3-Pole Manual Transfer Switch Which Will Switch The Neutrals .
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3-Pole Manual Transfer Switch Which Will Switch The Neutrals

Click Here But perhaps one that isn’t understood as well as it should be is whether to specify a 3-pole or 4-pole automatic transfer switch (ATS). At the heart of this choice is one simple consideration: whether or not your emergency power system will be separately derived. This is known as a solid neutral, and it’s bonded to ground at only one location: the facility’s utility service entrance. If there is a ground fault when the loads are on the emergency source, the fault current travels through ground to the bonding point at the service entrance, then back to the emergency source on the neutral. This is known as a switched-neutral system, and the neutral switching can be open or overlapping (closed). Such systems have no direct connection from circuit conductors of one system to circuit conductors of another system, other than connection through the earth, metal enclosures, metallic raceways, or equipment grounding conductors.” It’s important to consult the appropriate code when planning your system to ensure there is clarity regarding the need to have the emergency system as a separately derived source. Ground-fault protection is a complex topic. But one simple way to see how it affects a system is to model the three phases as one phase and assume that all the current produced by a source, a transformer, or a generator returns to its point of production along the neutral line. The switchgear shown in Figure 1 is the service entrance for the facility, and based on its current and voltage ratings, the NEC requires that this service entrance have ground-fault trip (indicated as GF). In this example, because all phase current flowing through the ground-fault sensor equals the current returning on the neutral, the algebraic sum of the current flow through the ground-fault sensor equals zero and there is no ground fault for the sensor to detect. It will find its way back to the neutral at the neutral-to-ground bond at the service entrance (shown as point B).


  • 3-pole manual transfer switch which will switch the neutrals.

Because the neutral-to-ground link is on the source side of the ground-fault sensor, the ground-fault sensor registers only the outgoing phase current and cannot detect any current returning on the neutral. Therefore, the algebraic sum of the current flow through the ground-fault sensor equals the outgoing phase current only. Because there is now a 3-pole ATS in this system, the neutral is continuous and the generator is not considered to be a separately-derived source. There is no neutral-to-ground link at the generator. The only ground connection at the generator will be the equipment ground for the generator. Because the generator is producing the power, the current flows out of the generator phase, does its work at the load, and returns to the generator along the neutral. Again, the algebraic sum of the current flowing through the generator’s ground-fault sensor equals zero, and there is no ground fault. Its only option is to flow along the ground to return to the system at the neutral-to-ground bond at the service entrance (shown at point B). As with normal current flow, the algebraic sum of the current through the generator’s ground-fault sensor equals zero. This means that the ground fault is not being picked up by the ground-fault sensor on the generator. The ground-fault sensor in a generator is often integrated into the circuit breaker, so in this case, the breaker will not open during a ground fault. In fact, the ground fault may not be correctly sensed by the system until the ATS returns to utility power. However, it might be seen at the normal-source breaker, causing the breaker to trip, even though the fault is not fed from the normal source. As previously mentioned, because the neutral is continuous in a 3-pole setup, the generator is not a separately-derived source and, therefore, there is no neutral-to-ground link at the generator.


In this case, because the neutral is switched with the phases, the generator is a separately-derived source and must have its own neutral-to-ground link. With this link in place, the sensor will be able to detect the ground fault from the previous example. As with previous examples, consider what happens if there is a ground fault at point A. As before, the current must return to the generator along the neutral. This means the ground-fault current cannot return using the utility service entrance neutral-to-ground link (as it did with the system with the 3-pole ATS). Instead, the current returns to the generator through its neutral-to-ground link (at point B in Figure 5). Because the generator’s neutral-to-ground link is between the source (the generator) and the ground-fault sensor, the algebraic sum of the current flow through the ground-fault sensor equals the phase current only. And because the algebraic sum of the current flow through the ground-fault sensor is greater than the ground-fault trip setting, the ground-fault sensor will trip its associated breaker. In other words, all the transfer switches serving 3-phase, 4-wire loads should be of the same type-either all 3-pole or all 4-pole. This is essential for maintaining the integrity of the ground-fault scheme. If the emergency power system is a separately-derived source, then a neutral-to-ground link may be in place at each generator, or there may be a single neutral-to-ground link in the paralleling switchgear. Above all, remember to consult with a proven supplier. There’s a famous expression among carpenters that you should “measure twice and cut once.” The same applies here. If you get your system design right at the planning stage, then you’ll encounter fewer problems in the operational stage. He was previously the manager of the switchgear engineering department and has worked for the company since 1995.

Pincus holds a BS in Electrical Engineering from the University of Wisconsin-Madison and an MBA from the University of Wisconsin-Milwaukee. He is a member of IEEE and a registered professional engineer in the state of Wisconsin. It only takes a minute to sign up. I certainly won't buy it and don't recommend one, but the huge hank of wires going from switch to panel only has one neutral wire in it. OK, I buy that. All generator imbalance load for all circuits gets carried on that single white wire. Is there a section of NEC that authorizes this style of use? Any specifications on the gauge of the neutral? Is this one a manual transfer switch? This is important because many portable generators actually come with a neutral bond installed by default (and would need their bond removed to work properly with this transfer switch). Read on for details. This is codified in NEC 702.11, by the way. Some generator manufacturers provide instructions for pulling that bond for use as a standby generator in a non-separately-derived system, but that means that the bond has to be reinstalled if you ever wish to use that generator for portable power. If you have an automatic transfer switch, note that residential-grade ATSes almost never have a neutral pole of any sort; commercial-grade units are available with a switched neutral pole, but are generally not seen in anything on-topic for this site. All that unit is is one big switching device and switches do not need a neutral. It's probably only there to measure the load. In which case this device has a certain Inlet where it may be 30 amp Max. When the neutral is properly balanced it will have very little current on it. My Generac Ats has 16 circuit breakers in it, so it needs to not only bring the hot, but also the neturals from the main panel Please be sure to answer the question. Provide details and share your research. Making statements based on opinion; back them up with references or personal experience.


To learn more, see our tips on writing great answers. Browse other questions tagged electrical-panel code-compliance or ask your own question. The answer may surprise you. You want to preserve the integrity of your ground fault protection system without compromise, so what do you do when it comes to switching the neutral. Among many benefits, you've heard 3-pole transfer switches with overlapping neutral contacts Paul McMorrow Aug 01, 2000 Which method is best for switching the neutral: 3-pole transfer switches with overlapping neutral contacts or 4-pole switches. The answer may surprise you. Among many benefits, you've heard 3-pole transfer switches with overlapping neutral contacts operate with little or no arcing. You've also heard 4-pole transfer switches offer positive isolation of the source neutrals. Which is best? Base your decision on what benefits are important to you. Regardless, you should know the operational details of each type of transfer switch. This type of transfer switch offers many advantages, including the following: One disadvantage is the design and construction of the neutral pole and contacts. On some manufacturer's switches, it's not identical to that of the power poles and contacts. Malfunctions of this accessory can occur because the neutral contact does not operate by the same mechanism as the power contacts. This could lead to the following conditions: Suppose a system suffers a cable fault downstream, and one of the phase poles shorts to neutral. The overlapping contact (if not fully rated the same as the power contacts) could melt down and create a permanent open-load neutral condition. However, you can avoid this problem if you make sure the overlapping contact is rated the same as the power contacts. Nevertheless, let's look at this issue more closely. We know a resistive load has no such characteristic, so let's consider an inductive load.


The energy stored in a transformer primary, secondary, and the leakage reactances are small contributors to the transient situation. The largest contributor to possible transient voltage generation is energy stored in large motor windings or similar loads. In fact, the transient voltages normally found in distribution circuits in industrial or commercial installations are far more severe than the ones the switched neutral might produce. In fact, the magnitude of AC voltage transients found on most industrial, commercial, and residential power systems far exceeds anything detected during 4-pole switch tests. Since you must apply the same criticism to the other poles in the switch, the assumption that neutral contact arcing and erosion of the load switching contact could result in discontinuity and eventual disconnection of the neutral conductor may be unrealistic. The transfer switch does this by operating the neutral contacts with the same high-speed transfer mechanism as the power contacts. Which method is best for you. Ultimately, both offer segregation of the grounded circuit of the two sources feeding the transfer switch. Now, the choice is yours. Reflecting back on the past year, we thought it would be worthwhile to revisit the 10 most popular photo galleries of 2016. Presented in descending order, these galleries are ranked based on total website traffic over the last 12 months. All rights reserved. The X Series is perfect for use with generators having GFCI protected outlets, bonded neutral generators and installations requiring a separately-derived system. On GFI protected generators, the X Series will prevent a ground fault which will, in turn, prevent the circuit breakers on the generator from nuisance tripping. The XRC Series has 10 branch circuit spaces and will allow up to 18 circuits with the use of tandem breakers.


Options include a selection of watt meters, for balancing generator load, and flanged inlets for direct generator connection where permitted. For use with: GFI-equipped generators Bonded neutral generators Separately-derived systems. In home generator applications it is utilized to connect building's wiring either to a backup generator or to the service lines. When AC line is normal, a TS allows powering your house from the grid. When the grid fails, TS can switch the home wiring system to a generator while isolating it from mains. An electrical transfer switch is a must if you are hooking up a generator to your house. This concise guide will tell you why you need it, how it works, how to choose the right one, and how to wire it (an example of a wiring schematic is at the bottom of this page).Backfeeding (also called islanding or interconnection) by definition is supplying electricity back into electric grid when it's down. Here is why it should be absolutely avoided. The voltage fed back into the lines that serve your house poses an electrocution hazard for utility workers and for your neighbors who may not know the voltage is present in the line. It can easily be damaged if power is restored while it is working. The nominal voltage between each line and neutral is 120 VAC and between two lines is 240 VAC. Note that both lines still belong to a single phase- they are obtained by grounding the center tap of the utility transformer. Double pole means it transfers both line wires (poles). Older 2-wire 120 volt residential systems require a single-pole double throw switch. The TS generally should be installed indoors within 2 feet of the main service panel and within 30 feet of your genset inlet box, which is placed outdoors. When switching between LINE and GEN, they always pass through the OFF position. Such break prevents arcing or short circuits during the transition.


If power rating of your genset is not sufficient to feed the entire house, you may install an additional distribution panel (a sub-panel ) for the essential lines your want to backup. This sub-panel will then be wired to the transfer system. Many commercially available TS come already with a pre-wired sub-panel. An automatic changeover is used with standby systems. It includes a control circuit that senses mains voltage. When utility power is interrupted, the control circuit starts up the genset, disconnects your house from the utility and connects it to the genset. It then continues to monitor mains status. When it's restored, it commutates your household wiring from the generator back to the utility. When the generator is disconnected, it goes into a cool-down process and then automatically shuts down. Generac and other standby systems usually include a 100A or 200A auto TS, or offer it as an option. Note that you can always set it to a manual mode if desired. A manual transfer switch is normally used with portable gensets. The dotted lines symbolically show the metal cases. In this diagram neutral is not grounded inside the genset. For simplicity an inlet is not shown, but if you are going to hook up a generator to house panel you would need to install it too. Many portable models sold in US nowadays have a GFCI (GFP) and their neutral is bonded to the metal frame. This causes a problem when you are trying to use them with a TS: when neutral is grounded in two places its current will split, and the GFCI on the generator trips. As the result, no outlets will function. There are several possible solutions to this problem. The safest one is to install a so-called neutral switching device (3-pole isolation switch). It will control neutral along with two power lines. Another solution is to lift inside the transfer equipment the ground wire from the genset (just isolate its loose end). Your genset will still be grounded via its neutral bus.


Finally, one may remove the neutral bond inside the genset, which disables GFCI. This option is not quite safe though-- if you will ever use such a device in the field without a TS (for example on a job site), you will not be protected from electric shock. Such modification may also void the manufacturer's warranty. In any case, all installations should be done by a licensed electrician. And of course, for everyone's SAFETY, make sure the main circuit breaker is turned OFF BEFORE any wiring work started. Also see how to connect a portable genset to house wiring in an emergency without a changeover system.See complete Disclaimer linked below. Please upgrade your browser to improve your experience. I’m having dificulty selecting the transfer switch. (I have a bonded neutral generator now.) My existing generator is 12KVA, however I’ll be able to get a 100KVA Diesel Generator for the cost of hauling it. I’m in a rural area where power outages are far from uncommon, especially in the whiter months. I believe the 3 pole is what I need to match my existing gen.As I understand it, the generator will be grounded with its own electrode. Any thoughts or opinions jump out at you? (It appears to me that a 2 pole switch would leave the main service neutral connected all the time regardless of the transfer switch lever position, NO ?) The gensets were NOT separately grounded via a rod, but they were grounded back through the building grounding electrode system. The utility co's don't have any problem with the permanant neutral connection. There's little or no chance for any power to get back into their line through the neutral. And any ground-loop created is restricted to the feeder between the genset and the service equipment. Now that I've got my permit pulled, I'll be putting a call (or multiples most likely!) into the inspector to get his take on this. (Until you've got the permit in hand ESA won't give you the time of day.).


The office suggested the only time to reach him in the office is before 08:00. After that, just to keep dialing his cell until you get lucky.A few years back during some foundation work the incoming neutral only was severed on the u'ground service supply line by accident. It was momentarily shorted to one of the hot supplies but didn't trip the pole fuse or any of the service breakers. The upshot was multiple 120 V appliances failures due to over voltage.I'd like to highlight a few areas where folks typically screw up their generator (or other 'alternative power') arrangements. Have you measured just how much electricity you're using under normal conditions. Or, with everything running. There is absolutely no need to 'match' the size of the PoCo service.This makes things a lot simpler.Not to worry. even with the neutral 'switched,' the grounds remain connected. This means that there is still an INDIRECT neutral connection. (Then generator grounding electrode MUST be connected to the household grounding system). In the simplest terms, electricity tries to go 'home' - back to where it was made. Electricity made by your generator should have no other place to go, but back to that generator. There is no reason to keep a neutral connection with the utility neutral. For example, if you measure your home as actually using 10kva.Smaller than that, and you'll have to choose what to run. Bigger is NOT better.This 'exercising' is accomplished by one of two ways. If you have an automatic transfer switch, an 'exerciser' can actually switch your home over to generator power at regular intervals. With a manual transfer switch, the generator will need a 'load bank' to simulate the load of the house. A 'load bank' is nothing more than an enormous toaster. Thank you for the reply. Assorted other connected and auto-start loads and provision for a few helpers in the shop running the larger draw machine tools add up to the worst case. Until then I'll presume that the 12KVA gen.

If it is bonded in the fusible entry service switch then it will indeed still be connected through the building ground electrode regardless of the transfer switch position. I question what has been accomplished by this. Now, looking at some of your specifics: As a rule, I always have the transfer switch break the neutral. To not do so seems to only create another opportunity for trouble. The genny and the PoCo should be kept as separate as possible. Just my perspective. No, for another word about load calculations. Sizing a service and sizing a generator are two different matters. There are a few important things that simple load calculations fail to take into consideration. Looking at a machine's nameplate is a good starting point - but that's all it is - a starting point. There are a few other matters to consider. Then there is the matter of starting current. There used to be a 'rule of thumb' that said you should consider the starting current to be 6 times the full load amps. Today, one can no longer apply that rule across the board. With the advent of variable speed drives and 'soft start' technology, the starting current may actually be lower than the full load current. This is especially true if the machine starts without a load on it (as a table saw would). This current surge, in any event, will almost certainly be 'lost' in the overall load the genny is supplying. Simply having magnetic starters for your equipment will ensure that you will never have every machine start at once, either. That's why I said you should turn it all on, and actually measure the current you're drawing.and base the genny selection on that. If you measure 40 amps, than 40 amps is what you need. If you are concerned about several large machines starting at once, then the solution is a capacitor bank - not a larger genny. If you go ahead and get a larger genny, you will definitely need a load bank.

Load banks typically have controls that adjust how much load they add, depending upon the current being used. This means that you will need to 'waste' 80 of the power it makes. Running a big genny to provide for a small load is a very bad idea. It is also likely that the used genny was neither cared for, nor operated properly. Generators are not cheap to fix, or maintain. The associated equipment - transfer switch, exerciser, load bank - can often cost as much as the new generator itself. Some brands - Generac comes to mind - seem to be specifically designed to operate only with brand-specific, unreliable parts. Some bargain! I am seeing many, many 'bargain' generators these days. In every case, the application was doomed from the start. The generator was over sized. Costs were saved on the installation by failing to have the proper associated equipment. Maintenance and exercising were neglected - many times because the unit came with the standard muffler, rather than the optional 'noise package.' Noisy generators annoy you and piss off the neighbors. Large occasional loads from large machinery. Currently only get 17KW as my sole PTO tractor is small, but I use it all when I plane wood. The welder is much lower draw. As I'm typically at capacity (on the rare occasions I use the generator), I did measure draw. Dull those planer knives and my tractor doesn't quite keep up. Good-sized planer obviously. My confusion was the relatively low rating for the switches I've seen advertised, compared to my 200A service. As you point out, I'm never drawing 200A. The 2 vs 3 pole switching never occured to me. Presumably you're aware that this isn't very common information you're sharing. But as you point out, buying an insufficient bargain is no bargain at all. Losses are obvious, but I've already got the machinery. Then I'll have all the current I can use. No neighbors, noise not an issue with the tractor down the mountain a ways.

I already maintain the tractors, for other uses. Assuming that my generator has the same low-load risk you're talking about. Rare that we lose grid power for very long, but I've been idly prospecting the possibility of going off-grid. Just a thought, but if your only large load is the planer maybe you could replace the electric motor with hydraulic hooked to a larger tractor and bypass the energy loss on the generator. A smaller generator could still service welder, etc. Planer actually has 2 motors, drive and feed. Plus a third one for the blade grinder. Weighs 4500 lbs. Never dreamed I'd have such tools when I was setting up here.Mennonites around here. Arranged to get a wood planer originally powered that way for my machinist, converted to a jack shaft. Techs are knowledgeable. Plenty of flow. Considered buying one from a buddy just to use as a vehicle lift.I'd say you can get by without one, as long as periodically flipping the transfer switch and running your normal loads off the generator isn't an inconvenience. Also, I believe many automatic transfer switches (at least the ones I've worked with) have exerciser circuitry built in. On the other hand, if you have the emergency loads all connected to a sub-panel that is fed from a branch circuit from the main panel, and the auto transfer switch is in between the main panel and subpanel, it only needs to have the same ampacity as the branch circuit feeding the sub-panel. Not a small issue with a 200A service. Sub-panel I understand and appears a better option. 3 wires between the house and there, but no inspections. If I start accepting commissions again, more often. You're correct, the tractors have other duties and are exercised often, one of my attractions to a PTO generator. Less required maintenance is better. It's when you try to design a transfer switch that things get hairy. This is because, in a fight between the PoCo generator and your's something is going to go BOOM.

Engineers have figured this out to the point where there exist transfer switches that make the change-over without any noticeable dip in power to you. Because that's what a transfer switch does: it disconnects your panel from the PoCo service, and hooks it up to the generator. Your generator supplier is the best source for the accessories appropriate to your generator. See them for transfer switches, noise reduction, exercisers, and load banks. Indeed, I strongly suggest that anyone wanting a generator work with the supplier in the selection and design of their system. A distant second choice is a QUALIFIED engineer. I have a customer who has had me install two generators.These two are good examples of what's involved. In common, both have automatic transfer switches and exercisers. That's where the similarity ends. The 400kw unit is set up to automatically switch the establishment over to generator power for two hours every Tuesday. Timing was selected to assure the greatest chance of the generator operating at full load. The 260kw unit has automatic start, and transfer, in the event of a power failure. Otherwise, it also is exercised weekly - but without the load transfer. This provides the load that the generator serves during exercising. Both of these units have the 'standard' mufflers.Contrast this to another customer, who paid for the optional 'noise package' when they ordered the generator. This unit operates at about 67 decibels, right next to the unit. Inside the building (30 ft.Onan, Cumins, and Cat all have loads of great info on their web sites. Use it. On the other hand, I would shy away from Generac; they seem too heavily focused on their marketing plan. For those planning on a different source of power, most generator principles apply. The simplest, best solution is to separate your system from the PoCo when you are supplying your own power. If you're going to make the transfer manually, you MUST turn everything OFF before you make the transfer.

Then turn the loads back on again. You do NOT want to operate that switch under load.It's not unusual for even an electrical contractor to have had little direct experience with generator installs. Again, your local generator dealer ought to be able to tell you who he has worked with in the past. Third owner, second one couldn't figure out which two legs would give 240v (3 phase generator, what I wanted). Web search for the mfg.No web site. Not anything they'd ever done. Poco's a coop. Find it highly amusing to blow one up. Which hardware, considerably more difficult. Noise from the tractor isn't an issue. Cat's very good about specific issues.I am NOT anticipating it will be inexpensive, however! (Aside: I've been hunting for a long time for one of these suckers at distress pricing with absolutely no luck, so I'm afraid I'll just have to bite the bullet!). The numbers get serious in hurry! A seamless switch over more appropriate perhaps to a financial, or medical facility for example is not what I am after. Rather than tie myself down to a set of predetermined emergency loads that can be sized in advance to utilize the optimum gen.The center Knife portion can connect to only one of the ends at a time.Related, as you point out. If not exactly normal HO related. We have no problem running the whole house on 50A. That's 700' from the generator (speaking of trenches).More than switching, I have to move a tractor and hook up the generator. Thought about doing a Junkhound approach with a surplus gas 3 L V6 and decided against it. I generally jump on heavy switches when they come up at auction. Unfortunately, it's clear I should have been more attentive. Hey, at one time I was the only guy in town who could repair the new car radios. The ones with transistors. LOL Thought about it for the larger ones but didn't have adequate current to do so until I added another poco service at that outbuilding. 3 phase generation made perfect sense.