portable generator grounding/bonding

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don_resqcapt19 said:
Pierre,

The ones that I have seen are portable generators designed for cord connected equipment...it is an ungrounded system.
Don


Don,
I was not thinking of a portable generator. We do not see too many of the portable types during our inspections...maybe those types are not being filed, as the need for the POCO is not necessary for portables.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
I've been following this thread and with so many replies I still find it so confusing as to what the proper method is. Some time ago I had installed a remote generator hook up for a gas station. The station owner had purchased a 7KW portable generator (with a 30 amp, 240 volt twist-lock receptacle) and an engineer for the generator manufacturer insisted that the neutral should float when the transfer switch was in the generator position and the generator was operative. So, I installed a sub-panel with approx 10 circuits but I pulled out the branch circuits from the main panel and installed them (along with their respective neutrals) in the sub-panel. The transfer switch was a 3-pole unit and I switched the neutral.

So, to recap, with the transfer switch in the POCO position the neutrals were bonded to the EGC (via the main breaker panel). With the transfer switch in the generator position the neutrals floated.

Did I do the right thing or did I over-kill this job ? It doesn't make any difference to me $$ wise at this point in time - I got paid for the job. I just want to know for the future so I can be competetive and code compliant. From all the promotional mail I receive they're claiming that back-up generators are going to be the next boom in our industry since air conditioners.

Phil
Gold Star Electric
New Jersey
 
A portable generator that is not earthed in any way does not generally pose a shock hazard in the way you're used to thinking about it. It isn't connected to the earth, so standing in a puddle and touching one wire isn't going to hurt you.

Of course, thats what my primitive cro-magnon brain was not taking into account, hence my confusion.

an engineer for the generator manufacturer insisted that the neutral should float when the transfer switch was in the generator position and the generator was operative. So, I installed a sub-panel with approx 10 circuits but I pulled out the branch circuits from the main panel and installed them (along with their respective neutrals) in the sub-panel. The transfer switch was a 3-pole unit and I switched the neutral.

It seems to me that if the genny neutral is floating, you should not switch the neutral at the transfer switch. Im a little unclear though, were you said floating, were you referring the neutrals in the subpanel or at the genny? What is the purpose of the sub-panel?
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
electrofelon said:
were you referring the neutrals in the subpanel or at the genny?
The neutral at the 30 amp twist lock receptacle of the generator was a floating neutral (according to the manufacturer's rep).

electrofelon said:
What is the purpose of the sub-panel?
All the circuits in the sub-panel were emergency circuits (gas pumps, lights, air compressor and a few receptacle circuits). The 40 circuit, 200 amp CH panel was packed with wires and making additional splices in it would have made the situation worse, so I installed the sub-panel. As I mentioned, with the transfer switch in the POCO position all neutrals were bonded to the EGC via the main breaker panel. When transferred to generator the neutrals floated. This is the way it was installed based on the engineer's recommendation. However, the more posts I read here makes me think that I did something completely wrong. I think the basic problem is determining whether the portable generator is considered a SDS or not. I don't want to shift attention away from the original question but if anyone can point me in the right direction here it would be greatly appreciated. Thanks.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Gold,
In your case, you should not have switched the grounded conductor. That way the service main bonding jumper provides the fault clearing path and the service grounding electrode system provides the required grounding for both when on utility or generator power.
Don
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
Thanks Don,

So basically, to correct my mistake, all I would have to do is tie both neutrals together inside the transfer switch ? I know it sems like a Rube Goldberg at this point but I want to be code compliant and safe.

Phil
 

dnem

Senior Member
Location
Ohio
goldstar said:
However, the more posts I read here makes me think that I did something completely wrong. I think the basic problem is determining whether the portable generator is considered a SDS or not. I don't want to shift attention away from the original question but if anyone can point me in the right direction here it would be greatly appreciated. Thanks.

The basic problem can be answered by a very basic answer.
The transfer switch and the generator need to have matching setups.
If the transfer switch transfers the neutral, the generator must have a main bond between the neutral and equip ground. . This is the SDS, separately derived system setup.
If the transfer switch doesn't transfer the neutral, the generator must not have a main bond. . This setup is commonly referred to as "subpanel" wired or "floating" neutral generator.

It's really as simple as that.

If the transfer switch transfers the neutral, you get cut off from your neutral connection to the main bonding point so therefore must establish a new main bonding point for generator power. . The position of the transfer switch determines which power supply is used and also which bonding point is being used.
If the transfer switch doesn't transfer the neutral, the main bond at the utility service disconnect continues to function as the single bonding point regardless of the transfer switch position. . It's the single bonding point while utility power is supplying or while the generator is supplying.

goldstar said:
All the circuits in the sub-panel were emergency circuits (gas pumps, lights, air compressor and a few receptacle circuits). The 40 circuit, 200 amp CH panel was packed with wires and making additional splices in it would have made the situation worse, so I installed the sub-panel. As I mentioned, with the transfer switch in the POCO position all neutrals were bonded to the EGC via the main breaker panel.

The addition of subpanels doesn't change anything either way. . If its a SDS setup or not, subpanels continue to be subpanels, it's only the generator connections that vary according to the transfer switch setup.

If your situation makes the use of an additional subpanel or two desirable, go right ahead and add them. . It doesn't affect the bonding question.

goldstar said:
The neutral at the 30 amp twist lock receptacle of the generator was a floating neutral (according to the manufacturer's rep).

..... As I mentioned, with the transfer switch in the POCO position all neutrals were bonded to the EGC via the main breaker panel. When transferred to generator the neutrals floated. This is the way it was installed based on the engineer's recommendation.

If the engineer or manufacturer is requiring or recommending generator bonding either one way or the other, then that shouldn't be a problem to comply with their desire. . You just have to match up the right transfer switch according to how they want the generator bonded.

David
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Phil,
So basically, to correct my mistake, all I would have to do is tie both neutrals together inside the transfer switch ? I know it sems like a Rube Goldberg at this point but I want to be code compliant and safe.
Based on my understanding of your installation, that should do it.
Don
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
Thanks David and Don. I appreciate the time you've taken to straighten me out.

Regards,

Phil
Gold Star Electric
New Jersey
 
Let's start with the power pole. The pole is grounded with a driven ground rod and the bare grounding wire goes from the ground rod to the neutral terminal in the meter can. The last meter socket (can) I hooked up had a seperate screw for the grounding wire and the neutral conductor, but they both hooked into a single lug.

Now let's go to the panel. 3 service entrance conductors enter the can from the meter socket (2 phase conductors and the neutral). A bare grounding wire also enters the panelboard--it is connected to a second driven ground rod right outside the house. Everything is wonderful so far.

Now, the utility loses power. The quickest way to hook up a generator is to:

1. Shut off the main in the panelboard.
2. Bring a 3 wire from the generator (2 phase and 1 neutral conductor).
3. Hook the 2 phase conductors to an appropriately sized breaker.
4. Hook the neutral to the neutral bar in the panel.
5. Start the generator, flip the breaker being used as the main and, voila!

The question is: for absolute safety for utility workers, would it be best to disconnect the neutral service entrance conductor from the neutral bar in the panelboard?

Some say that is not necessary because the return voltage on the neutral will go back to the generator since it is closer to the load than the transformer on the utility side.

What do you think?
 

benaround

Senior Member
Location
Arizona
I think you better change your ways and start hooking up your gen. in a

code compliant manner. The NEC requires a transfer switch for ALL gen.

installations.

Linemen get hurt,injured,and worst by the type of install that you described.
 

iwire

Moderator
Staff member
Location
Massachusetts
greggeshack@hotmail.com said:
What do you think?

I think that we can not recommend installing generators in a non code compliant way on a code forum.

You need to take a look at Article 702 and likely 250.30.


The question is: for absolute safety for utility workers, would it be best to disconnect the neutral service entrance conductor from the neutral bar in the panel board?

No the neutral does not have to be disconnected.

What has to happen for the lineman's safety and NEC compliance is some sort of transfer device must be used.

It could be as little as a breaker interlock device that physically prevent someone from having both the Gen main and the Service main on at the same time.
 
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