Grounding, System and Equipment [250.4, 2020 NEC]

250.4 Grounding, System and Equipment - www.MikeHolt.com/bonding. In this video on the “General Requirements for Grounding and Bonding” we’ll discuss bonding and grounding of electrical systems and equipment and explain exactly why these terms have two entirely different meanings and why it is so important that you understand the purposes of the two. We’ll explain electrical system “grounding” and also equipment “bonding” which essentially means that any current-carrying conductive materials (metal) that are likely to become energized, be connected to an “effective ground-fault current path.
This video is extracted from Mike Holt's 2020 Bonding and Grounding Textbook and video program, for more information visit www.MikeHolt.com/bonding or call 888.632.2633.
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[@TrendyStone]

These videos are fantastic. I’m an engineer and spent plenty of time on math, equations and story problems (bookwork) and not nearly enough time on practical real-world examples. These videos help fill the gap.

[@MikeHoltNEC]

Oh... thank you. God Bless, Mike

[@thomasmateo3241]

thanks Mike for your video. I have been working electricity in ny for 5 years, I am very grateful, with my progress thanks to your video I hope God gives you a long life. thank you Mike

[@MikeHoltNEC]

Thank you and I'm honored to be part of your life story.

[@mahmoodmirza3301]

I'm very glad to get your kind attention enough to get answered by you. Thank you, MikeHoltNEC!

[@Ibrahim-tv7rv]

Thanks for making these videos free, hope you add more about pv systems grounding

[@MikeHoltNEC]

Probably not, but I have a book with three DVDs on this topic.

[@pl4834]

I really enjoy and understand your explanation. It took me a few jobs to figure out that this is really what I love "ELECTRICITY". I'm 35 years old now but I hope one day I am as good as you sir. Many blessings for you and your family.

[@MikeHoltNEC]

You can and I welcome others to take over my legacy of making a difference in our electrical industry.

[@krakenwoodfloorservicemcma5975]

you can work with electricity every single day of your life and still not cover 10% of everything. That is the great thing about the trade. Never stop learning.

[@ryanjourneymanwireman4937]

These pow wow sessions you do are so easy to watch and are very educational.

[@MikeHoltNEC]

Thank you!

[@SURRYHOUSE2]

thank you brother for what you do. 30 years in trade and still learning something new every day.

[@MikeHoltNEC]

You are most welcome.

[@stella24oz]

30 yrs in the trade, what you been learning? Triming outlets all this time.

[@SURRYHOUSE2]

@@stella24oz more than you know

[@deanb949]

@@stella24oz If you gave up learning in this field, everyone should be praying to you, most holy one,....

[@lawoull.6581]

...always learning something new in the field. ⚡️

[@Architekt2]

This video was so helpful in understanding grounding - thank you!

[@krakenwoodfloorservicemcma5975]

that was one nasty lightning strike, Awesome video.

[@beekeeper8474]

As an RF guy thanks for the video

[@cristinaaguilar9242]

Thanks Mike you are the only one I truly understand

[@MikeHoltNEC]

Oh how sweet.

[@ericanderson8606]

31:40 Love that hat, Panama Jack!

[@dans4406]

Thank you very much for your time dedicated to improve the knowledge of random people from internet. I have a question about inverters. The shield is suppose to be conected on both sides, drive and motor, and thus create an alterate path for the current. This is not a problem for safety?

[@garfieldwood8315]

16:37 Eric's statement regarding lightning strikes being ~1MHz: "takes about a millisecond" should say "1/4 microsecond" assuming it is a 1MHz SINE wave. If so the volt peak occurs in 1/4 microsecond or .0000025 second - 4000 times faster. A lightning strike is more like a square wave pulse; so, the time period from 0 volts to strike voltage is far quicker than that.

[@MikeHoltNEC]

Thank you for the feedback. You are correct that the duration of a lighnting strike is much faster than a millisecond, it's actually about 30 microseconds (3% of a millisecond). www.public.asu.edu/~gbadams/lightning/lightning.html#:~:text=An%20average%20duration%20of%20time,immediately%20around%20the%20lightning%20strike.

[@garfieldwood8315]

@@MikeHoltNEC Duration =~30 microseconds, but how fast does it rise to peak voltage? The "rise time" of a lightning strike EMP pulse is more like a square wave, i.e. virtually instant rise to full voltage. The slope of that rise is "~1MHz" (sic) per Eric. A 1 MHz sine wave goes from 0 volts to peak voltage in 1/4 cycle, or .25 microsecond (uS). A 1MHz square wave is, well,... much shorter than that. Virtually instantaneous. Pretty much at the speed of light.

[@eddieo9424]

Mike I have a question. If you use grounding bushings on the pipe from the meter to panel . Do you put the or include the ground wire from the meter ground rod and make it one loop .or just ground the meter box to the ground rod .

[@trilltrav]

Perfect

[@mahadihasan93]

Sometimes, I wonder the selection process of IEC grounding method, one that I see in your graphics resembles TN-S system. But IEC proposes several other methods TT, TN-C-S. Also to add to my confusion resistance grounding and reactance grounding?

[@MikeHoltNEC]

I totally understand your comments, it takes years of studying the different systems, start here kzbin.info/www/bejne/o6HKcol7abqqfNk then read www.studiecd.dk/cahiers_techniques/System_earthings_worldwide_and_evolutions.pdf. If you email me, I'll send you lots of documents I have on this topic. [e-mail].

[@mahadihasan93]

@@MikeHoltNEC the article and video links are exactly the right resource for me. 👍

[@Ed-uu9eo]

Mike at minute 2:00 can I get rid of the supply side bonding jumper and instead use a main bonding jumper in the panel? Is this an option?

[@thetruthexists304]

I'm a PV electrician. Wondering if you can help me understand this because it seems like what you've said about driving ground rods is contradictory..so on the one hand if you have a remote building you need to be driving an auxiliary ground rod at the building (for induced voltage by lighting) but you've said you shouldnt be grounding at 2 different points because of the potential for electric going up one ground rod, through your equipment and down the other? And so, we don't drive ground rods for PV arrays on buildings anymore but would this mean we should be driving ground rods at ground mounted arrays? That would seem silly after hearing you talk about driving rods at light poles. Appreciate any clarification! This issue has been bothering me for some time.

[@MikeHoltNEC]

For sure you don't drive 'ground rods' to 'ground' grounded-mounted PV systems; they are already in the 'ground,' so they are actually already grounded. Maybe you'll enjoy watching these to videos- kzbin.info/www/bejne/o6HKcol7abqqfNk and kzbin.info/www/bejne/j6anoot8q7epb5Y

[@AngelRomero955]

Typical Solar guys. Lmao

[@agussurachman5246]

mike, please elaborate. i saw there is slide about ungrounded system showing Delta-Delta Transformer. how do we ground that type of transformer? you mention that we need to ground the system to dissipate induction energy from electromagnetic, but you also said that we need to unground the system to avoid lightning current dissipation through the earth. please your explaination.

[@MikeHoltNEC]

Please watch this video - kzbin.info/www/bejne/b4u9i4VugspnpKc

[@SpybottleMessuage]

Look at the question I have: I studied the Electricity Apprenticeship in 2005-2008. The Code got changed in 2012, 2017 and 2020. Now, I have the plain simple question. The COMMERCIAL CAFETERIA, as like McDonald's, has the MDP panel, grounding electrode with the ground rodes driven into earth, and.... If the blue print has the plumber pipes to be bounded to the grounded electrode...if it should be 250.66 table or 250.104 Table? What the size of the attachment must be installed, the required 2/0 max Copper from pipes to the outside grounding electrode conductor? Look at, the Commerce Kitchen has a lot of water related appliances, as like the dishwasher, the sinks, the water heaters, the water filtration stations, so, it MUST BE GROUNDED. But if the water pipes from outside the building have NO DIRECT CONNECTION TO EARTH as like minimum 10 feet bare metal - the water pipes are the plastic, and even the water collector in a mile away may be the metal, the feeding pipes are the white plastic. So, my question, if it MUST BE 3/0 or 2/0 size of the bonded to the grounding electrode conductor from tye water pipes attachment, or it may be concerned the need to be bounded at tye copper pipes inside the building with the only number 6 copper, or number 4 aluminum?! So, the question is the need to attach the copper pipes to the GROUNDING ELECTRODE CONDUCTOR WITH ITS SIZE dependable on the service phase conductor size, or tye appliances must be bounded just by the #6 AWG at rye points of their installations ?!! What the main reason in that? I may woundering if the #6 or even #4 wire may have the "taps" - or it MUST be service size grounding electrode conductor SIZE of the building frame. Before 2012 it was easier, but the later time the Nation Security abuse began to do complication in the clear things making special access to the plain NEC. Look at, it foreign country might want to begin their introduction of the business, and the foreign builder might entering the market building the new constructions for the competitors of the US, how they will be know the right NEC installations?!! The Military Fort troublemakers just created the problems in such questions. I am just beginner in tye Trade, but I Need to have the answer.

[@BrentFreyEsq]

Why are these videos still unlisted? They were all released for a few days then hidden.

[@MikeHoltNEC]

The release was a mistake but all have been released now.

[@core4X]

Loved your videos ,even when I barely started the trade and didn't know what the hell you were saying.

[@Ibrahim-tv7rv]

Question: can we connect the EGC with ECG ? if answer is no : why not? and what if we don't have EGC from the service (TT earthing) Thanks in advanced (Note I've watched your old videos about grounding and bounding)

[@MikeHoltNEC]

I don't understand your question, please give an example based on the USA National Electrical Code and our wiring system.

[@Ibrahim-tv7rv]

Sorry for misinformation, I mean: Can we connect the EGC that comes from the service transformer to my house, with the equipment grounding conductor (which we use it to make equipotential in metals)? What would happen?

[@MikeHoltNEC]

@@Ibrahim-tv7rv There is no EGC that comes from the utility transformer.

[@markmueller1735]

In the graphic it shows GEC terminated on grounding bar shoudnt it be directly to neutral on secondary of transformer?

[@MikeHoltNEC]

Please review 250.30(A)(5) Ex. 1, does the graphic termination of GEC to the EGC bar comply with that rule?

[@m.ostein5565]

A paradigm in quality

[@MikeHoltNEC]

What do you mean?

[@Orgakoyd]

Hi, Mike. Firstly thanks for all your videos. Especially the ones regarding grounding, they are among the few voices on the internet that explicitly explain what grounding is for and ISN'T for! I have a question. In the picture at the beginning of this video showing the transformer, let's say it was a dry type transformer inside a building for the purposes of obtaining a different voltage for some branch circuit (lets say to step up 240 to 480 for some equipment that needed it). If this transformer was fed off of a breaker from the main breaker panel where the main EGC is bonded to the incoming neutral provided by the service entrance, could you just run 4 wires (3 phases and the EGC) to supply the transformer, connect the EGC to the enclosure, and also connect the X0 terminal of the Wye secondary and the outgoing EGC to this point on the enclosure, without actually having a secondary gorundED connection to the steel column with the GEC shown in the picture? My logic here being that the incoming EGC supplied to the transformer from the main breaker panel is groundED by the utility wires coming into the building, so no need for a second earth electrode at the transformer inside the building right? In case anyone is confused I am NOT suggesting not having the SBJ that connects X0 to the EGC, just not having the GEC.

[@MikeHoltNEC]

Electrically you are 100% correct that we don't need to run an grounding electrode conductor from the secondary of a transformer to a grounding electrode system, since the primary circuit must have an equipment grounding conductor. Me an others have submitted requests to permit exactly what you suggest for the 2026 NEC.

[@Orgakoyd]

@@MikeHoltNEC Thanks for your reply. I'm really happy to hear that, it seems like a nice simplification of the grounding arrangement. Do you think there could be potential issues with voltage differentials between multiple ground electrodes, such as the one shown here with a GEC and the supply ground at the pole?

[@MikeHoltNEC]

@@OrgakoydWhat kind of 'potential issues?'

[@Orgakoyd]

@@MikeHoltNEC What I meant (now thinking about it pretty sure I'm wrong!) was if having a ground electrode in a building in addition to the Utility grounded neutral could ever introduce voltage differences between the ''true'' local ground and the utility ground and maybe causing issues. Along the lines of what you guys talked about in your grounding videos and people driving ground rods at CNC machines etc. I appreciate your replies, you guys must receive so many questions!

[@MikeHoltNEC]

There is nothing electronic between the utility ground and the service ground; so there is no problem.

[@benjaminpotter2650]

Any benefits to an ungrounded system?

[@MikeHoltNEC]

Yep, like everything in life, but there are trade-offs. I cover this in my Bonding video/book. MikeHolt.com/Bonding.

[@ironman145614]

I’m confused. You stated it doesn’t matter how big the system is it’s always a #6 yet the GEC is required to be sized based on service wire size? Is this just for a rod electrode?

[@MikeHoltNEC]

Please review all of 250.66, including (A) and (B)

[@catfish4346]

What about bipolar diodes they give a lot of protection to electronics I seen for myself a piece of equipment with a bipolar diode in the circuit and it saves the equipment it burnt the diode the traces leading up to the diode and save the equipment

[@jimthewindmillman9317]

How to connect my backup solar inverter to my grid tied utility subpanel grounding the inverter shows open ground witch is I guess common for this pure sine inverter any info on this would be greatful

[@mikeholt9781]

I'm sorry, I don't know anything about this. Contact a local PV contractor.

[@saurabhbhardwaj9667]

Hello Mike, I would like to thank you for all the videos that you have made available for free on your KZbin channel. I really liked and enjoyed your 1 hour video on Grounding fundamentals. I am curious to know if there is any video on your KZbin channel which talks about grounding of different voltage systems (AC/DC) which are derived from the voltage system available at the service entrance in a typical industrial installation. Are there any special grounding requirements for switch mode power supplies which are often used in industrial automation applications?

[@MikeHoltNEC]

Post your question on MikeHolt.com/Forum

[@timflory4767]

Mike , I've Ben told the NEC requires 2 grounds minimum on any residential service . Where is this ? This comes from our utility company

[@MikeHoltNEC]

See 250.52(A)(3) and it's associated exception.

[@bhut1571]

Should a metal roof be grounded?

[@MikeHoltNEC]

It's not required by the NEC.

[@V21IC]

I think that I've clearly understood the subject! One is a 'COMMON BONDING SYSTEM' that provides an effective low impedance current path to source for the purpose of clearing of faults due to unintentionally or accidentally energizing of non-current carrying & non-circuit elements! NOTHING ABOUT GROUND! The other concept, is connecting via the shortest [common] low impedance DISCHARGE path to the EARTH(GROUND) all electral system components and COMMON BONDING SYSTEM in the event of any abnormal and indirect induction of voltages.

[@MikeHoltNEC]

Yes, and watch MikeHolt.com/Fundamentals.

[@stashmark7105]

The lightning doesn't induce a CHARGE. The charge in nearby conductors (systems) CANNOT be created or destroyed . The lightening does however induce A VOLTAGE on the charge that is in the nearby conductors. The charge of the lightning goes into the ground where it stikes. Yes the field from the lightening does induce a voltage in nearby conductors not directly struck by the lightening... BE PRECISE IN OUR LINGO ! Good advice for any conversation.

[@MikeHoltNEC]

Excellent point... I'll be more careful next time. Thanks.

[@stashmark7105]

Yes the lightening definately raises the nearby charge in conductors to heretofore unseen levels of voltage ⚡

[@V21IC]

So what causes electron flow? A charge, a voltage, current? Voltage is a pontential. It measures the magnitude of a charge. Current is the rate of flow of a charge. It's measured in amperes. Charge is an opposition of electron and protons. You can look up Madame Currie, Cuolomb, Voltaire, Henrie, and other scientific minds for more technical information. Voltaje is not inducted because it has one dimension. It's passive. Charge has a time dimension. Remember, without the time dimension there's no movement. Induction is not passive! However, in everyday parlance, it is well understood when we say voltage is induced. Why? Because our focus is the magnitude of the charge induced. We always refer to a transformer as stepping up/down voltage o isolating voltages. We don't refer to them stepping up/down nor isolating charges.

[@V21IC]

As a matter of fact, lighting induced on conductor creates 2 things. 1. It creates a high charge in that conductor and the potential difference between others conductors nearby can be a very high voltaje. That affects anyone between these conductors or conductive surfaces. (Sideflash) 2. Lighting current through a conductor has a higher inductive magnitude of (voltaje) as the length, turns/coils are increased. The voltage of this charge could be induced into circuits/equipment/devices not designed for that operating voltage. In addition, to touch contact voltages of the normally non-current carry surfaces may be extremely high!

[@buckaroundandfindout]

Wait does not the sudden spike I in current then create a sudden change in voltage due to magnetic pressure? So what is actually moving?

[@donberg01]

Faraday's law of electromagnetic induction!

[@surenbono6063]

..it does not look like a ground-earth to me ...thats a 2nd neutral, maybe lesser floating (earth linked/pull down) than the 1st neutral...a chassis-ground-earth (earth 2) is total isolation from hot1-hot2 or hot-neutral grounding of the transformer side ( earth 1)..and breakers should detect abnormal sine/arc faults..the idea of ground is to direct current toward a lesser resistant path via a conductor to earth than the human/buildings/appliances ..including shorts/surges/lightning/statics..etc..this is truly my current understanding on the subject..it may vary in the future..I'm not an electrician just a Computer Science student..

[@cvictor8999]

all this equipment grounding talk is to me a theory but has anyone actually gone out to test the theory whether in fact statistically speaking avoids all those mishaps that are theorized to take place? Given lightning is rather random i guess it must be hard to verify with any experiment well controlled to see any effects

[@MikeHoltNEC]

Please read IEEE 142 so that you can better understand this topic. Also get a copy of Beeman's book www.amazon.com/Industrial-Systems-Handbook-Donald-Beeman/dp/0070043019

[@RustyJeepHole]

7:35 my brain

[@allenshepard7992]

All the graphics apply to a wye secondary. Are delta secondaries also grounded ? US sites mention a zig-zag transformer and the Russians use an earthing transformer en.wikipedia.org/wiki/Grounding_transformer#/media/File:Earthing_transformer.png

[@MikeHoltNEC]

Rarely, but we do have what is called a 'corner grounded' delta secondary.

[@allenshepard7992]

@@MikeHoltNEC Thank you. Saying "Seperatly derived system floats in mid air" helped me understand wires picking up stray charges. Once the insulation is gone or damaged trouble follows. Linemen pressure check their gloves for pin holes. Is there a video covering when to ground a Delta derived system? I would always want to. Either from a transformer or generator. Have not see an PV delta system yet.

[@MikeHoltNEC]

@@allenshepard7992 I don't understaned your last comment about PV delta system yet. PV systems are not separately derived systems, they are a 'functional grounded system.' See Article 690 in the 2017 or 2020 NEC

[@allenshepard7992]

@@MikeHoltNEC _ The 2017 handbook has taken me down a "rabbit hole" Lots of stuff I did not know as the commonwealth of Virginia still uses the 2014 NEC.

[@stevenworsley5659]

@@allenshepard7992 Part II of Article 250 gives us requirements for system grounding. While not explicitly stated, a delta is not required to be grounded in accordance with 250.21(A)(4): "Other systems that are not required to be grounded in accordance with the requirements of 250.20(B)" If you have a High-Leg Delta (3-phase, 4-wire), that is required to be grounded in accordance with 250.20(B)(3). If you establish a corner-grounded delta, its breakers must be marked "One-phase/Three-phase" per the requirements in 240.85. Circuit breakers for these systems are two-pole, but have to have the capability to handle three-phase faults, and are tested and marked as such.

[@danielmalack3714]

why did the lightning pick the tree over everything else? The truth telling is why the tree was hit!

[@MikeHoltNEC]

I can't answer that question via a this platform. But this is covered in my Electrical Theory Library, see MikeHolt.com/Theory.

[@youtubeuser2372]

Jacob! Are you still listening?

[@MikeHoltNEC]

Yep

[@flinfaraday1821]

Why would a line surge discharge to ground? I thought I was beginning to understand just a little bit until you said there at 31:33 that equipment grounding is not for protecting equipment inside but system grounding is... and then "this is equipment grounding here, not equipment grounding"... ?? In fact, every 10 minutes I'm getting thrown off the bus.