wire sizing 400 amp residential

[Dennis Alwon]

Tom I hear you but in many areas the power company will not hook up if it is not done to their standards. I have heard many cases were the power company oversteps their ground.

In this case if they say it is okay and the nec say it isn't then IMO you must do it as the nec states. In some states the power company decides things they have no business looking at. Some will not allow just a ufer but want 2 rods also....

 

[James L]

One of our merged POCOs here used to require overhead risers be strapped within 1ft of the hub and weatherhead, and every 2ft between. They've come together with the other company with updated specs, so not sure yet if that one stayed.

Another POCO requires all ground rods have to be 18" below grade to the acorn - even for the grounds coming from panel. The won't hook up otherwise.

 

[infinity]

Since this riser is serving two 200 amp service disconnects wouldn't one need to know the calculated load to determine the riser conductor size? It might need to be anywhere near 400 amps if the calculated load is low.

 

[kwired]

Throw a little fly in the ointment.. I don't believe parallel, 4/0s in one conduit will meet the required ampacity once derated.

Throw more flies in it, OP says this is feeding 2-200 amp service panels. Service conductors feeding multiple service disconnecting means can have ampacity as low as the calculated load. Many would install at least 320 or even 350 amps worth of conductor to get to the "next size up" level.

 

[kwired]

Since this riser is serving two 200 amp service disconnects wouldn't one need to know the calculated load to determine the riser conductor size? It might need to be anywhere near 400 amps if the calculated load is low.

didn't read all the way through posts before posting similar thing

 

[infinity]

didn't read all the way through posts before posting similar thing

I figured that you were typing when I posted it.

 

[hornetd]

One of our merged POCOs here used to require overhead risers be strapped within 1ft of the hub and weather head, and every 2ft between. They've come together with the other company with updated specs, so not sure yet if that one stayed.

Another POCO requires all ground rods have to be 18" below grade to the acorn - even for the grounds coming from panel. The won't hook up otherwise.

I hope I will be forgiven for opining that that POCO's requirement for burying the Grounding Electrode Conductor and it's connections to the Driven Rod Electrodes is, at least, rational. Can anyone quote me the exception that excludes Grounding Electrode Conductors from the NEC's Minimum Cover Requirements. Maybe I just never found it and I'm all wet but the NEC seems to require that underground electrical conductors must be buried 2 feet deep if they are not enclosed in an appropriate raceway. I'd love to be shown I am wrong about this because it is extra work. Please except that I'm unwilling to read argument as to why it is unnecessary. What I'm after is what code language excludes GECs from the NEC's Minimum Cover Requirements.

I'll make a confession here. Once I had dug down to 2 feet I sometimes went to 2 & 1/2 feet and installed the rods twice there length apart. I got that out of a white paper published by the National Institute of Standards and Technology (NIST) on effective grounding for surge protection of residential services. I only did that in properties that didn't have other more effective Grounding Electrodes. If the well doesn't have a metal casing or it is too far from the service to actually be "present at each building or structure served" with plastic used for the water lines you can run out of other electrodes pretty quick. In the same vain I would usually make the connection of the Grounding Electrode Conductor to the Neutral Service Entry Conductor just on the building side of the splice between the Neutral Service Entry Conductor and the POCO's Service Drop Neutral Conductor. I never worked in a State were that splice was not the demarcation point. Making the Grounding Electrode Conductor connection at that point is a requirement which many electrical cooperatives retained from the service standards of the Rural Electrification Administration (REA). The NEC has always allowed the connection to be made there, although I think that there was a proposal for the 2020 Edition to require that the connection be made in an enclosure. I have no idea whether it got adopted or not.

--
Tom Horne

 

[Greentagger]

250.62(B)(4).

 

[hornetd]

250.62(B)(4).

OK. You got me fair and square. I have been retired since 2015. I just checked back to the 2011 which was in use when I left the craft and I didn't find it there. I found a section with a lot of the same wording but without the exception to 300.5. I did find it in the 2014. Did they add that in the 2014 or did they already have it in prior additions somewhere else?

 

[Dennis Alwon]

It is actual 250.64(B)(4)

 

[kwired]

I hope I will be forgiven for opining that that POCO's requirement for burying the Grounding Electrode Conductor and it's connections to the Driven Rod Electrodes is, at least, rational. Can anyone quote me the exception that excludes Grounding Electrode Conductors from the NEC's Minimum Cover Requirements. Maybe I just never found it and I'm all wet but the NEC seems to require that underground electrical conductors must be buried 2 feet deep if they are not enclosed in an appropriate raceway. I'd love to be shown I am wrong about this because it is extra work. Please except that I'm unwilling to read argument as to why it is unnecessary. What I'm after is what code language excludes GECs from the NEC's Minimum Cover Requirements.

I'll make a confession here. Once I had dug down to 2 feet I sometimes went to 2 & 1/2 feet and installed the rods twice there length apart. I got that out of a white paper published by the National Institute of Standards and Technology (NIST) on effective grounding for surge protection of residential services. I only did that in properties that didn't have other more effective Grounding Electrodes. If the well doesn't have a metal casing or it is too far from the service to actually be "present at each building or structure served" with plastic used for the water lines you can run out of other electrodes pretty quick. In the same vain I would usually make the connection of the Grounding Electrode Conductor to the Neutral Service Entry Conductor just on the building side of the splice between the Neutral Service Entry Conductor and the POCO's Service Drop Neutral Conductor. I never worked in a State were that splice was not the demarcation point. Making the Grounding Electrode Conductor connection at that point is a requirement which many electrical cooperatives retained from the service standards of the Rural Electrification Administration (REA). The NEC has always allowed the connection to be made there, although I think that there was a proposal for the 2020 Edition to require that the connection be made in an enclosure. I have no idea whether it got adopted or not.

--
Tom Horne

As mentioned 250.64(B)(4) exempts this form 300.5 burial requirements. For design reasons you can do more than code minimum requirements.

POCO's can also set specifications on certain things and refuse to connect if you don't comply with their specs.

Going deeper or more than six feet between rods is not a NEC violation, is just more effort in many cases than minimum NEC requirements.

 

[infinity]

OK. You got me fair and square. I have been retired since 2015. I just checked back to the 2011 which was in use when I left the craft and I didn't find it there. I found a section with a lot of the same wording but without the exception to 300.5. I did find it in the 2014. Did they add that in the 2014 or did they already have it in prior additions somewhere else?

This was added to the NEC in 2014 based on a proposal that I had written to add a note #6 to T300.5. CMP3 sent it to CMP5 and it ended up in Article 250 instead.

From the ROP:
Grounding electrode conductors and bonding jumpers are under the jurisdiction of Code-Making Panel 5. Whether to apply Table 300.5 or not to
these applications must be decided by Code-Making Panel 5. Code-Making Panel 3 recommends that this proposal be sent to Panel 5 for comment.

 

[hornetd]

This was added to the NEC in 2014 based on a proposal that I had written to add a note #6 to T300.5. CMP3 sent it to CMP5 and it ended up in Article 250 instead.

Rob

Well that clears up how I completely missed the change but it does leave me with a question. What is there now to protect the GEC and Electrode Bonding Conductors if any from the errant gardening spade or rototiller and also from powered landscaping equipment such as edgers and the hard bladed trimmers that have recently become so popular with lawn care companies. I'm not trying to be a complaint artist here but would it not have been better to set a minimum depth of bury of say 1 foot direct buried and maybe less if in schedule 80 Rigid Non Metallic Conduit. The reason that I'm asking is that an open in the GEC is unlikely to be detected. If it is worth installing in the first place isn't it worth some effort to protect it from being severed?

 

[hornetd]

As mentioned 250.64(B)(4) exempts this form 300.5 burial requirements. For design reasons you can do more than code minimum requirements.

POCO's can also set specifications on certain things and refuse to connect if you don't comply with their specs.

Going deeper or more than six feet between rods is not a NEC violation, is just more effort in many cases than minimum NEC requirements.

Well in most of the homes which I worked on the design reasons were simply that I thought it was better practice once I read that NIST paper on grounding services for additional surge protection. Again I only went to that effort were there were not other more effective Grounding Electrodes available. If the job called for trenching in order to supply outbuildings, new water pumps, or even a lighted sign for a bed and breakfast in one case I would also run the trencher to either a metal well casing when there was one within ~50 feet, or clean around the building if there was nothing else to use. But I was only willing to dig the 20 to 30 feet that the NIST paper suggested when I was doing it by hand.

The POCOs should be made to get their service standards approved by the States electrical utility regulating office. I can understand their wanting their meter at a readily readable height without obstructions but when a Service Entry Conductor Raceway is not supporting one end of their Service Drop I cannot see were they should have any say in how it, or anything else on the premise's side of the demarcation point, should be built.

I did know that providing additional grounding was not a violation of the US NEC. In livestock handling operations, such as dairy farms, doing only the NEC minimum will cause the farmer / rancher a lot of financial hardship. That's why the opening language says "This Code is not intended as a design specification..."

 

[infinity]

Rob

Well that clears up how I completely missed the change but it does leave me with a question. What is there now to protect the GEC and Electrode Bonding Conductors if any from the errant gardening spade or rototiller and also from powered landscaping equipment such as edgers and the hard bladed trimmers that have recently become so popular with lawn care companies. I'm not trying to be a complaint artist here but would it not have been better to set a minimum depth of bury of say 1 foot direct buried and maybe less if in schedule 80 Rigid Non Metallic Conduit. The reason that I'm asking is that an open in the GEC is unlikely to be detected. If it is worth installing in the first place isn't it worth some effort to protect it from being severed?

There was never a requirement for the GEC to be buried at a certain depth. The proposal I had written only clarified that the depth dimensions in T300.5 did not apply to GEC's and bonding jumpers so nothing changed from the previous code cycles prior to the 2014 NEC. If there was a need to require a certain burial depth (IMO there isn't) then some legitimate substantiation would be needed (like these things are be damaged all over the place) to change the long standing requirement that GEC's and bonding jumpers do not need a minimum burial depth.

 

[hornetd]

Tom I hear you but in many areas the power company will not hook up if it is not done to their standards. I have heard many cases were the power company oversteps their ground.

In this case if they say it is okay and the nec say it isn't then IMO you must do it as the nec states. In some states the power company decides things they have no business looking at. Some will not allow just a ufer but want 2 rods also....

Dennis

That just blows my mind! Requiring 2 driven rods as a supplement to an Ufer Ground is moronic. I have ground impedance tested a lot of installed Ground Rods and Ground Rod Arrays; including the notorious 2 rods 6 feet apart; and when I got down to less than 25 OHMS I considered myself blessed. I've seldom had a Concrete Encased Electrode come in above ~10 OHMS except when the concrete contractor forgot to stub up an actually tied piece of Rebar and had shoved a spare scrap of rod in during the pour to try and get over. The clue was that the stub was not plumb. There was no way a fully tied piece of rebar was going to get 20+ degrees out of plumb.

I told the concrete contractor right to his face that I didn't believe it was actually installed and he threatened me. I turned to the GC's Site Superintendent and said "Utterance Of Threat." He already new that he had to ban the man from the site or the Bull Steward would have all of the unionized workers drag up and idle the job. He was banned with over half of the 200 foundations not yet poured. He had to hire someone to supervise the work because the Bull Steward would not relent on the threat ban. I put my head together with the Electrical Inspector and his chief with hat in hand humility and found out that none of the 70+ pours had ever been called for inspection. The Code enforcement guys were good to me and excepted Ground Rings as substitutes. With none of the foundations yet back filled it didn't even cost the GC a lot of money and I didn't mind groveling in order to get the situation back under control in the regulatory relations department.

Funny thing the supply house sold me quite a few cut lengths of 2/0 Copper at the scrap price which I used in place of the minimum size of #2 AWG. I didn't even ask how they happened to come into having those hanging around. All but a couple of them were more than long enough to go completely around the footers with enough left to reach the Service panel. One buriable high pressure crimp connector per house and we were good to go.

Therein lies a question. I the crimped the Ground Ring Conductor back to itself were it came back to the Service Equipment on those houses because it seemed like a good idea but does the NEC actually require that? I'm really starting to dislike being so out of touch with current practice and having forgotten NEC stuff that I used to know from memory! The superintendent for my employer had no reason to question the cost because the Ground Rings were an extra for us. I'll just go ahead and admit that superintendents and project managers have had to curb some excesses that I came up with a few times over 40 + years although it was not anything like a frequent thing.

At least once I turned out to be right after being told that using 4/0 Aluminum to each of 2 200 Ampere panels which made up the service for one home was perfectly OK. I was arguing that the code didn't allow us to use the exception for service conductors when sizing feeders unless it was THE supply to the entire dwelling. You older guys and gals will remember that the exception was not terribly clear when the McMansion era began and double 200 amp panels became pretty routine. I know that a lot of those split loads were wired under the exception table before the NFPA code committee made the language clearer that it could only apply to a single set of service or feeder conductors for each home. The inspector did make us replace it with the full size calculated for the load. The superintendent thought I had asked the inspector to do it just to win the argument but when I pointed out I had been in hospital for a fire service injury for that inspection and had not even met that inspector yet he apologized.

--
Tom Horne

 

[Dennis Alwon]

Tom- sorry about the fire injury, as many of you know my dad died from an electric accident before PPP equipment was really used. Fire is vicious

I did a 3 point test also with 2 rods compared to a Ufer.. I got 89 ohms with 2 rods--if you got 25 ohms that is incredible- you would get that here. The Ufer was 13 ohms--- amazing difference. The test was done at the same site

 

[hornetd]

Tom- sorry about the fire injury, as many of you know my dad died from an electric accident before PPP equipment was really used. Fire is vicious

I did a 3 point test also with 2 rods compared to a Ufer.. I got 89 ohms with 2 rods--if you got 25 ohms that is incredible- you would get that here. The Ufer was 13 ohms--- amazing difference. The test was done at the same site

Dennis

I never meant to say that I regularly got 25 OHMS but rather that it was a blessing when I did. The only time I cared a lot about the Grounding Electrode System impedance to earth was when I had to build the only Grounding that a home would have. In the rural properties, in the North end of the area that I used to work in, that was often the case because the water piping had been changed to plastic and the metal well casing was too far from the premise to make it's use practical.

For fellow amateur radio operators I will bring out the electric demolition hammer and a ground rod driving cup and we will put in sectional rods until we cannot get any further. That usually happens at 24 to 30 feet. We then wrap bare copper strap conductor that has a cross sectional area greater than #2 AWG copper wire as a kind of Ground Ring Electrode from there around the house to the point were the antenna cables will enter and drive another 2 to 3 Sections of Rod there. I do realize that it is not a true Ground Ring if we do not encircle the entire building but as long as it is more than 20 feet long It's better than the RODS would be by themselves. The biggest expense is renting the trencher to run the 3 foot deep trench for the bare copper strap that will bond the 2 separated Driven Rod Arrays to each other. So that copper strap conductor isn't a real Ground Ring but can anyone tell me that the electrons will know the difference. When I do Grounding Electrode Arrays similar to this I call <25 OHMS a good result. It is often less though.