what's going on my friends i am dustin stelzer with electricianu. today i had a question that was
asked that i'm going to answer that is why do we bond metal boxes but we don't bond plastic boxes
now before we get started i want to remind everybody you can go to electricianu.com
we have a whole bunch of classes that you can take we even have one-on-one tutoring
so you can get in with an instructor so you don't have to sit in an entire class
but there's one-on-one tutoring there's classes so go check out our class schedule electrician.com
all right now this may seem like a relatively straightforward thing for those that are in
the know but as i do not believe in the phrase common sense i think common sense is only common
to those who it is common too uh people that have the same kind of knowledge so there's a
lot of people that just don't know so they don't know what to do with the grounds and
they get in a metal box and like well if we don't do it for the plastic boxes like who
cares if we do it for the metal boxes but that's not correct so let's look in code
the national electrical code if you look in article 250 under grounding and bonding look
at the very very beginning of it we're going to be in 250.4 a under grounded
systems so usually we're working on grounded systems grounded just means there's a neutral
not always sometimes there are things that are grounded that aren't neutral but usually we are
talking about a neutral when we say a grounded system when we're talking about grounding we're
talking about the grounding conductor we are uh you know the the conductor that goes out to
a piece of equipment and hooks to the metal stuff that's what we out in the field called ground but
it's the grounding conductor in code they call the neutral the grounded conductor but they also
understand that there are some things that you ground that are not a neutral and they are still
grounded conductors so that whole thing is going to be really confusing just always remember in
code they're talking about ungrounded and grounded being the hot and most of the time the neutral
and the ground ding conductor the one with the ing is talking about the actual ground that we
talk about out the field as a ground so in 250.4 a we have a3 which is bonding of electrical
equipment and it says normally non-current carrying conductive materials enclosing
electrical conductors or equipment or forming part of such equipment shall be connected together and
to the electrical supply source in a manner that establishes an effective ground fault current path
okay so what is an effective ground fault current path for that we have to go back to article 100
under the definitions go to the ease and we have effective ground fault current path which is an
intentionally constructed low impedance electrically conductive path designed and intended
to carry current underground fault conditions from the point of a ground fault on a wiring system to
the electrical supply source and that facilitates the operation of the over current protective
device or ground fault detectors so basically we have to connect anything metal around electrical
equipment just in case something happens sometimes terminations come loose sometimes things overheat
conductors break or burn or terminations you know go bad in an electrical circuit nothing
ever happens in the middle of the circuit right conductors don't just like break in the middle
they're always at a termination point or a problem spot you could have a place in the middle of a
circuit where there's corrosion that's introduced to the circuit and yes at that point since there's
something weird going on at that specific point you could have damage to a conductor and it could
break but the vast majority of the time out in the field that you're going to come across problems
it's never in the middle of the wire it's always at a termination point where heat is starting to
build up because of a loose termination or you know some something's failing in that circuit
so when we bring conductors uh out to a piece of equipment we have to run a ground but the
ground doesn't run to the equipment the ground always runs to the metal that's surrounding that
equipment so people are like well isn't just a ground just like a backup neutral
no a neutral is intended to always have current on it uh or maybe not always but it's supposed
to afford for their to be current on it and it will carry an imbalance if that's the case
between a bunch of different circuits but it's not a ground is different a ground or
an equipment grounded conductor as they call it in code is always meant to not have current on it and
the only time that it should have current on it is if a ground fault occurs and what that is is
let's say a hot conductor just for some reason it's a loose termination or something like that
and it just flops off and it hits the case the metal enclosure that all those conductors
are in well that metal case would then become energized and it would have potential between
that and anything else that you might touch so if you go to touch that piece of metal
and you touch something else and you give current a path through your body to travel
all the way back to the source you can become electrocuted shocked so it's a really dangerous
thing to have the metal enclosures that we are hooking up live electrical conductors to
not grounded so without the ground the equipment ground and conductor the the hazard or the danger
of getting electrocuted is extremely high so what we do is we run an equipment grounding
conductor out to any kind of metal anywhere that's around electrical conductors that could
possibly become energized so that if we were to touch them we're not going to get electrocuted if
anything were to you know flop off a hot or to flop off and like hit let's say a wash machine
i use this example all the time but that wash machine is hooked to this ground conductor and
that ground goes all the way back to the surface and it's bonded to the neutral so
if something were to flop off of a termination and hit the case of that electrical equipment we have
a effective ground fault means or an effective ground fault path through that equipment grounding
conductor or ground that goes all the way back and goes up to the transformer and it
makes a complete circuit so that it will trip a breaker because current is now allowed to flow
and in a ground fault or a short circuit situation a ton of current is going to flow
all at one time so that breaker is probably going to get way over 200 percent of its rating of
current flowing through it so it's going to pop immediately because there's a completed circuit
now if the neutral and the ground at the service are not bonded together
then a breaker's not going to trip you're just going to have an energized ground conductor and
it's really dangerous so in the situation where we're in a commercial building and we're using
metal boxes everywhere we've got like these what we down in the south called 1900 boxes
um we will put you know devices and things in that we'll run our mc in it we put a mud ring over it
and then we put a device in that metal box so that metal box itself has to be bonded because it
said in our definition in 250 normally non-current carrying conductive materials enclosing electrical
conductors or equipment or forming such as a part of the equipment so uh that is any boxes
around any kind of electrical conductors that's equipment that are metal themselves
you'll see things like pool equipment you know we run an equipment ground inside of the thing
and hook that up but there's also usually a grounding conductor that goes to the body or the
frame of the pump itself so anything metal uh and the reason in a switch box or in a receptacle box
the reason that we bring a ground in there is to hook up to the metal strap of the device so you'll
notice a duplex receptacle has plastic all around it it's pretty much a plastic device but the strap
or what we call the yoke in code is the thing that holds it onto the box so there's still metal on or
around the uh the devices themselves so we have to make sure that that metal strap is connected
to all of the rest of the metal parts and the box that is enclosing all the
conductors also has to be bonded so let's go over the board real quick i'll just show
the whole like complete circuit thing and talk a little bit more about that
all right so let's review a little bit about how a completed circuit works and all of this stuff so
from a receptacle we have to have a completed circuit right we have current that goes down
on our hot out of a breaker and a panel goes to one of our gold screws and then out of the silver
screws comes back to the neutral and then goes back to the transformer so up at the transformer
they're actually connected as well we'll get into that in a second but when somebody plugs a piece
of equipment they connect the neutral through the piece of equipment to the black that is how
just a standard circuit works and without those being connected there's just potential there's
voltage but there's not actually any current that's able to flow so the green conductor is
really just there to protect anything that's metal in case one of these two conductors comes off or
something happens where they touch the metal box and now this metal box is part of the circuit
so you'll notice that the green goes back to green over here and it's not actually part of
neutral so if this is a panel where we don't have neutral and ground bonded together this
metal enclosure the metal strap everything would just remain uh energized or not even energized
it'll have potential there won't be any current flowing on it because it's not actually connected
to neutral and the only way that we get a breaker to trip is if we have a completed circuit through
the load or through your body or anything that is in that circuit to actually help it be conductive
so in services what we do is we take this ground and we bond it to the neutral so now say that
this uh this hot actually breaks and it comes in contact with this metal well now there's a path
through the metal through this metal and into this green equipment grounding conductor and then it
has a path all the way back and goes over here keeps going through finds neutral and now it's
able to go back and complete the circuit so you have the circuit going out on black coming through
the metal coming back and so much current is going to go through that at one time but that breaker
over here is going to detect way more than 20 amps and foam it's going to magnetically rip apart
so that's how that's why we have that conductor to begin with look at this whole like completed
circuit through a piece of equipment a lot of people don't like look at circuits this way they
don't see the the kind of like expanded outside picture but say we have a transformer out at the
street really all that we're doing is we've got our primary coil and it's completely isolated
from the secondary so at a transformer there's not your conductors at a house don't go up and hit a
transformer and get connected to the lines that go back to the utility there actually is an air
gap there's a separation so we'll get into that in a later video about mutual induction and all that
how it works but there's a completed circuit on the secondary side of this that goes to your house
so if we didn't have the breakers there in a panel we could literally just hook up
right from the transformer black all the way over to a wash machine hook the red all the way over
the washer machine and now we have a completed circuit we've got a 120 volt circuit here
we have another 120 volt circuit here we have a 240 volt circuit not all dryers are gonna
have a neutral there's a lot of three wire ones that just have a black and a red in the ground
but you'll notice i didn't draw the ground with the circuit so if for some reason one of these
conductors just broke and touched the case of this thing this whole thing is going to become
energized and the ground as well but it doesn't matter there's no current that's going to flow
so how do we trip a breaker with that well we have to hook it up to an actual neutral to get that
current to have somewhere to go so that it has a complete circuit so it can go boom
and all the way through here so the whole point of the ground is just to make sure that that case
has a way to come back to the neutral so that a completed circuit can be made otherwise it's just
gonna sit there energized and if you touch between that energized case and the wrong thing you can
send current through your body so another example i figured you'd just be easier to draw like in a
house same kind of thing though we've just got our two ungrounded hot conductors that come through
a panel go to a piece of equipment we've got a neutral that neutral may or may not go out to this
piece of equipment i drew some yellow in between so you can see the neutral and ground are bonded
and but say we have a fault here at this piece of equipment now we have a path that current
can take and it's going to go all the way on this black go through the piece of equipment go through
the ground and it wouldn't trip the breaker if it was just energized and if there was no
bond between our ground and our neutral it has to get over to neutral to make a completed circuit so
that it can go through the breaker and trip so that's why we bond our grounds and our
neutrals together now we have a full completed circuit with these electrical charges just
flying as fast as they can through this thing at way too high of current and if there wasn't
a breaker there it would just keep going and getting so hot to the point where this conductor
would just melt the insulation and probably start liquefying and uh we'd have a huge hazard
eventually it would burn down it would burn itself out um at whatever the weakest points are in the
system so that it could disconnect itself but that's how the completed circuit thing works
um so in the case of the metal boxes and the blue boxes you know blue plastic boxes or pvc
boxes whatever you're buying at home depot these blue boxes there's no conductive parts to them
so in code it says any non normally non-current carrying conductive parts or enclosures around
equipment so because it's plastic we don't have to hook that ground to anything we just go right
from the ground to the device but in the case of a metal box that's why we have to bring this green
because this box is metal and the strap on this thing is metal so we have to make sure that we
you know wrap our conductor around there have put a little bonding jumper or something so that that
box itself once this is all put back together if something were to happen a ground fault were
to happen and you know conductor flops off and hits the box itself it'll trip the breaker or
if it hits you know like the strap on here it'll trip the breaker sometimes there's metal covers
and things like that um that we also have to put like a clip on and make sure that we're bonding
the metal cover too because again it is just metal that is surrounding or around electrical
conductors that are before you go make sure you get your ucrew merch so we've got electrician u
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but go get your merch right now uh we sell out very very quickly so they're for a limited time
only so get your merch and become one of the dorks like us all right so i hope that that helps again
i know that for advanced people that have been doing this for a while it's pretty simple video
um but just understand the neutral and the ground completely different things one is uh designed
to carry current um in in a lot of situations even though you might not want to have current
on it you want to have a fully balanced system but it is designed to carry current
um and therefore it can be classified as a current carrying conductor so in that way it's a little
bit more like an ungrounded conductor or a hot than it is like a ground so let me know what you
guys think leave some comments below love you crazy people and i'll see you in the next one
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