Sub Panel wiring question

[Henro]

Earth "grounds" are different ......even though that sounds CRAZY as hell. In a house, there is typically a "ground" and the meter base or a ground via an underground "pipe" or both.

A ground at the house is not the same as a ground 125' away - I know that sounds weird..... the point really is this - electricity is a lot like water, spill water- it will FIND the lowest point on the floor/ground ....
Electricity will FLOW to the "easiest" way back to ground.......

for that reason you want to have a separate ground at a "new" sub panel.

Here is more on the subject manner:

copy and pasted



Rule #1: The grounded conductors (neutrals) and the equipment grounds must always be isolated after the main service panel. There are two essential reasons for this rule:

To provide a low-resistance path for current travel to the transformer in the event of a ground fault. This path should not be energized to ensure that it is fully available for the fault current in the event of a malfunction.

To prevent the ground wires from conducting returning neutral current during normal operation. Neutral current in the equipment ground wires can energize the casings and enclosures of appliances and equipment.

Rule #2: In a subpanel, the terminal bar for the grounded conductors (commonly known as the neutral bus) should always be insulated from the enclosure. The reason for this rule is to prevent the enclosure from conducting current.

This is interesting and I will need some time to digest and think about it...thanks for posting!

Edit: First thought is why should a sub panel in a house be different than a sub panel in a shed not far away?

Keep thinking they should be the same, as a sub panel is a sub panel...

Need to keep thinking at my end...Thanks again...

 

[85Hokie]

This is interesting and I will need some time to digest and think about it...thanks for posting!

Edit: First thought is why should a sub panel in a house be different than a sub panel in a shed not far away?

Keep thinking they should be the same, as a sub panel is a sub panel...

Need to keep thinking at my end...Thanks again...

Sub panel is a sub panel ............the spot on the earth changes when it leaves the house (not trying to be a smart ass either)

YOU don't want the stray electrons to have to travel BACK to the house ground ..... shortest path is best

 

[Henro]

Sub panel is a sub panel ............the spot on the earth changes when it leaves the house (not trying to be a smart ass either)

YOU don't want the stray electrons to have to travel BACK to the house ground ..... shortest path is best

I kind of get that, but the shortest path back to the source seems to be through a copper conductor, rather than the earth, which likely has more resistance.

Granted, I may be thick brained with respect to this, so give me a little leeway, and please do not think I am being adversarial in any way.

I kind of just think electrical power from a distribution system is different than a lightning strike.

 

[North Idaho Wolfman]

Trying to completely understand the NEC codes...
Well it's like trying to understand some women...
Better left to the experts!

 

[85Hokie]

Trying to completely understand the NEC codes...
Well it's like trying to understand some women...
Better left to the experts!

like to know one of them experts..... you sure there is one?

 

[GreensvilleJay]

re: The grounds should be hooked to an approved grounding rod and if there is a water well casing nearby, it should be a continuous uninterrupted bare grounding wire from the bus bar to the ground rod and then to the water well casing.

had a good chuckle about this. I Had some electrical work done 35 years ago, 'master electrician' (his words ,not mine) used the 3/4" copper water feed as the 'ground'' said it's going into the well head /pump/casing.a great ground....
odd thing was the 3/4" was connected to the 1"' POLY PIPE from the well head at the main house shut off

After he left , I drove 2, 10' ground rods, 3' either side of the 'stack' entrance.

 

[Henro]

re: The grounds should be hooked to an approved grounding rod and if there is a water well casing nearby, it should be a continuous uninterrupted bare grounding wire from the bus bar to the ground rod and then to the water well casing.

had a good chuckle about this. I Had some electrical work done 35 years ago, 'master electrician' (his words ,not mine) used the 3/4" copper water feed as the 'ground'' said it's going into the well head /pump/casing.a great ground....
odd thing was the 3/4" was connected to the 1"' POLY PIPE from the well head at the main house shut off

After he left , I drove 2, 10' ground rods, 3' either side of the 'stack' entrance.

I get your point. Kind of...

BUT my thinking is that if one uses a same size conductor for the safety ground as is used for all the other conductors, that lead back to the service entrance panel, that the net effect is the same, or maybe better, than whatever local ground rods could provide?

Just trying to understand the reasoning...

 

[DeepWoods]

While I feel comfortable doing all my own electrical on my own property, I will never take ANY advise from anyone regardless of what they think they know. No disrespect to anyone on this forum, but I go right to the source, and that would be the AHJ, whether it be State, County, or City. For me, at my location it would be the county electrical inspector. He is the one that is going to be inspecting my work, and putting his stamp of approval in my panel.

All it takes from me is a phone call, and he will, and has, answered any and all questions or concerns regarding what he will pass. And since He does have the final say as to what is acceptable and safe, I depend on him to keep me safe, and up to code without having someone else tell me what they think is the RIGHT WAY to do it.

The AHJ has walked me through installing all of the main panels at my home, garage, shop, and a standby generator/transfer switch. In all instances where he corrected me, it was an updated code that I was not aware of, and easy to modify or correct before final inspection. My advise to anyone looking for electrical advise is call your AHJ, he has the only correct advise, and puts his name on it come inspection time.

 

[North Idaho Wolfman]

While I feel comfortable doing all my own electrical on my own property, I will never take ANY advise from anyone regardless of what they think they know. No disrespect to anyone on this forum, but I go right to the source, and that would be the AHJ, whether it be State, County, or City. For me, at my location it would be the county electrical inspector. He is the one that is going to be inspecting my work, and putting his stamp of approval in my panel.

All it takes from me is a phone call, and he will, and has, answered any and all questions or concerns regarding what he will pass. And since He does have the final say as to what is acceptable and safe, I depend on him to keep me safe, and up to code without having someone else tell me what they think is the RIGHT WAY to do it.

The AHJ has walked me through installing all of the main panels at my home, garage, shop, and a standby generator/transfer switch. In all instances where he corrected me, it was an updated code that I was not aware of, and easy to modify or correct before final inspection. My advise to anyone looking for electrical advise is call your AHJ, he has the only correct advise, and puts his name on it come inspection time.

Had to look up AHJ:

NFPA codes classify the AHJ as “an organization, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation, or a procedure.”

DeepWoods, The NFPT makes the NEC codes, the AHJ only enforces the NEC codes, they don't make them up.

And from my experience in a bunch of locations, the inspectors will not tell you how to do it, they will just tell you that it's wrong and fix it.

 

[DeepWoods]

Had to look up AHJ:

NFPA codes classify the AHJ as “an organization, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation, or a procedure.”

DeepWoods, The NFPT makes the NEC codes, the AHJ only enforces the NEC codes, they don't make them up.

And from my experience in a bunch of locations, the inspectors will not tell you how to do it, they will just tell you that it's wrong and fix it.

I guess I am fortunate enough to have an inspector that will tell me how to correct my mistakes, and not leave it up to me to find the “correct” way to pass his inspection.

 

[North Idaho Wolfman]

I guess I am fortunate enough to have an inspector that will tell me how to correct my mistakes, and not leave it up to me to find the “correct” way to pass his inspection.

Yes 100% agree, we have some inspectors up here that will help, but most won't.
As they put it, there job is to inspect work we do, not do the work for us.

 

[aaluck]

do both of yourselves a favour... run the cable IN 4" conduit ! Adss a little cost up front but allows for other wires to be pulled in, later and adds a layer for detection/protection in the future.

This is excellent advice. The guy that did the wire to my workshop suggested this to me.

 

[RCW]

Everyone's covered it with more expertise than I have.

I did a true subpanel in my attached garage years ago. 60A to run a welder and air compressor. Compressor didn't work out; not enough space for a large one. Have a couple 20A lighting and tool circuits also.

Did some research with folks in the business before I did it.

What I recall:

If attached to the house/building, subpanel does not need ground rods or main breaker. Treat it like any other new circuit.

Detached/other building: essentially treated like a new service with grounding and another main - - see post #18 by Wolfman. Perfect rendition per my recollection.

A friend really cautioned me from using aluminum wire to feed the subpanel. Copper was pricey then. He suggested that if aluminum wire were used, it should be re-torqued at the lugs on occasion, and you should use dielectric grease (?)...not sure...was 10 years ago.

He advice caused me to use copper over aluminum...

 

[85Hokie]

Everyone's covered it with more expertise than I have.

I did a true subpanel in my attached garage years ago. 60A to run a welder and air compressor. Compressor didn't work out; not enough space for a large one. Have a couple 20A lighting and tool circuits also.

Did some research with folks in the business before I did it.

What I recall:

If attached to the house/building, subpanel does not need ground rods or main breaker. Treat it like any other new circuit.

Detached/other building: essentially treated like a new service with grounding and another main - - see post #18 by Wolfman. Perfect rendition per my recollection.

A friend really cautioned me from using aluminum wire to feed the subpanel. Copper was pricey then. He suggested that if aluminum wire were used, it should be re-torqued at the lugs on occasion, and you should use dielectric grease (?)...not sure...was 10 years ago.

He advice caused me to use copper over aluminum...

Yes - the no-oxidize is a must + re-torque, Aluminum is perfectly fine - as LONG as you up the gauge, copper is by far the better conductor - but 99.99% of feeds to houses are Al - copper to feed a house would more expensive than a couple gallons of gas - per foot!!!!!

 

[MapleLeafFarmer]

for those interested I asked an engineer at the company who makes wire and he responded as follows:
__________________________________________________________________

Radoslaw Kochanowski (Southwire Cable Tech Support) Mar 15, 2022, 6:01 PM EDT

Hello,

URD cables are typically used by the utility company to deliver electricity from a pad-mounted transformer to a building's service equipment or meter. They are not usually used by homeowners and are generally reserved for outdoor applications. From your description, it seems like at least part of your wiring would be inside your house and barn.
I would recommend using Southwire's RHH/RHW-2/USE-2 conductors (linked below).

For a 125-foot run supplying 100 amps (assuming a 240 V, single phase system), you will need either size 2 AWG copper or size 1 AWG aluminum conductors.
Copper: https://www.homedepot.com/p/Southwire-500-ft-2-Black-Stranded-CU-USE-2-Cable-11349805/206490390
Aluminum: https://www.homedepot.com/p/Southwire-By-the-Foot-1-Black-Stranded-AL-USE-2-Cable-27283199/205001910

Note that final approval for any installation lies with your local inspector.

Thank you for using Southwire's CableTechSupport™ Services. If you have any further questions now or in the future, please contact us again.

Radek Kochanowski
Applications Engineer
Southwire CableTechSupport™ Services

 

[SRRGC1]

Sure created alot of information on this post. I built an ATTACHED garage to my residence and install a grounding rod prior to concrete. Wired a 240/60a sub from my main panel for welder, lighting, recp., etc. Anticipated grounding to installed grounding rod. After much contact with electricians and google I was advised because garage was ATTACHED to the residence, ground conductor should be tried back to the service panel. Neutral and ground is separated in sub.
My son build a DETACHED pole building, approx. 40' away from residence and service it with a 240/100a sub. Because the sub was in an DETACHED building I again anticipated needing a grounding rod because building was DETACHED. Electrician doing the job said NO with ground conductor again being attached to main panel ground. Again ground and neutral were separated in sub. I guess there is a world of different opinions.

 

[Vlach7]

I have a large metal workshop with 1/0 copper wire run to it 250" to a 200-amp panel set up with 100 amp breaker, put a 8.25 Kw solar PVS on the metal shop roof, permitted and tied to the grid. wanted to go with a bigger system but with the 1/0 copper wire I was limited per code. BIGGER is always better in this situation where plans may change. When it comes to trenching I always put down extra PVC for possible future projects, trying to never to trench again around existing buried utilities.

 

[Henro]

Opinions are like a certain part of the body, everyone has one.

At the end of the day, IF you need to get the work inspected, you better do it according to the code the inspector follows, or you WILL be doing it a second time.

If you do not need an inspection for whatever reason, then be sure to do it the safest way possible, which likely means following NEC guidelines.

I've concluded that driving a ground rod or two at the remote sub panel should not be a big deal. I did not use a ground rod for my remote building, and just wired the sub panel up the same as if the remote building were part of the building itself. I am now certain THIS IS NOT CODE COMPLIANT. I did up-size the safety ground conductor to be the same as the power feed wires. However, I think I am just going to drive a ground rod this summer and call it good.

What I do not quite see yet, is why a ground rod at the remote panel would be desirable, at least if all the wires connected to the panel are the same size. The transformer on the pole feeding the location will have the center tap of the transformer connected to a ground rod. The Service panel at the building will have a ground rod connected to the grounded conductor and safety ground buses. So the remote panel will add a second ground to the local system, and a third ground to the general wiring setup.

Also, if more than one building (neighbor's perhaps) is supplied by the distribution transformer on the pole, there will be other grounds introduced to the total picture...

None of this matters in the end though, and only intellectual curiosity drives the question.

Conclusion: Just follow the code, and spend time thinking about things to do with one's tractor!

 

[Chanceywd]

Sure created alot of information on this post. I built an ATTACHED garage to my residence and install a grounding rod prior to concrete. Wired a 240/60a sub from my main panel for welder, lighting, recp., etc. Anticipated grounding to installed grounding rod. After much contact with electricians and google I was advised because garage was ATTACHED to the residence, ground conductor should be tried back to the service panel. Neutral and ground is separated in sub.
My son build a DETACHED pole building, approx. 40' away from residence and service it with a 240/100a sub. Because the sub was in an DETACHED building I again anticipated needing a grounding rod because building was DETACHED. Electrician doing the job said NO with ground conductor again being attached to main panel ground. Again ground and neutral were separated in sub. I guess there is a world of different opinions.

I added a 100a service to separate garage I built 120' away. That was 19 years ago and no additional ground rods just separate ground and neutral bars as a sub feed panel and inspected when I completed. I run welder compressor, lift lots of lights etc. Never notice lights dimming when compressor or lift is used.

 

[Henro]

I added a 100a service to separate garage I built 120' away. That was 19 years ago and no additional ground rods just separate ground and neutral bars as a sub feed panel and inspected when I completed. I run welder compressor, lift lots of lights etc. Never notice lights dimming when compressor or lift is used.

That was 19 years ago. Things might have changed since then, for whatever reason. I did the same thing essentially, but I did use the same size conductors for all conductors.

Still, we need to live with today's standards...

So I would follow whatever today's standards and requirements might be.

Bottom line: Just do what current standards require. Like it or not, they are there for a reason.