MEP-003A hook up question

Steel Soldiers is supported by:

acesneights1

Member
1,449
12
20
Location
CT
This is a very good Thread and I suspect will help alot of people in the future in hooking any kind of genset.
I vote to Sticky it...Any seconds ?[thumbzup]
 

steelypip

New member
753
3
0
Location
Charlottesville, VA
Gotcha! Thanks again. Will connection to L-0 accomplish the same thing for the ground?
If you're using a non-separately derived system (see Speddmon's post #25 and #32 (with the very helpful pictures)), then you need to break the connection between L[whatever] - the neutral connection point on the gen head windings and the frame ground and connect the frame ground to your meter box/load center ground rod. This is why residential generator connection cable is always four-wire: two for the hot legs, one for the neutral and one for ground.

Simply put:

If you're grounding neutral at the house (non separately derived system) then you disconnect the neutral leg from frame ground on the generator, hook frame ground to house ground and generator neutral to house neutral, and switch the hot legs between utility power and the generator as needed with your transfer switch or interlock kit.

If you're grounding neutral at the generator (separately derived system) then you have to switch neutral conductors along with hot conductors in your transfer switch and you ground neutral at the generator to a driven ground rod at the generator.

Almost all residential backup generator installations are non separately derived systems. The military generally doesn't have utility power in the picture when using a generator, so they don't have to worry about there being more than one ground rod or multiple neutral connection points. That's what causes the confusion when using a military generator for utility backup power.

The take-away:

  1. If you have more than one connection between grounding rods and the house neutral wire at any time, you're doing it wrong.
  2. If you have zero connections between house neutral wire and grounding rod at any time, you're doing it wrong.
  3. If the generator housing and frame are ungrounded at any time, you're doing it wrong.

Any of the above cases can result in equipment damage, injury, or death (and not necessarily in that order).
 

cucv1833

New member
533
4
0
Location
Lake Charles, LA
Great thread!! So I'm installing a transfer switch soon just want to double confirm

Here's the description.
GE Outdoor rated 200 Amp boxed Transfer Switch; 2 Pole with Neutral
*2 Pole Double Throw Switch with a Third non Switching Neutral Pole.
includes 2 Inputs (1 for Utility, 1 for a Generator) and 1 Output (to your Ppanel)

It looks like a NON SDS. So I should disconnect the neutral at the generator ground and bring L1-L3 to hot and L0 to neutral and ground to the ground lug all in the transfer panel correct? A 4 wire system. Just like a civy generator

My champion 7-9kw has a floating neutral on the generator for the panel or stand alone.
 

212sparky

Active member
1,801
15
38
Location
Monroe/ Ohio
That is correct. Make sure you have the frame of the gen set grounded. If you are using aluminum wiring use a no oxide compound. It is also good practice to use it on copper that is out doors as well.
 

Isaac-1

New member
1,976
1
0
Location
SW, Louisiana
In general you always want to use stranded copper when connecting to generators, motors, etc. due to vibration, MTW (Machine Tool Wire) rated wire is best, as it has finer strands than regular stranded and holds up to vibration better, SO (SOOW,SOEW, SJOW, etc.) cord is another good choice. It sounds like you have it right, (bond neutral to ground at service entrance only, unbond L0 from the frame) for safety it is best to drive a separate ground rod for the generator frame, that way if you have in internal short the frame will not be live, this is not as much of a concern on residential generators, but these MEP's do have control panels on them so people are much more likely to touch them while they are running.

Ike
 

212sparky

Active member
1,801
15
38
Location
Monroe/ Ohio
Your grounding conductor will keep the frame grounded and drain short circut current. the finer the strand the more flexible and more current the cable will carry. Inspect your cabling before each use for dammage as well.
 

dependable

Active member
1,593
23
38
Location
Tisbury, Massachusetts
unbond L0 from the frame) for safety it is best to drive a separate ground rod for the generator frame, that way if you have in internal short the frame will not be live, this is not as much of a concern on residential generators, but these MEP's do have control panels on them so people are much more likely to touch them while they are running.

Ike
So it is ok to ground frame as well in a non SDS system? This seems different advice again.

I am back feeding (in power outage mode w Interlockkit) to panel though old 3 pronged range plug I use for my welder, so this is a Non SDS system. Have run it w frame still bonded to neutral and it seemed OK, but understand I should un bond gen frame from LO. Do have a generator ground rod in place. Sounds like I should have a 4 pinned plug. Am confused about ground rod now.
 
Last edited by a moderator:

dependable

Active member
1,593
23
38
Location
Tisbury, Massachusetts
Been thinking about this last post of mine and understand why no one wants to answer it (besides the dead horse thing). Anyway, I want to thank all of the folks who post here and know electrical theory and code.

All of us getting great advice from this forum should realize that no one can tell you if your rig and hook up is safe without looking at it and testing it. What we are getting is free advice and is usually worth more than that.

Anyone who is buying and using these generators should get help from real electrician if they are not sure of what they are dealing with when hooking to grid. Even if they are a good mechanic. ( I have been doing stupid things for years and am now an expert at it. ) Anyway, am having an electrician come over to check my set up out.

I may continue to ask 'uninformed' questions. I did have an electrician come by, his help kept me from miswireing a couple breakers when I moved them for the Interlockkit. (separate circuits w common neutral have to be on alternating breakers in panel) Glad I called him.
 
Last edited:

Speddmon

Blind squirrel rehabiltator
Super Moderator
Steel Soldiers Supporter
4,678
11
38
Location
Cambridge, Ohio
Your last post should be self evident if you think about the question. Your generator frame, whether used in a Non SDS or an SDS, is ALWAYS grounded. It must be or bad things can happen (to you if something goes wrong with the wiring). That is why you are running 4 wires for the hook-up, one of them is a ground to hook to the gen frame.

Now, whether or not you drive a second/separate ground rod is entirely up to you and your local codes/inspector, but again, the gen frame will ALWAYS be grounded
 

Isaac-1

New member
1,976
1
0
Location
SW, Louisiana
Speddmon, I think this should be, will always be grounded IF hardwired to the transfer switch, if using some type of twist lock cord, etc. it may not be.

Ike
 

n1oty

New member
Steel Soldiers Supporter
170
0
0
Location
Taunton, MA
Speddmon, I think this should be, will always be grounded IF hardwired to the transfer switch, if using some type of twist lock cord, etc. it may not be.

Ike

Which is why I use a 6 AWG, 4 conductor "shore power" cable with a 125/250 Hubbell connector. It includes both hots, my neutral and a ground for the frame.

John
 

Speddmon

Blind squirrel rehabiltator
Super Moderator
Steel Soldiers Supporter
4,678
11
38
Location
Cambridge, Ohio
Speddmon, I think this should be, will always be grounded IF hardwired to the transfer switch, if using some type of twist lock cord, etc. it may not be.

Ike
No, it shouldn't be. The only thing I might have left out is "If you have things hooked up properly, anytime you are running the set the frame will be grounded" It doesn't matter if you have it hooked up permanently to a transfer switch, through a cord and plug or as a stand alone generator out in the field, a proper hook-up will always have a ground on the frame ALWAYS!
 

ChesapeakeJohnny

New member
14
0
1
Location
Eastern Shore, MD
Forgive me if this has somehow been covered, but it seems that much of this discussion is for transfer panels downstream of the main panel.

In my circumstance, I intend to place a whole house transfer switch upstream -- that is, between the meter pan (termination of Utility feed) and my main panel.

My main panel neutral buss is grounded directly via a copper wire/copper rod to earth.

In this circumstance, if I wish to have a SDS, and utilize a 3 pole switch and switch both hots plus the neutral:
1) Should I ground the generator to earth at the generator even though the Main Panel neutral buss is grounded with its own rod? Probably not, but I don't see how the SDS derivation would work if the house main is grounded as well.
2) The ground from the genset (4th wire) would get to the Main Panel via what route?

My understanding, while possibly wrong, was that if I left the neutral ground bond intact at the frame and utilized the 3 pole switch, I will still be picking up the ground from the ground wire (4th wire) coming from the genset, and the neutral ground bond must be either at the genset or the main panel that is being fed by the genset, but NOT both.

This would obviously not be safe if I ran the generator while disconnected from neutral of the main buss, since it wouldn't then be earth grounded.

If SDS requires me to ground the genset @ the unit via ground rod, how should I avoid having the generator grounded to earth at the unit AND at the neutral buss/ground wire-to-earth of the Main Panel? In this case, am I forced to simply use a 2 pole switch and use that main panel neutral buss grounding + disconnect the neutral-ground bond at the genset?

Thanks,
Johnny


Andy, I am not aware of any specific code prohibiting it, but I highly doubt that you would pass any kind of an inspection simply because there would be no way to ensure that you couldn't possibly have the switch in the wrong position at any given time. That's the whole point of having the transfer switches, and some other codes in the NEC relating to disconnecting means used in industrial installations...They want the stuff to be as fool proof and safe as posssible.



It's actually J10 in that picture (the lower, innermost connector on the back side of the AC reconnection box) . The neutral bond wire is the one that has the funky black polygon drawn around it. It actually bonds to the frame on the inside of the ground splitbolt in the picture.


Here are some pictures that Bjorn asked for.

To clarify the differences of the two types of systems, the generator, the load center and the main service have nothing to do with whether it is a Separately Derived System or not. The deciding factor is whether or not your neutral wire remains electrically connected to the main service entrance from the power company. If it remains connected, then you have a Non SDS, and no ground rod should be driven, as well, the wire in the connectors coming from the generator head that ties the neutral to ground should be disconnected and isolated from the frame (wrap it in electrical tape if necessary, but this wire should not be touching the frame for a proper installation)

You’ll notice in the first picture of a SDS, the generators’ neutral wire is bonded to the frame of the generator, and the generator is grounded via a separate ground rod.

In the second picture of the Non SDS, you can see how the neutral remains electrically unbroken throughout the entire circuit. Also, that the generator neutral conductor is not bonded to the generator frame. The generator frame ground is still tied together with all of the other grounds in the system, but there is not a separate ground rod.
 
Last edited:

steelypip

New member
753
3
0
Location
Charlottesville, VA
In my circumstance, I intend to place a whole house transfer switch upstream -- that is, between the meter pan (termination of Utility feed) and my main panel.

My main panel neutral buss is grounded directly via a copper wire/copper rod to earth.

In this circumstance, if I wish to have a SDS, and utilize a 3 pole switch and switch both hots plus the neutral:
1) Should I ground the generator to earth at the generator even though the Main Panel neutral buss is grounded with its own rod? Probably not, but I don't see how the SDS derivation would work if the house main is grounded as well.
2) The ground from the genset (4th wire) would get to the Main Panel via what route?
This is actually the layout I want to go to (am currently using an interlock kit), mostly because it will get me a whole-house cutoff switch as a bonus.

The principles are still exactly the same as if you were going into a sub panel or an interlocked backfed breaker on the main panel.


  1. There must be only one ground point bonded to the generator.
  2. That same ground point must be bonded to the neutral at the one connection point (usually your main panel in the house)
  3. There must never be zero grounds for either the generator frame or the panel.
If you're doing it with switched hot and neutral in a switch between meter and panel then you still only have a single ground point in the house. You connect that to the fourth (ground) wire in the generator cable and that grounds the generator frame all the time just like it grounds the main panel and the neutral bar at the main panel. You have to break the generator frame ground connection as previously discussed.

I don't believe code ever supports switching ground connections on equipment- it sounds like a sketchy idea anyway. I know that it never supports multiple connections between ground and neutral after the meter base.

Your other option is to do a separately derived system by disconnecting the house ground rod from the neutral bus in the switch box and connecting it to the neutral leg switch terminal on the utility service side of the transfer switch. You would then drive a ground rod for the generator, leave ground and neutral tied at the generator. That's your separately-derived ground for the generator side of the circuit. The transfer switch (and house) is always connected either to utility service (and is thus grounded by the ground bond on the service side neutral switch pole, or to the generator, and is grounded at the generator by the generator grounding rod and ground bond.

My plan is to skip this fun by doing a non-separately derived system and not switching neutral at all. That way I have one ground rod at the house going into the panel just like always and I ground the generator through the house ground. Only the hot conductors get switched between utility service and generator.
 

ChesapeakeJohnny

New member
14
0
1
Location
Eastern Shore, MD
I will ask this question at the end: "What of the 4th wire/ground wire that folks have said should extend from genset grounding lug to meter to transfer switch to main panel?":

However, let's first see if I have the following correct. If I want to safely utilize my genset at any time as a standalone power source out in my shed, e.g. plugging in 120V devices at the duplex on the genset, and at times or permanently I wish to use it as a whole house power source/SDS that is completely isolated from potential power surges on either hot or neutral from the utility feed:

- I understand that I must utilize a 3 pole switch in order to switch hot, hot & neutral;

- I understand that I must remove the earth ground from my main panel's neutral buss bar and run that earth ground instead to the neutral lug on the utility side of my transfer switch;

- I understand that I must then drive a ground rod at the genset and retain the neutral-ground bond on the frame;

- I understand that the neutral-ground bond and driven grounding rod at the generator satisfies the need for a ground for the entire house when the transfer switch is switched to the genset as power source (but is not duplicating such a bond on the main panel because that former bond was removed and tied instead to the neutral lug, utility side of the transfer switch).

- I understand that I will then have a switched neutral, hot and hot, with the ground bond essentially switching with the neutral.

However, What of the 4th wire/ground wire that folks have said should extend from genset grounding lug to meter to transfer switch to main panel?" If I understand correctly, I will not be running that if it is an SDS and the genset is grounded to a an earth ground rod right there.
How will the transfer panel and main panel housings be grounded? Am I still to run a ground wire from the genset frame all the way to the transfer switch housing and subsequently to the main panel housing (but not to the main buss)?





Just checking!!:)



This is actually the layout I want to go to (am currently using an interlock kit), mostly because it will get me a whole-house cutoff switch as a bonus.

The principles are still exactly the same as if you were going into a sub panel or an interlocked backfed breaker on the main panel.


  1. There must be only one ground point bonded to the generator.
  2. That same ground point must be bonded to the neutral at the one connection point (usually your main panel in the house)
  3. There must never be zero grounds for either the generator frame or the panel.
If you're doing it with switched hot and neutral in a switch between meter and panel then you still only have a single ground point in the house. You connect that to the fourth (ground) wire in the generator cable and that grounds the generator frame all the time just like it grounds the main panel and the neutral bar at the main panel. You have to break the generator frame ground connection as previously discussed.

I don't believe code ever supports switching ground connections on equipment- it sounds like a sketchy idea anyway. I know that it never supports multiple connections between ground and neutral after the meter base.

Your other option is to do a separately derived system by disconnecting the house ground rod from the neutral bus in the switch box and connecting it to the neutral leg switch terminal on the utility service side of the transfer switch. You would then drive a ground rod for the generator, leave ground and neutral tied at the generator. That's your separately-derived ground for the generator side of the circuit. The transfer switch (and house) is always connected either to utility service (and is thus grounded by the ground bond on the service side neutral switch pole, or to the generator, and is grounded at the generator by the generator grounding rod and ground bond.

My plan is to skip this fun by doing a non-separately derived system and not switching neutral at all. That way I have one ground rod at the house going into the panel just like always and I ground the generator through the house ground. Only the hot conductors get switched between utility service and generator.
 
Last edited:

Speddmon

Blind squirrel rehabiltator
Super Moderator
Steel Soldiers Supporter
4,678
11
38
Location
Cambridge, Ohio
You're making this way more complicated than it needs to be.

First and foremost, unless your transfer switch is a double throw (meaning it has a center position on the handle, with no connection to anything anywhere) then you WILL need some means of service disconnect between your meter and your transfer switch. Period. You must install a service disconnect in all installations, so unless your transfer has a big sticker with it that says "Suitable as service disconnect" you cannot do as you have planned.

NOW, once you install a suitable service disconnect immediately AFTER your meter can and BEFORE your transfer switch, then just hook everything up EXACTLY as the picture I posted for an SDS system, and you're done.

simple.
 

ChesapeakeJohnny

New member
14
0
1
Location
Eastern Shore, MD
Thanks.

Yep, the switch we intend to use is on-off-on and marked as service rated for our 200a utility.

Here's the confusion: In your picture, there are two simultaneous neutral-ground bonds occuring via the gound to neutral connection at the utility main AND the uninterrupted connection of that ground back to the bonded generator frame. Shouldn't the grounds be separated? That's the nature of my question -- how do I ground the housings without creating a double neutral-ground.


You're making this way more complicated than it needs to be.

First and foremost, unless your transfer switch is a double throw (meaning it has a center position on the handle, with no connection to anything anywhere) then you WILL need some means of service disconnect between your meter and your transfer switch. Period. You must install a service disconnect in all installations, so unless your transfer has a big sticker with it that says "Suitable as service disconnect" you cannot do as you have planned.

NOW, once you install a suitable service disconnect immediately AFTER your meter can and BEFORE your transfer switch, then just hook everything up EXACTLY as the picture I posted for an SDS system, and you're done.

simple.
 

Speddmon

Blind squirrel rehabiltator
Super Moderator
Steel Soldiers Supporter
4,678
11
38
Location
Cambridge, Ohio
There you go thinking too much into it again....remember, the switch you are using switches the neutral...so, when you are on utility power, the neutral coming from the generator is not used. It's not connected to anything because of the nature of the switch, so it does nothing...can't have any double neutral-ground bond on a wire that goes nowhere.
 
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website like our supporting vendors. Their ads help keep Steel Soldiers going. Please consider disabling your ad blockers for the site. Thanks!

I've Disabled AdBlock
No Thanks