Hey all. Been a while. Life has a way of getting busy with a house full of teenagers.
Anyways -
Quick question. My garage has a sub panel with no ground. Just 2 hots and a neutral (Black, Red, White). In the sub panel the ground bar is tied to the neutral. I was going to wire a 30 amp RV plug in.
Simple questions is, can I use this panel without a ground in essence having the ground tie into the neutral at the sub panel or would that have the propensity to light up my bus shell?
Thanks!
-Sean
You have a 50 amps using two hots and a neutral and ground, which is 240 volts. You can hook up a 30 amp RV receptical using one hot, one neutral and the ground which will give you 120 volts. Google 30 amp RV plug for a diagram.
Not sure your sub panel is wired correctly, at least not according to what's done around here. The neutral & ground should be bonded at only one place, which is usually the main panel. There should be a separate ground at the sub panel.
Is it possible to run a ground wire to the sub panel?
The 30-amp RV outlet should have one 120v hot, a neutral, and a ground. It should be protected by a 30-amp single-pole breaker.
Quote from: richard5933 on July 14, 2018, 09:46:58 AM
Not sure your sub panel is wired correctly, at least not according to what's done around here. The neutral & ground should be bonded at only one place, which is usually the main panel. There should be a separate ground at the sub panel.
Is it possible to run a ground wire to the sub panel?
The 30-amp RV outlet should have one 120v hot, a neutral, and a ground. It should be protected by a 30-amp single-pole breaker.
Richard,
Well aware. Its an old house that was knob and tube and still has a bunch of 2 wire runs. Slowly updating.
I'd love to rerun another 2aught 4 wire cablle and get this sub panel done correctly. Unfortunatley that will take some digging up of concrete.
I was just wondering what the danger would be of wiring a 3 prong 30 amp connector to this sub panel box with the neutral and ground bonded at the sub panel.
Thanks.
-Sean
Quote from: Geoff on July 14, 2018, 09:12:01 AM
You have a 50 amps using two hots and a neutral and ground, which is 240 volts. You can hook up a 30 amp RV receptical using one hot, one neutral and the ground which will give you 120 volts. Google 30 amp RV plug for a diagram.
Geoff,
No issues here wiring 50amp or 30 amp. Just wondering about the neutral bond to the ground in the sub panel and if I could wire a 30 amp plug to this sub panel without issue.
-Sean
What I would do is first, trace the wire back to the main panel and find out if the white wire is actually a neutral, or actually a ground. Probably it's a neutral. If it is, then this:
Edit; this assumes the garage is in the same building as the main panel.
"The three wire allowance is an exception to 250.32(B)(1), which allows existing installations that were compliant with previous code versions to exist. If you want to bring the installation up to current standards, you can install a properly sized grounding conductor between the panels and separate the neutral and grounding bars in the second panel.
The reason you need to bond the neutral bar in the case of a three wire feeder, is to provide an effective ground-fault current path. Remember, electricity is trying to return to the source, not to the ground (earth). In the event of a ground-fault, you want the fault current to be able to have a low resistance path back to the source. This low resistance path should allow the fault current to be great enough, so that a circuit breaker (or other protective device) can activate and open the circuit.
If you read the text of the code, you'll find that it says "the grounded conductor run with the supply to the building or structure shall be permitted to serve as the ground-fault return path". By bonding the grounded (neutral) and grounding bars in the panel, you're using the grounded (neutral) conductor as a ground-fault return path."
So what you have is old, probably still meets code, and is OK. According to this source, anyway... The modern way is to install a four wire feed to the sub-panel. I would not install a separate ground stake/point for that panel.
This one is if the garage is a completely separate building. You have to know if there is conduit, or any other metallic path between the buildings. In something I find confusing as hell, even though I've been dealing with this stuff for decades, "ungrounded" means a live feed wire, one of the red or black cables, "grounded" means neutral, usually white, and "grounding" means the bare copper ground wire. Calling all of the cables subtle variations on "ground" just seems somehow wrong to me... :)
"You have two ways to handle a feeder between two buildings.
With both methods you need a grounding electrode as required by 250.32
Method one
Run separate ungrounded, grounded and grounding conductors from one building to the other, do not bond the grounded conductor to the grounding conductor. Put in a grounding electrode at the second building and connect it to the grounding conductor.
Method two
If there are no other metallic paths between buildings (water pipes, coax cables, gas lines, whatever) you are allowed to run just the ungrounded and grounded conductors out the to second building.
In this case you must bond the grounded conductor to the panel enclosure and again install a grounding electrode connected to the grounded conductor."
This is from the Mike Holt Electrical web site, a very good site for US electrical code questions. If your garage is separated per the explanation, you could use Method two above. In all cases, the whole point of the grounding (bare copper or green wire) connection is to guarantee a fault path so that an electrical fault can blow the fuse/breaker. In the setup you have now, you are using the neutral (which may be at ground potential as far as voltage is concerned, but is carrying all of the return current back to the main panel) as that fault path in case of a failure. I have seen situations (in my driveway, of all places, so I knew the electrics were totally up to code) where I had around 30 volts of float voltage at the end of a 100 foot long extension cord. I could measure it, but barely feel it, and it went away when I stuck a screwdriver in the ground and ran a jumper cable to it. Weird. I remember Sean Welsh once said he was parked under a high voltage cable system and he picked up a stray voltage, probably inductively.
Brian
Brian you made some excellent points. I had question if the garage was a separate structure, and myself like and use the method one. Bygosh the ground rod installation around me can be a real pain. Lots a rocks and then a test with meter is a good followup.
Again great tips
Floyd
Brian,
Awesome stuff. Thanks for the info. The garage is technically the same structure connected by a walkway roof and carport. But the power runs from the main breaker under the house and then 90s through about 12' of poured concrete.
I need to check and see if they pulled that thrpugh conduit or just poured it.
If its conduit, ill just run another piece of 8 gauge copper for a ground and call it a day.
You guys are awesome. Best place in the world to get solid help.
Torally appreciated.
Thanks.
-Sean
My head hurts ....
Is it possible to just re run over head through attic roof or in a conduit or rat-run back to the panel? :)
Out and down a wall in conduit to beyond the concrete and through the grass in a trench with Burial cable etc. Your a Busnut come on Think man think, LOL ;)
Simple way to find out if the sub panel is grounded back to the main panel is to take a 120v test light and touch one leg to a hot wire then touch the other leg to the sub panel .If it lights ,your ground is correct if it doesn't you are not grounded.
Thats a good option to consider ( what Dave mentioned ) I say that because the sub panels may have a restriction on switches/ breakers they can have, regardles of amps.
There are as I was told by the electric guy several years ago meter boxes now to better address this particular issue. In that they can have built in breakers in the box for out buildings. This eliminates going inside to your run from your main panel.
Good day
Floyd
Sean, since it's the same structure I would say you have a legal 3 wire connection to the sub panel, so I wouldn't change it. Changing it on your own without a permit or a license is technically illegal (we all probably do it) and what you have would seem to meet current code through an exemption. At the same time, easy to call an electrician to inspect and advise on what you have in place.
Quote from: Seangie on July 14, 2018, 08:13:31 AM
Hey all. Been a while. Life has a way of getting busy with a house full of teenagers.
Anyways -
Quick question. My garage has a sub panel with no ground. Just 2 hots and a neutral (Black, Red, White). In the sub panel the ground bar is tied to the neutral. I was going to wire a 30 amp RV plug in.
Simple questions is, can I use this panel without a ground in essence having the ground tie into the neutral at the sub panel or would that have the propensity to light up my bus shell?
Thanks!
-Sean An easy way to ground your sub panel if it is mounted on an out side wall would be to drive a ground rod in to the earth (eight ft is legal six ft is frequently used) get enough #6 bare copper to reach the sub panel and a ground clamp suitable for under ground (so you can have the ground clamp below ground level ) Run the bare copper from the ground rod/clamp to the sub panel neutral ,remove the screw that ties your neutral and ground together. Ignore the other post about the test light! I missed where
you said the ground and neutral were tied together .
On a 3 wire feed to a sub-panel the old practice was to tie ground to neutral inside the sub-panel, with no other external ground in the panel. That preserved the single ground-neutral bond in the main panel, and in the absence of a fourth grounding wire the 3rd grounded neutral was used to provide the ground fault path to make sure breakers could blow if a ground fault developed. It's still a good fault path to ground, it just shares the load carrying neutral to provide it.
This stuff gives me a headache sometimes. The reason they went to a fourth wire is to allow for current carrying capacity in the grounding conductor in the event of a ground fault failure. The fourth conductor never carries any current until a failure occurs, and then it carries the current that blows the breaker. In the three wire hookup Sean has, the third conductor normally carries the sum of the currents in the two load paths, which because they are opposite phase would normally add up to a quite small current if the panel is properly balanced. In the event of a ground fault failure, the third conductor would carry an overload current from one of the two load conductors, plus whatever other load current was present, so a possibility of a momentary overload on the conductor. A pretty small possibility, but still present.