Generator and GFCI

[tom baker]

I am trying to determine if a portable generator with an integral GFCI will have the GFCI trip if there is a neutral to ground connection.
If this is the case, this generator, when used with a Manual Transfer Switch, with a portable cord and plugged into the generator the GFCI will trip.
So if you have a portable generator, with a 30 amp 120/240 volt receptacle, can you connect a jumper from neutral to ground at the receptacle to see if it trips the GFCI? Mike Holt and I were discussing this and this is what he recommended for a test.
Thanks

 

[stud696981]

I might be missing something here so if I'm wrong some else please chime in.

As I understand you are connecting to the 120/240 receptacle. The portable generators that I have seen, including the one I have, do not have GFCI protection on this outlet. Only the standard 120 outlets have GFCI protection.

So in your case a GFCI is probably not on this outlet and making a jumper for a test will do nothing.

 

[ceb58]

I might be missing something here so if I'm wrong some else please chime in.

As I understand you are connecting to the 120/240 receptacle. The portable generators that I have seen, including the one I have, do not have GFCI protection on this outlet. Only the standard 120 outlets have GFCI protection.

So in your case a GFCI is probably not on this outlet and making a jumper for a test will do nothing.

Tom is talking about the upcoming 2011 code for gen. that are15 KW or less. They will be required to have GFCI protection on the outlets.

I am trying to determine if a portable generator with an integral GFCI will have the GFCI trip if there is a neutral to ground connection.
If this is the case, this generator, when used with a Manual Transfer Switch, with a portable cord and plugged into the generator the GFCI will trip.
So if you have a portable generator, with a 30 amp 120/240 volt receptacle, can you connect a jumper from neutral to ground at the receptacle to see if it trips the GFCI? Mike Holt and I were discussing this and this is what he recommended for a test.
Thanks

In the case of a man. transfer switch I think it will trip the GFCI unless the neutral is switched. Your test is worth a try.

 

[don_resqcapt19]

Many portable generators do not have their neutral bonded to the frame and or EGC, so those types of generators should not trip with a downstream neutral to ground connection.

 

[tom baker]

I might be missing something here so if I'm wrong some else please chime in.

As I understand you are connecting to the 120/240 receptacle. The portable generators that I have seen, including the one I have, do not have GFCI protection on this outlet. Only the standard 120 outlets have GFCI protection.

So in your case a GFCI is probably not on this outlet and making a jumper for a test will do nothing.

If you have a generator with a 120 volt GFCI receptacle can you test it by jumping from the neutral to hot?
The honda construction generators have a common GFCI trip for all 4 receptacles, including the 120.240.

 

[hurk27]

Over the years I have gotten away from using portable generators for job sites as I now use inverters, but I can remember the 5kw ones we used that had a 4-wire twist loc receptacle and also had 2 GFCI receptacles mounted on the same panel as the twist-loc would also have a switch that had two positions 120 volt/240/120 volt which would remove the neutral to frame bond when in the 240/120 volt position for use as a stand by generator, this was common across most brands.
I know a few contractors that would use a break out box because you can't utilize the full capacity of the generator if you just use the two GFCI receptacles on a 5kw or above so they would make up a twist-loc to a 4x4 box with two 20 amp receptacles in it, which also would not provide GFCI protection and or a neutral to generator frame bond, it would also allow more than 20 amps per duplex to be loaded on each receptacle which would cause problems with extension cord over heating, but this would not be uncommon to see around here on job sites, and maybe could be the reason behind why the change to require all receptacles to now be GFCI protected?

 

[hurk27]

If you have a generator with a 120 volt GFCI receptacle can you test it by jumping from the neutral to hot?The honda construction generators have a common GFCI trip for all 4 receptacles, including the 120.240.

answering the above in red?

you can't test any GFCI by jumpering from hot to neutral, only from hot to ground or neutral to ground, a short from hot to ground will most likely provide a fault large enough to open the OCPD before the GFCI can react (depends on the AFC), most GFCI's have a very small delay to prevent false trips, this delay can also allow many breakers to open first in a case of a bolted fault, this is why it is better to use a resistance fault such as a loaded voltage meter (wiggy) if checking a GFCI from hot to ground

 

[acrwc10]

I am trying to determine if a portable generator with an integral GFCI will have the GFCI trip if there is a neutral to ground connection.
If this is the case, this generator, when used with a Manual Transfer Switch, with a portable cord and plugged into the generator the GFCI will trip.
So if you have a portable generator, with a 30 amp 120/240 volt receptacle, can you connect a jumper from neutral to ground at the receptacle to see if it trips the GFCI? Mike Holt and I were discussing this and this is what he recommended for a test.
Thanks

If I understand what your asking, the problem may occur when you connect to the house via the MTS. The neutral ground bond on the house service panel would cause current on the ground this would trip the GFI. Simply putting a jumper, from neutral to ground, on the generator receptacle would not cause a trip, unless there is a load on the circuit. No current, no magnetic field, no tripping.

 

[hurk27]

If I understand what your asking, the problem may occur when you connect to the house via the MTS. The neutral ground bond on the house service panel would cause current on the ground this would trip the GFI. Simply putting a jumper, from neutral to ground, on the generator receptacle would not cause a trip, unless there is a load on the circuit. No current, no magnetic field, no tripping.

this is not true with the GFCI's that have been produced with the newer requirements in the past 15 years.

these newer GFCI's have a extra current transformer in them that works the opposite of what the detection CT does, this coil injects a 120 hz signal into the hot and neutral conductors of the circuit that passes through the GFCI, this signal provides the current that will cause the GFCI to detect a grounded neutral without any 60 hz current being placed on the circuit, this was part of the newer GFCI requirements by UL to require a GFCI to not allow a GFCI to provide any voltage at the load side if the GFCI or circuit is mis-wired.

I try to look up the link tomorrow to the article that explains this better then I can, and even has a circuit diagram that shows this. or maybe someone else has this link at hand can post it.

 

[hurk27]

Ok found the web site with one of the best explanations of all about how a GFCI works, scroll down to the middle of it "where you see the graphic of two CT's"

It will explain about the 120 hz injection to detect a neutral to ground fault.

How A GFCI Works

 

[jwelectric]

would using one of these on a receptacle let someone know if the neutral point was bonded to the frame?

 

[acrwc10]

this is not true with the GFCI's that have been produced with the newer requirements in the past 15 years.

these newer GFCI's have a extra current transformer in them that works the opposite of what the detection CT does, this coil injects a 120 hz signal into the hot and neutral conductors of the circuit that passes through the GFCI, this signal provides the current that will cause the GFCI to detect a grounded neutral without any 60 hz current being placed on the circuit, this was part of the newer GFCI requirements by UL to require a GFCI to not allow a GFCI to provide any voltage at the load side if the GFCI or circuit is mis-wired.

I try to look up the link tomorrow to the article that explains this better then I can, and even has a circuit diagram that shows this. or maybe someone else has this link at hand can post it.

I think we may both be correct on this, if the GFI has been "reset" it is my experience that they will not trip by simply jumping the ground to neutral without a load,(like with a solenoid tester) But when it is in the "tripped" position it will run a quick test to verify the ground is separate from the neutral. It will not reset if there is a ground neutral connection, but will stay set UNTIL load is introduced to the circuit.

 

[hurk27]

I think we may both be correct on this, if the GFI has been "reset" it is my experience that they will not trip by simply jumping the ground to neutral without a load,(like with a solenoid tester) But when it is in the "tripped" position it will run a quick test to verify the ground is separate from the neutral. It will not reset if there is a ground neutral connection, but will stay set UNTIL load is introduced to the circuit.

A solenoid tester will have too high of an impedance to allow the 120 hz signal to trip the GFCI which is very weak to start with, but if you use a solid jumper to jump between the neutral and ground it will trip, I do this sometimes when I forget to bring in my GFCI tester from the truck. try it next time your around a GFCI and theres no load on it. just make sure you hit the neutral (big blade) and not the hot(small blade)

 

[ELA]

A solenoid tester will have too high of an impedance to allow the 120 hz signal to trip the GFCI which is very weak to start with, but if you use a solid jumper to jump between the neutral and ground it will trip, I do this sometimes when I forget to bring in my GFCI tester from the truck. try it next time your around a GFCI and theres no load on it. just make sure you hit the neutral (big blade) and not the hot(small blade)

Here is a scope trace of the current that flows when you do as hurk27 indicated, using a direct short.

 

[goodcode]

don_resqcapt19 has hit on the issue at hand. Some small generators are bonded while others are floating neutral. GFCI is only part of the issue. The other question is to bond or not to bond.

This issue is born through design and will only be resolved through design. The manufacturers of small single pole 120-volt transfer switches strongly oppose the new requirement in 590 as it will impact all smalll generators. The problem began becuase there was no standard to bond or not to bond. The use of floating neutral generators opened the door for the 120-volt, 15/20-amp transfer switch. Many are in use today. Mandating GFCI protection built into these smaller generators means that they will not work with the small 120-volt, 15/20-amp transfer switch, they will be bonded to facilitate GFCI operation. The GFCI will trip, as it should. What is missed in most of these discussions is that the use of a floating neutral generator to supply a 120-volt, 15/20-amp transfer switch is a violation of the NEC. See the definition of premises wiring and 250.20. As soon as you power the premises through the generator, the generator is part of the premises wiring and subject to 250.20.

For further information follow proposal 13-19 through the 2011 revision cycle.

The use of a small floating neutral generator for recreation poses no hazard. There is no ground fault current path unless a double fault exists. Now consider that same small generator with six 120-volt 15 amp contact devices. During a severe rainstorm power is lost. A homeowner takes the small generator, fires it up and supplies the transfer switch. A solid connection is made to the grounded conductor and the floating neutral is no more, the generator is a grounded system. There are now five more 120-volt 15 amp contact devices that the homeowner will use to supply a sump pump, wet vac or other equipment. They are now outdoors in a rain event using power at 120-volt 15 amp without GFCI protection. See 210.8.

This issue will continue into the next cycle.

 

[tom baker]

If you have a generator with a 120 volt GFCI receptacle can you test it by jumping from the neutral to hot?
The honda construction generators have a common GFCI trip for all 4 receptacles, including the 120.240.

Sorry, its neutral to ground. Tom