add a grounding bar to the panel.
 
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Old 11-20-17, 10:41 AM
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When was the subpanel installed on the 3-wire circuit feeding it? This could be grandfathered. There was a time when a 4-wire feeder was not required, but am not sure in what code version it was changed to require a 4-wire feeder. I believe the code changed somewhere around the 2005 edition.
 
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Old 11-20-17, 01:16 PM
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But he wrote there was metal water pipes so may not have been code if there were existing metal pathways at time of installation..
 
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Old 11-20-17, 02:59 PM
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With the metal path between buildings it was not to code when installed.
 
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Old 11-21-17, 07:48 AM
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With the metal path between buildings it was not to code when installed.

That's a good point, but it also makes me wonder what was installed first, the water lines or the subpanel?
 
 

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