Generator and Manual Transfer Switch for 480 V Wye Service with Unused Neutral

[SnakNest]

A customer wants a manual transfer switch installed to provide an input / switch for backup power for a 480 V wye service. They already own a generator which is currently at a different site, and would like to utilize that. I'm still waiting on details about the generator itself, but for now, I'm assuming it's a 480 V wye generator (don't know the ground / neutral bond status of the generator yet).

The existing service from the meter into the fused main disconnect has 5 incoming wires - 3 lines, a neutral (taped white), and a small green-insulated ground wire. The incoming neutral and insulated ground are bonded together with an earth ground inside the disconnect. From the load side of the main disconnect, there are two feeds: first is 3 lines and a neutral feeding a fused surge protective device that's mounted on the side of the main disconnect; second feed is 3 lines, a neutral, and a ground feeding a 100 A, 3-pole main breaker with a neutral lug at the side of the breaker. All equipment on the system is fed from that breaker. The neutral ends at the lug in that main breaker and is not used for any equipment on the circuit.

I would like to put the manual transfer switch between the load side of the main disconnect and line side of the 100 A main breaker. Since the neutral ends at the lug in the 100 A main breaker and isn't used anywhere on that circuit, can I remove the neutral between the main disconnect and 100 A main breaker and then treat it as a 4-wire system (3 lines and a ground) for the generator / transfer switch, with no neutral connections inside the transfer switch? I would like to do this so that a 4-wire cable and 4-pin IEC pin / sleeve connector can be used to supply power from the generator to the transfer switch.

If this is allowable, what is the proper way to handle the neutral from the 480 V wye generator?

Here's a link for photos of the fused main disconnect and 100 A main breaker connections for reference:

Main Disconnect and Breaker

Thanks in advance for your time and advice.

 

[ActionDave]

It sounds like you will be using a portable generator. You would need a generator with a bonded neutral even though you would have a Non Separately Derived System. That is an odd arrangement. Why not use a five wire connector?

 

[SnakNest]

Yes, I apologize for not stating in my original post, but it's a portable gen set.

The reason for wanting to use the four wire connector is primarily due to cost, as the customer already has a 3-pole transfer switch with 4-pin connector from another site that they'd like to repurpose, as well as 4-wire cable to go with it. It's from a site that I know based on experience has a 480 delta system, but not the same site that the generator is coming from.

 

[kwired]

The white and green coming into the fused (presumably service disconnect) that has it's neutral bonded are redundant, and can even be taken as being improper use of conductors in parallel, because that is what they essentially do is run parallel to one another. That only needs to be one conductor.

If your generator only has 4 wire cord/cable assembly then it should have it's neutral bonded at the generator if it is a wye system. If it is a delta system then there becomes more possibilities including grounded vs ungrounded systems, but since it is going to be tied to a grounded system it probably still should have grounded conductor bonded at the generator and bring both grounded and grounding conductors to the transfer switch - still resulting in 4 conductors being used.

The fact there is no neutral loads to be served, there is no reason to bring a neutral conductor to the transfer switch other than possibly unintended circumstances because of code wording. The reasons for separate grounded and grounding conductors is to prevent non current carrying parts to carry parallel current of the grounded conductor, you don't have that situation here, only time that fourth conductor would carry current is during a ground fault condition.

If you do have a delta source for a generator, you possibly need to consider whether there are any items supplied that have max volt rating to ground of 277 (or maybe stated as 300) though, because you will either have a 416 high leg or a full 480 on the corner grounded conductor, and the other option of ungrounded gets complicated to maybe not even possible if used as standby for something that is otherwise grounded.

 

[SnakNest]

I had the same thought about the incoming parallel white / green at the service disconnect. But since this is the first time I've ever done any work on this system, and there's an inspection sticker inside the disconnect enclosure implying that it was approved as-is, I figured I'll leave that issue alone.

I did verify that the portable gen set is 480 wye.

So assuming I make sure the generator neutral is bonded at the gen set, I should be good to:

-use the 4-wire cord & pin/sleeve connector between the generator and transfer switch (3 phases + ground conductor)

-remove the existing unused neutral wire between the service disconnect and 100 A main breaker

-land the generator and power company grounding conductors together on the ground bar in the transfer switch

-leave the transfer switch neutral bar unused

-use the transfer switch to switch only the 3 phases, then run 4 conductors (3 phases + ground conductor) from the transfer switch output to the 100 A main breaker

Is that correct? That would be what I was hoping to do initially.

 

[hornetd]

Any Wye or high leg delta source of supply must have a neutral run with the energized conductors brought to the service disconnecting means and bonded to its enclosure. It's sole purpose is to provide a low impedance fault current path back to the source of supply. If I remember correctly your permitted to size the neutral conductor using the table for Equipment Grounding Conductors based on the ampacity of the disconnecting means.

That said every pin and sleeve fixed plug inlet for 3Ø that I ever saw had 5 conductors in the form of 5 pins or 4 pins and a circular shield connection for the Equipment Grounding conductor. Those large pin and sleeve connectors are all over some of the federal facilities in this area.

Tom Horne

 

[SnakNest]

This is the type of pin and sleeve inlet that is installed on the transfer switch, which is a plastic housing with 4 pins (3 phases + 1 ground):

Pin and Sleeve Inlet

Then there is a corresponding connector for the cord coming from the gen set:

Pin and Sleeve Connector

Since the portable generator would be considered a non-SDS, will be located adjacent to the service disconnect and transfer switch, and has a main breaker that's accessible (the access door cannot be locked), wouldn't the breaker on the generator serve as the disconnecting means, and then having the neutral bonded at the generator would suffice? Maybe I'm thinking about it incorrectly.

 

[hornetd]

This is the type of pin and sleeve inlet that is installed on the transfer switch, which is a plastic housing with 4 pins (3 phases + 1 ground):

Pin and Sleeve Inlet

Then there is a corresponding connector for the cord coming from the gen set:

Pin and Sleeve Connector

Since the portable generator would be considered a non-SDS, will be located adjacent to the service disconnect and transfer switch, and has a main breaker that's accessible (the access door cannot be locked), wouldn't the breaker on the generator serve as the disconnecting means, and then having the neutral bonded at the generator would suffice? Maybe I'm thinking about it incorrectly.

Let me be sure that I understand your situation.

• Is the Service Disconnecting Means for this Service the fused switch?
• Is there an Equipment Grounding Conductor (EGC) between the fused switch and the 3 pole breaker?
• Is there an EGC from the 3 pole breaker onward to the rest of the system?
• Is the system that your working on 480 Wye configured without line to neutral loads or is it Delta connected supply with a phase which has a higher voltage to ground than the other 2 phases. This question is critical.
  • The reason that I'm asking is because the Orange tape on the center conductors in both the top and bottom of the fused disconnect and the top of the circuit breaker would suggest a Delta Supply with the center conductor having a higher voltage to ground then either of the other 2.

I will list the concerns that I would have if this installation were mine to do.

• If you bond the generator's neutral to the frame of the generator you will have made a code violating connection to ground from the neutral on the load side of the service disconnecting means.
  • The remedy for that would be to have a 4 pole transfer switch which would switch the neutral from the one from the SDM to the neutral conductor from the generator. I believe switch you have in hand is only 3 pole.
• If you do not bond the generator neutral to the frame then, I believe, the code requires an EGC from the generator frame to the transfer switch.
  • The connectors you have in hand will not then carry the fifth conductor which is the required EGC.

Something has to change. You need 5 conductor connectors or a 4 pole switch to bring this off in a code complaint manner. There may be an add on pole kit for the transfer switch you already have. If that turns out to be true then it is likely to be the least expensive way to make the installation code compliant and reduce the extra costs to a minimum.

If, by any chance, the transfer switch is marked "Suitable For Use As Service Equipment" then that will open up an alternative that has not yet been written about here.

 

[kwired]

Let me be sure that I understand your situation.

• Is the Service Disconnecting Means for this Service the fused switch?
• Is there an Equipment Grounding Conductor (EGC) between the fused switch and the 3 pole breaker?
• Is there an EGC from the 3 pole breaker onward to the rest of the system?
• Is the system that your working on 480 Wye configured without line to neutral loads or is it Delta connected supply with a phase which has a higher voltage to ground than the other 2 phases. This question is critical.
  • The reason that I'm asking is because the Orange tape on the center conductors in both the top and bottom of the fused disconnect and the top of the circuit breaker would suggest a Delta Supply with the center conductor having a higher voltage to ground then either of the other 2.

I will list the concerns that I would have if this installation were mine to do.

• If you bond the generator's neutral to the frame of the generator you will have made a code violating connection to ground from the neutral on the load side of the service disconnecting means.
  
  • The remedy for that would be to have a 4 pole transfer switch which would switch the neutral from the one from the SDM to the neutral conductor from the generator. I believe switch you have in hand is only 3 pole.
• If you do not bond the generator neutral to the frame then, I believe, the code requires an EGC from the generator frame to the transfer switch.
  • The connectors you have in hand will not then carry the fifth conductor which is the required EGC.

Something has to change. You need 5 conductor connectors or a 4 pole switch to bring this off in a code complaint manner. There may be an add on pole kit for the transfer switch you already have. If that turns out to be true then it is likely to be the least expensive way to make the installation code compliant and reduce the extra costs to a minimum.

If, by any chance, the transfer switch is marked "Suitable For Use As Service Equipment" then that will open up an alternative that has not yet been written about here.

I probably need to read through requirements carefully, but is that a violation if there is no neutral load being supplied?

As I mentioned earlier possible neutral current on non carrying components is the main reason for the separation of grounded and equipment grounding conductors beyond the main bonding jumper. If there is no neutral there is no chance of this happening, but maybe it is worded that there is no exception for this sort of situation? From electrical theory perspective I have no issue with bonding at the generator here and not running a neutral to anything.

 

[hornetd]

I probably need to read through requirements carefully, but is that a violation if there is no neutral load being supplied?

As I mentioned earlier possible neutral current on non carrying components is the main reason for the separation of grounded and equipment grounding conductors beyond the main bonding jumper. If there is no neutral there is no chance of this happening, but maybe it is worded that there is no exception for this sort of situation? From electrical theory perspective I have no issue with bonding at the generator here and not running a neutral to anything.

I know of no exception to the prohibition to connecting thee neutral to ground on the load side of the Service Disconnecting means.

Please answer the questions at the top of my previous posting. On those everything else depends.

Obtain and study the manual for the Alternator used as part of the Engine Alternator Set (Generator). That is often just a part of the generator's overall manual but not always. Can the generator be reconfigured to 480 Delta with or without a grounded phase? That information will help the people advising you to understand what is possible.

With just the information which we have so far I would have to say that you cannot reuse the existing 3 pole transfer switch AND the connectors that you have on hand on this install. With more information we might be able to devise a way around the present equipment's limitations.

Tom Horne

 

[kwired]

I know of no exception to the prohibition to connecting thee neutral to ground on the load side of the Service Disconnecting means.

Please answer the questions at the top of my previous posting. On those everything else depends.

Obtain and study the manual for the Alternator used as part of the Engine Alternator Set (Generator). That is often just a part of the generator's overall manual but not always. Can the generator be reconfigured to 480 Delta with or without a grounded phase? That information will help the people advising you to understand what is possible.

With just the information which we have so far I would have to say that you cannot reuse the existing 3 pole transfer switch AND the connectors that you have on hand on this install. With more information we might be able to devise a way around the present equipment's limitations.

Tom Horne

But with no loads using a neutral this is essentially an EGC from the generator to the transfer switch.

I did some looking and you are probably right, but I think the NEC dropped the ball for this circumstance. A conductor not carrying any current is not a problem here, but there is probably so many installs where there is neutral loads this is easy to kind of overlook.

In a small facility that maybe only has motor loads and not any lighting on the 480 volt system you may not have any neutral loads, and in those places you may actually be utilizing a service rated transfer switch and are landing at the service equipment anyway, though as written you still don't bond the generator and need to run a return conductor to the generator for equipment grounding of the generator.

 

[SnakNest]

Let me be sure that I understand your situation.

• Is the Service Disconnecting Means for this Service the fused switch?
• Is there an Equipment Grounding Conductor (EGC) between the fused switch and the 3 pole breaker?
• Is there an EGC from the 3 pole breaker onward to the rest of the system?
• Is the system that your working on 480 Wye configured without line to neutral loads or is it Delta connected supply with a phase which has a higher voltage to ground than the other 2 phases. This question is critical.
  • The reason that I'm asking is because the Orange tape on the center conductors in both the top and bottom of the fused disconnect and the top of the circuit breaker would suggest a Delta Supply with the center conductor having a higher voltage to ground then either of the other 2.

• Yes, the existing fused switch is the service disconnecting means.
• Yes, there is an EGC between the existing fused switch and 3-pole breaker.
• Yes, there is an EGC from the 3-pole breaker to the rest of the system.
• The system is 480 wye with no line to neutral loads (with the exception of the SPD mounted on the side of the fused switch, to which a neutral is connected). All 3 phases measure 277 V to ground.

 

[hornetd]

But with no loads using a neutral this is essentially an EGC from the generator to the transfer switch.

I did some looking and you are probably right, but I think the NEC dropped the ball for this circumstance. A conductor not carrying any current is not a problem here, but there is probably so many installs where there is neutral loads this is easy to kind of overlook.

In a small facility that maybe only has motor loads and not any lighting on the 480 volt system you may not have any neutral loads, and in those places you may actually be utilizing a service rated transfer switch and are landing at the service equipment anyway, though as written you still don't bond the generator and need to run a return conductor to the generator for equipment grounding of the generator.

I didn't try to follow your examples because I still need to know what the situation actually is there on the site being discussed. Until that information becomes available I'm going to avoid speculating any further. It really doesn't matter if the Code Making Panel for section 250 failed to anticipate every possible use configuration. [I don't see how any organization staffed with human beings possibly could.] What he needs is a code compliant means of using what he has to connect the generator to the loads. There may be one but without additional information I just don't know.

 

[hornetd]

• Yes, the existing fused switch is the service disconnecting means.
• Yes, there is an EGC between the existing fused switch and 3-pole breaker.
• Yes, there is an EGC from the 3-pole breaker to the rest of the system.
• The system is 480 wye with no line to neutral loads (with the exception of the SPD mounted on the side of the fused switch, to which a neutral is connected). All 3 phases measure 277 V to ground.

I should have asked these question earlier but I had not examined the photographs closely enough to spot the things I have additional questions about.

• There is a conductor that goes through the breaker enclosure, without any splice or tap, which looks like it is smaller than the three phase conductors. Since it isn't coded as as to function in the breaker enclosure I cannot tell what its purpose is. Can you tell us were that conductor originates in the Service Equipment?
  • I suspect that it is the smaller white coded conductor which is connected along with 2 other conductors to the neutral block of the fused switch.
    • Would you check if that multi terminal lug is bonded to the Fused Switch's enclosure or not?
• There is another conductor in the Service Equipment that is coded green which also appears to go into the liquid tight Flex to the breaker enclosure.
  • I would guess that is the conductor which is bonded to the breaker enclosure just at the lower right corner of the breaker's case. Can you check if that is correct?
    • If that is how it is run then I suspect that it is actually the bonding jumper run through the Flex because the flex is not listed as an Equipment Grounding Conductor.
• Were does the conductor which passes right through the breaker enclosure terminate?
  • If it is a neutral conductor; which appears to be what it is coded as; why was it run past the Service Disconnecting Means at all? Again I need to ask, are there any phase to neutral loads beyond the breaker regardless of how small they might be?
• Which conductor in the breaker enclosure is the Equipment Grounding Conductor (EGC) which runs on to the supplied load? I cannot see one. I do know that the raceways could be serving as the EGC once your past the Flex which the original installers bonded around.

Yes I do know that the raceways could be serving as the EGC. If that is the case here then that is all taken care of.

Other than recoding one of the phase conductors to a color other than orange; which is merely bad practice and not actually a code violation; the existing issues I would want to clean up would be the improper termination of 3 conductors in a single terminal port of the neutral lug and the way that surge protector is installed. A straight forward way of correcting the three conductors terminated in a terminal only listed for a single conductor would be to move both of the EGCs and the bonding conductor through the flex to the breaker enclosure to a triple barreled lug fastened directly to the enclosure of the Fused Switch. If you use that solution make sure that you use screws with fine enough threads that 2 full threads are in contact with the switch enclosure. Self tapping screws generally aren't fine threaded enough for that purpose so you might have to drill and tap a hole in the enclosure's back wall. Since a 32 TPI screw is used as the main bonding jumper in so many Service Equipment enclosures I would think that would be the type of screw I would use. It would also be better practice to use a lug that is designed for 2 or more mounting screws. In either case use a right angle cut off tool with a grinding wheel or wire brush wheel to remove the paint from beneath the lug and apply a conductive past between the lug and the bare metal of the enclosure. After the lug is mounted touch up the paint on any still exposed bare metal to prevent corrosion.

The surge protector is very badly installed. It is axiomatic that the conductors between the surge protector, the phase conductors, and bonding point should be as straight and short as practicable. A best practices installation may not be possible here but it could be markedly improved. Reposition the fuse block so that the length of unfused conductors is as short and straight as practicable. Run the surge protector's conductors to the fuse holder using a maximum practical radius curve if they cannot be run straight. Connecting the white conductor to the Grounding Electrode Conductor just before it leaves the enclosure would be best practice and is easily done using a split bolt connector of the proper size after you shine the part of the GEC were the split bolt will be attached to bright copper free of any copper oxide. Apply a conductive copper corrosion inhibitor paste to the cleaned area immediately after cleaning it. Use a split bolt that has a maximum conductor size as close as you can find to the size of the GEC so that the white conductor from the surge arrester will be as close to the minimum size of wire for which the split bolt is listed as it can be. That will eliminate the wire nut splice used to lengthen the discharge conductor of the surge arrestor to reach the neutral block. There is no particular virtue to connecting the discharge conductor to the neutral. The other thing to do to improve the performance of the surge protector and the GEC is to use a listed bonding fitting were the GEC exits the enclosure.

This eliminates the choke effect of the wall of the enclosure through with the GEC has to pass. If you want to be a true grounding fanatic, like those of us who had to travel by helicopter to do a service call on some of our installations, then you substitute a bronze lock nut and clean the paint from the contact surface area on both sides of the enclosure metal. Following installation reapply paint to any exposed bare steel.

 

[ActionDave]

......

• If you bond the generator's neutral to the frame of the generator you will have made a code violating connection to ground from the neutral on the load side of the service disconnecting means.
  • The remedy for that would be to have a 4 pole transfer switch which would switch the neutral from the one from the SDM to the neutral conductor from the generator. I believe switch you have in hand is only 3 pole.

• 
  
  I don't think this is correct. 250.6 only says you need to avoid Objectionable Current and there will not be any chance of that because all the loads being discussed are line to line.

 

[ActionDave]

Other than recoding one of the phase conductors to a color other than orange; which is merely bad practice and not actually a code violation;

What bad practice? Brown, Orange, Yellow is standard for 480V systems

The other thing to do to improve the performance of the surge protector and the GEC is to use a listed bonding fitting were the GEC exits the enclosure. This eliminates the choke effect of the wall of the enclosure through with the GEC has to pass. If you want to be a true grounding fanatic, like those of us who had to travel by helicopter to do a service call on some of our installations, then you substitute a bronze lock nut and clean the paint from the contact surface area on both sides of the enclosure metal. Following installation reapply paint to any exposed bare steel.

How much choke effect is less than one sixteenth of an inch of steel going to cause?

 

[SnakNest]

• There is a conductor that goes through the breaker enclosure, without any splice or tap, which looks like it is smaller than the three phase conductors. Since it isn't coded as as to function in the breaker enclosure I cannot tell what its purpose is. Can you tell us were that conductor originates in the Service Equipment?
  • I suspect that it is the smaller white coded conductor which is connected along with 2 other conductors to the neutral block of the fused switch.
    • Would you check if that multi terminal lug is bonded to the Fused Switch's enclosure or not?
• There is another conductor in the Service Equipment that is coded green which also appears to go into the liquid tight Flex to the breaker enclosure.
  • I would guess that is the conductor which is bonded to the breaker enclosure just at the lower right corner of the breaker's case. Can you check if that is correct?
    • If that is how it is run then I suspect that it is actually the bonding jumper run through the Flex because the flex is not listed as an Equipment Grounding Conductor.
• Were does the conductor which passes right through the breaker enclosure terminate?
  • If it is a neutral conductor; which appears to be what it is coded as; why was it run past the Service Disconnecting Means at all? Again I need to ask, are there any phase to neutral loads beyond the breaker regardless of how small they might be?
• Which conductor in the breaker enclosure is the Equipment Grounding Conductor (EGC) which runs on to the supplied load? I cannot see one. I do know that the raceways could be serving as the EGC once your past the Flex which the original installers bonded around.

I can only answer some of what you're asking right now until I get back to this site, which I don't know when that will be. Hopefully later this week. However:

• The smaller conductor that passes through the breaker enclosure is a grounding conductor. I didn't notice until after I had posted the pictures here that there is only one smaller (grounding) conductor going into the liquid tight conduit and two coming out, but I definitely traced the conductor in question beyond the breaker enclosure and verified that it is landed as the equipment grounding conductor. I just don't remember where exactly it first lands. That's also how I know that there is no other neutral wire beyond the block at the right of the main breaker. I can't say how (or if) a splice occurs on the grounding conductor inside the liquid tight conduit (or why anyone would do that) that accounts for the additional wire coming into the breaker enclosure from the conduit. I will verify that there's a proper ground connection for that at some point. But the smaller conductor that enters the liquid tight conduit from the fused switch is the green-taped black wire that is bonded with the same screw as the small white and green wires on the neutral block of the fused switch.
• My assumption at this point is that the green-taped black wire that originates at the neutral lug of the fused switch is the same wire that passes through the breaker enclosure and serves as the equipment grounding conductor beyond the main breaker. I will have to verify this with a site visit, as well as determine the origin of the wire that is bonded to the breaker enclosure.
• The white-taped black (neutral) conductor that originates at the neutral block of the fused switch is connected to the block at the right side of the main breaker, and it definitely only goes that far. I am 100% certain that there are no neutral loads on the system beyond that main breaker, and that there is no continuation of that neutral conductor beyond the main breaker enclosure. Hence my original question about just removing the grounded/neutral conductor between the fused switch and main breaker, since it isn't used.
• I can't say right now whether the multi-terminal (neutral) lug is bonded to the enclosure of the fused switch. That's something I'll have to check next time I see it.

At this point, is there still any chance that I can use the 4-wire connector from the generator to the transfer switch?
If there's not, I'd like to tell the client ASAP that they're at least going to have to change to a 5-wire cable and connectors to carry the generator neutral into the transfer switch. I'm assuming at this point that if I carried both the service and generator neutrals into the 3-pole transfer switch and bonded them together on the neutral lug of the transfer switch, that I could at least use said 3-pole transfer switch as a non-SDS 480 wye setup?

 

[ActionDave]

....At this point, is there still any chance that I can use the 4-wire connector from the generator to the transfer switch?

Electrically it will work. The question is will it meet code?

If there's not, I'd like to tell the client ASAP that they're at least going to have to change to a 5-wire cable and connectors to carry the generator neutral into the transfer switch. I'm assuming at this point that if I carried both the service and generator neutrals into the 3-pole transfer switch and bonded them together on the neutral lug of the transfer switch, that I could at least use said 3-pole transfer switch as a non-SDS 480 wye setup?

You can always do that.

 

[kwired]

Electrically it will work. The question is will it meet code?

You can always do that.

If a non SDS it comes down to is it really necessary to extend the generator neutral all the way to the service equipment then via the main bonding jumper extend a EGC all the way back to the generator frame? If there is neutral loads then definitely yes if no neutral loads what is the reason to say no?

 

[ActionDave]

I don't think there is a reason to say no.