Our truck mounted generators do not have a stake driven into the earth for ground. Sometimes when my operators touch the frame of their saws or drills and they are wet, they get a tingle. Can be 480V 3phase, or 110V single phase, and we have some 200V 400Hz 3 phase. It's noticable but never more than a tingle. There is a move to ground the truck mounted portable generators, but I wonder if this will put them in an earth ground loop in other circumstances like dropping the drill in water, although all circuits are GFCI. Why do they get a tingle when the circuit is not defective and their is no connection to earth ground?
Grounding Portable Generators
- Thread starter cmeng
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highkvoltage
Senior Member
Re: Grounding Portable Generators
400Hz? That's new. Are the tool double insulated or old relics? Are the plugg ends 2 or 3 pronged and if the are 3 pronged was the ground prongs cut off? Are you using GFCI protection for your workers as required in most areas to protect them? Is the generator in good shape? It could be leaking voltage to the frame and the frame touching the truck with your workers completing the curcuit? This really sounds like a safety issue not a electrical one.
400Hz? That's new. Are the tool double insulated or old relics? Are the plugg ends 2 or 3 pronged and if the are 3 pronged was the ground prongs cut off? Are you using GFCI protection for your workers as required in most areas to protect them? Is the generator in good shape? It could be leaking voltage to the frame and the frame touching the truck with your workers completing the curcuit? This really sounds like a safety issue not a electrical one.
Re: Grounding Portable Generators
The trailer mounted generators are bonded to the frame. The portable generators typically sit in a stand, metal to metal contact, but not truly bonded.
The equipment is generally well maintained. The 400 hz stuff is 200V 3 phase with a fourth wire that is case ground, not electrically tied in. I agree that this is a safety issue - I'm the safety officer - and part of this question is because we have revamped our safety program and one result is GFCI - no exceptions. So, would it be better to ground the frame now? And, does an above ground system have any reason to try and go to earth ground through a wet operator, or is that only an indicator that something is leaking in the above ground system?
The trailer mounted generators are bonded to the frame. The portable generators typically sit in a stand, metal to metal contact, but not truly bonded.
The equipment is generally well maintained. The 400 hz stuff is 200V 3 phase with a fourth wire that is case ground, not electrically tied in. I agree that this is a safety issue - I'm the safety officer - and part of this question is because we have revamped our safety program and one result is GFCI - no exceptions. So, would it be better to ground the frame now? And, does an above ground system have any reason to try and go to earth ground through a wet operator, or is that only an indicator that something is leaking in the above ground system?
highkvoltage
Senior Member
Re: Grounding Portable Generators
cmeg. Using a volt meter measure the voltage at the receptacle at the generator. Make use you have a good reading. Then measure from the receptacle (hot,neutral and ground) to the frame of the generator to see if there is any leakage at the generator. Also measure from the receptacle (hot, neutral and ground) to a ground source as a ground rod again from. There has to be a problem with the generator. Also using the same method plug a drill in and take some measurements. You should be able to narrow the problem down. By the way I'm still working on the 400 Hz thing.
cmeg. Using a volt meter measure the voltage at the receptacle at the generator. Make use you have a good reading. Then measure from the receptacle (hot,neutral and ground) to the frame of the generator to see if there is any leakage at the generator. Also measure from the receptacle (hot, neutral and ground) to a ground source as a ground rod again from. There has to be a problem with the generator. Also using the same method plug a drill in and take some measurements. You should be able to narrow the problem down. By the way I'm still working on the 400 Hz thing.
stew
Senior Member
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- federal way,washington
Re: Grounding Portable Generators
I think you may have a partially grounded generator winding. I would definatly check the winding insuslation with a 100o v megger to see just what the integrity of the winding insulation is. Because you are operating at 400 hz winding insulation is more prone to leakage due to the hicher frequency. A weak insulatiom system in the windings such as the slot cell insulator will have a tendency to break down faster when wet especially at hi freq.
I think you may have a partially grounded generator winding. I would definatly check the winding insuslation with a 100o v megger to see just what the integrity of the winding insulation is. Because you are operating at 400 hz winding insulation is more prone to leakage due to the hicher frequency. A weak insulatiom system in the windings such as the slot cell insulator will have a tendency to break down faster when wet especially at hi freq.
Re: Grounding Portable Generators
It is possible you have a slight ground somewhere in the system but if I am reading your post right the tingling is coming from touching the electrical tools and not the truck bed. If the problem were with a ground in the generator it would seem like you would get the tingle when you touched the truck. I don?t know how much cable you have running from the truck to the work area but there is always a certain amount of capacitance caused by current flow through power cable. It is possible that with the generator being isolated on the truck that this capacitance is being discharged through the workers when they touch the tools in a wet condition. I am sure there are others on the forum that is more knowledgeable than myself on the subject of capacitance cause by power cables. Maybe some of them can add more information.
Don Mclain
It is possible you have a slight ground somewhere in the system but if I am reading your post right the tingling is coming from touching the electrical tools and not the truck bed. If the problem were with a ground in the generator it would seem like you would get the tingle when you touched the truck. I don?t know how much cable you have running from the truck to the work area but there is always a certain amount of capacitance caused by current flow through power cable. It is possible that with the generator being isolated on the truck that this capacitance is being discharged through the workers when they touch the tools in a wet condition. I am sure there are others on the forum that is more knowledgeable than myself on the subject of capacitance cause by power cables. Maybe some of them can add more information.
Don Mclain
Re: Grounding Portable Generators
I really appreciate the thoughts on this subject. This is a situation that has occurred many times over the years. We are a Concrete Demolition Company and have many portable generators nationwide. From time to time I will hear about an operator getting a "tingle" when he touched the truck, or trailer or sometimes the saw frame. He is almost always wet. This has raised the question for our company - should we try driving grounding rods into the ground when we park the genset or truck? I've said no in the past because I don't want to put an equipment operator in between an earth ground and a "grounded" above ground system. But, now with GFCI on everything, I wonder if it would be better. I've always had a suspicion that the "tingle" was occurring due to some relationship between above ground systems and earth ground - that some bleed off current still wanted to go to earth ground thru the wet operator???? It was the only explanation I could muster given that there are many generators, 400hz and 60hz, some brand new, that have done this over the years. Any more ideas would be greatly appreciated. And yes, a grounding rod alleviates the problem, but puts my operator at risk. (I think)
[ March 01, 2004, 09:01 AM: Message edited by: cmeng ]
I really appreciate the thoughts on this subject. This is a situation that has occurred many times over the years. We are a Concrete Demolition Company and have many portable generators nationwide. From time to time I will hear about an operator getting a "tingle" when he touched the truck, or trailer or sometimes the saw frame. He is almost always wet. This has raised the question for our company - should we try driving grounding rods into the ground when we park the genset or truck? I've said no in the past because I don't want to put an equipment operator in between an earth ground and a "grounded" above ground system. But, now with GFCI on everything, I wonder if it would be better. I've always had a suspicion that the "tingle" was occurring due to some relationship between above ground systems and earth ground - that some bleed off current still wanted to go to earth ground thru the wet operator???? It was the only explanation I could muster given that there are many generators, 400hz and 60hz, some brand new, that have done this over the years. Any more ideas would be greatly appreciated. And yes, a grounding rod alleviates the problem, but puts my operator at risk. (I think)
[ March 01, 2004, 09:01 AM: Message edited by: cmeng ]
hbiss
EC, Westchester, New York NEC: 2014
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- Hawthorne, New York NEC: 2014
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Re: Grounding Portable Generators
Leave it to Bennie to tell us there are anti- static tires!
-Hal
Leave it to Bennie to tell us there are anti- static tires!
-Hal
Re: Grounding Portable Generators
I am not positive but I think all tires made today have carbon mixed in the latex or whatever other tire material to prevent static charge build up on automobiles and trucks.
I know that aircraft tires are constructed to equalize the static charge on landing.
I once saw a boom truck blow out all the tires when the metal boom hit a 13.8 KV line.
I am not positive but I think all tires made today have carbon mixed in the latex or whatever other tire material to prevent static charge build up on automobiles and trucks.
I know that aircraft tires are constructed to equalize the static charge on landing.
I once saw a boom truck blow out all the tires when the metal boom hit a 13.8 KV line.
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