LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Generally speaking, the non-SDS system is easier and cheaper.
Portable generator
- Thread starter hhsting
- Start date
In the above with the 3p transfer switch, if there was a ground fault at the load, seeing as how the neutral and ground aren't bonded at the generator, the only way to clear that fault would be if that fault current would travel back through the EGC to the transfer swtich, from the transfer switch back through the EGC to the Service Equipment where it bonds to the system neutral back through the source neutral to the generator to trip the OCPD at the generator.
Does that neutral to ground bond at the service equipment then not also cause some unwanted neutral current on the system during normal generator operation ?
or,
Does the neutral return current in generator mode go directly back to the generator without any unwanted return current on the system even though it's bonded at the service equipment?
JAP>
Seven-Delta-FortyOne
Goin’ Down In Flames........
- Location
- Humboldt
- Occupation
- EC and GC
If there is a redundant N-G bond in the MTS, and the N-G bond is not removed in the genny, and there is only a flexible gen cord between them, then the fact is, “Absolutely nothing”.
Just like the exception that allowed a 3 wire feeder to a separate structure if no other bonded materials existed between them, that was removed a few code cycles back.
Still a code violation though.
This is what I had pictured, when I mentioned the return current when in generator mode should be trying to make it back to the source (or generator), yet the above graphic is showing objectional current going towards the service disconnect also even though that is not the source when in generator mode.
If that's the case, even If you switch the neutral in the Transfer Switch, yet that switched contact is closed when in generator mode, and there is still an EGC connection between all the componants of the system, what changes about the above current return path?s
To me it would still impose objectional current on parts of the system regardless.
Oh well,,,
JAP>
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Agreed that if the MTS is service-rated, so the N-G bond is in the MTS, then the upshot is that the MTS-generator EGC is just in parallel with the MTS-generator neutral. Which itself is a violation of the parallel conductor rule. But as far as objectionable current, it will be restricted to that MTS-generator EGC connection.
Cheers, Wayne
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
In the graphic, look at the point labeled "Solidly Connected Neutral." From there, in generator mode, neutral current "wants" to get back to the generator neutral connection, the winding midpoint. The point of the graphic is that there are now two paths for current to get from that "Solidly Connected Neutral" point to the generator winding midpoint.
The first path is the intended path, along the white wire directly to the generator. The second path is along the white wire to the service disconnect, across its N-G bond to the EGC, along the EGC back to the MTS, back to the generator, and across the generator's N-G bond.
Current will take all paths in inverse proportion to their impedances. So as this second path is longer, and thus higher impedance, less current will flow on it than the intended path. But it will still be significant current on the EGC.
Cheers, Wayne
Agreed.
Jap>
Yes, but there is still an EGC connection between all the components of the system and where it bonds to the generator's neutral.
If the objectional current can go out of it's way to travel towards the service disconnect (which is not it's source neutral in generator mode) and back to the generator in a non switched neutral connection, I dont see why it couldn't also do that somewhat even with a switched neutral and a bond between the Neutral and EGC at the generator where you have to bond them together to clear a fault.
In the end,, is there not always some objectional current on normally non-current carrying parts of the system regardless of our efforts?
JAP>
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
With the neutral switched at the MTS, there is no second path.
You could imagine the current going from the N-G bond in the generator down the EGC to the service disconnect, and then back again on the same wire. But in that case, the two currents on the same wire would be of opposite magnitude and just add to zero net current.
The issue arises when you have a loop, and switching the neutral breaks the loop in the previous example.
Cheers, Wayne
So if the installation is permanent like a whole house (Generac/Kohler or others) it most likely does not have an N-G connection made whereas portable generators might be used by themselves and need a ground rod connection elsewhere.
It is a one-time decision when connecting the Auto/Manual Transfer Switch, to switch the neutral or disconnect the N-G connection at the Generator.
It is a one-time decision when connecting the Auto/Manual Transfer Switch, to switch the neutral or disconnect the N-G connection at the Generator.
Seven-Delta-FortyOne
Goin’ Down In Flames........
- Location
- Humboldt
- Occupation
- EC and GC
Ground rod has absolutely nothing to do with it.