Grounding a Portable Generator
#1
11-05-12, 09:59 AM
Grounding a Portable Generator
Hi, I have a few questions about this.
1) I have a 5500 Homelite portable gas generator. The user manual talks about proper grounding. However, I cant remember where, but I recently came across a publication, letter or something stating that it can be dangerous to ground a generator. Am I making that up? Or is it possible my user manual is out of date?
2) If I do ground, I know I dont have the ability to drive a steel rod 8' into the ground. It says the other option is to bury in a trench. My question is: for the normal DIY'er whats the best and safest way to ground the generator? I can buy a 5/8" diameter rod at Home Depot, I think. And I can probably did a trench down a foot or so.
Thanks!
Bryan
1) I have a 5500 Homelite portable gas generator. The user manual talks about proper grounding. However, I cant remember where, but I recently came across a publication, letter or something stating that it can be dangerous to ground a generator. Am I making that up? Or is it possible my user manual is out of date?
2) If I do ground, I know I dont have the ability to drive a steel rod 8' into the ground. It says the other option is to bury in a trench. My question is: for the normal DIY'er whats the best and safest way to ground the generator? I can buy a 5/8" diameter rod at Home Depot, I think. And I can probably did a trench down a foot or so.
Thanks!
Bryan
#4
11-09-12, 05:38 PM
I'm no expert, but...
My research indicated that you do want your electrical system grounded. But you only want it grounded in one place, so if you plug things into your gen, ground the gen, but if you backfeed your home, you'll be using your homes' ground. you also need to address the neutral: is it bonded to the ground or floating? It gets complicated and apparently controversial, but dont' worry about it if you just run a spider web of extension cords, only if you plug your home into the gen.
m
m
#5
11-11-12, 08:48 AM
r u sure?
probably the three prong is a twistlock 110, not 220 you can check with a AC meter checking each possible pair: if its 220 i'm not sure how you tell about the ground or neutral, so ask in the electrical forum, but be carful about having a bonded neutral in the home and gen, i think if ur home is bonded then you need a floating neutral in the gen.
m
m
#6
11-11-12, 04:16 PM
Join Date: Mar 2006
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Mitchella, when you are not certain of something it is perhaps better to not post at all. Giving erroneous information, especially with electricity might cause someone with even less knowledge to seriously injure or kill someone.
Two terms have been used that are not universal and do not mean the same thing. In addition some erroneous assumptions have been made. Bonding and grounding are NOT the same although they often involve the same wires and connections. They are for two very specific and very different reasons. There are also different rules and different reasons used for portable generators and fixed-in-place generators.
When I write about grounding a portable generator I mean connecting a suitable wire (conductor) from the generator frame to a suitable electrode driven into the earth. This is almost never necessary and rarely of any benefit. Bonding, however, always needs to be considered. Bonding is the intentional connection of the power source "neutral" connection the the equipment grounding conductors and also to the earth. The reasons why the "neutral" is bonded to the earth are complex and mostly of little import when using a portable generator so I will spend little time on them. The primary reason for the neutral-to-earth bond is to limit the potential difference between the earth and the so-called "hot" conductors. In certain areas this neutral-to-earth bond will also limit induced voltages as a result of lightening.
The bond between neutral and the equipment grounding conductor is for an entirely different reason. The neutral-to-equipment ground bond is to facilitate the tripping of circuit breakers or blowing of fuses under a fault condition. Consider this scenario: A metal-cased electrical appliance has developed a fault connection from the "hot" conductor to the case. With no equipment ground (a two-wire cord) there would be no apparent problem and the appliance would operate normally. However, with the neutral to earth bond if a person were to touch a water pipe (which is normally connected to the earth as well) at the same time they touched the appliance case they would complete the circuit and get severely shocked.
Now at first glance this would seem to argue against the neutral to earth bond but as I stated earlier there are other reasons for this bond and so it was necessary to find another method to alleviate the hazards and that method is the equipment grounding conductor. Consider the same appliance with the same fault but this time there is a three-conductor cord and the house wiring has the independent equipment grounding conductor. This equipment grounding conductor (usually shortened to just ground conductor) plays no part in the normal operation of the appliance or the electrical system. However, when there is a fault from the "hot" conductor to the metal case of the appliance there is now a short circuit from the source of the power (we'll say the service panel in this case) to the appliance and immediately back to the service panel via the equipment grounding conductor. Since the resistance of this path is considerably lower than the normal path through the appliance the current flow is considerable and it almost instantaneously causes the circuit breaker to trip or the fuse to blow. This action removes the power from the appliance which both makes it safe to touch and alerts us to there being a problem.
The above is the normal operation of the utility supplied electrical system. When a portable generator is used then there are several safeguards that MUST be incorporated for both personnel safety and for proper operation of the generator and safety systems. Generators are available with several different arrangements of voltages, total capacity and connection styles. The majority of homes will be served from the electric utility by a single phase dual voltage system having 240 volts and 120 volts and a maximum capacity of 48,000 watts. This is known as a 200 ampere residential service. Lower ampere rated services are also common and some large homes will have a higher capacity service. While a common misconception is that a home is supplied with two 120 volt supplies the truth is that it is supplied with ONE 240 supply and that 240 volt supply has what is capped a center tap (from the supplying transformer) that allows either 240 volts by using only the two "outside" or transformer "end" wires OR it can also supply 120 volts from either "outside" ("end") wire and the center tap. The center tap is connected to the earth and to the equipment grounding conductor in the service panel which is the first (often only) fuse or circuit breaker panel after the utility's meter. This is the ONLY point where the equipment ground, the neutral and the earth ground are connected together. Having additional points where any of these wires are connected creates a hazardous condition.
I'll now discuss the connection of a portable generator to a home when the utility power is lost. For several reasons there is only ONE acceptable method to connect the generator to the home's system and that it to make it utterly impossible to have BOTH the utility and the generator connected at the same time. Any method that allows both utility and generator power at the same time is unlawful and extremely dangerous. The best method, and the only fully approved method is to disconnect all three wires from the utility (hot, hot and neutral) and in their place connect the generator. Up until the last code cycle it was allowable to only disconnect the two hot wires and leave the neutral connected. There are reasons why this earlier method was acceptable and there are probably thousands of installations that still use this method without any problems. Most of the transfer switches and transfer panels today STILL use this method. (Note, a transfer switch is only a switch and has no additional circuit breakers or fuses; a transfer panel DOES have circuit breakers or fuses along with individual circuit transfer switches.) Panel interlocks, where a mechanical linkage prevents closing (turning on) the generator circuit breaker unless the main circuit breaker is open (turned off) also will not switch the neutral conductor and earth bond. A transfer switch may be for a single appliance or it may feed an additional circuit breaker panel that would contain the circuit breakers for the specific circuits that are to be energized by the generator.
In addition to the different voltages and capacities, generators will be connected internally in one of three different methods. The first method is that no output wire is bonded to the generator frame nor is there a bond between the equipment ground and the generator output. This is known as an unbonded generator and strictly speaking it has no "neutral" and no "hot" leads. Both output leads in the case of a 120 volt generator are "hot" and in the case of a 240/120 generator all three leads are "hot" with respect to the equipment ground and the earth. In some applications this is safe but it is not the norm when it comes to the dual voltage generators. Most dual voltage generators WILL have the neutral conductor bonded to both the generator frame and the equipment grounding conductor internally.
(I don't know how much more room I have so I will continue this in a new post.)
Two terms have been used that are not universal and do not mean the same thing. In addition some erroneous assumptions have been made. Bonding and grounding are NOT the same although they often involve the same wires and connections. They are for two very specific and very different reasons. There are also different rules and different reasons used for portable generators and fixed-in-place generators.
When I write about grounding a portable generator I mean connecting a suitable wire (conductor) from the generator frame to a suitable electrode driven into the earth. This is almost never necessary and rarely of any benefit. Bonding, however, always needs to be considered. Bonding is the intentional connection of the power source "neutral" connection the the equipment grounding conductors and also to the earth. The reasons why the "neutral" is bonded to the earth are complex and mostly of little import when using a portable generator so I will spend little time on them. The primary reason for the neutral-to-earth bond is to limit the potential difference between the earth and the so-called "hot" conductors. In certain areas this neutral-to-earth bond will also limit induced voltages as a result of lightening.
The bond between neutral and the equipment grounding conductor is for an entirely different reason. The neutral-to-equipment ground bond is to facilitate the tripping of circuit breakers or blowing of fuses under a fault condition. Consider this scenario: A metal-cased electrical appliance has developed a fault connection from the "hot" conductor to the case. With no equipment ground (a two-wire cord) there would be no apparent problem and the appliance would operate normally. However, with the neutral to earth bond if a person were to touch a water pipe (which is normally connected to the earth as well) at the same time they touched the appliance case they would complete the circuit and get severely shocked.
Now at first glance this would seem to argue against the neutral to earth bond but as I stated earlier there are other reasons for this bond and so it was necessary to find another method to alleviate the hazards and that method is the equipment grounding conductor. Consider the same appliance with the same fault but this time there is a three-conductor cord and the house wiring has the independent equipment grounding conductor. This equipment grounding conductor (usually shortened to just ground conductor) plays no part in the normal operation of the appliance or the electrical system. However, when there is a fault from the "hot" conductor to the metal case of the appliance there is now a short circuit from the source of the power (we'll say the service panel in this case) to the appliance and immediately back to the service panel via the equipment grounding conductor. Since the resistance of this path is considerably lower than the normal path through the appliance the current flow is considerable and it almost instantaneously causes the circuit breaker to trip or the fuse to blow. This action removes the power from the appliance which both makes it safe to touch and alerts us to there being a problem.
The above is the normal operation of the utility supplied electrical system. When a portable generator is used then there are several safeguards that MUST be incorporated for both personnel safety and for proper operation of the generator and safety systems. Generators are available with several different arrangements of voltages, total capacity and connection styles. The majority of homes will be served from the electric utility by a single phase dual voltage system having 240 volts and 120 volts and a maximum capacity of 48,000 watts. This is known as a 200 ampere residential service. Lower ampere rated services are also common and some large homes will have a higher capacity service. While a common misconception is that a home is supplied with two 120 volt supplies the truth is that it is supplied with ONE 240 supply and that 240 volt supply has what is capped a center tap (from the supplying transformer) that allows either 240 volts by using only the two "outside" or transformer "end" wires OR it can also supply 120 volts from either "outside" ("end") wire and the center tap. The center tap is connected to the earth and to the equipment grounding conductor in the service panel which is the first (often only) fuse or circuit breaker panel after the utility's meter. This is the ONLY point where the equipment ground, the neutral and the earth ground are connected together. Having additional points where any of these wires are connected creates a hazardous condition.
I'll now discuss the connection of a portable generator to a home when the utility power is lost. For several reasons there is only ONE acceptable method to connect the generator to the home's system and that it to make it utterly impossible to have BOTH the utility and the generator connected at the same time. Any method that allows both utility and generator power at the same time is unlawful and extremely dangerous. The best method, and the only fully approved method is to disconnect all three wires from the utility (hot, hot and neutral) and in their place connect the generator. Up until the last code cycle it was allowable to only disconnect the two hot wires and leave the neutral connected. There are reasons why this earlier method was acceptable and there are probably thousands of installations that still use this method without any problems. Most of the transfer switches and transfer panels today STILL use this method. (Note, a transfer switch is only a switch and has no additional circuit breakers or fuses; a transfer panel DOES have circuit breakers or fuses along with individual circuit transfer switches.) Panel interlocks, where a mechanical linkage prevents closing (turning on) the generator circuit breaker unless the main circuit breaker is open (turned off) also will not switch the neutral conductor and earth bond. A transfer switch may be for a single appliance or it may feed an additional circuit breaker panel that would contain the circuit breakers for the specific circuits that are to be energized by the generator.
In addition to the different voltages and capacities, generators will be connected internally in one of three different methods. The first method is that no output wire is bonded to the generator frame nor is there a bond between the equipment ground and the generator output. This is known as an unbonded generator and strictly speaking it has no "neutral" and no "hot" leads. Both output leads in the case of a 120 volt generator are "hot" and in the case of a 240/120 generator all three leads are "hot" with respect to the equipment ground and the earth. In some applications this is safe but it is not the norm when it comes to the dual voltage generators. Most dual voltage generators WILL have the neutral conductor bonded to both the generator frame and the equipment grounding conductor internally.
(I don't know how much more room I have so I will continue this in a new post.)
#7
11-11-12, 04:31 PM
Group Moderator
#8
11-11-12, 07:28 PM
thank you, but if you'll re-read my posts i have not misused the terms nor confused them. I just didn't define them to your liking it looks like. So post, but no need to criticize unless you think i gave wrong advice. the last sentence of one of your many paragraphs is agreed, and why I warned about the grounding in two places or have the neutral bonded in two. I think i gave accurate advice but i didn't go ad nauseum w/ detail. I guess you know more than the generator manuals that advise grounding and provide a grounding lug to ground the generator if used alone as a portable, so thanks again.
