Sub Panels Explained - Why are neutral and ground separated?

sponsored by surfshark why are ground and neutral wires separated in subpanels when do we need a sub panel when do we need a grounding electrode and how are the panels connected let's find out the electrical panel is where all of our circuits get their power from each circuit has a circuit breaker if we run out of space for a new breaker then we need a sub panel or we can install one in another room where lots of circuits exist that's much easier to install than running multiple wires additionally we can use a sub panel to provide Power to an external structure the subpanel is basically just an extension of the main panel so grab a pen and paper to make some notes and sip from your engineering mindset mug let's understand how the system works remember electricity is dangerous and can be fatal you must be qualified and competent to carry out any electrical work you should also check with a local inspector to ensure compliance with regulations electricity is generated at the power station and then transmitted at high voltages over long distances to substations here the voltage is reduced and the power is then distributed locally on power poles a pole mounted Transformer connects to this and reduces the voltage to a safer level for residential use notice the power is distributed using three different phases but our pole mounted Transformer typically just connects to only one of these phases for Residential Properties we then find three wires or service conductors running from the Transformer to the property these are two hot wires or ungrounded conductors and a neutral or a grounded neutral conductor this part is known as the Service drop they enter the property through a Weatherhead or a service head from here they run down to the electrical meter inside the meter box the neutral passes straight through but the two hot wires are separated by a gap the electricity meter slots into this Gap providing a path across it and from here it can then measure the current flowing through the hot wires to your property you are then billed for this consumption of energy removing the meter while current is Flowing can cause arcing which is very dangerous from the meter we have three different typical scenarios one the wires run to the main panel mounted externally two they run to an internal main panel and three they run to an external disconnect and then to the main panel the disconnect could also be built into the meter box in the first two scenarios inside the main panel we first find a main breaker which looks something like this we can see there are two lug terminals on top the two hot wires or service conductors will Connect into these coming out of the main breaker are two separate hot bus bars and that's these oddly shaped metal plates each hot wire connects to just one of these bus bars through the main breaker in this case it is our main disconnect allowing us to energize or de-energize the entire home with scenario 3 our main disconnect is outside we may or may not find another breaker in the main panel the main breaker is a double pole breaker so both hot wires are connected or disconnected at the same time we can manually flip this on or off but it will automatically trip if we exceed the current rating printed on the latch this provides our main overcurrent protection notice this one is just two 100 amp Breakers tied together that does not quite give us 200 amps though sure you could provide 100 amps on each bus bar and have 200 amps combined but if just one of the bus bars uses over 100 amps both Breakers will trip together the panel will provide Power to different circuits for lighting receptacles air conditioning Etc these are Branch circuits each branch circuit has a circuit breaker which looks something like this these simply hook into the casing and then slot onto the protruding metal plates of the bus bars we can place them on either side notice that if I use the top slot on either side it would connect to hot bus bar 1 whereas Slot 2 connects to hot bus bar 2. we then run a hot wire or ungrounded conductor to power the load for example a light fitting the white neutral wire or branch circuit grounded conductor then connect X from the fittings and goes back to the neutral ground bus bar which looks something like this our service neutral or grounded conductor then connects to this bus bar we also find the ground wire or equipment grounding conductor running back to the main panel and connecting to all metal Parts in that Branch the circuit is now complete so we can control the light using the switch if we measure between either hot bus bar and the neutral we will read 120 volts but if we measure across both hot bus bars then we read 240 volts we typically have a bus bar on either side of the panel on one of the bus bars we find a thick copper wire running down to a grounding electrode this wire is therefore the grounding electrode conductor the two bus bars are then joined in the main panel if the service disconnect is located in there so these become neutral ground bus bars we also find this green screw on the neutral bus bar this is the main bonding jumper which connects the neutral to the metal casing we will see why that's important later on in this video however scenario 3 is different the service hot wires connect to the main breaker then they connect to the hot bus bar lugs in the main panel there may or may not be an additional disconnect here from the circuit breaker the hot wire goes to the load but the neutral comes back to a separate neutral bus bar which is not bonded to the metal case the ground wire also comes back to a separate bus bar these travel back to the main disconnect box and both connect to the same bus bar this is where we find the main bonding jumper the service neutral connects to this bus bar also and we also find a connection going down to the grounding electrode the current flows through the main breaker through the main panel hot bus bars and then through the light fitting it then travels back on the neutral to the dedicated neutral bus bar and then back to the bus bar in the service disconnect the ground and the neutral do not connect in the main panel same as we have a subpanel which we'll look at in just a moment now this electrical system is different from other parts of the world but oddly so is Netflix this is the US version and this is the UK version even YouTube Blocks videos based on your location luckily our sponsor surfsharkvpn solves this problem just choose the location you want to appear in click connect and your device virtually appears there and so the content is unlocked major new sites are completely different based on your device's location even Home Depot blocks you unless you virtually change your location and you basically just connect to their server it gives you a local IP address and then they encrypt the connection that's it they have an app and a browser extension which is super easy to use personally whenever I connect to a public Wi-Fi I always use a VPN to keep my browsing and personal information Protected Their clean web feature also blocks ads trackers malware phishing attempts Etc and you can try it now by clicking the link in the description and using Code engineering mindset for three months extra for free do check them out links down below for the sub panel this will either be mounted next to the main panel in an additional room or in an external structure in each case we use a double pole breaker which looks something like this slot into the main panel and connects to both hot bus bars this should be compatible and approved by the main panel manufacturer from the breaker we have our two hot wires and these run to the sub panel and Connect into the lugs of the two hot bus bars notice the sub panel typically doesn't have a main breaker it just has these lug connections so this is a main lug panel board the power disconnect and over current protection is controlled through the double pole circuit breaker in the main panel in this example we then have our neutral conductor running from the neutral ground bus bar and this connects to a dedicated neutral bus bar in the sub panel this is not bonded to the metal casing then we have our equipment grounding conductor running from the neutral ground bus bar and over to a dedicated ground bus bar this group of four wires traveling over to the subpanel are known as the feeder where the sub panel will be installed in a separate building or structure we need to install a grounding electrode and we connect it to the equipment grounding conductor terminal bus bar however if the panel is installed in the same property then we do not need an additional grounding electrode now we can attach a circuit breaker to the panel and provide Power to our loads the neutral will come back and connect to the dedicated neutral terminal bus bar the ground wire will connect to the dedicated ground bus bar otherwise known as the equipment grounding conductor terminal bus bar this is bonded to the metal enclosure the neutral and the ground wires must always be separated in the sub panel but they can be connected in the main panel if the main disconnect is located there if the main disconnect is external then they are separated in the main panel so let's find out what the reason is for that under normal conditions the current will flow in from the service connection through the main breaker down the hot bus bar and out of the circuit breaker it then travels on the feeder over to the sub panel down the subpanel hot bus bar out of the sub panel circuit breaker to the load then back to the subpanel neutral bus bar then to the ground neutral bus bar of the main panel and then back to the Transformer notice the ground wire isn't used at all however under a normal ground fault condition where the hot wire touches the metal casing the current will flow from the breaker across the metal casing back along the ground wire to the subpanel then back to the main panel and from here it can get to the neutral to complete the circuit because there is almost no resistance in this route this will cause a huge and instantaneous surge in current this would cause the breaker to trip and cut the circuit that is why we must Bond the neutral and the ground together at the main disconnect this provides a complete circuit so that the breaker can trip under a fault condition if the main bonding jumper was removed so we had no connection between ground and neutral in the system then when a ground fault occurs where will the current flow well there's no connection so all the metal Parts become electrified we might get some current flowing through the grounding electrode maybe something like 4 or 10 amps for example but if the breaker is rated for 20 amps then it will not trip however if we accidentally bonded the ground and neutral in the subpanel and we also bonded it in the main disconnect what will happen well the ground fault current would flow along the ground wire back to the main panel and out the Transformer but it will also flow in parallel back through the neutral from the subpanel and to the main panel and then to the Transformer if there was a metal Raceway between the panels the current will flow on this also or if you touched both panels it will flow through you as you now also provide a path so we definitely don't want this occurring we just want the fault current to flow on one wire which is the ground wire back to the main panel if for some reason the neutral became disconnected on the sub panel while it's incorrectly bonded then all the return current will flow on the ground wire back to the main panel we do not want that if we remove the incorrect bonding then the current can't flow as there is no complete path now so now we know that there is a problem in the circuit however if we correctly bonded just the main disconnect and then we lost the service neutral what will happen well the rest of the circuit is fine but we have a path from the neutral ground bus bar through the grounding electrode back to the Transformer and so we might have some current flowing here as the case is bonded to the ground and neutral it too becomes electrified we would read a lower voltage because the load resistance and the ground path resistance are now effectively a series circuit and as you might know voltage divides between resistors in series additionally if we have correctly bonded our system but then we have a ground fault occur while the service neutral is disconnected then the ground fault current will flow to the neutral ground bus bar but its only path is to the grounding electrode attached to this is the metal casing though and as there is no resistance at the point of the fault the panel casing and all the metal surfaces become 120 volts there is a very large resistance in the path between the two grounding electrodes so some current might flow here but it might not be enough to trip the breaker to trip the breaker we need a GFCI or a ground fault circuit interrupter this monitors the current flowing out of the hot and back onto the neutral and if these two currents are not equal then the current must have found an alternative route so the breaker trips to cut the power don't forget to check out surfshark click the link and use code engineering mindset for three months extra for free check out one of the videos on screen now to continue learning about electrical engineering and I'll catch you there for the next lesson don't forget to follow us on Facebook Tick Tock LinkedIn Twitter Instagram Etc we also have the website theanderingmindset.com

Channel: The Engineering Mindset

Views: 1,133,120

Keywords: sub panel, how to wire a subpanel, main panel, sub panel wiring, sub panel grounding, sub panel installation, national electrical code, load center, wiring a subpanel, electrical contractor, nec, panel board, terminal block, dustin stelzer, master electrican, electrical engineering, electrician, electrical, electrical panel, electrical wiring, wireman, electrican, electrical exam prep, multiple ground rods, journeyman, ground rods, journeyman electrician, gfci, ground fault, panel

Id: NUSNa-7Hecw

Length: 16min 22sec (982 seconds)

Published: Mon Jun 19 2023